Shims won't budge

[Normk]

Is there a compression test "check list" posted here somewhere?

It could be a very useful resource rather than having to rely on someone thinking to post a critical point such as surviverguy's regarding the need to have wide open throttle.

If not, let's start a thread and work on one until we think it covers the subject adequately. Having the throttle wide open is such a basic thing that I often don't even think to mention but can take someone down the road to an overhaul....

Another couple are making sure that there is clearance on the valves as a valve staying open to any degree will drop compression markedly. Doing compression testing of a badly flooded cylinder can also provide low readings. Add another which is that deposits of ash on the valve face and seat can make for a low compression pressure and engine disassembly when the engine only needs a combustion chamber clean or even a good run at significant load.

I used to see Honda Civics on a weekly basis which were diagnosed for hard starting due to low compression. The owners would bring them to various shops for an estimate to over haul the engine after a winter of short, in city trips in the north. I'd send the car for a four hour return trip on the highway and compression would be back up to new. Gained every one of those customers...... The other shops weren't being dishonest but simply did not recognize the issue.


Anyone else use running compression tests?

That's another subject but can be useful in diagnosis.

Have the throttle open wide when testing.

 

[surviverguy]

I'm no engine guru- but this is my proceedure-
have throttle wide open
have fully charged battery
have all spark plugs removed
have ignition off or disabled
allow at least three compression strokes (gauge needle bumps 3x)
test all cyclinders dry then wet
record all readings as taken

not sure if there is thread or sticky on compression testing.
Results-generally 90-100 psi is the bare minimum to fire
120-150 normal pressure
above 150 is high
above 165 is too high
readings of cylinder pressures should all be within 10% of other cylinders

 

[surviverguy]

Low readings both dry and wet generaly indicate a bad valve. Low reading dry cylinder which goes up when wet generaly indicates worn/broken ring/s. Wet means about a teaspoon of motor oil poured into cylinder through sparkplug hole.