470 Compression results after engine rebuild

[Rake722]

Hi All,

ive just installed the 470 after a full rebuild and she runs nice and quietly but I have odd compression results.

tested cold I get

100
125
115
120

i would have expected closer to 150 psi ?

now the head has been skimmed flat and the valves reworked.

coukd the compression result reflect tight valve clearances ?

i don’t have the tool to depress the lifters which are also new.

the gauge I used was a cheap £10 eBay item so it could be a poor quality gauge.

any advice would be appreciated

thank you

 

[Scott Danforth]

for a rebuilt motor, the numbers look low. cranking compression numbers from the mercruiser book are 150 psi. http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/18

if someone came to me with those numbers, I would say it needs a rebuild.

do a leak down test. that will tell you where your issue lies

get a good quality gauge

 

[Scott06]

You ran this cold ? Get it warmed up first and maybe borrow another tester or test yours vs a known gauge

 

[Rake722]

Thanks both.

i did the test both cold and at op temp.

similar results of not a touch higher when warm.

will try the leak down test.

so you don’t think valve clearance could be the issue ?

 

[Scott Danforth]

the leak down test will tell you where the problem lies.

it could be valve clearance. did you measure the pushrods? I believe that there is a process called out in the manual

did you switch to adjustable valve train? (google ford FE engine adjustable valve train)

stock steel head, or did you upgrade to aluminum?

 

[Rake722]

Hey Scott thanks for the reply.

i did not measure the rods nor did I switch to and adjustable system.

its the stock steel head sent to an engineering company who reworked the head.

im very much hoping it’s valve clearances in this case