Low Compression after valve adjustment

[Mbodd42]

Great site and I’ve found a lot of useful information to get a recently purchased 2001 TXT in working order. Recently I’ve replaced the plugs, fuel lines, cleaned the carb and adjusted the valves to .004. Initially we were having issues starting and taking off from a dead start. The valve adjustment fixed that.

It seems to run rich and after a dry and wet compression test I continue to get 90lbs on each side. Any suggestions on where to go next before getting into the valves? If valves are the logical next step should I start with lapping them or does it make sense to do more?

Thanks in advance for any advice.

[Cartmaster]

After equal wet and dry comp tests, then it is almost certain the inlet valves will need replacing. I doubt very much lapping will solve the issue. The earlier engines had "soft valves" which gave you an indication to poor air filtration as you find the need to adjust the lash as the valve edges wear out. The only other thing to give poor compression would be a leaking head gasket, so as you need to remove the head one way or another, just source new inlet valves and head, carb, exhaust gaskets and then it should all be good. Once you have done this, check the air filtration for leaks and repair as necessary.

EDIT.

If you will be driving hard set the new valves at .006

[Mbodd42]

Originally Posted by Cartmaster

After equal wet and dry comp tests, then it is almost certain the inlet valves will need replacing. I doubt very much lapping will solve the issue. The earlier engines had "soft valves" which gave you an indication to poor air filtration as you find the need to adjust the lash as the valve edges wear out. The only other thing to give poor compression would be a leaking head gasket, so as you need to remove the head one way or another, just source new inlet valves and head, carb, exhaust gaskets and then it should all be good. Once you have done this, check the air filtration for leaks and repair as necessary.

EDIT.

If you will be driving hard set the new valves at .006

Thanks a ton. I find myself adjusting the lash pretty often. I’ll take your suggestions and let you know how it works out. Thanks again.

[Cartmaster]

That pretty much confirms my suspicions! regular adjustment means that the edges of the valves are wearing thin and they are moving up into the valve seat. I guess it is the middle two valves needing regular attention?

[Mbodd42]

Originally Posted by Cartmaster

That pretty much confirms my suspicions! regular adjustment means that the edges of the valves are wearing thin and they are moving up into the valve seat. I guess it is the middle two valves needing regular attention?

Correct. The middle right valve seems to go out of adjustment almost immediately. Do you think I should go ahead and replace the exhaust valves while I’m at it?

[Cartmaster]

I don't think I have ever replaced any exhaust valves in my time lol.

[Mbodd42]

Good news and bad news. The top end rebuild was a success for a first timer. Both intake valves were in pretty bad shape. The engine runs much quieter now but.... the compression is still at 90. I replaced the air filter with an OEM filter and checked for a secure fit.

The only think I can think of is that I didn’t add enough oil when I tried the wet test originally. I’ll give that another look this week. I’m hoping those results change so I know which direction to go in.

[Cartmaster]

Ok, so once you have redone the wet compression test, we can decide where your problem lies. Hopefully you are doing the tests with the throttle wide open? If you get a good rise then it may be time for either just new rings and hone, or most likely a full rebore, new pistons and rings.

If you did not have the throttle wide open then do both wet and dry tests again and give us the results.

[Mbodd42]

Posting a few pictures of the valves before removal and replacement for others who are interested.

Also, I worked from the rebuild manual but rather than removing the clutch and components I was able to remove the cover from the timing belt, move it to the side, and remove the top pulley only which allowed me to remove the valves. I made sure to mark a position on the pulley and the corresponding tooth on the belt before removal. This allowed me to properly reinstall the pulley without messing up the timing.

[Mbodd42]

Well, another wet compression test with more oil and the compression shot up to 120. I have the rebuild manual which was easy to follow on the top end. Any recommendations on a rebuild kit sold online? Anything I can do without replacing and any items I shouldn’t overlook?