470 engine compression results, good?

[dccordell]

Since I finally got the 470 running the other day, I wanted to do a compression test before it goes back in the boat. I did it today.. results:

1: 145
2: 160
3: 150
4: 160

As far as I can tell, those seem like pretty good numbers. I do wonder why 2 and 4 are higher than 150 though, since 150 is what is listed in the manual. Could this be sign of a sticky valve?

Should I be satisfied and move on?

 

[madman2021]

Re: 470 engine compression results, good?

theres wet and dry tests. wet is with fuel or small amount of oil dry is no fuel or oil. those cylinders might have had some exxcess fuel in them causing your higher than normal compression.

 

[GLENN M]

Re: 470 engine compression results, good?

as far as i know valves dont stick closed,not without breaking something .they stick open,giving you less compression.your discrepancies could be in gauge,a earlier rebuild ie;head milled,block decked,thinner head gasket.or carbon on piston.

 

[dccordell]

Re: 470 engine compression results, good?

Ok, sounds like I don't have anything to worry about then. Really didn't have a clue on the valves because I know only the very basics on how all that works.
I didn't add any oil to the cylinders because I understood that oil was only added if one cylinder was low and the oil would indicate worn rings. But I did crank the motor and let it run for about 10-15 seconds before I did the test. I just wanted to let the rings and valves move a few times before testing..

Thanks for the responses.. moving on to the next thing! Fiberglass and wiring.. ehh

 

[stonyloam]

Re: 470 engine compression results, good?

Yeah I would say you are OK. What you want to look for in a 470 is significantly LOW compression especially in #3 of #4 (especially 4) cylinders.

 

[dccordell]

Re: 470 engine compression results, good?

What you want to look for in a 470 is significantly LOW compression especially in #3 of #4 (especially 4) cylinders.

Yeah I was worried about that.. got lucky again I guess. Does that problem with #3 and #4 usually come up with an overheat?

 

[stonyloam]

Re: 470 engine compression results, good?

Yeah I was worried about that.. got lucky again I guess. Does that problem with #3 and #4 usually come up with an overheat?

Yes, BUT could happen even if it never overheated, mine did! I think that for a 470 it is a good idea to do a compression check as part of the annual maintenance. If you do it at the end of the season you have all winter to fix, if anything is wrong. Good luck.

 

[zbnutcase]

Re: 470 engine compression results, good?

Being within 15psi from high to low is just fine

 

[dccordell]

Re: 470 engine compression results, good?

Yeah compression test is easy enough to do every year... gives good piece of mind too.

Thanks for the input everybody... next time I'll be posting about compression will be when it's low