Is it blown?

[Arkie55]

I bought a 1978 35 hp Johnson for a parts donner to my 1979 35 hp Evinrude. The history of the Johnson is that it overheated, steam came out from under the cowling, and it died. I bought it mainly for the lower unit, coils, and carb. <br /><br />Now last night I decided I would pull the head on the Johnson and just see what damage there was. The head gasket is blistered. There is only metal between the cylinders. One side of the gasket is black the other side a brownish color. By side I mean left and right not front and back. Bottom cylinder looks good and smooth. Top cylinder has a littl scuffing but I don't think it is very deep. Before pulling the head, both cylinders mesured 60psi compression, at lest that's what I was told.<br /><br />My question is, do you think this motor needs a complete rebuild or would you just buy a new head gasket, install it, and see what the compression is then. This is very clean motor. I don't know if it's worth messing with or not. Input please.

 

[BoatBuoy]

Re: Is it blown?

I don't know what "There is only metal between the cylinders" means. I wouldn't waste money on just a head gasket if there's cylinder scoring. Considering the price of parts, generally, if you can get buy with pistons, rings, rebore, it's probably worth the trouble if you can do it yourself. If there is rod or lower end damage, it may not be.<br /><br />oversize pistons - $90.00 ea.<br />ring set - $30.00 ea.<br /><br />On the other hand:<br />crankshaft - $678.00<br />connecting rod assembly - $140.00 ea.<br />crankcase head & seal - $58.00<br />etc. etc. etc. etc.

 

[Steve135]

Re: Is it blown?

First did it overheat from fuel stavation or lack of water EG: water pump, big differance here.If it was fuel than its probally toasted but lack of water means it may be saved. If the heat was enought to fry the head gasket than you'll need to replace them for a compression check. The 60 you got could be from bad gaskets. If the cyls were wiped than you would be lower than that.But first check that scoring really good!<br />The next thing is new head gaskets and compression check it than go from there. I would buy a complete gasket set if you have the same motor as you can always use the extras and a complete set can be had for a little more than the cost of the head gaskets. If you think its a chance for repair than you'll need to replace the rest of tose gaskets anyhow! and don't leave out the motor to exhaust gasket at the bottom of the motor you need to pull the motor to replace this one. I have done this before with good results.<br />steve

 

[Arkie55]

Re: Is it blown?

Update:<br />yesterday afternoon I pulled the lower unit to check the water pump housing and impeller. It was toast. The housing had some melting and the impeller was melted down almost to the hub. The overheating was caused by lack of water, there is no doubt about that now. I really looked that scoring over yesterday and it's pretty light. I think this motor is rebuildable and will be a good learing experience for me. I got the parts I needed, (lower unit) and will now turn my attention to buying parts to fix the parts motor. I'm pretty sure I'll just pull the block, disassemble and inspect everything to determine what parts I need to buy. I know it will be needing a head gasket, water pump kit, thermostat, and power pack at the very least. I'll probably go ahead and buy a gasket set and install the head gasket and check compression. That will tell me a lot about what else I might need to look at. Thanks for the advise. I'll be back for more I'm sure.

 

[Skidooosl]

Re: Is it blown?

why not just replace the head gasket since you now know that it was due to water and check the compression... if good see if it will start and run. THEN if you decide you want to rip into it you will atleast know you had a good running motor to start out with.