compression Baaad. now what?

[bounce]

just checked my 240's compression and found:

115

75

75

50

50

115

the first three plugs were black and sooty...the other three were almost new looking...becasue they are...(maybe an hour on the new plugs)

what are options? Leakdown test first?

buy another motor? rebuild mine?

Sea Foam? check valves/adjust? timing chain?

thanks

Edited August 26, 2010 by bounce

[d240zx2]

First, describe how you conducted the test.... If done incorrectly, you will get real erroneous readings...

[Gary in NJ]

Those numbers look unusually low. Was the engine working at all? I ask because I do not believe those values would support combustion. Do you perform the test at WOT? Is the compression check gauge in proper working order?

[bounce]

ahh OK...

I borrowed a comp tester from my mechanic...he said to watch the needle twitch 5 times to get the number....

got home, pulled plug #1 (closest to radiator), screwed in air hose to plug hole going about 50-60 % of hand tight....attached comp gauge to the hose fitting..... turned engine over watching the compression gauge needle tick 5 times....

I let it go a couple more times as well on #1 and it almost reached 125psi

replaced plug#1

removed plug #2 (second away from radiator)....screwed in air hose...hand tight....attatched gauge....turned engine over watcing five ticks on the needle occur...

yes the engine runs right now.

Edited August 26, 2010 by bounce

[d240zx2]

Nope. You did it wrong... that's why your numbers are so screwy...

Warm engine to normal operating temp.

Remove all spark plugs.

Wedge throttle to wide open.

Conduct your compression test, preferably with a screw-in type of tester.

Your numbers should now be accurate.

[bounce]

WTO ...had to look that up..... it's the same as WFO

thanks for the quick responses....I owe ya'll beers when you pass through AZ...

yeah...engine was cold....pulled one plug at a time.....and no throttle setting

so...with the first three plugs being completely black and sooty...and the last three being in new condition after one hour of driving on new plugs....is that a carb setting?

Edited August 26, 2010 by bounce

[d240zx2]

Potentially. Your front carb could be overly rich (and likely is, based on what you described). Have a conversation with Bruce Palmer about that.

Go re-run your compression test and let us know the revised numbers. I think you'll be surprised!

[Shade133]

could be. replace all plugs to new condition and check regularly.

and WOT = wide open throttle. important while doing compression test.

[bounce]

heh, I gave Bruce my credit card info earlier this moring for shiny carbs.

yes, reborrowed the threaded comp tester.... will check them out later this afternoon..

Edited August 26, 2010 by bounce

[bounce]

could be. replace all plugs to new condition and check regularly.

and WOT = wide open throttle. important while doing compression test.

and WFO? wide &^%&% open

[Shade133]

aha nice. let us know how the compression goes.

[bounce]

so after the intial compression test...should I add oil to the cylinder to see if compression goes up to isolate weak rings if compression is below a certain number? and how much oil should be squirted in a cylinder?