Over heat-Rebuild

[socketholder]

I ran my 35 hp through the mud last night and the an hour later I lost power. Motor was hot. Ill be taking it apart to see the damage and I was wondering If these blocks can be bored larger.

The crank shaft uses a barring , I would assume the connecting rod and crank should be fine. It will try to start but does not have enough commpression.

What should I be looking for when I get in there? scored cylinder walls? broken rings? hole in pistions?

thanks for any help

 

[crb478]

Re: Over heat-Rebuild

I would start by checking the compression on it to know which cylinder was low or normal, then I would pull the head and look at the cyllinder walls and pistons as well as the flatness of the head. If you are lucky you my just have a blown head gasket. I would flush out the cooling system before I tried to crank it again.

 

[tashasdaddy]

Re: Over heat-Rebuild

welcome to iboats. tell us more. 35 hp what? year model. we need to know what you have. do as above and check compression before anything else. and report back.

 

[socketholder]

Re: Over heat-Rebuild

Its a 1984 Johnson/evenrude 20" -35 hp remote steering on a duck boat.

Ill will check the compression today btw I never though about the head gasket.

How do I check the head to see if its warped?

will it be noticable?

Thanks for the help

chuck

 

[flabum]

Re: Over heat-Rebuild

You will need a straight edge and a feeler gauge. Clean the gasket surface and using the straight edge across the gasket surface in different directions, chek for clearance at the middle of the head. There should be no more than .002" of gap anywhere.

With the head off, you can see the cylinders and tell if there is damage. If there is any scoring that you can feel with your fingers or any aluminum on the walls, time to rebuild.

 

[tashasdaddy]

Re: Over heat-Rebuild

get the compression before taking anything apart. don't get the cart ahead of the horse.

 

[wbeaton]

Re: Over heat-Rebuild

You want compression over 100 psi in both cylinders with both results being within 10% of each other. I picked up a 1983 Johnson 25 hp (basically same engine) that had been overheated. To my surprise it had 70-75 psi and still ran strong after I replaced the water pump and housing and cleaned out all the water passages. Of course it overheated again the day I tested it and now its down to 50 psi in both. Damn Zebra mussels.

 

[socketholder]

Re: Over heat-Rebuild

The compression was 60 on the first pull, 75 on the second, and 90 on the third for both cylenders. The starter seemed to be weak, so I tried to pull-start it.

The motor tried to start last night, but it will not start now.
I have an OMC service manual and a Seloc service manual.


should it be 100+ on one pull?

 

[Benny1963]

Re: Over heat-Rebuild

just went thru same thing on a 150 evinrude , ended up changing thermos
head gskets water pump, poppetts , checked head with strait edge .had 4 ths
reinstalled got water on plug . pulled heads back off checked again and th same head was 010 had both heads cut 010 and now it runs great .
but i also had no cyl damage check everything carefully and be sure to surface head if all cyls are good its not worth skipping machine work if cyls are good .i poaid 20 a head for the surfaceing

bennyb

 

[wbeaton]

Re: Over heat-Rebuild

should it be 100+ on one pull?

No. Just pull it until you achieve the highest reading. I would expect that engine to run on 90 psi. Post back with your results.

 

[socketholder]

Re: Over heat-Rebuild

I can get 90 on the third pull. I remover the head and the cylinders are glazed but not much in the way of scoring. I can see where a sligh score but you can not feel it. This motor will not start.

 

[crb478]

Re: Over heat-Rebuild

Have you checked for spark? at 90 lbs if there is gas, air and spark at the proper times it should run. Your coils may be weak.

 

[tashasdaddy]

Re: Over heat-Rebuild

well you need a new head gasket now anyway. drop the lower unit, remove the tstat, and poppet valve, flush cooling passages. new impeller. there are a lot of motors running on 90-100 psi. they are just hard to start. it need to turn +- 300 rpms to start. charge battery.

 

[Benny1963]

Re: Over heat-Rebuild

check your coils i lost two coils on the side that had slightly melted the poppett check for fire on coils
be sure to surface head or you will probaly have prob because mine were
decent cold and after i ran they wouldnt seal because they were 010
surfaced flushed changed head gaskets water pump thermos plugs poppetts
flushed and i also changed exhaust plte gasket and cover gasket
on my 150 it was only 125 $ in parts includeing full water pump kit .
bennyb

 

[socketholder]

Re: Over heat-Rebuild

OK, I got it running. It starts on first pull now. Water pump is fried, head gasket is good but the water jacket gasket is bad. Going to pick up parts this week.

How can I test to see why I never heard an over heat alarm, it has one in the controller box but never sounded.


Thanks for the info

chuck

 

[DJ]

Re: Over heat-Rebuild

OK, I got it running. It starts on first pull now. Water pump is fried, head gasket is good but the water jacket gasket is bad. Going to pick up parts this week.

How can I test to see why I never heard an over heat alarm, it has one in the controller box but never sounded.


Thanks for the info

chuck

Look for the tan wire coming out of a pocket, in the head. Ground that wire with the key on. Alarm should sound.

 

[tashasdaddy]

Re: Over heat-Rebuild

get a new head gasket also if you did not replace it. that one won't last.

 

[tashasdaddy]

Re: Over heat-Rebuild

that age if it has been in a salt environment, the horn may be toast. you should see some of the ones i've changed. the just rust to pieces.

 

[Benny1963]

Re: Over heat-Rebuild

sounds like you got lucky .run new omc head gasket and ex gaskets
and even if you strait edge your heads and find 003 it willprobaly seal
but if tou want to know for sure your not going to a leak have head cut to
the minimum to guarntee a good seal
bennyb

 

[flabum]

Re: Over heat-Rebuild

The thermostat is under the water cover jacket you are going to replace, may as well change the thermostat and components while your'e in there