Author Topic: crankshaft end float  (Read 2001 times)

Offline huddie

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crankshaft end float
« on: 12.12. 2009 15:18 »
Hi you guys, I have just started the bottom end rebuild on my 57 Gold Flash (small journal crank). Having determined that there is more than the .003" maximum endfloat, I was about to shim up under the drive side bearing when I decided to read my really old workshop manual again, where I was suprised to read that the shims should be spilt between the drive and timing side to centralise the crank. Do you guys agree with that?. The shims I have are .010, .005, .0025. Unfortuneately I cannot get an even split as I am looking for about .0085 to .0090 each side. In your experiences how have you solved similar? and do you know if it is possible to get shims of other sizes or even better machined to the sizes I need?.
Regard Huddie

Offline MG

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Re: crankshaft end float
« Reply #1 on: 12.12. 2009 19:18 »
Hi Huddle!

imho splitting the shims doesn't make any sense at all. put them behind the inner race of the drive side bearing and you are fine. I did so with both my engines and everything works perfectly well.
It doesn't make sense to put a shim from unknown material and hardness between two surfaces of the sliding bearing on the timing side, which has to bear reaction forces of the primary drive in longitudinal direction as well.
Btw you can shim down to almost zero clearance. The alloy crankcase has a far higher thermal expansion rate than the crankshaft, so side play can only become more during operation. I went down to 0.0005" and this is alright, at least as long as you don't drive at temperatures below 0°C.

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline MG

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Re: crankshaft end float
« Reply #2 on: 12.12. 2009 19:27 »
btw, forgot to mention before:

If you are doing a complete bottom end rebuild, I would recommend considering rehardening the crankshaft (camshaft and followers as well).
I had mine reground and then nitrogen hardened. This process is true to size and delivers a thin, but very hard surface layer, leading to longer lifetime of the sliding bearings and better fatigue strength. You just have to polish the bearing surfaces with very fine abrasive paper (grit 1000) until they are shiny again. The cams and followers can be left as they are, because the nitrogen hardening process forms a very good running-in layer for friction surfaces.
I found a company here in Austria, that is doing this for approx. 3 pounds per kg of material, the result of over 50 HRC is well worth the money.
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline A10Boy

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Re: crankshaft end float
« Reply #3 on: 12.12. 2009 20:18 »
I'm with MG on this one. The shims go between the drive side crank web and the lipped roller bearing - Not between the timing side bush and crank.

The TS bush has a thrust face for the crank to run against and shouldn't have shims in there. Definitely not.
Regards

Andy

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Offline BSA_54A10

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Re: crankshaft end float
« Reply #4 on: 12.12. 2009 20:21 »
nitriding the crank is an essential job if you take it out of the bike.
It dose not actually harden the crank but it dose make it several orders of magnitude tougher ( more resistant to fracturing)
Bike Beesa
Trevor

Offline MG

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Re: crankshaft end float
« Reply #5 on: 12.12. 2009 20:31 »
BSA_54A10 - Sorry, I have to disagree here. Nitiriding does significantly increase the hardness of the crankshaft by forming iron nitrids, albeit the hard layer is very thin (few micrometers). With the high-alloyd nitriding steels one can reach hardness values of more than 60 HRC.
The increase in fatigue strength (and also the tribological behaviour, btw) is a nice side effect, cause by the diffusion of nitrogen into the ferritic matrix of the treated steel.
Believe me, I've studied this stuff and am dealing with it in my every day work life.  ;)

 Regards, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline huddie

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Re: crankshaft end float
« Reply #6 on: 13.12. 2009 08:25 »
Hi All, Thanks for the replies. Looks like it's drive side only then. Makes it much easier for me. I take the point re expansion and will shim it tighter rather than looser.
Regards for now Huddie