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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Help in making a diagnosis
Post Info TOPIC: Help in making a diagnosis
ttrist


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Hi guys!

Sorry for my english. It is not my native language, I learn it from the book =).

Please help me with the crankshaft bearings of my Yamaha TTR.  I had remove the cylinder head and cylinder. I found that the crankshaft has a backlash.

I took the side of the engine cover to see the bearings.

1. Bearings. Should the crankshaft bearing inner race rotate freely? I - rotates separately from the crankshaft, but I'm not sure that this is the norm.

2. The longitudinal play of the crankshaft. Should there be? If you push the crankshaft, you can see how he moves a little along its axis. It is evident that moves inside the cage. So it should be? For some reason I thought that there should be a tight fit.

It is still a movie gash to make it clearer.



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Cubber


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Welcome, ttrist, to the TTR forum.

It looks like you have a tired TTR. cry
The inner race of the bearing should be a tight fit on the shaft, just as the outer race should be a tight fit in the casing.

I must add that I haven't had any bother with my engine's bearings so I don't talk from experience.

I'm sure our TTR Guru, Brian, will know exactly what the fault is and how to rectify it.

Brian's guide with some brief details is here http://ttr250.activeboard.com/t43805944/ttr250-fitting-a-325cc-big-bore-kit/

Have patience - he'll be here in a short while. smile

Martyn



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ttrist


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Hi, Cubber!

While I think that still have at least change the bearings. I very much hope that the seats on the crankshaft are not affected and new bearings will sit with interference.

I disassembled the engine for the first time and, therefore, a little worried



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TTRfan


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I am sorry not to have replied before. Such faith from Martyn that I know the answer!

Looking at the workshop manual, Yamaha expect that you will need to pull the crank into the RH case with a special tool which suggests the inner race should be an interference fit.

However, in my experience quite often the RH case comes off the crankshaft easily suggesting that the inner race is free on the shaft. I have some engines that have been split in the workshop but am not going to have the chance to look at them today as its gonna be a busy one.

The bottom line is that is incredibly unlikely that the crankshaft journal on which the race sits has worn or that the inner race of the bearing has worn. My guess is that when its all tightened up the bearing will run properly rather than the inner race spin on the crankshaft.

Brian



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peteBLUEttr


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Yeah I always thought a slip fit would be ok to allow an oil film between inner race and journal and to allow for thermal expansion maybe a 0.1 - 0.2 mm of end play is ok... confuse



-- Edited by peteBLUEttr on Tuesday 11th of August 2015 09:19:27 PM

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ttrist


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I looked at the rest of the bearings and shafts in the engine closer.
Similarly behave balancer shaft bearings and bearing of a primary shaft of a transmission (the one on which the clutch). Inner bearing race rotate freely. And all the shaftы have a small axial play as the crankshaft in my video. I can not understand all the bearings are faulty?
I know for sure that the output shaft (which secured a leading star of chain transfer), the TTR has some backlash as my. May be it is normal?

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TTRfan


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ttrist wrote:

 

1. Bearings. Should the crankshaft bearing inner race rotate freely? I - rotates separately from the crankshaft, but I'm not sure that this is the norm.

 

Sorry for the delay in replying but I checked this on ttrsteve's engine which I am working on at the moment and, yes, the inner race moves freely on the crankshaft journal.

Brian 



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ttrist


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Thanks for the reply, Brian. I nevertheless decided to change the bearings of the crankshaft and balance shaft, because they have a free play.
 I wanted to ask, Is there an alternative to the original gearbox bearings? There are two interest bearing with "tab" on the inner race. They are not labeled (though I do not take them out of the crankcase).

25-08-2015 9-51-59.jpg



-- Edited by ttrist on Tuesday 25th of August 2015 07:55:04 AM

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TTRfan


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The balancer shaft bearing (original part #93306-30210) is a Koyo 6302 15x42x13 which is readily available.

The layshaft bearing (original part #93306-20427) is an NSK 6203DLA8 but don't seem to be available. The best alternative is the double sealed NSK 6203 and just remove one of the seals.

Brian 



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ttrist


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Thank you, Brian. Already I found this information in the next topic =). And, I can not find NSK 6203DLA8 on sale too (

I do not understand it and I want to clarify: both bearings in the transmission with these "tabs"(original numbers 93306-00320-00 and 93306-20332-00) are  NSK 6203DLA8?  

 



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TTRfan


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Just to clarify:

The balancer shaft bearing (original part #93306-30210) is a Koyo 6302 15x42x13 - same bearing on both sides of the balancer.

The layshaft bearing (original part #93306-20427) is an NSK 6203DLA8.

I didn't look for an after-market version of 93306-00320 and bought the Yamaha bearing. The bearing that came out is an NTN TMB904 - 20x37x9

It looks like 93306-20332 is a Koyo 62/22 

Sorry if I confused the situation but I thought you just needed advice on the blind bearings.



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