Is my compression okay? 160 to 115, 1978 350 chev.

[Half Fast]

#1 is 135, 2 is 160, the rest are between 135 & 115. This boat runs fine & I had no idea the compression was so wide ranging but I checked it just to see because the vacuum gauge wiggles a little bit. Now I'm wondering how long this engine may run before needing some work? Regards, HF.

 

[rodbolt]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

usually a wiggling vacum guage indicates a valvetrain problem. time for a leak down test. continued running with a valve train problem can lead to bad things. a flat spot on the cam can produce the same readings but will require valve cover removal to find. normally if a cam lobe goes bad the oil will be mettalic oil. but no that spread is bad. usually if you fix it before it dies its a bit cheaper.<br /> saltwater motors are usually not worth opening up at that age.

 

[Bondo]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

Now I'm wondering how long this engine may run before needing some work? Regards, HF.

Ayuh,............<br /><br />I'd say Now IS the Time............ <br /><br />rodbolt has you headed in the Right direction...........

 

[Half Fast]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

Yep, I was afraid of this response. I found the actual breakdown just now & it is, 1 to 8, 135, 160, 150, 150, 145, 140, 140, 115. Sorry I didn't have this on the first post, I couldn't find it then. I'm afraid the response will be the same anyway. Regards, HF.

 

[rodbolt]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

try a good decarb following the directions of whatever solution ya buy, you may wish to shock treat it as well. then run it under a load for 15-30 min and rerun the test, or have a leakdown test run to confirm or elimiate a leaking valve, leakdown gets my vote. a broken valve spring will give ya about the same indications, on the intake side the plug will be oil fouled more so than a broken ex side.

 

[Don S]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

Not sure how you did the compression test, or if you completed the compression test. But before you do a decarb, retry your compression test by the method in the Merc service bulletin link below. <br /><br /> Compression Test

 

[SeaRay24Sorrento]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

No mention of warming engine up prior, does that make much difference?

 

[birdy3897]

Re: Is my compression okay? 160 to 115, 1978 350 chev.

A warm engine will give higher reading since parts will expand and create a tighter seal in the cylinder. I do my testing with a warm engine