Overhauling my 1988 MerCruiser 4.3 ltr. engine

[Rivergator]

.....continued from "Engine Removal on 1988 Sylvan"
We had 2 nasty hurricanes in the last 3 months and I am just now caught up with cleaning up everything. 2 weeks ago I was finally able to start taking the engine apart and to my surprise, the engine looks very good inside. No visible deterioration or wear and tear. Compared to a car engine I would say this engine may have 25000-30000 miles on it, that’s how new and clean everything looks. Most of the damage is on the outside, mainly lots of rust, which damaged the dip stick tube, left side valve cover, timing chain cover, intake manifold, starter, alternator, carburetor, fuel pump. Of all the peripherals what were still salvageable was the power steering pump, distributor and the engine water pump. I just got through acid washing all the water passages on the 2 heads and the engine block. Next step will be a thorough inspection of the heads and valves and then I go on to do the same with all the pistons, piston rings etc. and a honing of all cylinders.
Today I started to remove the pistons and my worst fear came true. The crankshaft is broken (see pictures). I had this fear because when I tried to crank the shaft by hand it just didn’t feel right. What would cause the crank to brake? I think I can probably answer that myself. A sudden lock up of the outdrive and the cylinders that have just fired will force the pistons down on the crank which is no longer turning....and bang, something has got to give. There may be other reasons as well, but this is probably the most logical one I can think of. I haven’t even started on the out drive yet but I am afraid to look, probably busted gears inside. Well, that’s a new chapter. Right now I need to find a good crankshaft. Does anyone have one or knows somebody who has one. Again, my engine is a 1988 MerCruiser 4.3 ltr (w/o balance shaft). Btw, that is not my engine, but a picture of one like mine.

 

[Scott Danforth]

Leading cause of crank failure is a dead plug or a bad damper

 

[Rick Stephens]

Amazing picture.

Last crank I broke was a Cummins VT903 V8 crank. Balancer went bad and the crank broke off between it and the front bearing journal. No torque load there at all, just vibration.

 

[Scott Danforth]

reversing loads of the balancer are a biotch

 

[Rick Stephens]

reversing loads of the balancer are a biotch

Back then, it was only a little over $20k biotch. Great motor other than the tendency to bust cranks from over torquing. The 4.3L V6 isn't known for that particular problem. Rivergator has an unusual cause of death here.

 

[Scott Danforth]

agreed, a broken crank is a rarity

common for a dead spark plug on a balance shaft motor and not know it, especially if you dont push it often.

since the exterior of the motor is rusty, rust is the #1 cause of the damper rubber to come debonded from the weight ring.

 

[Lou C]

Agreed I have not heard of cranks breaking in 4.3s, yes the crank may not be as strong as a V8 due to the offset even fire crank but never heard of this or even read of it once on any of these forums. A bad hydrolock?
When I took mine apart (just the top end) the cam and lifters looked like new. That surprised me because at that time it was 29 years old, had one bad overheat and blew both HGs a few years later.

 

[Scott Danforth]

hydrolock will bend a con rod and blow a head gasket long before a crank goes. cranks go from imbalance, either a dead cylinder or a bad damper. the reversing loads that result are what takes out the crank. normally there will be beach marks on the crack. once it starts, its only a few revolutions before it lets loose.

 

[Lou C]

Interesting glad I did not have that problem lol! Only harmonic balancer I ever had to change was on our '98 4.0 JEEP six.

 

[kvkon]

What you really need is a complete rotating assembly (possibly from an engine block that's been freeze busted?). Matched harmonic balancer, crankshaft, rods and pistons and flywheel. Even when the rotating assembly is matched and balanced the 4.3 are shakers. That's why the later models have balance shafts.

 

[Scott Danforth]

What you really need is a complete rotating assembly (possibly from an engine block that's been freeze busted?). Matched harmonic balancer, crankshaft, rods and pistons and flywheel. Even when the rotating assembly is matched and balanced the 4.3 are shakers. That's why the later models have balance shafts.

A used running motor would be cheaper.

Attempting to use a used rotating assembly is a fools errand. The crank and rods can be conditioned, however that usually costs more than new rods and crank. the pistons and rings are a one-time use thing as the block would need to be bored and honed.

So there is no benefit to buying a used rotating assembly

 

[kvkon]

A used running motor would be cheaper.

Attempting to use a used rotating assembly is a fools errand. The crank and rods can be conditioned, however that usually costs more than new rods and crank. the pistons and rings are a one-time use thing as the block would need to be bored and honed.

So there is no benefit to buying a used rotating assembly

I've bought a number of "used running" engines. All were turds that I'd never install in anything without a complete overhaul. I'd use the reconditioned rotating assembly (crankshaft, resized rods, bearings balancer, flywheel and new pistons and rings) from a donor engine and install it in the original block after having it bored, decked and align bored. New camshaft, lifters etc if required. Also have the heads done. End up with a better than new engine at a lower cost than a long block built by a pimply 19 year old in a sketchy shop.

 

[nola mike]

Why not just a new crank? I can't imagine these engines were balanced after assembly, were they? BTW, is that a break at the main or rod bearing?

 

[Scott Danforth]

Why not just a new crank? I can't imagine these engines were balanced after assembly, were they? BTW, is that a break at the main or rod bearing?

exactly, new crank, new bearings, drop in and run it as long as the pistons were not pulled from their bores.

 

[Rivergator]

This is all extremely interesting to hear you experts exchanging thoughts. Wow, what did ever happen to that poor engine? The number on the crank is 10105865 2. What does the 2 stand for? The break is right in the middle of the crank between 3 and 4. What do you call those polished sections of the crank where the rods attach to? I did pull all the pistons from the cylinders but carefully marked all of it so they go back exactly the same way they came out. Any advise on how to remove the crank (right now it is still in the block awaiting what further action I shall take)? Obviously besides removing the main bearing caps and the timing chain gears what else needs to be removed for the crank to come out? Do I have to remove the rear crankshaft seal etc.? The rear seal looks like this (see picture). Is it the one piece or 2 piece rear seal? I also took a very good look at the damper. It looks very good actually. The rubber ring is not hardened, shows no cracks or any kind of damage or deteriorations and is solidly attached to the metal parts.

 

[Scott Danforth]

This is all extremely interesting to hear you experts exchanging thoughts. Wow, what did ever happen to that poor engine? The number on the crank is 10105865 2. What does the 2 stand for? The break is right in the middle of the crank between 3 and 4. What do you call those polished sections of the crank where the rods attach to? I did pull all the pistons from the cylinders but carefully marked all of it so they go back exactly the same way they came out. Any advise on how to remove the crank (right now it is still in the block awaiting what further action I shall take)? Obviously besides removing the main bearing caps and the timing chain gears what else needs to be removed for the crank to come out? Do I have to remove the rear crankshaft seal etc.? The rear seal looks like this (see picture). Is it the one piece or 2 piece rear seal? I also took a very good look at the damper. It looks very good actually. The rubber ring is not hardened, shows no cracks or any kind of damage or deteriorations and is solidly attached to the metal parts.

some light reading https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

if you pulled the pistons out, you must at a minimum hone and re-ring. best to bore, hone and ring

only the 1985 motor was a 2-piece RMS motor.

as stated, primary 2 reasons cranks break. either the damper goes, or a cylinder was not firing for a long time.

all that is ever needed to remove a crank. with engine on the stand, spin the motor so the oil pan is up, pull timing cover and oil pan, remove timing chain, remove bearing caps and remove crank. as you remove a bearing cap for a hole, push the piston down (up in the hole to the head)

however since you pulled the pistons out of the bores, you have more work to do. contact your local machine shop to get a price on align hone, decking, boring and honing.

 

[kvkon]

When a crankshaft breaks due to torsional vibration (from a failed damper, long term operation with a dead cylinder or vibration feedback from the load it's driving) the fracture will appear to be a "twisting" type of failure often at about a 45 degree angle thru the shaft. Can't tell from your photo what the fracture looks like.

 

[Rivergator]

Thanks Scott for all that good info. Kvkon I will put up a better picture of the crack when the crank is out of the block. Another question. Das anybody know what this can is (see pic)? It sits at the end of the engine block off to the side near the distributor. It's not on the intake manifold but right behind it screwed into the engine block

 

[Rick Stephens]

Oil pressure sensor.

 

[Lou C]

or what's left of it!