1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

[ajgraz]

Trying to remove the powerhead on my 1978 Mercury 70hp 3 cylinder.

Stripped the powerhead bare (carbs, starter, all electronics/wiring, fuel lines, bracketry, etc.) . Removed the lower unit to make sure the driveshaft doesn't bind.

Got all 8 powerhead stud nuts off (one rounded and dremeled), got the 4 bolts in rear from exhaust plate to powerhead removed; as far as I can tell from all resources and diagrams I have found, there is no other hardware holding the powerhead on, just gaskets/surfaces.

On the starboard side, the powerhead seems like it's loose from the exhaust plate; but on the port side, it appears to be tenaciously stuck or "glued down" with some sort of tough, whitish goop. (Don't know if this is factory or if the powerhead's been removed before.)

I've got a lifting ring in the flywheel, and an engine hoist; but it won't pull the powerhead off, it just lifts the whole boat and trailer from the transom. Right now I've got it hanging from the hoist, with the powerhead nut studs just a few threads on, hoping it will "pop" itself free over time...but it's been a few days already.

The gap between the powerhead and exhaust plate is so small it is very tough to get anything in there to pick away at the stuff. Also part of the seam is in a place I can't get to because of an upward "lip" on the front of the exhaust plate.

Any ideas?

 

[Chris1956]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Some of those motors have 2 nuts under the lower cowling, roughly directly down from the carbs. The block ususally needs to be lifted a bit after the nuts are loosened, in order to fully remove the nuts. Did you get those?

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Some of those motors have 2 nuts under the lower cowling, roughly directly down from the carbs. The block ususally needs to be lifted a bit after the nuts are loosened, in order to fully remove the nuts. Did you get those?

If you mean the two nuts on the studs that go into the front half of the cylinder block, yes I got those.

I got all 8 stud nuts and the four exhaust plate bolts off. I have studied the online diagrams and the diagrams in a .pdf copy of the condensed service manual I found somewhere, and I can't find any other hardware that should be connceting the powerhead to the rest of the motor. But the powerhead just isn't lifting/budging from the exhaust plate (on the port side). I am almost entirely certain it's because of whatever goo/sealer was used (I picked away what I could reach), though of course I have no idea what the sealer is--could be 5200 for all I know.

Anyone else run into this? How to soften or dissolve the goo? Heat? Some kind of chemical or stripper "injected" into the seam with an eye dropper? Try to pull the powerhead and exhaust plate together and soak the bottom few inches of that assembly in a bucket of kerosene (or something) until the gaskets/goo disintegrate?

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Have you removed the shift shaft lever. The roll pin must be removed and the lever separated from the shift shaft

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I removed my 1979 70 3 cylnder powerhead again yesterday Bought this a short while ago and when checking the exhaust baffle cleaning and adding new gaskets I noticed pitting on the bottom piston. The water port was leaking into the exhaust (loose exhaust plateI ) and corroding the inside that fried the wrist pins and rod needle bearings. You do not need to unbolt the 1" adapter plate just the 8 studs and the shift shaft lever. I would suggest dropping the lower unit to make sure the water tube and exhaust tube are seperated from the powerhead as well.

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Maxz695, so glad you've just done this, you've just been recruited as a resource!

I removed my 1979 70 3 cylnder powerhead again yesterday Bought this a short while ago and when checking the exhaust baffle cleaning and adding new gaskets I noticed pitting on the bottom piston. The water port was leaking into the exhaust (loose exhaust plateI ) and corroding the inside that fried the wrist pins and rod needle bearings. You do not need to unbolt the 1" adapter plate just the 8 studs and the shift shaft lever. I would suggest dropping the lower unit to make sure the water tube and exhaust tube are seperated from the powerhead as well.

I too suspect water intrusion into my bottom cylinder, either from an issue in the exhaust baffle or from bad lower crankcase oil seals/bad exhaust plate gasket (the very gasket/sealing area giving me issues now). That's why I'm (trying to) remove the powerhead.

So you're saying I have to remove the shift shaft lever (drive out the roll pin) to remove the powerhead from the exhaust plate? From what I can see I'd have to do that only to remove the exhaust plate from the mid-unit/leg...???

(The only bolts in the exhaust plate I am aware are 4 that go upward into the back end of the powerhead...those are out, too).

Can I get to and remove the lower end cap THROUGH the exhaust plate? And if so, can the powerhead be separated, front half removed, and crank/rods/pistons be removed even if the exhaust plate is still "stuck/gooped" to the powerhead? Number one goal right now is thorough examination of the cyl 3 bore.

Anyway, LU is off. I'm likely going to have to remove the powerhead and exhaust plate together (after removing the shift shaft lever); I expect the water tube and exhaust tube to come up with the exhaust plate, according to diagrams I can separate them from the exhaust plate once I've got that lifted out a bit.

So then I'm going to have a powerhead half-glued to an exhaust plate with whatever sealant/goop...what then to separate those?

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Your being able to drop the unit tells me the shift shaft isn.t stuck or corroded to the lower shaft. In any case i would remove the exhaust palte with the powerhead. If you do not remove the shifter lever your gonna be trying to pull the whole shift shaft up with the powerhead. When I tryed that the shaift shaft got stuck in the swingarm. I couldn,t get it to give and ended up removing the shift lever anyway. After removing the powerhead with the exhaust plate, then you can inspect better for a bolt you may have missed. I have one bolt that is not 1/2 inch but smaller 7/16th head that goes up into the exhaust port Did you remove that bolt?

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Your being able to drop the unit tells me the shift shaft isn.t stuck or corroded to the lower shaft. In any case i would remove the exhaust palte with the powerhead. If you do not remove the shifter lever your gonna be trying to pull the whole shift shaft up with the powerhead. When I tryed that the shaift shaft got stuck in the swingarm. I couldn,t get it to give and ended up removing the shift lever anyway. After removing the powerhead with the exhaust plate, then you can inspect better for a bolt you may have missed. I have one bolt that is not 1/2 inch but smaller 7/16th head that goes up into the exhaust port Did you remove that bolt?

There were four bolts oriented upward at the rear of the exh plate (just under the rear water jacket cover), attaching it to the powerhead; I do recall three were larger head than the fourth...are those the ones you mean? They are out.

Are there hidden bolts attaching the exh plate to the powerhead? Something I can't see because thir heads are inside the top of the leg? (Saw none in the diagram, but that would certainly explain my issue)

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I just went out to look at my exhaust plate and other than the 8 studs and the four bolts and the shift shaft lever, The only other thig holding it would be the back bracket lower mount. I figure you removed this already so your gonna have to chip away between the block and the exhaust plate with a putty knife

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

"Back bracket lower mount" meaning the protrusion on the back of the exh plate that holds the contraption that holds the clamshell cover? Yeah that broke off years ago, holding that together now with huge cable ties, ha ha!

OK, getting this powerhead off is my project for the weekend, so I'll post progress (if there is any!)

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

That white stuff is definitly NOT factor. whoever removed that powerhead may not have used a gasket and used some sory of appoxy resin. Maybe acetone or nail polish remover may halp some but if he covered the whole plate your gonna have a time trying to get it seperated without doing some damage

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Well, I'm hoping that if I can pull the powerhead and exhaust plate together, at least I can chemically and physically attack the problem from the outside AND the inside.

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Thats the thought and it will be easier to menuvor as well

 

[Moody Blue]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I just pulled the powerhead off my 1971 Merc 800 a couple weeks ago. I ended up using a prybar carefully placed between the exhaust plate and base of the powerhead at the rear of the motor. With a little persuasion, it "popped" loose and I was able to lift it off with the lifting ring.

On my motor, there is a single flathead boat that attached the exhaust plate to the midsection of the motor. This bolt head is not accessible until the powerhead is pulled.

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I hope he reads this soon mine is a 1979 and his is a 1978 his is probably a 700 with that type of set up. Mine being the first year of the 70 that bolt was obsolete I guess. The problem is if he can,t acces that bolt and the powerhead was appoxied to the exhaust plate he,s gonna have a big problem

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Maxz, our 78 and 79 70hp Mercs are probably identical in every way.

I did get the powerhead off with enough prying and knocking. What was hanging it up was some sort of epoxy or sealant, SPECIFICALLY someone had let it (or purposely placed it) into some of the holes in the exhaust plate and leg that the powerhead studs go through, which just made for a heckuva tight press fit on the studs. I really don't see why they did it, the sealing surfaces do not look cracked or terribly gouged???

Haven't cracked open my powerhead yet, but at least I can already see that the carrier is there, unlike yours Maxz695:
http://forums.iboats.com/showthread.php?t=578608

(But one of the spring garters from an oil seal was laying loose on the exhaust plate; maybe there's my water intrusion)

It maybe looks like that carrier fits into a recess in the exhaust plate, I wonder if that helps stabilize the rotating crankshaft? Although granted there is no bearing or even bushing there...I dunno, just a thought.

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I can,t understand how all three crankshafts My 79 40 HP A replacement crank for the 40 HP I bought from a woman in Tampa and the 79 70 HP all looked the same as my picture above with No Carrier. I,m really glad to hear you got the power head separated Be careful when removing the lower end cap. The intake must come off first the the crank must be lifted a little as there is a Notch in the intake holding the end cap in. I removed both upper and lower bearings today. I had to drill out to snapped bolts for the endcap in the intake manifold and retp them. I found the wear sleeve on ebay and I also purchased the carrier and the seal. I,m waiting for all my parts to get here. I still need a piston though.

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

I got the crankcase separated today. There appears to have been terrible water intrusion into cyl 2 and cyl 3, very likely from the exhaust baffles. The entire bottom 2/3 of the crank/rod/piston/bearing assembly is terribly rusted. The bottom piston's rings were totally toast (and that piston in bad shape), the middle piston and rings were getting there.

The bottom of the crank would definitely need a sleeve, I'm guessing it got rusted from the inside.

The bores in the cylinder block were in surprisingly good shape.

At a crossroads here as to whether to even consider a rebuild, or to look for a replacement powerhead. Probably will start a new thread about it.

 

[Maxz695]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Where in the same boat sort of speak. I,ve already started purchasing new parts and very low on $$$ Cha Ching. The crank probably is wiped out. Thats the main problem and most expensive. As long as the cylinder walls are ok or at least borable used pistons can be purchased at a reasonable price. some with the rods already attached on ebay.I,m still needing a piston for mine from the corrosion damage it suffered. I have two rods off my 40 HP same casting numbers 6225667 I have 1 spare if yours is the same and need it. My reeds all look good and tight. I,m waiting on the parts I already bought, and information on a crank for compatinility on monday. Maybe you can find a powerhead for parts on ebay cheap

 

[ajgraz]

Re: 1978 Merc 70 3cyl; powerhead stuck ("gooped?") to exhaust plate

Yeah. This motor is (was) used extensively in saltwater. All the bolts holding on the rear cover and exhaust cover look as if they'd break off if I just breathed on 'em. Another reason I'm about ready to abandon this powerhead altogether. I'm sure we'll be trading notes as we go along.

A total repower likely ain't in the cards for me. Like everything else in S. Cal., everybody wants 5x more than what something's really worth. No deals on cars, trucks, boats and motors here like back in DE where I grew up.