Loose keepers?
What causes the OHV's to go out of gap ?
I think I worded it ok.
What causes the valves go out of gap .. I seam to have to fix this problem a lot..
How do you stop it from doing so often ?
This is on my Craftsman Lawn tractor.
What causes the valves go out of gap .. I seam to have to fix this problem a lot..
How do you stop it from doing so often ?
This is on my Craftsman Lawn tractor.
1 - 18 of 18 Posts
Lots of things can cause the valve lash to change..
Rocker arm studs pulling out of the cylinder head.
Rocker arm adjusting screws wearing down where they touch the valve stem or where the push rod seats..or the adjustment screw doesn't hold its setting.
Cam lobes wearing down.
Push rods bent.
Valve lifter or follower worn down.
Excessive valve guide clearance..
Rocker arm studs pulling out of the cylinder head.
Rocker arm adjusting screws wearing down where they touch the valve stem or where the push rod seats..or the adjustment screw doesn't hold its setting.
Cam lobes wearing down.
Push rods bent.
Valve lifter or follower worn down.
Excessive valve guide clearance..
Couple of random thoughts here.
Assume this is an OHV engine and requires adjustment much more frequently than the manual recommendations, poor fitting adjusting nuts or jam nuts or the studs might be working loose. Depending on engine, studs may be pressed in or threaded.
You might try putting a mark on the nut/stud after the next time you adjust. After a time, if the valves go out of adjustment again, check to see if the marks are misaligned, indicating the adjusting nut is loosing grip and allowing it to back off. At the base of the stud where it enters the head casting, you might try the same thing. Mark it with a scratched line. A pressed in stud will be harder to detect, and may require a depth gauge to compare before and after stud to casting height. A screwed in stud will show the misaligned marks if it is working loose from the head casting.
Check all contact surfaces too. Improperly heat treated valve tips or other contact points can wear.
Not sure if overheating can impact valve adjustment, maybe someone with more experience with overheating can comment.
Assume this is an OHV engine and requires adjustment much more frequently than the manual recommendations, poor fitting adjusting nuts or jam nuts or the studs might be working loose. Depending on engine, studs may be pressed in or threaded.
You might try putting a mark on the nut/stud after the next time you adjust. After a time, if the valves go out of adjustment again, check to see if the marks are misaligned, indicating the adjusting nut is loosing grip and allowing it to back off. At the base of the stud where it enters the head casting, you might try the same thing. Mark it with a scratched line. A pressed in stud will be harder to detect, and may require a depth gauge to compare before and after stud to casting height. A screwed in stud will show the misaligned marks if it is working loose from the head casting.
Check all contact surfaces too. Improperly heat treated valve tips or other contact points can wear.
Not sure if overheating can impact valve adjustment, maybe someone with more experience with overheating can comment.
On my old tractor with a 17 hp Briggs I used to have to set the valves once a year otherwise it would build compression and not even turn over. Their tricky devils to set valve lash on.
I ended up setting it on the loose side and it’s been good for a year and a half so far.
I ended up setting it on the loose side and it’s been good for a year and a half so far.
They should not need frequent adjustment. Most of the wear occurs in the first couple of years and then everything is polished up nicely and little wear occurs for many years.
Most valves wear in the valve sealing area margin and all that stuff. They sink further into the head as they wear and make clearance smaller.
The OHV briggs don't do that enough to make up for the metal wear off of the rocker arm and push rod and rocker arm and valve stem cap mainly and I assume the push rod and lifter too. It wears so much that the gaps always get larger NOT smaller.
That is why they are hard to start when out of adj. The gap is too much for the ACR to move the valve open enough.
EVERY time I am in briggs valve cover I remove rocker arm so I can check stud for tightness. Epidemic of the (esp exhaust) loosening up.
Tighten well or take out clean and loctite then tighten.
Now assuming you have the hardened valve stem cap on each valve stem and the oil is not nasty black and gritty, they should stay in adjustment for years.
Most valves wear in the valve sealing area margin and all that stuff. They sink further into the head as they wear and make clearance smaller.
The OHV briggs don't do that enough to make up for the metal wear off of the rocker arm and push rod and rocker arm and valve stem cap mainly and I assume the push rod and lifter too. It wears so much that the gaps always get larger NOT smaller.
That is why they are hard to start when out of adj. The gap is too much for the ACR to move the valve open enough.
EVERY time I am in briggs valve cover I remove rocker arm so I can check stud for tightness. Epidemic of the (esp exhaust) loosening up.
Tighten well or take out clean and loctite then tighten.
Now assuming you have the hardened valve stem cap on each valve stem and the oil is not nasty black and gritty, they should stay in adjustment for years.
If it's an ohv 31xxxxor 33xxxx that is opposite of how it is supposed to work.On my old tractor with a 17 hp Briggs I used to have to set the valves once a year otherwise it would build compression and not even turn over. Their tricky devils to set valve lash on.
I ended up setting it on the loose side and it’s been good for a year and a half so far.
Loose valves MAKE it hard to start. Well loose intake actually.
I like exhaust valve to be on the loose side as they cool when they are closed..or so the story goes. I don't have a way to test that rule of thumb.
It ACR pushes up a little bitty bit on the intake lifter and if the clearance is too great is just takes up the gap and doesn't even move the rocker arm enough to open valve.
I adjusted them on the looser side of the specs. If the called for say 3-7 thousandth I went on the 7 side.
7 will work, but tighter will keep it in adjustment longer
Bad idea.I adjusted them on the looser side of the specs. If the called for say 3-7 thousandth I went on the 7 side.
Walt Conner
The intake and the exhaust do not both set at the same spec on a single. I think we were talking about a single. Or at least over head valves in general and singles definitely do not set to the same spec intake and exhaust.
Most are intake .003-.005, exhaust .005-.007
You should keep the intake at least a tight .005 so you can compression release will work longer.
Most are intake .003-.005, exhaust .005-.007
You should keep the intake at least a tight .005 so you can compression release will work longer.
I was just using the one measurement as an example. I set both valves different but more on the looser side of the specs
As was said... Normally they stabilize after the first few adjusting till the engine gets to the point that wear takes over. Im guessing they are getting looser? Really unless there is unknown background on the engine, or you are using it in a different environment then expected, you can really set the specs on the tighter end of the range and be fine. Also checking clearances can be a little bit of a art form. Are you sure your not going to loose to start? the gauge should barely go in.. I normally check with the go/no go system... Ill take a gauge that's the tight end, and one at the loose end.. set it so the tight just slips in, and the bigger one will not... that will get you smack on in the center of the range.
" Also checking clearances can be a little bit of a art form. Are you sure your not going to loose to start? the gauge should barely go in.. I normally check with the go/no go system... Ill take a gauge that's the tight end, and one at the loose end.. set it so the tight just slips in, and the bigger one will not... that will get you smack on in the center of the range."
I agree, I set the Intake close to the minimum.
Walt Conner
I agree, I set the Intake close to the minimum.
Walt Conner
weak valve springs are a possibility as well
Don't forget most OHV engines have a compression release that works at 300 rpm or less to make the engine easier to start. When you adjust the valves you need to turn the engine past top dead center. I usually like to see the piston move about a 1/4" down the cylinder so I'm fairly certain the valve is fully closed or seated.
Also invest in a torque wrench, you don't want to guess at the tightness of the locknut or you may snap off the valve adjuster stud. It's easy to think you have it tight enough when you don't and then next time when you think you didn't tighten enough really twist it and snap it off.
Also invest in a torque wrench, you don't want to guess at the tightness of the locknut or you may snap off the valve adjuster stud. It's easy to think you have it tight enough when you don't and then next time when you think you didn't tighten enough really twist it and snap it off.
Good point... The last Briggs Vtwin I adjusted, the manual showed to set it just a bit off TDC on the cyl.. I don't remember the deg... but it was in the book.Don't forget most OHV engines have a compression release that works at 300 rpm or less to make the engine easier to start. When you adjust the valves you need to turn the engine past top dead center. I usually like to see the piston move about a 1/4" down the cylinder so I'm fairly certain the valve is fully closed or seated.
Also invest in a torque wrench, you don't want to guess at the tightness of the locknut or you may snap off the valve adjuster stud. It's easy to think you have it tight enough when you don't and then next time when you think you didn't tighten enough really twist it and snap it off.
All Briggs v twins and pretty much all Briggs overhead valve engines at least all that I have ever seen or know of set the valves at a quarter inch past top dead center on the compression stroke.Good point... The last Briggs Vtwin I adjusted, the manual showed to set it just a bit off TDC on the cyl.. I don't remember the deg... but it was in the book.
You can pretty much just assume that if it's a Briggs & Stratton overhead valve you're going to set the valves this way at least a quarter inch past top dead center. A lot of people get all hung up on the quarter inch part. That is just the minimum you need to go to make sure the valve which is typically the intake valve it's not still on its compress release bump and being held slightly open. You can go 1/2 inch you can go 1 inch, you can go two and a half or three inch if you want. The only thing that matters is that you don't go down so far that the exhaust valve is starting to open because the Piston is getting ready to come back up and exhaust he spent Fuel and combustion gases.
On most engines there is a nice little flat spot that you can feel when you turn the flywheel over right after top dead center which is just slightly past 1/4 inch down. That is a fine spot to set them at.
If it's a Kohler Courage, you set them at top dead center. If it's a Kohler Command, you don't set them because they have
hydraulic lifters and they do not have or need adjustment.
Kawasaki sets at top dead center also.
The adjusting nut on the Briggs is hardened steel and will snap if you tighten it too tight but you should not be tightening that way anyways. The way Briggs & Stratton tells you to do it is to adjust the adjusting nut and hold it with your open end or box end wrench. Then you take the T20 nut driver and tighten the lock nut by hand. I don't know of anyone with enough hand strength who can crack one of the Adjusters with a T20 nut driver that's not a T handle. So if you do use a T handle or one of the fold-out wrench sets don't go crazy on it remember it only needs to be hand type of a screwdriver handle and may be ever so slightly more. I have never seen an adjuster loosen up on a Briggs & Stratton engine but I have seen many rocker arm studs loosen out. So apparently the lock nuts are not a problem.
1 - 18 of 18 Posts
- This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
My Tractor Forum
A family friendly forum community dedicated to all Tractor owners and enthusiasts. Come join the discussion about specifications, modifications, troubleshooting, maintenance, and more!
Full Forum Listing
Join now to ask and comment!
