Oh man... might need to rebuild the crankshaft

[cmac2012]

I'm experiencing the knock from hell in my 300SD. Almost has to be the crankshaft bearings, hopefully not a seriously damaged crank as well.

I've only had a couple of different types of engines out in my life (the Saab V-4 about 9 times) and the only one I rebuilt was the Saab.

What do you think? Is pulling the engine just to get the crank out a worthy endeavor? Am I going to need bou-coups special tools?

The engine is strong in all other depts. and felt strong before the knock went terminal. I'd like to save this car, I mean dang, I'd just found and installed front seats in excellent shape, same color, the hard to find dark brown, a couple of months before this happened. Got 'em off a low miles, totaled '89 560 SEL. I mean, of course I've got to keep this car running now.

**EDIT** Uhhh... beaucoup is actually spelled beaucoup. French for mucho mas.

I'd look for a used engine. It would be cheaper and much faster.

[Chas H]

Drain the engine oil thru a paint filter. If you have lost a bearing, you'll have beaucoup evidence in the filter.

[engatwork]

Don't be afraid to pull the engine and remove the crank. Not really any special tools required. We can tell you how to make em if you need.

[TheDon]

only thing important is the torque specs when re-installing and maybe other things( guessing here but torque specs would be priority)

[kerry]

Someone had a bad knock on here recently and it turned out to be a loose alternator pulley. What precisely are the symptoms? How did they occur? Did you run it low on oil? Is this the one you were having turbo problems on?

[dkveuro]

My advise is get a good std crank.
Turning European cranks is not to be done.

Mercedes, BMW, Audi or VW...nearly all are forged.
The hardening is shallow and not repeatable. The radius fillets on the journals are rolled and they induction or flame harden the journals.

A std good crank should run cheaper than a regrind, and even if not...an untouched crank will do stirling service again..



.

[cmac2012]

Originally Posted by ellington

i agree, replace the engine if the crank is shot. are you sure though that the engine is gone? 181K for a diesel is pretty low mileage wise.

if you do go the used engine route, try these guys:

http://www.stocktonauto.com/

i used to work at a shop where we'd get used engines from these guys and had good luck.

Good advice here. Unfortunately, the 181 K figure may or may not be accurate. A number of fishy things about this car. Such as, I took the VIN into the dealer to get a really good key made from factory specs and they shipped out something totally different. The guy checked it for me and claims they made no mistake. Goodbye $50. Maybe all the locks were changed (including the glove box? ), doesn't mean a lot but the interior was pretty beat up although the engine had good power compared to some other 617s I've driven.

[cmac2012]

Originally Posted by kerry edwards

Someone had a bad knock on here recently and it turned out to be a loose alternator pulley. What precisely are the symptoms? How did they occur? Did you run it low on oil? Is this the one you were having turbo problems on?

Same one and it wasn't the turbo. I was way naive on that one. I probed more thoroughly with my stethoscope (whew! THAT could sound steamy under other circumstances... ) and the loudest hit I got was from the oil filter body, which is down near the crank more. No loose pullies. Man, that would have been nice.

This knock conforms to engine speed perfectly and goes away under hard increase in throttle, which I imagine is due to the sudden increase in oil pressure.

[cmac2012]

Originally Posted by TheDon

only thing important is the torque specs when re-installing and maybe other things( guessing here but torque specs would be priority)

Good call. I've got a couple of decent torque wrenches -- 3/8 and 1/2. Not sure if the big one rates high enough to do the main crank nut. I'll check it out next time I'm at my shop.

Originally Posted by dkveuro

My advise is get a good std crank.
Turning European cranks is not to be done.

Mercedes, BMW, Audi or VW...nearly all are forged.
The hardening is shallow and not repeatable. The radius fillets on the journals are rolled and they induction or flame harden the journals.

A std good crank should run cheaper than a regrind, and even if not...an untouched crank will do stirling service again..

That's good advice to hear. A friend with a 300D told me he'd heard that rebuilt 617s are not as good as stock most of the time. When I said "rebuild the crank" I was mainly thinking about just replacing worn bushings (does it have the bronze bushings at the tie rods?) but having it turned did cross my mind.

If I pull mine out and it's clearly bunged up, I'll have had fresh practice and there are a couple of 617s at the nearest Pick 'n Pull; can't cost too much, I mean they only charge $50 for a head w/cam. They've got engine hoists for rent.

Any idea on what the other pitfalls of rebuilding are? I was thinking that trying to replace the rings and hone the cylinders might be trouble.

[cmac2012]

Originally Posted by Chas H

Drain the engine oil thru a paint filter. If you have lost a bearing, you'll have beaucoup evidence in the filter.

Good idea. I read someone talk about having the oil analyzed. I guess that would be a cheap self analysis.

Originally Posted by ForcedInduction

I'd look for a used engine. It would be cheaper and much faster.

I can imagine you'd be right here. Getting the engine to my shop and storing or disposing of the original would be a big problem. Plus I have this urge to try to understand how to do every damn thing. Gets me in trouble.

I'm certainly not ruling out getting another engine. I see 300SDs on Craigslist all the time with major body damage or blown tranny with a still working engine.

[riethoven]

Two ways to look at things here.

1. These engines are typically pretty bullet proof and getting a used longblock would be a safe bet. Then all you are doing is swapping engines. And since the demand for these engines is not so great anymore figuring the newest ones are 22 years old, the price should be favorable.

2. If you do it yourself it is a pretty huge undertaking, especially if you haven't rebuilt an engine in a while, but when you are done, you know what you have. There will be no doubts as to the reliability of the engine if it is done correctly.

My wife's 1985 300TD got a new engine under warranty at 78K. I read the service receipt when I bought the car but I can't remember what the symptoms were. I think it was knocking. It could also have had something to do with three teenage sons in the family. I bought it from one of the sons about a year ago with 178K on the odometer, and every service record since day one.

[Hit Man X]

Originally Posted by ForcedInduction

I'd look for a used engine. It would be cheaper and much faster.

Yup.

[t walgamuth]

i would be careful. bearings out is a rare occurrance with the benzes. the bottom ends are about the most robust thing made this side of a truck cummins. i would be tempted to get an expert opinion from maybe someone from the sf who is more experienced.

we have had mb diesels apart with 300k on them and put them back together without touching the bottom ends, after measuring the wear of the major parts.

about the only way to kill them is running them low on oil or very very dirty oil.


tom w.

[Mustang_man298]

Originally Posted by t walgamuth

i would be careful. bearings out is a rare occurrance with the benzes.

tom w.

Welllll..... I dunno, I hear the 616's and #1 rod bearing arent a happy pair in many cases......what killed the original in mine before I got it. Rod cut the oil pump in half, then went thru the engine block and upper pan, must've been a spectacular show indeed, I of course had to take pics of the carnage before tossing it.