Kohler compression release and valve clearance?

[2burning 1]

Has anyone else run into the compression release not releasing if they run their valves at the most clearnce specified? Kohler 16hp. I routinely set valves on mechanical lifter engines at the max specified, as I am told the normal wear pattern is for them to tighten up over time. But now it seems my compression release may not be working, or my starter (or battery cables, or ...) is getting weak? I haven't started working on it yet, just thinking about what it could be. Thanks!

[HubbardRA 19]

I have found several engines, that had quite a large number of hours on them but had never been worked on, that essentially had no valve clearance. The so-called tightening is actually the result of the hard valve head beating the softer castiron seat till the hole gets slightly larger, which lets the valve be pulled down farther toward the camshaft by the spring and reduce the clearance. On the other hand, since on the Kohler K series engines, there are small levers on the camshaft that trip open the exhaust valve at low turning speeds to reduce compression, the less valve clearance the engine has, the better this compression release will work. These releases on the Kohler engines are centrifugal in function and will kick-out and stop tripping the valves at around 1000 rpm. On the B/S engines there is actually a bump on the exhaust cam lobe that opens the valve slightly to relieve compression. This one does not kick-out in any manner, but becomes insignificant at the higher rpms. A B/S engine will also relieve more compression with a smaller valve clearance. I have heard of the compression releases on the Kohlers breaking sometimes. If this happens, it will be very hard to turn the engine over. I have a 10 Hp B/S that no longer has the compression release. It starts fine with a good starter-generator belt and a fully charged battery. It is definitely much harder to turn past compression than one with a functioning compression release.

[plastikosmd 952]

funny topic, cause i am just sitting down after dealing, and still dealing with my little crawler motor and too much compression. have cooked the original starter, 6v, so had an extra 12v sg from one of my allis's so welded up a bracket/mount and put that in hopin it would solve the problem. Sadly still have too much compression...every 4th stroke or so starter hangs. was lookin for one of those compression release fitting that can be put in a plug hole...just havent wrapped my mind around why i am having this problem. Dont know a great deal about small engines..and maybe am dealing with a worn "lobe" as mentioned above..will keep searchin.. scott

[HubbardRA 19]

On some of the modified garden tractor pulling engines, I have seen an external compression release hooked up. Usually it is made from a small valve from a very small 4 stroke engine. They use the valve and spring, and machine the valve seat into the adapter. The valve spring can be compressed, either by hand or with a lever controlled from the seat. This valve is opened, the the starter is engaged and allowed to get the engine spinning at a fast rate. The valve is then closed, and the engine usually starts instantly. It takes some design and machining to make one of these units, but they seem to work well.

[PeppyDan 3]

Last year I had a Honda Spree (scooter)with a 2 stroke engine. It suddenly seemed to gain a great deal more compression. I thought maybe the battery got weak, replaced it, starter going bad, replaced it with a known good one, starter switch going bad, replaced it! It was driving me nuts. I finally decided it had to be an internal problem. I started to remove gaurds & covers to remove the engine, and thats when I noticed some rust and debris wedging itself against the flywheel. I cleaned it up and fixed the mysterious increase in compression! I doubt this is the fix for you but just thought it would be worth looking at another angle to the problem! Dan

[JimS 1]

Anybody know how to fix the compression release on Tecumseh engines? I am working on a neighbors mower that is very hard to turn over and wants to kick-back.

[BLT 717]

quote:

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Originally posted by JimS
Anybody know how to fix the compression release on Tecumseh engines? I am working on a neighbors mower that is very hard to turn over and wants to kick-back.

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Before you worry about compression release, check for a partial sheared key on the flywheel. It has the symtoms.

[Al 6]

HI, I have fixed a number of these through the years. Probably 30 or so. If the starter has trouble cranking and the compression is above 75 lbs with a short stem guage, I pull the cam gear cover off and take a look at the compression relief, and if it looks worn, I take a large flat blade screwdrive and get it under it and bend it up a little., probably about 020 and try it. I know you are not supposed to do it this way, but it has fixed a number of engines for me and I have not had to tear them apart. Be careful not to overdue it. Better too little than too much. Al Eden

[2burning 1]

I finally had time to look at this. Compression is at 125psi cold, with throttle wide open. Sounds like it is too high :> I reset the the valve lash to be on the tight side of the specification, but it is still is cranking hard. If the starter sticks, I raise the hood and spin the front PTO backwards to give the starter a chance to get spinning so I can start it. Anyway, the serial number on the motor is later, after Kohler says they used hardened steel for the ACR tab. Al, or anyone else, when you bent these, were these the newer hardened ones or the ones previous to the serial number 9006118? If you have had success bending the hardened ones, I will try that too. If not, I was thinking about mounting a KT twin starter onto it to see if that will spin it over?

[D-17_Dave 12]

Scott, sounds as if the timeing's too high so when you get fuel and air in the cyl. and it starts to fire it fires too soon and kicks back against the starter. Just a thought.

[2burning 1]

Scott may be gone from this old thread, I was just starting it up again to report back. But my timing is acurate checked dynamically with a timing light :>

[HubbardRA 19]

Are you sure that you don't just have a tired starter? I have known guys who built Pro Stock pulling engines, with much higher compression and no compression release, yet they were still able to start them with a stock starter. The starter for the twin may not be as strong as the one for the single. Remember that on a twin there are two, much smaller cylinders and only one is on compression at a time. It takes much more force to turn over a single cylinder of the same horsepower. I still suspect starter and/or wires. I have a 10 Hp B/S that has had the compression release bump filed off the cam. So there is no compression release. I had problems starting it till I installed a 51R battery in that tractor. I still have to keep a good belt on the starter-generator, because it really likes to slip when that engine hits compression. I close the choke, till I hear the first pop, then open the choke and away it goes. It starts great and is my primary work tractor.

[2burning 1]

The twin starter is longer with the same OD, but Rod you are right you can't assume it has more power than the K starter just becasue it's bigger. Anyway, I see now it would hit the dipstick tube. I ended up getting a new K series starter. By mistake (ignorance) I ended up with a 10 tooth starter. After pulling mine off I see it had 13 teeth. So now I had to figure out if they interchange. I liked the idea of the 10 tooth becasue it would have a better advantage at spinning over a hard turning motor, but spin it a little slower. I ended up counting teeth on flywheels (all I could find and mine had 105) and comparing flywheel and starter part numbers on Kohlers web site and found many many instances of the same flywheel part number using a 10 and 13 tooth starter, so I bolted the starter on and it is working much better!!! No stopages so far! But it does labor pretty good. While describing my timing earlier I must have used some bad boy words that someone edited out, sorry I will use the acronym from now on - DOBA. Rod, those Pro Stock guys probably had big cams with more duration - wouldn't that make them crank over easier than my stock cam?