compression on looper engine

black1

Recruit
Joined
Jul 16, 2008
Messages
3
Hello I have a 1989 v6 johnson looper engine and was wondering what would be concidered good compression: I have 72-75 psi on all cyl but dont have the power I think it should -brought to marina -they striped spark plug hole, didnt tell me till later just said the engine is wore out . starts up good and idles fine it is on 19' statos bass boat with 14.5x26 prop top rpm was 3500 --changed prop to 14.25x17 4 blade and still only could get 4900 rpm any help is appreciated thank you
 
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tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: compression on looper engine

Welcome to iboats. there are no published numbers. guide we use is ; over 100psi, but most important is that they are within 10% of each other. post your results, you will get opinions.
 

black1

Recruit
Joined
Jul 16, 2008
Messages
3
Re: compression on looper engine

does that indicate a rebuild ?could i get away with rings and have the bores honed? thank you
 

crb478

Lieutenant Junior Grade
Joined
Dec 6, 2006
Messages
1,036
Re: compression on looper engine

Hello I have a 1989 v6 johnson looper engine and was wondering what would be concidered good compression: I have 72-75 psi on all cyl but dont have the power I think it should -brought to marina -they striped spark plug hole, didnt tell me till later just said the engine is wore out . starts up good and idles fine it is on 19' statos bass boat with 14.5x26 prop top rpm was 3500 --changed prop to 14.25x17 4 blade and still only could get 4900 rpm any help is appreciated thank you

Have you checked the compression on the engine? 72 - 75 is low, but I would expect the cylinders to be more than 3psi apart if it was indeed worn that far. All guages read different. Get a screw in compression tester that holds the reading and take all of the plugs out. Make sure the battery is fully charged and turn the engine over 4 or 5 revolutions on each cylinder until it reaches the highest reading. Then report back what you find.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: compression on looper engine

If the psi numbers are close and the engine runs well forget compression, Black1.

I think you are still overpropped. What boat is it on?
 
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