83 70hp powerhead reassemble?

[larry.mahoney]

Over heated; top piston melted some. New piston; now to reassemble do I need to use the gasket set or can I just use permatex right stuff or equivalent? Also the O ring seals look fine should I replace them anyway?

The carbs were clean inside I can't figure out why it overheated I've had this engine for 20+ yrs. How could it run so lean to overheat? Also is there some add on for overheat lite or gauge?

Thank you experts

 

[racerone]

Re: 83 70hp powerhead reassemble?

You must determine the cause of piston scoring.--------Was water pump impeller replaced every 3 years ? --Was poppit valve and thermostat looked at recently ?------Assembling the block requires meticulous care and the right sealant.----Loctite 518 is one of them. You can install a water pressure gauge and location may already be there on water jacket cover.

 

[jbjennings]

Re: 83 70hp powerhead reassemble?

You must determine the cause of piston scoring.--------Was water pump impeller replaced every 3 years ? --Was poppit valve and thermostat looked at recently ?------Assembling the block requires meticulous care and the right sealant.----Loctite 518 is one of them. You can install a water pressure gauge and location may already be there on water jacket cover.

I have a '73 65hp slightly similar to yours. I think that's good advice you've been given.... Did you remove the exhaust cover and inspect the water jackets for cracks, along with the thermostat and poppet valve? I would also check lower and upper crank seals.
JBJ

 

[Faztbullet]

Re: 83 70hp powerhead reassemble?

Also double check the timing as a bad trigger/switchbox bias can cause preignition....

 

[larry.mahoney]

Re: 83 70hp powerhead reassemble?

Thanks

Loctite 518 do I remove all gasket material or just apply it even to torn gaskets? I would like to use just the loctite and no new gaskets unless necessary.

Haven't change impeller in yrs just been checking the water out from motor and was ok. Will replace.

There is no poppit valve or thermostat, bought this second hand and engine was only 2 yrs old. Don't see these parts in the parts breakdown either.

To place a water pressure gauge I see no access point. Is there a procedure to make one?

There are no exhaust cracks or any indication water got into the block. Carbon buildup on the overheated exhaust port only.

The engine is CDI don't know about bias, thought it was fixed to timing. Two wires from stator extremely corroded and one from trigger. The ignition seamed to work ok. Sprayed everything down with battery cleaner but the wires are in very poor shape.
Thanks for all the help

 

[larry.mahoney]

Re: 83 70hp powerhead reassemble?

Forgot to ask about fuel. The fuel I was using was old and not stabilized. I've heard this can cause a leaning condition, its it true?

The fuel pump hasn't been rebuilt, could this cause leaning. I will rebuild it.

I tried to attach pics of the block and exhaust ports but system wouldn't take them even after many tries.

Thanks

 

[racerone]

Re: 83 70hp powerhead reassemble?

The joint between the crankcase and the crankcase cover is a precisionn metal to metal joint.-It requires meticulous preparation before closing up the block.-----A thin bead of 519 sealant is all that needs to be applied and most of that should squeeze out.-------On more than one occasion have I measured the sealant film from that joint to be 0.008" thick.----Means that the builder was not aware of what needs to be done here.