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RT Crankshaft Shim

12 Jun 2019 05:01
PMK
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RT Crankshaft Shim #1
In the quest of getting the assortment of parts needed to save my RT2 gearbox, I have bought several motors, both DT and RT in hopes of building one nice motor.

During disassembly, I noticed that some cranks have a shim between the right. Earing and the crank. Others do not have the shim.

The parts manuals show the shim, however, I have yet to find mention in the service manual about the shim.

As best I can tell, the crank has a very specific specified width. The shims would adjust this width. So I ask, is the proper method of determining the shim thickness, or if needed at all, to accurately measure the crank width, and shim as needed to specs?

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12 Jun 2019 05:35
MarkT
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RT Crankshaft Shim #2

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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12 Jun 2019 05:50
PMK
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RT Crankshaft Shim #3
Yes, however DEETs method provides essentially a 0.0 clearance.

Yamaha does not seem to reference how to determine the shim thickness or crank end axial end play.

As I mentioned, best I can tell is build the crank with shim to their specified width. But would like to see Yamahas method to determine the shim thickness, and why.

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12 Jun 2019 06:31
DEET
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RT Crankshaft Shim #4
If you think “DEET’s method” strives for zero clearance, then you did not understand what you read.
The crank expands during heating and it needs a place to go. That place is towards the magneto.
The shim is not used to make the crank a certain width. That is done during crank assembly.
The shim is for crank position within the space between the main bearings.

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Where the Yamaha Enduro is still a current model...

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12 Jun 2019 06:42
PMK
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RT Crankshaft Shim #5

DEET wrote: If you think “DEET’s method” strives for zero clearance, then you did not understand what you read.
The crank expands during heating and it needs a place to go. That place is towards the magneto.
The shim is not used to make the crank a certain width. That is done during crank assembly.
The shim is for crank position within the space between the main bearings.


Agree, I went back and reread the other topic, yes divided by 2 will center the crank.

I have the original crank, shim, cases and bearings, measuring hopefully will not be difficult. Probably use a T gauge for the bearings and wide jaw caliper for the crank.

The odd part in this though, if the shim is installed on the drive end, and we know the drive end is fully secured and will not float unless the bearing moved, why did Yamaha use a tight clearance rather than loose clearance on the ignition side to allow the crank to be easily pulled towards the drive side?

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12 Jun 2019 07:37
DEET
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RT Crankshaft Shim #6

PMK wrote: , why did Yamaha use a tight clearance rather than loose clearance on the ignition side to allow the crank to be easily pulled towards the drive side?


I can only guess that after producing millions of engines, they knew what would work best.

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Where the Yamaha Enduro is still a current model...
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12 Jun 2019 18:29 12 Jun 2019 18:37 by RT325.
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RT Crankshaft Shim #7
My take 'is' the shim is there to get the crank hence the conrod close to central, Also if some home jobby like me pushed the crankpin through too far on the primary side it'll stop the pin rubbing on the outer bearing ring, well in theory. The crank is bolted tight to the primary side by the crank nut & is a slide fit in the bearing till the nut holds it. It's a tight fit in the left crank bearing because there's nothing to hold it tight other than the fit. So there'll be a gap to the left bearing. No doubt you could shim it but unless it's a perfect calculation the shim will just freewheel on the crank. Crank width doesn't always work out to perfect conrod side clearance so need to feeler gauge the conrod side washers. Actually dumby me years ago used to press it up & of course one more press & it goes too far--under clearance, so back it off & muck around, until i saw someone else at work doing it & pressed it up close then with reasonable pressure just under moving it pressure he gave the press a belt with his copper hammer & crept it up a gnats whisker till he got it right. Also if not close to being inline he'd press it down with a long bit of flat steel between press ram & flywheel & could force it to creep around as he pressed, so not too much smacking it after to align it--well in theory anyway.
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12 Jun 2019 19:20
Snglsmkr
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RT Crankshaft Shim #8
I might get tossed to the bottom of Gravity Cavity for this one ...
Out of pure curiosity, Should there be an allowance for the thickness of the Yamabond :?:

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12 Jun 2019 20:02
DEET
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RT Crankshaft Shim #9

Snglsmkr wrote: Should there be an allowance for the thickness of the Yamabond?



That's good thinking.... it should add a little more clearance on the un-shimmed side.
I wonder how thick it could be?

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12 Jun 2019 20:16
MarkT
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RT Crankshaft Shim #10

Snglsmkr wrote: I might get tossed to the bottom of Gravity Cavity for this one ...
Out of pure curiosity, Should there be an allowance for the thickness of the Yamabond :?:


Good thought! When building my six speed CT1 transmission I had to shim and space the transmission shafts. It's not easy! One surprising thing I found was installing all the case screws and torquing them actually made a slight but measurable difference.

I think by far the best method is to build the crank to spec and use the shim(s) that came from the factory with that case set, if any.

If that's not possible, DEET's method is what I'd do. :OnFire

My guess is that if the right crank wheel isn't rubbing the right case (happens sometimes if shim is left out) and the left crank wheel isn't rubbing or over too far to allow the cases to come together fully, the engine will be okay. There just isn't that much available leeway built in to where you could be far enough off center worse than say a bad bore job.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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