compression test

[thejinx]

:msn4: Ok. Not a full compression test but started today and had to stop. Tested number 2 and it came up 90 psi. Low I know. I am going to do the remainder on Friday. My question is what can I do. I put new rings and scrapers in 3 years ago. Should I be looking at new valves?

Just read. I am meant to have the throttle fully open. I didn’t.

Cheers

 

[sparkywig]

You need to test all the cylinders. 90 psi isn't low if they're all reading the same.

 

[thejinx]

Cheers Sparky

 

[thejinx]

Finally I have completed the compression test. They are as follows.

1 = 112
2 = 102
3 = 112
4 = 105

So I think that’s ok. That right?

Thank you

 

[sparkywig]

All about the same, which is good.
But all pretty low, did you do the test with the engine at operating temp?
Were the valve clearances checked before testing?

VW recommend compression pressure between 114-142 psi, with a maximum cylinder difference of 28 psi, and a wear limit of 100 psi.

 

[thejinx]

Read the books. Clearances were checked and were good. Engine had been running for half hour but stopped and had a brew before I removed plugs so warm not hot. I’m doing these checks as I am removing the engine over winter to change main oil seal (oil in bell housing). I want to check end float etc.

Thought it best to check incase I needed to do a top end rebuild. I changed rings etc less than 3000 miles back

 

[atafonso]

You probably need a good valve job and remember to replace the exhaust valves. When they drop is not pretty, i have a place in one of the walls full of "trophies" resultant of dropped valves lol

Abel

 

[thejinx]

By valve job (snigger) i take it you mean lapping them? i did this when i did the rings etc less than 3000 miles. I think i will just nurse this puppy for a few more years and see about a new or recon unit.

 

[atafonso]

By valve job (snigger) i take it you mean lapping them? i did this when i did the rings etc less than 3000 miles. I think i will just nurse this puppy for a few more years and see about a new or recon unit.

Laping would be the first thing to do, but after laping the valves could still be leaking. Sometimes the heat moves things and the seats can distort, so laping only will not do the trick. The seat would have to be reground or re cut.
You can test a valve leak by placing fuel inside the port and watching the chamber for any fuel signs, dead easy

Abel