COMPRESSION NUMBERS

[LEADLAP]

I'm getting 125 psi in seven cylinders, 135 psi in one. (5.7 engine).
At what point would you want to go into the short block for a rebuild ? Below 125 ? Below 100 ?
Thanks.

 

[Bondo]

Re: COMPRESSION NUMBERS

Below 100psi,.....
Or a Difference of more than 15% between any of the cylinders........

Your motor might be alittle Tired,..... But Not worn out......

 

[paulie0735]

Re: COMPRESSION NUMBERS

Are you doing the test wet with throttle wide open?

 

[Trent]

Re: COMPRESSION NUMBERS

Nothing wrong with your numbers... I do compression tests all the time. If you checked your engine next month, the numbers will not always be the same due to temp, carbon buildup and humidity and a couple of other factors. Like was said they need to be within fifteen percent of each other before id be looking for a problem.

 

[LEADLAP]

Re: COMPRESSION NUMBERS

Thanks for the responses. (To answer paulie0735, the test was done in accordance with Merc. service bullentine for compression test).
I may pull the heads anyway to give the pistons and heads a lookover. It'll only cost me the price of a set of head gaskets.

 

[LEADLAP]

Re: COMPRESSION NUMBERS

Thanks for the responses. (To answer paulie0735, the test was done in accordance with Merc. service bullentine for compression test).
I may pull the heads anyway to give the pistons and heads a lookover. It'll only cost me the price of a set of head gaskets

 

[paulie0735]

Re: COMPRESSION NUMBERS

It'll only cost me the price of a set of head gaskets

You may want to re-think that; exhaust manifolds, risers inlet manifold, carb, t-housing, valve covers just off the top of my head. There’s probably more but all those gaskets at least will need to be replaced and at the end of it unless your gunna have the heads serviced than you just wasted a load of time and effort and gained nothing. If those numbers are bothering you that much than do a leak down test as per the manual to find out where your compression is going. If it’s getting past the rings than pulling the heads will achieve nothing. If it’s the valves than your will only know by doing the test or by having the heads serviced. If it is the valves than you will need to have the heads serviced anyway. Just pulling and looking is just that…………..

 

[cobra 3.0]

Re: COMPRESSION NUMBERS

If it ain't broke...

 

[paulie0735]

Re: COMPRESSION NUMBERS

If it ain't broke...

yup!

 

[Don S]

Re: COMPRESSION NUMBERS

Since you did the compression test by following the Merc service bulletin, did you do a dry test first and then a wet test to see if the compression changed?

See step 8 in the bulletin. Here is the bulletin if you don't have it handy.

http://www.boatfix.com/merc/Bullet/97/97_25.pdf