Case repair

Bottom End (crankcases and crankshaft)
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StueyC
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Case repair

#1

Post by StueyC »

The threaded section of my left had case where the sprocket shaft bearing nut is usually fitted is badly damaged. When I first noticed the damage after removing the primary covers I thought the damaged area was aluminium. Now the cases have been cleaned and blasted it appears the damaged thread is steel and part of the complete bearing boss which is cast into the case. My original plan was to machine out the damaged area, press in a insert with a threaded inside diameter and scotch key it in place. Now that I've realised it is part of the steel bearing support I'm not sure if to follow the same plan?. I have searched the foum for info' with no luck and was hoping someone out there might have done this repair before. Any suggestions form all that knowledge out there?

Thanks.
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Re: Case repair

#2

Post by Schwee »

If you're talking about the three bold holes around the output shaft that are used to keep the inner primary attached, I had no problem drilling and re-tapping to a slightly larger size. You just need to make sure that
1. You don't drill or tap all the way through, and
2, Your new bols head is small enough to clear everything.
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Re: Case repair

#3

Post by TimmyV »

I think he's talking about the sprocket nut seal threads, not the 3 bolt holes that hold the inner primary cover on. Don't have enough experience with these ol gals to offer any advice though. There are lots of folks here who will be able to answer the question though so hopefully someone will post an answer to the question. Good luck to you Stuey.
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Re: Case repair

#4

Post by steinauge »

You can repair it as you describe or make a similar insert that accepts a -70 type seal(much less machine work).just stay out of the area where the Timken races are.You can easily install the inner snap ring,spacer and a set of races and take the dimension from there.
StueyC
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Re: Case repair

#5

Post by StueyC »

Thanks for the replies. I am talking about the nut that carries the seal and is screwed in just outside the sprocket shaft bearing. I was a little worried that machining a part of the steel boss to install an insert might weaken its retention in the case casting but is I'm only machining about 3/8" deep maybe it will be OK.

I was hoping there was someone else out there that had done the same and it would make me feel a little more confident with the repair I'm planning.

Stuey.
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Re: Case repair

#6

Post by steinauge »

As I said I have done them to accept a conventional seal and it works fine.I never tried to make an internally threaded insert to use the original type "seal" (too lazy)but there is no reason it shouldnt work. :)
StueyC
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Re: Case repair

#7

Post by StueyC »

Thanks for the reply steinauge. The seal is sometimes describes as a bearing retainer nut and tighterns hard up against the outer bearing. Is this part supposed to be a system of stopping the outer bearing from moving outwards and causing excessive end play? If this is what the nut is designed for is there any risk in machining out the damaged thread and fitting a standard seal as you recommend?

Stuey.
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Re: Case repair

#8

Post by steinauge »

Once the motor sprocket and nut is on and torqued the bearing cannot move.It is (or should be ) a pretty snug fit on the sprocket shaft anyway.If the outer race fits properly in the case its not going anywhere.If it tried to move out the bearing would stop it.I have never had a post 69 outer race walk in the case unless something pretty dramatic had happened! I HAVE seen them come loose and spin in the case but much more often in 90 and later junk than our old engines.
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Re: Case repair

#9

Post by partshunt »

StueyC:- I think stienaugs fix is the best way to go. Also, When the Timkin cups are installed, they be mounted internally and the Timkin cones are on the outside. Oter cups will be trapped. You must use the selected spacers matched with bearing kit. Regardlees tho, the outer cups cannot drift out as they are trapped between the cones mounted on the outer side. One suggestion I might make here tho, check to see if that Timkin boss is still tight in the case. Use air pressure, soap and water around the outer joint. Also check with a dial indicator to be sure. They do come loose after time or from an unballanced engine. Mine was visibly loose and I sent my cases to Advanced Cycle Machine in Superior Wiscosin. They have some kinda secret process to redo the Timkin boss tight again. Mine are tight in the case now. It would a waste d effort if you repaited a loose boss I think anyway. Just some suggestions....Joe
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