Cracked heads now used engine-gctid816716

[Chingwow]

Hello all i have another post up about my heads being cracked. 92 2655 is what i have. Its about 1000 for heads from good places i.e Michigan motorz and what have you. I came across a guy who took his 5.7 merc out of his 92 boat. And will sell me the motor for 1500 no manafolds or carb. No big deal to me im pretty sure mine will bolt up to it no problem. Im going to do a compression test on the cyclinders while its on the stand and running. My question is what is a good psi reading and what is low and no good psi reading? Thanks for the great info already!

[Download_Complete]

SHould be 140 - 160 or so with no variation across.

[driz]

"Download_Complete" post=816717 wrote:
SHould be 140 - 160 or so with no variation across.

Uhhhhh. Ain't that in that perfect world I keep reading about? For most of us earthly beings it's more like no more than 10 psi difference. Anything less is pretty meaningless unless you're racing in most circles.

[builderdude]

Used 5.7, mine was 142-145 ish. After new heads it's 152-155 ish.

[yachtman]

If it's used it will probably be close to 140 psi. Nothing wrong with that.. You will have variations probably up to 5-7 psi. Over 10.is a no go and even at 10 psi variation is concerning. If you do a compression test do it warmed up if you can throttle open all plugs out. A cold compression test can give you low readings it the most important thing is what is the variation

[Chief_Alen]

You could polish the valves to allow them to seat better. Old school.

Easy to do .

Fresh water lake engine i say go for it.

[Download_Complete]

"driz" post=816733 wrote:

"Download_Complete" post=816717 wrote:
SHould be 140 - 160 or so with no variation across.

Uhhhhh. Ain't that in that perfect world I keep reading about? For most of us earthly beings it's more like no more than 10 psi difference. Anything less is pretty meaningless unless you're racing in most circles.

I was in a hurry when I typed that, sorry. You are correct.

[Chingwow]

"Chief Alen" post=816815 wrote:
You could polish the valves to allow them to seat better. Old school.

Easy to do .

Fresh water lake engine i say go for it.

Thanks for all the info ots been great! Alen could you post a link to the old school polish, or possibly break it down for me? Got me wondering how thats done!

[88fourwinns]

An engine can have cracked heads and still have normal comp test results. I would rather put garanteed re man heads on a good block that take a chance on used ones from a unknown source. The port n polish referred to above is best performed by a speed or machine shop.