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low compression test results.
MrMaddog - 14/1/21 at 01:13 PM

In my ever running quest to get my 2.0 Pinto running well, I have the following results from a recent compression test.


The test was done with the engine hot, all plugs removed and full open throttle.
No1 190psi
No2 190psi
No3 160psi
No4 190psi

No3 plug was also black and oily looking.
The other three had a nice light brown tip.

when the engine is running it almost seems like its running on three cylinders with a lot of backfiring and spitting back into the carbs.
New coil, distributor, leads, plugs and carbs stripped and rebuilt.
I have also timed in the cam to be sure, but no change to the running.
I just can't get it running smoothly????

Any thoughts????

Thanks in advance.

joneh - 14/1/21 at 01:48 PM

Probably a snapped or worn piston ring, thinking about oil present and low compression. Could also be a knackered valve guide.

MrMaddog - 14/1/21 at 02:51 PM

The engine was allegedly rebuilt less than 2000 miles ago and has sat for almost 6 years .
Could it possibly be a stuck piston ring?

joneh - 14/1/21 at 03:06 PM

quote:
Originally posted by MrMaddog
The engine was allegedly rebuilt less than 2000 miles ago and has sat for almost 6 years .
Could it possibly be a stuck piston ring?


Maybe, I'm not familiar enough with a pinto to understand how that happens, or if its possible to get it to pop out of the grove without stripping it down. Try soaking the piston in oil overnight and crank by hand? Make sure its drained before firing back up?

I stripped down a freshly rebuilt crossflow a few years back and a unused piston ring had snapped.

Ignore my previous valve guide comment, I don't think this would show low compression.

rusty nuts - 14/1/21 at 03:41 PM

Have you checked and adjusted the valve clearances ? A tight valve will cause loss of compression and spitting back . Did you recheck the cylinder that had low compression? What carb(s) or throttle bodies are you using? Unbalanced or badly adjusted mixture would cause one plug to be black and that cylinder may have suffered borewash Have you eliminated any ignition problems which would cause black and oily plugs etc ?

MrMaddog - 14/1/21 at 06:40 PM

quote:
Originally posted by rusty nuts
Have you checked and adjusted the valve clearances ? A tight valve will cause loss of compression and spitting back . Did you recheck the cylinder that had low compression? What carb(s) or throttle bodies are you using? Unbalanced or badly adjusted mixture would cause one plug to be black and that cylinder may have suffered borewash Have you eliminated any ignition problems which would cause black and oily plugs etc ?


Yes I have checked valve clearances all ok!
Carbs are twin Dellorto DHLA 40

spiderman - 14/1/21 at 09:46 PM

Do a wet compression test, put a couple of squirts of oil into offending cylinder and redo compression test, if it rises it's the rings if there is no change then the valves are not sealing properly or possibly head gasket starting to go.

steve m - 14/1/21 at 10:11 PM

I would echo the above, do the same test, as in hot engine, with wide open throttle, and try again,
Then oil all cylinders with the same amount and do it again,

190 is a bit low in my opinion, as i was always in the 220-230 bracket on my xflows