Use Extra Sealant on Sierra Head Gasket for 1957 OMC motor – Yes or No?

[h20lew]

Hi All. I’m replacing a head gasket on a 1957 Johnson 35 HP motor. I have a Sierra Head Gasket 18-2951 and I’m wondering if I should put this on dry or use a sealant. I have a factory service manual for my 1975 6 HP johnson and it says in there to use sealant on the head gasket. I read differing opinions – some say dry, some say lightly coat with sealant (such as OMC Gasket Sealing Compound). Looking for recommendations on what is the proper thing to do here.

• This topic was modified 5 years, 4 months ago by Mumbles.

[Mumbles]

Your new gasket looks like a self sealing one and is meant to go on dry although a little bit of sealant might not hurt anything. It might even have ‘Use No Sealant’ stamped on it somewhere. Just make sure the block and head surfaces are clean and dry before installing.

If a gasket is the old paper kind, then a sealant is required.

• This reply was modified 5 years, 4 months ago by Mumbles.

[frankr]

I’m a fan of the OMC Sealant UNLESS the new gasket is pre-coated. Yes, the recommendation changed from dry to OMC sealant somewhere down through the years because the sealant way was better. Better is gooder

[fleetwin]

Well, it is important to understand that gasket sealer will be no help if there is a slight leak around the cylinder sleeves where the metal sealing ring is located on the head gasket. Like others have said, make sure the head surface is flat and the block surface is clean and free from obvious defects. Yes, some head gaskets say “do not use sealer”, but I believe there is no harm in using a very fine coat of the OMC sealer you have pictured on the outer edges to help prevent any external weaping….

[h20lew]

Thanks guys. You confirmed what I was thinking. I cleaned the surfaces and I used the sealant on the outer part of the gasket. Will report back once I get it up and running again.

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