1973 50 hp evinrude (50373r) bogs down past half throttle

[AlTn]

the head has a cover < small screws > and the head itself < larger screws around the perimeter of the head >...you'll find the thermostat when you remove them...on the exhaust plate where the wires were cut was/is a temp. sensor... do you have enough clearance to remove the head with the head cover in place?..I dunno..refer to your manual or try it and see, but surely it'll come off w/o having to remove the powerhead

 

[racerone]

The cylinder head comes off without having to remove the entire powerhead from exhaust housing !!

 

[jake83]

Well just got home and inspected the crankcase and I do not see any cracks or holes.

I am about to step outside and see about pulling the bolts off the head cover. As long as they are not too long I believe I will be able to pull them. Only one way to find out. I'll take some good pics when I get it pulled

 

[jake83]

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Only one bolt gave me trouble,a can of freeze off and some patience and I got it. The two in center were definately dirtier and more difficult to remove that the rest. I haven't taken cover loose from head yet but I broke all the bolts loose while assembled

 

[jake83]

Also one of the few times I had it running I heard a ringing noise kind of like a loose piece of metal rattling around. Sorry, probably should have mentioned that earlier but I had attributed it to something loose on the motor but I can find no such loose part. Maybe nothing but I thought it worth mentioning. I'm back on the grill cooking some burgers so it will be a minute before I can do anything else. So do the pictures tell anything?

 

[jake83]

Just got done with dinner. Just sitting here contemplating now, I sure wish I could get that exhaust plate cover off so I could see the rings. I would guess they are fine since the cylinder walls seem to be okay but hey, what do I know. I'm gonna see what advice the experts give me next. I am going to grab the head gaskets tomorrow and maybe exhaust plate gaskets as well if I can figure how to get the exhaust cover off (kind of tempted to break out the hacksaw and cut a little off some new bolts) I just see quite a bit of carbon build up on the lower exhaust ports, but maybe I can just decarb and be okay. Or maybe I am getting ahead of myself. I eagerly await your responses and I thank you for your help.

 

[AlTn]

to me... in the final photo of that series...it appears the head gasket has burned through on that upper cylinder < 3'clock > and there may be some aluminum transfer to the cylinder wall...what can you feel?..any roughness on the cylinder walls?...doesn't appear to be any major gouges, does your fingernail get caught running it around the cylinder walls?

 

[jake83]

There is no scoring that I see and I can run my fingernail around entire cylinder wall and it doesn't hang up anywhere. I am currently trying to get everything all cleaned up. Got both head gaskets as well as new thermostat and the pressure relief spring was missing so got that too. New gaskets too.

Any tips? Especially for removing old head gasket. I got the cover gasket pretty well removed with a razor but have reservations about doing that to the main head gasket too

 

[AlTn]

stick with the razor or scrapper being careful not to gouge the surface and also keep debris out of the cylinders...nothing appears different to your eye on that top cylinder wall above the ports?

 

[jake83]

No Title

Nothing seems wrong or different. Here are some more pics of the gasket both front and back

 

[jake83]

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And one of the top cylinder wall around 3 oclock

 

[jake83]

No Title

I have removed all the gasket material. I taped some 400 grit emery cloth to a piece of glass and started to lightly sand to remove an thing left behind, but it is not quite working as planned. I may just leave it alone or get it machined if it is necessary. Tomorrow I will chase all the threads in the block and clean the bolt threads. Then reassemble everything unless there is anything else I should be doing before that. Should I use anti seize or anything.? The manual only to install bolts in an alternating pattern, start in center and work out? I know not to use sealant on head gasket but what about the cover? High temp rtv? There was some sort of blue rtv when I disassembled it and the cover kind of rocks when on flat surface, so I worry about the seal. Maybe I worry too much. I have been told a million times that there is probably some simple fix to this and that I am just over thinking this, but none of those people can tell me what exactly that simple fix is so I guess I am just gonna keep on at it.

 

[racerone]

What you are seeing on the head gasket surface is classic.------------Every cylinder head that I have seen is warped in the same manner.---------Just keep going till it all looks the same.

 

[jake83]

Thanks. I'll have to do some more after work today, I was just nervous.

 

[AlTn]

head cover gasket sealant..yes..omc gasket sealant, permatex may make an equivalent but I don't know the name or no., on both sides of the gasket..I'd avoid the rtv...yep..just keep dressing the head,,,gets old, the other choice is to have it milled if you have a machine shop and want to wait

 

[jake83]

Avoid rtv...got it. I would imagine I have to go to a marine store for that. Anybody know what I can use from NAPA, it's just a little closer to home. I will look into it as well, NAPA may even carry it. And what about anti seize on the bolts, is that a no no?

As far as the head I will just keep going on it, just didn't know if it was right. Should I just leave the block side alone other than the scraper?

Sorry to post so many questions, just trying to be certain. I appreciate all the help I am getting. So one last question....I don't see any major points of failure on this head gasket,of course I'm no pro. So when I get this all back together do you think I will have the same problems out of the top cylinder? Just curious.

 

[racerone]

Likely the problem will still be there.-------What about the rattle, ?----Checked for loose rod bearings ?

 

[jake83]

Is there a way to check without visually inspecting them or am I opening this whole thing up for that?

 

[AlTn]

+1 with racer..unless you disassemble the powerhead and examine/measure you'll not know what it's going to take to fix it...as you've probably seen there are currently 2 or 3 threads going on powerhead removal and disassembly of the 50 hp.models...maybe a pm to these members can give you insight....43 year old outboards become like the old saying, " in for a penny, in for a pound "..sure it's disappointing and not what you expected, esp. with a first boat, but the disassembly and inspection should be your labor only cost wise...

 

[racerone]

Turn the flywheel slowly.---------When the piston is going down into the cylinder stop turning the flywheel.--------Now push on the piston with a thumb.-------Compare the cylinders.