Author Topic: How to take apart Crank to repace center bearing?  (Read 7362 times)

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Offline jjwithers

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How to take apart Crank to repace center bearing?
« on: July 16, 2015, 01:19:31 AM »
The center bearing on my BS 175 crank does not spin as freely as it should.  Also, that seal next to it needs to be replaced.

How on earth does one separate the crank to replace that bearing?  The only advice I've gotten is take it to a machine shop...
I happen to have access to a machine shop but I want to tell the machinists what to do. 

Or, if there is somebody who I can send this to to have it taken apart, and put back together properly, please let me know.

Thanks in advance.

-Josh
1967 175 HS
and some BMW's from the 60's and 70's

Offline dcr

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Re: How to take apart Crank to repace center bearing?
« Reply #1 on: July 16, 2015, 10:27:15 AM »
Dealing with this myself Josh. I was lucky enough to find a local guy that does 2 stroke race engines and he still works on the old classics. The crank must be pressed apart and pressed back together. It also must be reassembled back to original specs otherwise you will have a disaster on your hands. These cranks do not have splines and have no alignment marks on them from the factory. Before you press it apart, measure and document. It wouldn't hurt to scribe a few alignment marks across the entire crank for a visual reference when putting it back together.

Reassembly requires precision and the crank must be true. Truing is the alignment of the crank assembly on its straight-line axis.

If you have to replace the center bearing and seal, you also will need to get new rod bearings and pins. I would not reuse the old ones regardless of their condition. You will already have them pressed out so you may as well replace them now.
1966 175 DT and 1968 350 GTR

Offline jjwithers

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Re: How to take apart Crank to repace center bearing?
« Reply #2 on: July 16, 2015, 11:49:10 AM »
Dealing with this myself Josh. I was lucky enough to find a local guy that does 2 stroke race engines and he still works on the old classics.

Would you mind sharing this person's info?  You can private message me or send me an email to my username at gmail. 
The crank will hold up my restoration and I want to get it dealt with properly. 

-Josh
1967 175 HS
and some BMW's from the 60's and 70's

Offline bsracer

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Re: How to take apart Crank to repace center bearing?
« Reply #3 on: July 17, 2015, 09:53:17 AM »
Make sure you first can obtain all the necessary parts for rebuilding. The bearings are available. The connecting rods are getting rather scarce but I believe the bearings and pins are available. The center seals (later type with larger ID) have not been available. Maybe Richard has some still? Scott Clough at SCR (Scott Clough Racing in So Cal 760-365-4505) has rebuilt cranks in the past.

paul

Offline dcr

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Re: How to take apart Crank to repace center bearing?
« Reply #4 on: November 22, 2016, 03:30:05 PM »
As luck would have it - my "local guy" is no longer local. Back to the drawing board.

Utah Crankshaft claims to be able to press apart and reassemble vintage 2 stroke cranks. I am sending them a 175 crank to have the center seal and bearing replaced as well as new crank pins and lower rod bearings. They quoted me $200 plus whatever return shipping is. I had my crank previously pressed apart so i am sending them a box of pieces, but they asked that I provide them with the upper or lower case half so they can verify the reassembly fits in the case and the spec's are correct.
1966 175 DT and 1968 350 GTR

Offline bsracer

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Re: How to take apart Crank to repace center bearing?
« Reply #5 on: November 23, 2016, 10:24:50 AM »
Their website looks pretty good. As long as you have all the necessary parts for the rebuild. The request for the cases is good if you can provide them. I've had a couple of cranks built "too wide" and they didn't fit in the cases. They had to be pressed together more then trued again. $200 sounds pretty reasonable. I once had a tuner guy quote me $625 to rebuild a crank if I supplied him all the parts.

paul

Offline slawsonb

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Re: How to take apart Crank to repace center bearing?
« Reply #6 on: November 23, 2016, 10:41:02 AM »
Yikes! Sounds like a robber guy to me. ;D
...bert

 


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