What is acceptable runout at the crank/rotor end?

I was doing some other work on my bike the other day and decided to check the crankshaft runout at the alternator rotor. I had posted a question earlier about checking the runout with the engine running but it didn't seem there was a reasonable way to do that. So I ended up just putting a dial indicator on the shaft and rotating it with the alternator nut. There is .008" (8 thousandths of an inch) of runout. This seems unacceptably high to me but hey, I have never worked on any other engine from the 1940's before!

So, what's an acceptable number for crank runout at that point?

Trying to check the crank runout that way would not likely be giving you a very accurate reading as you will be reading the runout plus the bearing clearance plus the flexing of the shaft from applying the wrench to the end of the shaft.

Generally when I have a shaft setting in a set of bench centers I would be worried if I saw more that 3 or 4 thousandths. Jim

hello all hope you are all well
Mike, I reckon.001 is max. to be rough and ready .0015 per side .
8 thou does seem incredibly high. . does the bike run rough or vibrate excessivly. how are the mainbearings. this would cause other problems, especially with alternator rotor whizzing around. Listen to Comnoz advice. the 8 thou must be checked again to see if it does exist. I reckon if no other symptoms are present it may not exist. you should notice this amount of runout.

I think Phil Irving sums it up by saying if the total run out on both sides does not exceed 2 thou there is nothing to worry about

hope this helps
Bradley

~.003" would be risky to race on but last a long time in street use.
Jim covered the sources of errors but maybe my Peel has a clue for you. Put the pistons at TDC and see where the run out points, if 7:30 to 4:30 arc then subtract say .003" for C-3 bearing slack for ~.005" over rev jump rope injury.

If points more to rear Ie: 3 o'clock-ish, suspect an over tight hot primary chain event.

I ran Ms Peel 2000 miles as hard as I possibly could, as nothing much left to lose, with DS off 1/8" and TS 1/16" and nothing blew up or even felt rougher. After I came to grips to finally put Peel down, crank had self corrected to DS 1/16", TS 1/32". At these values what difference does a few silly 1000th's accuracy matter, ugh. If the cam lobe and cam tensioner loss had not cut her power down I'd of just shurgged it off and stuck on the blower regardless.

About only thing I can think of risking is the bearing races might be more prone to wallow and spin in their alloy bores. I have found a crank shop that can put er back within spec < .002" cheaply and quick if ya ever decide to.

There is no actual sign of roughness at all in the engine - I'm wondering if the crank shaft "stub" that protrudes from that side of the crankcase could actually be bent/warped slightly on its own while the actual crank runout on the bearing surfaces is fine. Or, it could be as Jim noted, that the measurement method is inherently flawed.

There has been no indication that there actually is any problem. So perhaps I'm creating an issue where none exists.

Yes its possible only external stub is tweaked which could risk fouling alternator at a lower hi rpm than otherwise. Puller er out and let us know tomorrow.

Peel's crank arrived at Ken Canaga's with offset of DS .012" TS .008". Repaired back to .002" with expectation to try it to 8000 at least a few times.

mike996 said:

There is no actual sign of roughness at all in the engine - I'm wondering if the crank shaft "stub" that protrudes from that side of the crankcase could actually be bent/warped slightly on its own while the actual crank runout on the bearing surfaces is fine. Or, it could be as Jim noted, that the measurement method is inherently flawed.

There has been no indication that there actually is any problem. So perhaps I'm creating an issue where none exists.

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If you don't see any signs of rotor to stator contact I don't think I would worry about it. Jim

The rotor that came with my 850 has a .020 run out, so into the bin with it! It has a deep scuff mark one side and can only imagine the extra vibes it produced?

The rotor that came with my 850 has a .020 run out, so into the bin with it! It has a deep scuff mark one side and can only imagine the extra vibes it produced?

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Dang that implies your crank may have been factory installed as is.

A survey would be educational and hopefully soothing in an ironic way.