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b25 (tr25w) crankshaft bearing questions #255927
05/28/09 2:23 am
05/28/09 2:23 am
Joined: Jun 2005
Posts: 47
Northridge CA
D
DavidB@northridge Offline OP
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DavidB@northridge  Offline OP
BritBike Forum member
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Joined: Jun 2005
Posts: 47
Northridge CA
Hello. Summer vacation is here and I finally tore down the 69 tr25w which after the last ride vibrated so badly I was in pain. When I pulled the piston there was considerable side play and I assumed the big end bearing was shot. And after tear down I found a small flake missing from it. The crank itself felt quite smooth but I assume that it will need to be reground when the undersized replacement goes in. But my question is, that when I split the case the crank came out stunk in the timing side and I needed to tap it out with a mallet. Both bearings are one the crank and the manual shows they should be in the case instead. Is this normal? also the Rupert book suggests using tire irons to pry them off but if I do this will muck em up so i need to replace them? any suggestions?
thanks
David


David B
01 T-Bird
69 tr25w
51 B31(in many boxes)
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Re: b25 (tr25w) crankshaft bearing questions [Re: DavidB@northridge] #256062
05/28/09 8:38 pm
05/28/09 8:38 pm
Joined: Dec 2004
Posts: 9,228
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,228
Scotland
If the crank pin is to spec do not regrind but fit new shells to suit. I would go for Aluminium/Tin bearings as made for the Triumph 500 twin and drill a hole for the top shell. The B25 bearings seem to be whitemetal which is not up to the job.

If the main bearings are on the crank then pry them off using the proper extractor or use tyre irons and fit new ones. Relive the crank main bearing journals to give a sliding fit for the main bearings, using emery cloth this takes 1hr per journal. Then fit the main bearings to hot cases and the crank will fit easily and will come apart the same next time.

Re: b25 (tr25w) crankshaft bearing questions [Re: kommando] #257267
06/04/09 3:25 am
06/04/09 3:25 am
Joined: Jun 2005
Posts: 47
Northridge CA
D
DavidB@northridge Offline OP
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DavidB@northridge  Offline OP
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Joined: Jun 2005
Posts: 47
Northridge CA
Crank pin looks and feels good but it mikes out 36.435mm where the manual says it should be 36.512-525 so I believe .10 under and a regrind will be necessary.


David B
01 T-Bird
69 tr25w
51 B31(in many boxes)
Re: b25 (tr25w) crankshaft bearing questions [Re: DavidB@northridge] #257401
06/04/09 7:25 pm
06/04/09 7:25 pm
Joined: Dec 2004
Posts: 9,228
Scotland
kommando Offline
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kommando  Offline
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Joined: Dec 2004
Posts: 9,228
Scotland
As its clean it should grind to -10 thou, make sure you get the ginder to give the right radius at the corners, too sharp and it will give a stress riser on the crank.

Re: b25 (tr25w) crankshaft bearing questions [Re: kommando] #257417
06/04/09 9:00 pm
06/04/09 9:00 pm
Joined: Jun 2005
Posts: 47
Northridge CA
D
DavidB@northridge Offline OP
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DavidB@northridge  Offline OP
BritBike Forum member
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Joined: Jun 2005
Posts: 47
Northridge CA
Will do, Thanks for the advice,
David


David B
01 T-Bird
69 tr25w
51 B31(in many boxes)

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