Author Topic: Crankshaft End Float  (Read 2336 times)

Online Zander

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Crankshaft End Float
« on: 14.05. 2017 07:28 »
Having got the bike up and running, and relatively oil tight, during the course of attending to primary chain alignment I noticed that there is a fairly significant amount of end play on the crankshaft.  I seem to recall reading somewhere that there should only be a few thou movement, and mine is in excess of that.  I don't intend to pull it apart as I want to ride it, and as I've mentioned before, the previous owner had done a lot of work on this bike - the piston heads are squeaky clean etc., and I can't imagine him putting it together without addressing this aspect of the engine, so rightly or wrongly I'm going to assume it's ok.  Unless, of course, the collective thinks otherwise!
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beezermacc

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Re: Crankshaft End Float
« Reply #1 on: 14.05. 2017 08:07 »
When building a new engine most people aim for a maximum of 0.002", ideally 0.001". The problem is that, as the engine settles in, it is likely that the endfloat will increase slightly due to highspots wearing off various surfaces. I don't think I've ever come across an engine, which has been used, where the endfloat hasn't become quite excessive. In my opinion you're probably OK up to about 0.010", but beyond this there is undesirable twist on the conrods which will cause the big end shells to wear on their outer edges and the bike will start to sound a bit rattly downstairs. I'm sure there are lots of A10's riding round with endfloat beyond 0.010". A couple of things to check....... 1) Check there is no debris in the sump - it wouldn't be the first time somebody found their distance shims in there! and 2) check the primary side crankshaft nut is really tight so that the inner race of the bearing can't spin on the crankshaft axle. Maybe a winter rebuild should be considered.
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Offline duTch

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Re: Crankshaft End Float
« Reply #2 on: 14.05. 2017 08:23 »

  ^^ What B-macc says, but also;
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.....Unless, of course, the collective thinks otherwise! 

 Be prepared to face a reasonably sized collective   *eek*

 Did you actually measure it? Even a very small float can give the impression of being much larger than it is- but don't let that be encouragement to neglect it I say measure it as best you can, and report back, and be prepared  *fight*  *smile*
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Online bsa-bill

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Re: Crankshaft End Float
« Reply #3 on: 14.05. 2017 09:03 »
Quote
The problem is that, as the engine settles in, it is likely that the endfloat will increase slightly due to highspots wearing off various surfaces.

correct of course (as I'd expect from beezermacc) what we perhaps forget or dismiss is that BSA would be well aware of this and would not have expected an engine to need stripped down every time crankshaft end float increased a thou or tree.
Maybe we should give those old guys a bit of credit now and then
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Offline muskrat

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Re: Crankshaft End Float
« Reply #4 on: 14.05. 2017 12:29 »
I agree ^^^ but 5 thou would be my limit before addressing it.
Cheers
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Offline jachenbach

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Re: Crankshaft End Float
« Reply #5 on: 14.05. 2017 13:23 »
BSA specified allowable endfloat while Ducati and Velocette are built with a few thou pre-load. I've seen pictures of Velo engines with the crank bearing boss broken right out of the case, presumably due to excessive sideplay of the crank hammering it out. I wonder if the endfloat is allowed in order to make up for variations in crankshaft big end journal/conrod placement/spacing? Side clearance on conrods and a bit of play in the piston to conrod plus endplay in the crankshaft would, I suppose, allow for a little self-centering of things to help prevent seizing. Darn, this is too much thinking for my first cup of coffee! *smiley4*
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Online RichardL

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Re: Crankshaft End Float
« Reply #6 on: 14.05. 2017 15:05 »
A couple of things to check....... 1) Check there is no debris in the sump - it wouldn't be the first time somebody found their distance shims in there! and 2)

Apologies if this is an unnecessary clarification, but there has been misunderstanding on this before. Here, in case you have a sump plate with removable drain plug, Andrew (beezermacc) is advising to remove the whole sump plate and check on top of the screen, not just the plug.

I think it is almost certain you will find shim bits in the sump if float is greater than 0.010". I am not confident enough to suggest continuing to ride with excessive float. Taking what Andrew says, that would be 0.010". However, if I find shim bits in the sump (it's happened to me twice now) I go for the fix regardless of what the measured float is.

Responding to jachenbach, end float is recommended as the minimum to let the crank spin. No excess is spec'd as far as I can tell. Zero float means no spin. I know jachenbach knows this.

Richard L.
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Offline muskrat

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Re: Crankshaft End Float
« Reply #7 on: 14.05. 2017 20:52 »
To add to RichardL's post.
Naturally end float is measured cold (just like revenge). At hot endfloat will be more as the cases expand a lot more than the crank. 5 thou cold could mean as much as 10 thou when hot. Not enough clearance will wear the thrust side of the main bush when cold and too much can wear it by hammering if there's a difference of compression between the two cylinders. That happened to my race motor, foolishly built with too much, thinking it would spin better  *pull hair out*
Cheers 
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beezermacc

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Re: Crankshaft End Float
« Reply #8 on: 14.05. 2017 23:52 »
With regard to Richard's comment, shim parts will only appear in the sump if the primary side crank nut has been allowed to come loose because the shims should be trapped between the inner race and the flywheel when the nut is tightened properly (solidly). If there are shim parts in the sump it can indicate that the nut has previously come loose and an owner might have retightened the nut without realising the shims had been lost causing the increased endfloat..... which is why I was suggesting to check for shim parts in the sump.
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Offline jachenbach

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Re: Crankshaft End Float
« Reply #9 on: 15.05. 2017 01:29 »
From Richard:
"Responding to jachenbach, end float is recommended as the minimum to let the crank spin. No excess is spec'd as far as I can tell. Zero float means no spin. I know jachenbach knows this."

Not necessarily. As I said, Ducati, Velocette, and possibly others are built with preload (no endfloat). From memory, I think it's about .003" preload. I guess you could think of it as negative endfloat? With ball and roller bearings, they still spin. As aluminum expansion coefficient is much greater than iron and steel alloys, they loosen as they warm up. It seemed strange to me when I went to Ducati school, but it works!
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Online Zander

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Re: Crankshaft End Float
« Reply #10 on: 15.05. 2017 08:29 »
Hmmm.... after getting it all back together putting oil in the prim. Ch case I'm reluctant to pull it all down again to measure the end float,  however, when I ride it I've noticed the bottom end sounds a bit " hammery" .  I put this down to the fact that I've not had a BSA before and as it goes well maybe it's a case of "they're all like that, mate".
Now I'm not so sure.  When I first got the bike, I removed sump plate and filter and checked for crap in the bottom of the case, but apart from a few bits of minor detritus, it was clear - certainly no shim fragments.  Looks like the sensible option is prim case off and do the necessary.  Bummer!
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Offline muskrat

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Re: Crankshaft End Float
« Reply #11 on: 15.05. 2017 09:08 »
G'day Zander.
You can measure it from the timing side. Tap the shaft in with a hide mallet, set up the dial gauge and prise the shaft back out with a screw driver.
Cheers
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Online orabanda

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Re: Crankshaft End Float
« Reply #12 on: 15.05. 2017 09:17 »
To check that the shaft is all the way back towards the drive shaft bearings, the crankshaft can be rotated until the RH bobweight can be seen through a hole in the RH crankcase casting (about 20mm diam), and a drift inserted (soft; aluminium) and a careful blow with a hammer will ensure that the crankshaft is all the way across (to the drive side); wonder if the assembly foreman at BSA requested the hole for this purpose?
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Online Zander

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Re: Crankshaft End Float
« Reply #13 on: 16.05. 2017 09:40 »
Thanks to one and all for the guidance and info.  This morning I measured the end float (cold engine) at 0.016".  *cry* Removed SRM sump plate and found bits of what looks like fibre washer fragments but no metal on the mesh filter.
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Offline muskrat

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Re: Crankshaft End Float
« Reply #14 on: 16.05. 2017 13:03 »
Bugga. So you'll be eating/sleeping in the shed for a while. *sad*
Cheers
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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