Engine stopped after loud clunk...

[anglosax]

Hi Don
I know this is best guess, but my 1978 A4 stopped running at 1500-1800 rpms cruising speed with a loud clunk and appears to be siezed. This sounds terminal but Im hoping for some crumbs of comfort from the All Knowing Guru [ that you BTW]. What if anything is the most likely to break. Sadly the access is so bad that hand turn over is impossible, teeth on the flywheel is only just accessable and the prop shaft is difficult and not a place Id like to try to shock an engine free.
Over to you...

[jhwelch]

Was the motor in gear and were you going along when this happened?
You may be "lucky" that something got caught up around the propeller.
I've picked up some amazing wads of line in my day. But from the sounds
of things it may be more serious and Don will come in with some suggestions.

-jonathan

[JimG]

I assume that in neutral the starter just dims the lights?

I thought my Ranger 33 had bad access, but yours is apparently worse (or your hands are bigger than mine). Given the trade-off of a few bloodied knuckles or pulling the engine, I always find the access seems to magically improve.

You don't need "much" access to try turning the flywheel via the starter port. A short screwdriver or cold chisel should be sufficient. A mirror is useful to fumble your way around in the opening.

Can you get to the center of the flywheel housing? Just take a piece of 3/4" ID pipe, cut a 1/4" slot across the end of the pipe, and combined with a pipe wrench, you have a poor man's starting crank (don't use it to actually start the engine or you'll break your arm without the properly angled slots). On my boat, you could cut a hole through the engine cover at the spot you need to insert the pipe, although the whole panel comes off with a few screws.

If the engine won't turn, you should probably remove the fan belt and water pump and try again, just in case the water pump or alternator is the problem.
If you have fresh water cooling, that would add another fan belt to remove.

If it's not a fouled prop, "clunks" sound pretty ominous.

[Don Moyer]

Anglosax,

Regarding the cause of the clunk and shutdown, it would be useful to have you comment on the following:

1) When the clunk occurred did the engine appear to freeze at that time, or did it turn over a few more times. In other words, did it make several clunks as it was stopping or only one clunk?

2) Was the oil pressure and engine temperature OK prior to the failure?

Circumstantially, and pending the answers to the above questions, a crankshaft failure would easily explain your symptoms.

Beyond that, Jonathan and Jim's advice is right on the mark. To summarize their most salient points:

1) Be sure the reversing gear is in neutral and then see if the starter will turn the engine over. This is important because it will differentiate between something getting caught on the prop and an internal failure of the engine.

2) If the starter will not turn the engine over and only dims the lights, it would be very useful if you could reach behind the engine and grab the prop shaft by hand and see if it turns. A free prop shaft in concert with the starter's inability to turn the engine over would pretty much confirm an internal failure of the engine and require its removal.

3) You could follow Jim's advice and have a local welding shop fabricate a crank to slip over the roll pin in the center of the flywheel, but I see little value in trying to force the engine to turn over in this situation. If an engine seizes after a long lay-up due to a little rust on the cylinder bores, it can frequently be freed and returned to useful service by forcing the crankshaft to turn, but I can't conceive of any malfunction in this particular situation that could be corrected by simply forcing the crankshaft to turn.

Diagnostically, and your limited access not withstanding, it's more important to determine if the prop shaft is free than to try to get the engine to turn over.

Good luck,

Don

[anglosax]

Hi Don and all contributors , Happy New Year.
After further investigations I can report that the prop shaft is free to rotate with the gearbox in neutral, and that the waterpump/aux drive is not directly hung up.
With the starter motor off, I can freely rotate the flywheel about 2 inches in either direction, ending the movement in a clunk in either direction. The rotation is very easy over this free travel, and if I force rotation after the clunk, there is resistance and the flywheel springs back against the motion, again in either direction.
There is a reaction at the piston [no2] that I can feel thru the sparkplug hole so at least one piston is still connected. The waterpump also wants to turn with the crankshaft.
The engine had normal oil pressure and temp at the time of failure. Sounds to me like conrod or piston failure, but Im confused why the flywheel moves so freely when it should be trying to drive at least 3 pistons with all the attendant friction.
So, its X-ray eyes time, can anyone think of a senario that fits the the bill, before I have to get aquainted with the bottom end of this engine.

[Don Moyer]

It's always challenging in these situations to be sure we're hearing what each other means as well as what we're saying.

For example, the accessory drive (or water pump) is geared so as to rotate one to one with the crankshaft. Since the gear that drives the accessory drive is at the aft end of the crankshaft, and you're turning the crank from the other end (the flywheel end), the fact that the accessory drive turns would be good evidence that the crankshaft is in one piece. However, if the accessory really only "wants to turn", meaning that it only twitches a bit as you turn the flywheel back and forth, the crankshaft could be failed in a somewhat normal way, which is on a diagonal. In these cases, both ends of the crank will turn in a way that convinces one that it is in one piece when it really isn't.

All that being said, I really believe it's engine removal time. You probably won't be able to know the mode of failure exactly before dropping the oil pan and having a look. If you do want to diagnose any further before actually disassembling the engine from below, you could remove the head and see which pistons are turning precisely with the crankshaft and which ones aren't. However, it won't change what you have to do to make the repair, which is to at least move the engine front into the cabin so that you can roll it over and remove the pan.

Don

[anglosax]

Don
Yeah , I believe you, and your reasoning makes sense , but No magic wand????
Given that Im into major rebuild here, what else would you replace/check regardless of the failure here, in the interests of a sensible rebuild
Thanks for your always exellent advice

[Don Moyer]

How far to go in rebuilding an engine is always a tough call. It depends mostly on your future plans for the boat and how well the engine was running prior to a failure.

Assuming that your engine was running ok at the time of the internal failure, I'd recommend delaying your final decision until you see what has gone on inside the engine.

Don

[anglosax]

Hey Don
Finally got that ole engine stripped and.... yep you were right on the money- crankshaft broken between flywheel and no 1 cylinder, added bonus of the camshaft in 3 pieces and lying in the sump. Is this common failure ?
Im thinking new crank,camshaft, main bearing shells, cam bearings, conrod shells, thrust brgs [ what end float?] rear oil seal[ GBox], water pump impeller and seals and all gaskets etc. do you recommend anything else while the engine is in pieces?
Im assuming [hopefully] that the top end is ok [compression not known at this point] All pistons are free and arear undamaged visually

[Don Moyer]

Hold everything! We've only ever seen one camshaft failure in over 15
years, and very few crankshaft failures. The odds of a crankshaft failing
simultaneously with a camshaft approaches the likelihood of a second virgin
birth (literally, and with absolutely no disrespect to the first).

Would you please give me a call at (410) 810-8920 so we can engage in a bit
of real-time conversation to save time? As soon as we talk, you can brief
the rest of the Form fraternity so that no one feels left out.

Don

[anglosax]

Don
After our conversation I inspected the damage and took some photos [alas some out of focus]
No 2 shows the crank break , not too clearly shown but there was granular fracture and shear tearing break as you predicted.
No6 shows “the smoking gun”, a bright contact mark on the web of the crank forging.
It is adjacent and slightly proud to No1 conrod cap, which appears not to have hit anything. The camshaft has the same impact mark across a break , and broke at the journals, front and center too. I estimate the normal working clearance between these parts at 1/8- 3/16 in so the broken crank end floated that far off center.
I would consider grinding off the small 1/8 in web that made contact – I don’t believe it would make any difference to the structural integrity of the crank [ ?] you may consider it worthwhile when you supply and rebuild so many engines to cut the risk of this occurance for anyone else. As you said its rare , and I suspect that the crank was doing Max rpm at the time to have enough kinetic energy to reach and break the camshaft, but as you know for many people , cruising speed is as fast as they can go!
No 5 shows the rear main brg shell, pretty badly gouged from taking all the abuse and deflection. The bearing cap seems unmoved or damaged beyond the shells, and came off the dowels easily and “felt right”
No 6 shows general view of crankcase with crank removed. All other bearings were in good condition, with few marks if any.

I would apprieciate your recommended parts list and it seems time to buy your manual [assuming it gives tolerances and clearances ] as Im now getting to know more about A4s than I ever wanted!
Best regards

[Don Moyer]

Hello,

We're still waiting to receive your pictures; but preliminarily, you'll
(naturally) need a replacement crankshaft and camshaft. You'll also no
doubt need new rod bearings, main bearings (depending on condition of the
existing ones), a complete gasket set, and an MMI Service and Overhaul
Manual (it does discuss wear tolerances in the overhaul section). Beyond
these major items, I recommend waiting until you disassemble and inspect the
rest of the engine. You can order parts online at moyermarine.com, or by
calling our telephone sales representative (Ken) at 610-421-4436. Ken will
also be able to provide technical assistance in your decision-making process
when selecting between different parts options. For more serious technical
assistance you can continue to email or call me.

Best regards,

Don