cracked lower engine block - 1987 merc 70hp

[JT!]

i just got myself a used boat for the hull; but want to keep the engine now.

the engine thats on it has a cracked casing on the front intake side of crankshaft

i am told this is common on these motors.
the motor otherwise looks great.

should i sell my functional 1971 evinrude 50 to repair this 1987 mercury 70?
someone told me if i fixed it, it would just break again. tell me otherwise please.

 

[Laddies]

Re: cracked lower engine block - 1987 merc 70hp

That's hardly normal, it was caused by a bad rod or something ingested into the top carb that the rod struck breaking the crankcase.

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

thats good news.

i dont think any debris got in there so maybe it'll be worse than i thought, ie: connecting rod big end failure.

letting the boat dry out now, and clearing my other boat and motors out of the carport to make room. hope to open it up soon and investigate the rest.

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

i did a parts lookup and found the part said 'no longer available' and it was 1700$ for the case & cylinder assembly

i have 3 omc's that i'm now dumping and getting into these mercs.

are parts for 1987's actually discontinued? in canada, older motors are often in great shape due to the short boating season.

although the engine case is damaged, the rest of the motor is spotless and looks barely used. even the prop is original and has no dings or paint wear.

if the rest of the motor checks out and the damage is minor, i can get that lower case welded (some will advise against it, but i dont have a forge to cast myself a new bottom case) ....

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

ok, located the problem.

failure in the connecting rod bigend bearing.
so far i think the damage is limited to the top 1/3 of the engine.

i'll teardown completely to see if the pieces of metal (there are small shards everywhere) made it to the lower cylinders.

just the 1 bearing alone is 90$ i hope i can limit the required parts to a minimum.

the engine wont turn by hand. again ill tear it down so i dont ruin anything further.

what is the most common cause of bearing failure, do i need to check the oil reservoir? or is it stupid human error? i'd hate to repair it to have same issue pop up, if there was a fault that caused the initial damage....

 

[thefairlaneman]

Re: cracked lower engine block - 1987 merc 70hp

hate to say it but its not worth fixing unless you are a very experienced engine machanic and can find parts real cheap. Even fixed its worth only 4 to 6 hundred and you can buy them all day long ready to go for thAT PRICE

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

i am an adept mechanic worked on 2-strokes since i was 13; however i dont have a ton of experience with merc's.

nowhere in canada can i find a motor for that cheap, let alone the trim controls for that price. used 70hp are in the 2500-3000$ range

remember our motors are used 2-3 months a year, and some years people dont even take em out. thats why we have 70's and 80's motors that are almost new (and dusty)

so far im at 90$ + gaskets, will check all crank bearings, and cylinders tomorrow.

 

[Laddies]

Re: cracked lower engine block - 1987 merc 70hp

There is a very good chance the crank will have to be rebuilt or replaced with one from a donor engine.

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

the needle bearings are smeared.

25$ - i found a needle bearing kit but they dont supply the cage.

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

i am still trying to figure out the reason for the bearing's failure in the first place.

does it have anything to do with the oil injection?

 

[Laddies]

Re: cracked lower engine block - 1987 merc 70hp

It could be oil injection but I doubt it the chances are poor winterizing caused rust on the journal and it self destructed. If it were lean or timing it would show on the piston so it almost has to be rust

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

i have been stripping it down all evening and took off the exaust port as well.

a piece of charcoal was forming in the exaust ports, near the top cylinder... is that excessive or normal?

i could barely see into the cylinders, so ill have to split the block and yank everything. to better diagnose it.

can i remove the powerhead without removing the engine from the boat? theres seems to be 1 bolt that goes upwards in the front; does that cowling come off easily?

any easy trick to pull the flywheel? a quick torch? ive tried a wooden mallet, but didnt dare try anything harder. (i threaded the nut on to be even safer)

 

[JT!]

Re: cracked lower engine block - 1987 merc 70hp

in the cooling passages, there was a huge piece of casting debris blocking the waters' flow by at least 70%

i poked at it and broke it off, was aluminium i think, as thin as foil, right along the seam.