johnson 4r71d smoking head! Water obstruction?

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terrybridge

Seaman
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Jun 28, 2010
Messages
53
After checking impeller I installed I am starting to think I have some type of obstruction in cooling system, what is the best way to check? Does anyone know what the compression should be for a johnson 4r71d? I'm thinking i will need new head gasket, because compression is now at 60psi. Any advise would be greatly apprieciated.:confused:
 
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Rick.

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Jul 30, 2006
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Re: johnson 4r71d smoking head! Water obstruction?

Many times the pump is working and the problem is the leg isn't deep enough in the barrel. 60 is getting low for sure so a head gasket is a good idea. A seafoam treatment might loosen your rings enough to bring up the compression too but if your sure you overheated it the head gasket may well be shot. Giving a bit of history is never a bad idea. With the leg and head removed, hook a hose to the water tube and let water flush through the motor to prove flow. Best of luck. Rick.
 
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terrybridge

Seaman
Joined
Jun 28, 2010
Messages
53
Re: johnson 4r71d smoking head! Water obstruction?

Thanks for your help. This is my first attempt at rebuilding an outboard. This motor was given to me and had not been run in years. I checked compression and it was right around 100psi. I got it running and then head started to smoke, so i shut it down. I checked it again and it dropped to 60psi. I have replaced impeller. I will try running water through leg as you suggested and replace head gasket. Can you please explain seafoam treatment that you spoke of?
 
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