I like to perform my own maintenance on my Briggs & Stratton engine and enjoy helping others do the same.
Is Your Briggs and Stratton Hard to Start?
Does the engine struggle to turn over, and it seems as though the starter must be bad or the battery dead? Is it time to pay big bucks for lawnmower repair? How will you get that lawn tractor to the repair shop?
Before you do anything too drastic, however, keep in mind that it may not be that serious of a problem. If this is an overhead valve (OHV) engine, then it may be that you have just overlooked a basic maintenance procedure. Sometimes you have an easy repair on your lawn tractor.
Most of the overhead valve engines have a compression release feature that allows for the starter to not have to work hard to crank the engine. It's a slight raising, or bump, on the lobe of the camshaft. What it does is open the valve a little early to allow excess compression to bleed off. At speeds over 300 rpm, the tappet just sort of floats over this bump, and it has no effect on engine performance. But at starting speeds, it's essential, otherwise the starter just can't turn the engine over.
If the engine will turn over easily and hiccups, won't rev or make power, or just won't start, then you may be looking at a fuel supply problem.
This guide will help you diagnose and fix your hard-to-start Briggs & Stratton engine.
How to Diagnose Your Lawn Mower Engine's Problem
To diagnose this problem, you will need a voltmeter.
First, check the battery voltage by using the voltmeter on each battery terminal. You should have about 12 volts.
Next, check the voltage at the starter with the key in the start position. You may need a helper at this point, depending on the equipment. What you have to do is ensure that all safety features are activated just as though you are starting the engine. With one lead from the voltmeter on the post on the starter where the cable connects and the other lead to a good ground such as the engine block, there should be about the same voltage as there was at the battery. A drop of a volt isn't a concern. If all this checks out okay, then it's a reasonable diagnosis to suspect the compression release.
Proper performance of the compression release requires proper valve lash adjustment. Adjusting the valves is a relatively simple project requiring only a few tools and once you learn how to do it, you should include it with your annual maintenance program.
- Ratchet with extension and 3/8", 7/16" and 1/2" sockets
- Feeler gauge in .004" and .006"
- 3/8" wooden dowel or substitute
- Torx or Allen driver to fit lock screw
How to Fix a Compression Release Problem in Your Briggs & Stratton Engine
- First, you need to access the valve cover. This will be the silver cover on top of the engine head. It will have OHV stamped into it and is held on with four screws/bolts. These screws are usually 3/8" or 7/16" hex head and are removed using a socket and ratchet. There is a gasket between the valve cover and head. If you are careful, you can usually re-use this. Then remove the spark plug.
- Now with the cover off, you can see the rockers, push rods, valve springs, and valve stems. The valves are the ones with the springs on them. If you turn the flywheel by hand, you will see the valves move up and down and see how the assembly works.
- Find the intake valve. This will be the one that the carburetor feeds fuel and air into. If you remove the pushrods, typically the intake valve will have an aluminum pushrod, while the exhaust valve has a steel pushrod.
- You will need to turn the flywheel clockwise until you see this valve open (move downwards) and then close again. Once the intake valve closes, the piston will be headed to the top of its travel, or Top Dead Center (TDC).
- At this point, take the wooden dowel and insert it into the spark plug hole. You should feel the top of the piston.
- Slowly turn the flywheel by hand while holding the dowel against the piston, and you will feel the piston move. Be careful doing this. If the dowel starts to become caught in a bind, back the piston up and remove the dowel. You only want the dowel in the cylinder when the piston is at or near the top of its travel.
- With the piston at TDC, rock the flywheel back and forth to find the highest spot of the piston travel using your dowel.
- Find a spot on the head that's easy to see, and mark the dowel where it lines up with that spot. Now remove the dowel and make another mark 1/4" above the first mark.
- The valve lash should be set with the piston at 1/4" past TDC. What you are doing is making a gauge to line up the piston travel with a reference point. Now put the dowel back in, and rotate the flywheel so that the piston is now 1/4" past TDC.
- On the rockers, the stamped metal pieces that open the valves, there will be a nut and a lock screw inside that nut. Usually this screw will be a Torx head, but whatever it is, loosen it and then loosen the retaining nut. You will notice the slack in the rockers, the amount of slack is what you are adjusting.
- For the intake valve, take the .004" feeler gauge and insert it between the valve stem and rocker. Then tighten the retaining nut until the feeler gauge will just barely slide in and out. It should be a snug fit, and the gauge should have some resistance when trying to pull it out.
- Then tighten the lock screw back down. That valve is finished.
- Repeat the feeler gauge process on the exhaust valve using the .006" gauge, and replace the valve cover.
- If the gasket tore when you removed it or it isn't in the best of condition, you can either purchase a new gasket or do what we do in the shop and use PermaTex Ultra Black to re-seal the valve cover. We also use anti-seize on the valve cover screws. Both PermaTex and anti-seize are available at any auto parts store, as well as the tools required. (Note: If you have a twin cylinder engine, you have to treat each cylinder separately. You have to bring each piston to its respective TDC to adjust each cylinder's valves.)
- Once you have the valve cover back on, you're ready to start the engine. Don't worry if it's still doing the same as before. It usually take a few tries to do this right if you've never adjusted valve lash. Just start over and try it a couple more times if necessary. If you can't get it right after several tries, you may have a different problem which will require further diagnosis.
Thank you for reading this, and I hope it is of some help. Several people have sent me messages asking for further help in diagnosis. But please understand, due to constraints within this type of forum, there is just no way for me to do that here.
Briggs & Stratton Compression Release Fix
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Dave Lovekin on June 10, 2018:
Fixed a compression blocked starter in 10 minutes. Great article, thanks for submitting.
Shayne Campbell on May 09, 2016:
It is a common problem also for the exhaust valve port to get hit, due to the cooling passages getting plugged with grass. This can cause the exhaust valve guide to slide out of the.passage and lock the valve up, causing the pushrod to bend. Fortunately if one is mechanically inclined, this is appx an $80 repair with oil, parts, and gaskets. To eliminate this problem in the future, I drill a hole in the side of the head where the exhaust valve guide is, and installed a loctited set screw into the valve guide, eliminating the possibility of any movement. I recommend the valve clearance adjustment annually, or as the no crank (high compression) issue resurfaces.
Doug Cutler from Temperance. Mich on August 14, 2015:
After working on these type engines I decided to do a hub. Did a search to see what hubs were already here. Found this one. May do another explaining why the 1/4" piston down and the carb. flooding problem.
You would think the shops would know about these problems. I got one in to repair that had the additional problem of gas getting into the cylinder from the carb. needle not seating. That extra gas in the cyl. will do the same as the decompression not working. I got the extra gas out and after jumping the battery it finally started. It was then starting easily but smoked badly. Turns out the the head gasket blew between the cyl. and push rod cavity. Another common problem with these OHV engines. Changed the gasket adjusted the valves. Engine returned to previous problem of not turning over. When it was starting easily and smoking badly the burned spot in the gasket was a built in compression release. So this means the compression release pin on the intake lob of the camshaft is not functioning. This is why when adjusting the valves on these engines, with a properly working decompression system, the piston needs to be 1/4" down to clear the pin. Next is to take the engine off and apart to fix the camshaft decompression system.
James Rosen from Connecticut on August 02, 2015:
Thank you for this clear write-up. I just acquired a Husqvarna tractor with a 20 HP Briggs Intek single cylinder motor that would not start easily. I found the exhaust at 0.010 and intake at 0.005. All looked like new when I pulled the valve cover no sludge or varnish. I reset both to factory spec using procedure you described and the motor now starts easily and runs smooth. Only issue left is it will run for about 10 minutes misfire 2-3 times repeat this about 4-5 times then stop running. A wait of 2-3 minutes and it will start and run fine for another 5-10 minutes and the cycle repeats. I found the gray wire to the fuel cutoff solenoid partially melted to the motor heat shield but still not the issue even after repair. The engine has 438 hour run time on the tractor hour meter. Could this be the electronic ignition starting to fail? I have an inductive timing light to check for spark during any misfire but is there any better test that does not require waiting for the misfire to happen short of replace and see. Also the plug was black and wet when pulled to set the valve lash. Is 438 hours on this engine considered a lot or should i expect many more with correct maintenance
James Rosen from Connecticut on August 01, 2015:
Thank you I have a 20 hp Intek single cylinder Hsuqvarna tractor just acquired as a clear it out of my garage find. I found the exhaust at .010 when I checked and intake at .005 438 hours on the meter guess valves where never adjusted. Used described procedure and starts like a champ. this was a great helpful post. last issue I have is after about 10 to 15 minutes the motor starts to miss fire 2 or 3 times in a row does this 4 or 5 times and then shortly dies. If I wait a minute or 2 it will start right up and run with no problem for another short period of time. though I found the issue with the gray lead to the fuel cut off solenoid partially melted to the motor heat shield but no luck. Could this be the ignition module. The ability to restart after a short cool down wait period seems to point there. I have an inductive timing light ( yes I run old Land Rovers which require old school tools) but have not checked for no spark yet.
Is there any known issue with fuel pump or vapor lock on these motors.
is 430+ hours considered end of life by Briggs for this motor.
bktrider on July 14, 2015:
Hi, had to register just to post this comment: I have watched videos of this procedure and learn best from watching, however, his article was one of the best that I have read about any topic. You have excellent writing skills and I really appreciate you posting this article. A friend of mine has a Snapper with a 7 hp briggs and it is hard to start. I rebuild/cleaned the carburetor and it is still hard to start.....about 11 y/o mower, I will adjust her valves and hope this takes care of her problem; I too remember briggs as being an outstanding engine and hope this turns out to continue to be the case.
blmgtnman on May 27, 2015:
My rider has been so hard to start these last 4-5 yrs. It's like it has a dead battery every time I'd go out to try and start it. I knew the starter was good because it turns over easily without the spark plug. I've purchased 3 battery's for this rider and finally gave up two years ago after a shop charged me several hundred and didn't get the engine to turn over like it normally should. I then bought a self propelled toro to keep my lawn looking decent. My bad! I'm very embarrassed right now.
I came across your article and your tutorial worked exactly as you described! Now I feel so silly for not knowing I should be adjusting the valves on my Craftsman B&S 18.5 hp ohv intek engine every season. Because of you and your article, I will perform this procedure first thing every season!
And yes, I found I needed to make several attempts adjusting the valves, but I eventually succeeded! The engine now fires off immediately! I'm not an engine person and rarely if ever will I attempt something like this. I'm so glad I was fortunate enough to come across your article! And if I may, my wife couldn't be happier that at 65 yrs old, I'm back in the saddle again!
You Sir, truly are a gem and I wanted you to know! Many, many thanks!! Hope you have a wonderful day! Be well! Rick
Cardinal Fang on April 17, 2015:
I signed up here simply to say 'thank you' for this great, user friendly tutorial! I just saved loading up a zero turn mower & lugging it into town, then leaving it for x number of days and then having them tell me (again!) that it's a 'weak battery'.
It took me maybe an hour, half of that time was just gathering tools & printing out the tutorial above. First hit of the key after doing this and it's purring like a rabid kitten on steroids. (Ok... so I need a beer.) Either way - it starts like a dream and my original plan for this weekend was to weld up a full size car battery tray... glad I took one last look online and found this page.
johng34 on September 25, 2014:
This was exactly my problem, Briggs and Stratton 19.5hp. Just died during a mowing. The key for me was the high compression clue. Put a new battery in it and it couldn't turn the engine over. Two problems needed correcting before it would start.
1) Exhaust valve rocker arm had 3/8in gap, due to it's mounting stud coming loose and backing out 3/8".
2) Intake push rod, aluminum, bent. Don't know how it got that way, could be the steel cap on the top of the exhaust valve, when it fell into the bottom of the OHV well stuck in the intake valve on the way down.
Installed new rod, loctite'd the stud back in, adjusted valves as described herein. Started right up. Put Kano Kreen in gas and oil, made it sound MUCH better right away. Going to prevent the input valve from sticking, which may have caused the bent push rod. Only 160hr on this 4yr old John Deere, that I bought used.
THANKS AGAIN, I've no idea how much money you saved me!!!!!
PK Jones (author) on January 15, 2013:
Hi, I really can't do diagnostics in this format. I'm not able to log in on a regular basis and this format just doesn't allow for it. I can direct you to another post I've made at the following link:
It sounds like you have a a crankcase full of gas or a bad breather.
Chuck 1 on January 06, 2013:
My engine was hard starting but once it started ran good for 10 mins. I turn up the throttle and started off then it started smoking really bad. Fulled the garage with heavy smoke. and then died. I did not try to start again. I took the valve cover off and it was full of oil and and air cleaner also had lots of oil. this is where I stopped. looking for answers to the problem. One side of the valve cover had oil residue. What should I look for now????? i'm thinking the head gasket and adjust the valves. Anything else????
PK Jones (author) on September 13, 2012:
The feeler gauge to be used is the flat style. The round one would be more difficult to hold in place when tightening.
The side valve engines do have a valve clearance procedure but it would be more than I can explain in a short comment. Typically if there's a cam wear issue in a side valve engine, complete disassembly is required and replacement of followers, cam or valves is needed. Or you may get away with TIG welding material onto the valve stem end and machining to shape, but that's also more than I can explain here.
On the side valve engine, start with pulling the heads and cleaning the carbon build up. Also, you may have another issue than the compression release, that would require a good bit of back and forth and I can't do that here. Thanks!
cwatersjr on September 07, 2012:
Is there a way to check the valves on a 16 hp twin II NON OHV engine that is doing the same symptons as the orginal problem above. Starter will only tunr the engine partially. If you take the plugs out it spins freely. Any suggestions would be great..
cwatersjr on September 07, 2012:
Is there an adjustment on the valves when the motor is OHV? I have a BS 16hp Twin II that is having this issue but is not OHV.
andrewharshbarger on September 04, 2012:
what type of feeler gauge should be used when doing this or does it matter
PK Jones (author) on August 31, 2012:
Hi, once you have the piston 1/4 Inch past TDC, you adjust both valves at the same time, no need to move the piston again. Now since this is a twin, you have to set the piston 1/4 Inch past TDC before adjusting on each individual cylinder. So you do one cylinder, then rotate the engine for the other cylinder and adjust it.
c- stanfield on August 26, 2012:
do you have to bring the piston to 1/4 past td. to adjust the intake valve then turn the engine again to adjust the exhust. i have a 20 hp. briggs vanguard twin cylinder. i adjusted them the other day and i made it worse. was my first time. at 4-6 ths. but i adjusted them at td. thanks for any help.
PK Jones (author) on December 14, 2011:
Robert is that the First part of the Family number or the Model number? If that's a Briggs engine, the model number is stamped into the valve cover or on the sheet metal.
Robert on December 13, 2011:
Any one know the valve lash on this model 2bu706 16hp ohv. I cant seem to find it on the chart. I appreciate the help. THANKS
PK Jones (author) on December 12, 2011:
You can change the spark timing slightly by changing the air gap of the coil to the flywheel. Tight to the flywheel gives you a little advance, further away from the flywheel retards the spark. On a stock engine, gaining that little advance improves performance. On most Briggs engines you can't back the coil up far enough to keep it from firing, but the spark may be late enough to cause hard starting and make it run a little weak.
The position of the flywheel on the crankshaft is the primary timing. On a performance engine we will either use offset keys to adjust advance or not even bother with a key and just adjust it according to dyno results. The key is nothing more than an alignment tool, it doesn't hold the flywheel in place, but offset keys make adjustment easier.
You typically won't see any advantage to advancing the flywheel on a stock engine, but by tightening the coil to the flywheel you may. The gains are small, but every little bit helps.
billybob on December 12, 2011:
Ignition timing is keyed to the crankshaft and flywheel.
Robert on December 12, 2011:
When i ajust the coil to flywheel to.010 is this not the airgap ?
PK Jones (author) on December 11, 2011:
Robert, I'm afraid I cannot do diagnosis on this site. But, if this is a Briggs Intek engine, then use the link to the Briggs spec sheet, http://www.nnyparts.com/briggsspec.pdf, and check your model number against that chart. The reason for using the factory adjustments is to prevent excess wear and ensure your valves are properly timed. Outside of the factory numbers, even by .001", will add wear to the cam and rockers as well as reduce performance. At .002" lash, the valves are opening too early and staying open too late, IF .002" lash is outside of the Briggs specs.
This will cause higher fuel usage as well as a loss of power. On a 16hp engine you may not easily notice the difference, however put it on a dyno and you're probably losing 1/2 to 3/4 hp, which in a small engine is quite a bit. Also air-cooled engines are very dependent upon proper valve and ignition timing for cooling and the prevention of carbon build-up.
For maximum performance on a stock engine, adjust the valves to the tight side of the specification and adjust your ignition timing by making sure that the coil is no more than the thickness of a dollar bill that's been folded three times. By having the coil tight to the flywheel like that, you advance the spark by maybe a couple of degrees which improves the fuel burn.
Remember, the lash adjustments are to ensure the valves are opening and closing at the proper time on the cam lobes. Too loose on the valve that provides the compression release and you also will either have no compression release or it will be reduced, causing unnecessary wear on the starter.
Robert on December 11, 2011:
I BOUGHT THIS ENGINE USED AND IT IS 16HP ohv. WHEN I PUT THE ENGINE ON THERE, I CHECKED THE VALVE LASH.IT HAD VERY LITTLE.I couldn't even get a .002 gage to slide between the rocker and the pistom was up right.This engine is running good.Should i just it .004 and 006 what it calls for or leave it like it is? Kneed some help THANKS
PK Jones (author) on December 07, 2011:
Sorry BillyBladez, I didn't mean for it to sound like you were Bob. Bob has used several different usernames to try and get posted and continues to try and make insulting comments everyday. I was letting his posts without the name calling and insults through but enough is enough. Good luck with your TroyBilt.
billybladez66 on December 07, 2011:
for the record pk, im not billy bob. I'm not gonna argue with somebody whose info saved my bacon and my dough. For whatever reason a slight adjustment to the formula was what it took for me. Had it not been for your posts, i would have been a sad sad pupy about my troybilt. You just keep doin what you're doin and i'll be happy to read what your doing...cheers to ya!!!!
La Purisima Golf Course on December 06, 2011:
Cheers to that. Small engine mechanic and was needing exact specs.. Thanks Ill post 2morow and report results!!!
PK Jones (author) on December 05, 2011:
Bob, you said, "You said in the end you adjusted the valves at .008 and .005 . What else did you find wrong ? Your saying that the engine was hard to turn over. The valve adjustments being out that little wont make the engine hard to turn over." and then you said, "Just for your information... .002 of an inch is less than a piece of paper. Not very much.
So you are directly contradicting yourself. You can try to recover by changing your story but you really need to accept that there is a proper procedure and that being precise matters. It's most likely that you are not being precise and therefore aren't really sure what your actual lash is.
This will be the last post of yours that appears on this page no matter how many different names you try to use. I have not allowed some of your other posts to appear because of your tone and am afraid that you bear the distinction of being the first I've had to do this to. This is not a forum to argue, it's an information forum. If you would like to adjust your valves however you like, feel free. However Briggs has a particular method they feel should be used and they would tend to know best. I've explained why the valves are set the way they are set repeatedly and that's not my recommendation, it is how Briggs designed the engines.
Attend a few Briggs training classes, and feel free to argue with them and try to convince their Engineers they don't know how their engines are put together. I've been attending factory small engine training since the mid-eighties and have yet to find a reason to tell a manufacturer that they don't know how to adjust their valves.
billy bob on December 05, 2011:
Yes .002" would make a difference if the adjustment was "out of specifications" like for example .007" like your saying. Im not saying that though. What Im saying is I can adjust the valves at .004",.005",.006" or anything in between .004" and .006" (which is a .002" difference) and according to the manufacturer they say this is fine because these are the actual specs. their recommending. What your telling me is this .002" difference is not acceptable. Tell me what you would set the valves at if the recommended specs. were between .004" and .006"
PK Jones (author) on December 05, 2011:
Think about it like this. As the lobe on the cam turns and the lifter follows it, the lobe begins to lift the lifter. If your lash is too tight, the valve will be opening early on the lobe's travel. If it's loose, it will open late on the profile.
From .004-.006" is the amount of lash required to open the valve at the proper time on the lobe. Add .002" to the gap and the valve will open many degrees later on the lobe than if it were at .006". The lobe has a very sharp rise once you enter the ramp so even .002" will be a large change. From .004-.006" in this case starts the valve opening at the proper point on the cam lobe.
Valve lash is an adjustment made to control the opening and closing timing of the valves. The valves have to start to open and close within a narrow window on the cam's profile. Most people think valve lash is set to control the total lift on the valve, but it's not, even though lift is affected. It's all about the proper timing of the valves.
The manufacturer does say .002" makes a difference, attend any Briggs training school and they will cover clearances repeatedly. .004-.006" is the acceptable range in this instance. .007" would be out of spec.
billy bob on December 05, 2011:
Your missing my point. If the manufacturer is giving me specifications like .004" .006" for the valve adjustments it means a minimum of .004 and a maximum of .006 . When I went to school they told me there is a .002" difference between those 2 measurments. Why is the manufacturer saying .002" wont make a difference but your saying it will ?
PK Jones (author) on December 04, 2011:
.002" is enough to make a difference when you are adjusting valves. Set the intake lash at .002" when the engine likes .004" and most engines will start popping as the intake begins to open several degrees early.
Valve lash is about when the valve starts to open. Too loose and the valve opens late, too tight, the valve opens early. This is why most people have to try several times before they get it right. The reason you turn the engine 1/4" past TDC is because of the cam's profile. This is how Briggs designed the system, and how the valves on these types engines are adjusted. The slight rise in the profile that creates the compression release does wear which will change the measurements, which is another reason why you adjust at 1/4" past TDC.
billy bob on December 04, 2011:
If .002" is going to make a difference why are the specifications between .004 and .006 ? These specs mean your adjustments can be either .004 or .006 or anything in between. Which is a .002" difference. This is why I set mine at .005" It runs fine.
billy bob on December 04, 2011:
I think your referring to .004 and .006 as being the limits. .004 being the smallest and .006 being the largest setting. Like I said before... I adjusted both valves at TDC to .005" (middle setting) and the followed your proceedure of turning the crank another 1/4 " past TDC and my original settings of .005" were the same. I found no difference.
PK Jones (author) on November 30, 2011:
.002" is enough to make a difference with the compression release. Although setting the valves tight is preferable to loose for performance issues. That said, not all OHV Briggs engines use the .004 and .006" specs, just most. I wrote this referring to Lawn Tractors specifically, which when having OHV Briggs engine, will have Intek engines 99% of the time and use the .004-.006" lashes. If in doubt, just refer to the Briggs chart at this link, http://www.nnyparts.com/briggsspec.pdf
billy bob on November 30, 2011:
Just for your information... .002 of an inch is less than a piece of paper. Not very much.
billy bob on November 30, 2011:
You said in the end you adjusted the valves at .008 and .005 . What else did you find wrong ? Your saying that the engine was hard to turn over. The valve adjustments being out that little wont make the engine hard to turn over.
billybladez66 on November 27, 2011:
great post. Had to attempt it about 4 times before i finally made progress. In the end i wound up setting the exhaust at .008 instead of .006 and the intake i set at .005 instead of .004. After setting it this way my flywheel finally purred over nice and smooth without the help of a jump start from the trusty F100. This is something i will make sure to keep on eye on from now on. Btw, on my troybilt (2002, 18 hp ovc) my exhaust valve was on top as i faced the engine. I could tell because the exhaust pipe was attached at the top, to the left of the valve, so i assumed it to be exhaust.
robare15 on November 19, 2011:
I had the same problem with my 16.5 Hp Briggs engine.
The instructions here are excellent and helped me solve the problem.
However, not before frying a starter motor.
I bought a new starter from dbelectrical.com ($43)and my tractor starts like new.
PK Jones (author) on November 15, 2011:
My statement reflects that if one valve is completely open, then the other valve would be at the same position as it would be at TDC, meaning it would be closed. Not that both valves are completely open. The inherent problem with using this method on Briggs engines is that the valve needs to be in phase on the cam with the piston 1/4" past TDC. The method of adjusting valves with one fully open and adjusting the other valve is an old method used on many pushrod engines. You simply bring one valve fully open, rock the crank back and forth to find the loosest spot in the other valve's lash and then adjust. Then repeat for the other valve. People have been using this method for decades on all sorts of engines, works pretty well for multi-cylinder engines when you don't have a book to tell you what cylinder corresponds to the other.
Frank on November 15, 2011:
This is what you've stated..."Having one valve completely open would have the other at the same position." Its impossible to have both valves "completely" open. Unless theres a problem with the engine timing.
PK Jones (author) on November 08, 2011:
On the Briggs engines it's important that you are beyond Top Dead Center and have the cam at the right position, which is the reason for going 1/4" past TDC. Using the method you mention, it would be difficult to know just where on the cam's profile you are. Having one valve completely open would have the other at the same position as at TDC so you would have to try to factor that in on each valve. Not that it couldn't work, just that the method in the article is the easiest way and insures both valves are adjusted in phase.
kandk920 on November 08, 2011:
I have also seen the valve lash adjusted by rotating the engine until one of the valves is completely open, then adjusting the lash on the valve that is closed, then repeating for the other valve. How is this different than the method you explained? Thanks
PK Jones (author) on October 17, 2011:
Hi, I can't do diagnostics on this site due to an agreement with another site and the format of Hubpages really doesn't allow well for it anyway. I will tell you that the muffler glowing red is probably an overly lean condition in the carburetor. Pull the spark plug and it's probably gray and ashy. This would mean you have a carburetor that needs to be rebuilt or replaced most likely, although an air leak could also cause this. There are a few other things that could be responsible but that would require more indepth diagnostics and I just can't do that here. A carburetor issue would be the most likely though.
If you look at the intake manifold, you should be able to see that it is in line with the intake valve, same for the exhaust valve and the exhaust manifold.
Bob on October 16, 2011:
Sorry Nick. The intake is usually larger and exhaust is usually smaller. The valve your describing on the top , is the intake.
Bob on October 16, 2011:
Hey Nick. The intake valve is usually smaller and is in the block closest to the carburater. The exhaust valve is usually larger and in the block closest to the muffler. When your asking if the valve is closest to the top... Im gonna say your describing the intake valve.
nick on October 16, 2011:
Hello,New to this but how do you know what valve is the intake and what valve is the exhaust?Is the valve closest to the top of the engine the intake or exhaust?
Bob on October 16, 2011:
The muffler was glowing red on my old Briggs. Is this because the valves are out of adjustment ?
PK Jones (author) on September 17, 2011:
Jerel on September 17, 2011:
Hey there, I am a 15 year veteran automotive technician with much experience in small gas engines. I had never ran into this one and the post helped a bunch.
dave on September 14, 2011:
Finally someone explains why it needs to be 1/4 past TDC.
I've always been curious.
PK Jones (author) on September 12, 2011:
Hi, I can't really diagnose in this forum. If the engine is still hard to turn over then you may have another issue or even a worn cam. It would require a good bit of back and forth to work through it and I'm just not able to do that here. Thanks, PK.
Joe on September 12, 2011:
I adjusted the valves to .005" at TDC and then checked the valves a 1/4" past TDC and there was no difference. The engine runs fine.
PK Jones (author) on September 12, 2011:
The valve stems shouldn't have any lateral movement, only up and down. If the valves are moving around side to side, then the guides are probably bad and head replacement is the best fix.
Jack th wack on September 11, 2011:
I will try your procedure. My initial problem was a broken push rod. I put it all back together but it only ran for a minute. . . Roughly at that. One Q though; The valve shafts are grooved circumferencely. If the valve shaft is supposed to be locked in and move only within a certain range, is it possible that they can move out of place within a range of travel resulting in a gap so wide it can't be adjusted to spec.? The rocker arm then flops around all over the place. More after I try the valve lash adj. Thanks for your help.
(Engine is a B&S model 310707, type0136-E1, 16HP Sears riding mower)
Bill on September 03, 2011:
Thanks for the tip. I replaced the head gasket on my craftsman lawn tractor, and afterwards it was hard to start with the symptoms you described. Did the procedure, and it works like a champ. Hardest part was finding a feeler gauge. (Went to Walmart and Ace before going to an Auto parts store).
PK Jones (author) on August 31, 2011:
The way the camshaft is ground requires you to move the piston 1/4" past TDC so that you have an accurate lash. Adjusting at TDC on many Briggs engines will give you too loose an adjustment. Other makes, and some Briggs engines, can be adjusted at TDC.
Joe on August 29, 2011:
Why do you have to continue to move the piston another 1/4 of an inch past TDC ? Is this minor movement going to make a difference ? Thanks
dakota on August 12, 2011:
My mower started doing this very exact thing this week. I went thru the entire electric from battery, sol and removing starter to test it. Removed plug engine spun fine, replaced plug and as soon as it hit compression it stopped. I can jump it with a jump box it does fine. Tomorrow I will do the above to the letter I will let you know. Thank you for your article. I feel sure its this.
Todd on July 30, 2011:
This is so true. Ive been building motors for my late model for 18 years and winning on good nights. Never thought my 14.5 BS had a valve lash issue. Ive been starting it with a jumper box all f n year. 20min an it is back like new. I used a pencil for the TDC -1/4 worked great. Thank you saved me buying a rider. One time a rain out at all three tracks was worth it.
Mike E. on May 15, 2011:
thank you, Exactly the problem .
PK Jones (author) on April 13, 2011:
Glad it helped y'all. Remember to include valve adjustment as an annual maintenance item.
J. W. on April 13, 2011:
Have had starting problems with my Sears riding mower for over 2 years. Last summer (2010) paid some small engine "expert" $180, and he replaced the starter and battery. Same problem after he left.
Saw your article and tried it. Had never adjusted valves on any type of engine. Took me a few tries to "get the feel" of what I was doing, but finally put the valve cover back on and gave it a try.
ENGINE STARTED IMMEDIATELY AND CONTINUES TO DO SO. Thanks very much for your valuable info.
Al on March 01, 2011:
That did it! Intake valve adjustment was .oo6" instead of .004", once adjusted correctly it made all the difference in the world.
Thank you for posting!
Mark on January 29, 2011:
The engine on my Craftsman lawn tractor would only crank once and not start. I was thinking it was the starter but found your article, followed the steps, and it started right up. Thank you.
PK Jones (author) on October 22, 2010:
Glad it was of some help. It's surprising the number of shops which fail to catch this one.
Mark on October 15, 2010:
Thanks a ton. Brought my Rider in twice to have the issue looked at. They just kept telling me the battery was bad. It took me 15 minutes start to finish and the engine starts and runs like a top. Yee Ha!
PK Jones (author) on June 12, 2010:
Hi, yes, the engine needs to be at 1/4" past Top Dead Center (TDC). At TDC, the intake valve has just closed and the exhaust has not begun to open. The piston must be at 1/4" past TDC, so be sure to follow the instructions above for how to find that spot.
D.J. on June 11, 2010:
does the piston need to be in same place for the intake and exhaust valve to be adj.?
PK Jones (author) on April 18, 2010:
Thanks! I'm glad it helped.
Pdemps on April 18, 2010:
Thank you, very helpful and save me $$. I appreciate it, best written article on the subject I could find.
PK Jones (author) on April 03, 2010:
Thanks for reading it.
electricsky from North Georgia on February 27, 2010:
Thank you for your article