617 Crankshaft/Woodruff key question? See pics... - PeachParts Mercedes-Benz Forum

paulh300sd · #1 11-05-2006, 07:30 PM

My crankshaft sprocket disengaged from the shaft recently (fortunately while I was idling). After getting the engine out, I discovered that someone in the past must not have torqued the crankshaft bolt down properly, and it put too much stress on the woodruff key and eventually disintegrated it. I have had the car for four years and 40000 miles and it has run very well. The good news is that there was no significant damage to the head (no valves were bent, eventhough a couple of the cam towers broke). I have posted more about this in another thread. The car in question is a 1982 300SD, 165K.

As I was studying the situation more closely this afternoon, I noticed something tonight that concerns me. It is the keyhole in the crankshaft were the woodruff key goes. Is it supposed to be this shape, or did it get worn to this shape by the key stressing it out because of the main bolt not being torqued sufficiently? I have looked all over for pictures of this part of a 617 crankshaft and can't seem to find anything with enough detail to tell me for sure how this key hole should be. It seems to me that it should not be this shape, but then it seems that the key should be of a slightly softer metal to not allow it to wear the shaft.

If it indeed is not supposed to be this shape, do you think I could have a machine shop grind out a keyhole of the proper specifications on the other side of the shaft? Would I be able to have this done without having to pull the shaft out of the block? It seems that this would not affect the balancing, and that this should be possible.

I am hoping that for some reason I do not understand now, that this is the shape of the keyhole. Then I can proceed without having to worry about this. Please let me know what you think. I look forward to your responses.

Thank you.

Paul

#2 11-05-2006, 07:35 PM

You can take the crank to a machine shop to have them TIG weld the hole and regrind it properly. You *should* be able to do it with the upper pan removed and the crank in place.

Otherwise, it might be time for a new crank.

paulh300sd · #3 11-05-2006, 10:26 PM

Thank you for the feedback about the welding. This gave me the idea of doing some different searches on the net, and now I understand the problem much better, and it is obvious now to me that the keyway on my shaft is worn and needs to be fixed.

From what I have read, it seems that the welding could be risky. I know a good machine shop here, and I will ask them about it. Maybe they have done it a lot before, and know exactly what do so as not to cause damage to crank and bearings due to the heat.

I did come accross the following link which I thought was very helpful and had an interesting way of tackling the problem.

http://groups.google.com/group/alt.hotrod/browse_thread/thread/255540c22d908bbf/b1e65e8c1b77e38b%23b1e65e8c1b77e38b

It still seems to me that grinding out a new keyway on the opposite side of the crank shaft is the easiest way (and least risk) of dealing with this.

If anyone else has feedback about all of this, I will be eager to read it.

Paul

Shorebilly · #4 11-06-2006, 08:33 AM

G'mornin',

First, from my experiences I think that somewhere, sometime, someone installed the wrong sized woodruff key...read that as smaller.....

Now, a possible fix.....I have had this done on a piece of ship's machinery before.....I do not think it can be done "in place", but maybe.....have your machine shop cut the keyway for the next size up woodruff key....a size that will allow for a good edge, and fit......then have them fabricate a "stepped key" to fit the "crankshaft sprocket".....

You need to look closely at the "sprocket"...the internal keyway is also probably damaged, similarly to the cranlshaft......

If you re-use the old "sprocket", the machinist can clean up the keyway, and then fabricate the "stepped key" to fit......

If you decide to use a new/used "sprocket".....check the keyway, and have the stepped woodruff key fabricated to fit snugly......

I have seen the "stepped key" approach work on really large keyways.....

Luck to ya......and I hope that you can find a sympathetic machinist that is willing to work with you......

SB

paulh300sd · #5 11-08-2006, 01:43 AM

I'm pretty sure it the right key was in there. The problem is that the previous owner didn't torque the crankshaft bolt on properly. See thread
Replacing piston rings on 82 300sd - need advice
for more details.
The machine shop I am dealing with was not interested in working on the keyway with the shaft still in the engine. I decided that I am going to attempt the repair myself. Wnat I plan to do is kind of like the stepped key you are talking about, but rather I am going to use to keys together (as suggested in a link above), and make them so there is an interference fit in the keyway. I may use a dab of liquid steel to hold the one key in place a little better, the one that will be flush with the shaft.

I'll let you all know how it all goes.

Shorebilly · #6 11-08-2006, 08:59 AM

If you are gonna use plastic steel.....try to find "Belzona Magic Metal" have never seen it for sale retail....industrial product...I'll do a look see onna net later and get back here.....

Belzona Magic Metal is a great product....there are several versions, most of which are machinable......

SB

Shorebilly · #7 11-08-2006, 09:14 AM

Link to the Corporate website...... www.belzona.com/

Link to the specific problem...worn keyway.. http://www.belzona.com/geq.aspx

I had never been to their website before....wealth of information here.....but I think that this is the product that you should use....and it ain't cheap....you will have to find out a supplier that sells it in your area....

And for the rest of the folks who are reading this.....go to the main web page....and browse the..."repair composites
know-how solutions for" ... especially the section on "engines and castings"

SB

NOTE: trust me...it ain't cheap....but it does work!!!

paulh300sd · #8 12-05-2006, 02:19 AM

Thank you SB for the advice. You are right on. I did not see your post until now, because I forgot to subscribe, but fortunately the shop that reworked my cylinder head had the same recommendation, and I have also done research into it, and Belzona products are definitely the choice. I was able to procure a small amount from the machine shop. Nevertheless, I was still reluctant to completely trust epoxy. After doing a lot of thinking about this, I decided to clean up the keyway (using a dremel tool) to create a nice edge that a second key could sit in the place that was wallowed out. I then used a little bit of Belzona to tack it in place. Attached are some pictures. It all took a bit of patience, especially since I had never done anything like this before. I replaced the sprocket whose keyway channel had also been slightly damaged. I finally did get everything back together, and we took the car on a 1500 mile trip and everything worked great.

Shorebilly · #9 12-05-2006, 08:17 AM

G'mornin',

Looks like you made a good repair......the Belzona products are amazin'......did you look in at their website???

And when I said "ain't cheap"......I think the cost was over $100 for a kit the last time I ordered the stuff, and that was over 10 years ago.....

But, it does work......and the bottom line was to effect a good repair....

SB

paulh300sd · #10 12-06-2006, 12:27 AM

Yes I did look in on the Belzona website, and their products are amazing. Fortunately, I did not have to pay an exhorbitant cost for it, as the owner of the machine shop I mentioned sold me a little bit out of his batch which he buys by the gallon. I just needed a tiny bit.

t walgamuth · #11 12-06-2006, 07:52 AM

i hope it works out for you.

i had a crank nose that was buggered up by some po while installing the hb.

it is my opinion that they are not likely to come loose just from being loose. if they happened to be loose yes, they would come loose, but usually i think it is because the pins were not installed correctly and were damaged in the process, the crank too.

when my machinist discovered the bad keyways he said just find a crank. which i did.

i hope yours lasts forever for you, but i wouldnt try to fix one that way myself.

but it is a very cheap fix and my way is very expensive since it requires changing the crank.

btw, it was the acquisition of this crank during which i was educated about the difference between the na and th turbo 617 motors. the small dismantler i got it from tried to give me a turbo crank. but we sat the two motors side by side on his shop floor and looked at them. at first glance they look the same without the manifolds installed, but the more you look the more you find different until it is clear the about everything is different! the head casting may be the same. not much else.

tom w