K301 Low Compression

[PWL216 890]

Hi. I have a C121 which starts right up but lacks power. A compression check indicated 30lbs of pressure. I took the head off hoping maybe it’s just a gasket, but I think the cylinder needs to be honed or bored out. Based on the attached pics, is this block still good and would honing fix it?

[PWL216 890]

I should mention that only the top of the cylinder looks bad, the stuff on the sides is just dust from my shop.

[squonk 41,311]

That engine has automatic compression release. You will get a low number unless you can spin the engine fast enough to override the release. A cylinder leakage test will give you more accurate results. Harbor Freight sells a decent tester.

 

 

[PWL216 890]

1 hour ago, squonk said:

That engine has automatic compression release. You will get a low number unless you can spin the engine fast enough to override the release. A cylinder leakage test will give you more accurate results. Harbor Freight sells a decent tester.

 

 

Thanks Squonk. Should I be concerned about the ridges at the top of the cylinder? 

[953 nut 55,744]

The ridge is the area above the ring travel. If it is just carbon build-up that is fine but it is probably a sign of the cylinder wear, you should be able to borrow or rent a "Ridge Reamer from most auto parts stores.

Here are two threads that should be helpful.

 

[richmondred01 2,238]

This looks more then just the typical ring ridge. Additionally, the cylinder appears to be pitted maybe from water sitting there at one point. 
I believe a bore will be required. 

Edited April 4, 2022 by richmondred01