Author Topic: Crank end float and bush clearance problems  (Read 1516 times)

Offline mikeb

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Crank end float and bush clearance problems
« on: 15.01. 2016 09:44 »
I'm still working on one of the world's slowest rebuild...
1. I’ve read a bunch of threads on shimming crankshaft end float – all good. But one question: I plan to put lots of gasket cement between the crankcase halves when I reassemble them as they are not exactly brand new – would that not add a few thou? And is that not significant if my target is 1-3 thou max end float? Does anyone take this into consideration when they do their test fit and measurements?

2. Despite specifying 0.0015” clearance on the timing side bush, it came back from the machinist at about 0.00225”. the threads say 1 to 2 thou max. So now it’s a bit worn out already :(. Would you put it back together at this clearance or bother to get another bush and try again (with a different machinist).

Thanks – possibly I’m over thinking all this to make up for my lack of experience

Mike
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Online bsa-bill

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Re: Crank end float and bush clearance problems
« Reply #1 on: 15.01. 2016 10:10 »
might be I'm just lucky but I've never put anything between the crankcase halves other than a smear with a finger which I then smear off again with a finger and they don't leak.
(does that makes sense) what I mean is the goo more or less just fills in any imperfections in the milled cast but can't really be seen
All the best - Bill
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1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online RichardL

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Re: Crank end float and bush clearance problems
« Reply #2 on: 15.01. 2016 14:34 »
Mike,

How did you measure the ID of the bush? I find telescoping gauges to be iffy (though some here will likely say they have high confidence in their own techniques). If your questionable machinist verifies that he screwed up, ask him pay for a new bush and try again. As long as he's not grinding the journal smaller I don't see the harm.

Regarding running on 0.00225", I'm probably not the one to advise on that one way or the other. My gut tells me that 0.00025" is a pretty small amount of oversize to matter and, at the same time, tells me that the cost of being wrong is a lot more than a new bush. I'm very interested to hear if anyone will endorse putting her back together with clearance greater than 0.002".

Richard L.

Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline KeithA

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Re: Crank end float and bush clearance problems
« Reply #3 on: 15.01. 2016 16:20 »
I also would like to know if 0.002" is too much clearance.
I made my bush today, (took me about 7 hours) and after fitting into the crankcase boss and fitting the crank, I can just get a 2 thou feeler blade in there, but not a 0.0025".
I thought my bush would have closed up a bit more than it did. Never mind.
I turned up a mandrel close enough to the exact size of the journal for use in measuring when boring out the bush.
I left 2 thou clearance with the idea it would close up a bit when fitted in to the crankcase boss.
I now have to assemble both sides, and see how it looks. I am working with mismatched cases unfortunately.
I find telescopic gauges are difficult to use, have to measure many times to find the average. A lot easier the bigger the internal bore being measured.
With sealer, I use a very light smear of Loctite gasket eliminator.
Keith


Offline mikeb

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Re: Crank end float and bush clearance problems
« Reply #4 on: 15.01. 2016 20:20 »
thanks for the comments so far
I fully agree about telescope gauges so I measured the id of the timing side bush by getting someone else to do it - a BSA owning guy who balances crankshafts professionally.
it sounds like the emerging view is a thin coat of sealant has negligible effect of case separation and therefore end float.
will be good to hear experienced views on max bush clearances.

cheers

Mike
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Offline BSA_54A10

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Re: Crank end float and bush clearance problems
« Reply #5 on: 15.01. 2016 21:16 »
A thin spray of Hylomar is all the case get.
The "trick" is a single strand of silk laid on the surfce .
When you tighten the halves together it acts like an O ring and makes a perfect seal.
Bike Beesa
Trevor

Offline mikeb

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Re: Crank end float and bush clearance problems
« Reply #6 on: 15.01. 2016 21:29 »
apparently silk is about 10 microns or 0.0004" so not too much effect of end float
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Online RichardL

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Re: Crank end float and bush clearance problems
« Reply #7 on: 15.01. 2016 23:47 »
I guess that would assume you were only trying to fill things less than 0.0004" deep, whereas, a schmear of gasket sealer won't care how deep the blemishes are and is still likely to add less than 0.001".

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline cableguide

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Re: Crank end float and bush clearance problems
« Reply #8 on: 15.05. 2016 12:07 »
I really think that if you like working on A series engines then a small lathe is as important as a box of spanners.

I too use an old sacrificial bearing which slides on and off the shaft easily, but as rightly mentioned above the back front measurement must be exactly the same as ur new bearing.

Bin the multiple shim idea and turn a new single solid shim a little bit thicker than u need and use a flat plate to gradually remove material until u reach the required thickness. But what metal should it be made from?...should it be mild steel therefore slowly sacrificial or from a piece of hard stuff....still haven't worked that one out yet.

And nipping up the cases from the middle working outwards as u would do with any casing seems to reduce the mis-alignment issue. Oh and for what its worth I use really thin dabs of Hylomar which doesnt appear to change the shim value.

Sorry for the ramble but I just love trying to figure out these badly designed old engines. When u hear one without the rattles and clonks it's heaven.

Cabe.


Offline jachenbach

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Re: Crank end float and bush clearance problems
« Reply #9 on: 15.05. 2016 14:54 »
I had the same question a few months ago, so I assembled my cases/crank with Yamabond 4, measured endplay, split cases, cleaned the joint and reassembled dry. Remeasured endplay, and there was no difference.

Offline edboy

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Re: Crank end float and bush clearance problems
« Reply #10 on: 15.05. 2016 20:49 »
if you put the crank journal into the t/s bush and it wobbles about then its worn out. if snug then fine.use 20/50 if your worried about bore clearances. i hope you line bored the bush or your wasting your time and money. i use wellseal on the crankcases which i dont consider adds any endfloat. my advice is whack the roller bearing on the crank facing the right way and it should be tight and difficult to remove without damage. assemble with the bearing outer fitted [from oven], work out endfloat shims and cut out and place behind bearing outer. use a smear of locktight on roller bearing outer on  final assembly.crank must spin freely or somethings wrong.
not german, bmw rocket science , but build it on a sunday morning in a shed. design i like to play with.
i had mine up to 80mph today on the m40 working on carb tuning and the crank was spinning as free as on the bench and very little vibration.

Offline jjbsa

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Re: Crank end float and bush clearance problems
« Reply #11 on: 31.05. 2016 09:23 »
My comments are a bit late, so perhaps the OP has made his decision, but here goes.

My RGS has just had its oil pressure go low (20-W50 oil, oil pressure gauge fitted, 0 at tickover, 25 running and 45 when cold started) and I’m investigating.  The figures used to be 20, 45, 70.  Now the up and down play on the TS main is a repeatable 2.1 thou measured with a .00005” digital clock gauge.  The motor was built up with 1.4 thou play.  So I’m splitting the cases to get to the bottom of this. 

Considering the OP’s problem, remember that once fitted, the pressure from the crankcase will shrink the bush, once fitted, by an amount close to the amount of interference of the bush in the crankcase.  So it could have been made OK if his 0.00225” slack was measured unfitted.  Fitting the bush will decrease the clearance in the right direction.  I don’t know what interference fit he is going for on his bush, but if he needs to close it up by a further small amount, he could get it plated with e.g. electroless nickel, so that once fitted it will be squeezed more.  If he puts on a thou measured as a diameter change, that will reduce the fitted bore size by about that much.

I reckon that a good fit to go for in these bushes is 1.2 to 1.4 thou.  Car engine mains seem to be typically 0.7 to 1.5 thou in the manuals that I’ve looked at.

A good finish in the bush is essential, otherwise you’re just measuring high spots.  Boring the bush, once fitted, with a very sharp cutter is a good start.  I measure bores while cutting using Starrett wedge gauges as these are very compact and give a very repeatable measurement and you can use a digital external mike on them to get accurate figures. I am not a huge fan of honing as knowing that all the abrasive has been removed from a bush is a matter of belief.  I think burnishing after milling might be a good solution.  Or bore about .2 thou small and let the motor do the burnishing.  HTH

Online muskrat

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Re: Crank end float and bush clearance problems
« Reply #12 on: 31.05. 2016 13:56 »
edboy I beg to differ. The shims should be placed behind the inner race. I know your way should give the same results but the shims are not clamped in position, only relying on the outer race fit in the case and the loctite.
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Offline jjbsa

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Re: Crank end float and bush clearance problems
« Reply #13 on: 31.05. 2016 17:07 »
Muskrat, I'm with you on this re where to put shims,  BSA always put them between the inside face of the d/s main inner and the crankshaft.  They have a nice quiet life there.  I would think on the assembly line they used a loose fitting inner race to tell them what was needed.  A10s have enough trouble with d/s main outers going loose without taking 'em in and out for shimming.  BSA used a C3 fit according to some old motors I have taken apart, and they should be a tight fit when hot, so they don't move in use.  Loctite is not a good answer for loose d/s outer races as there will be no interference fit when cold, so once hot they would sooner or later move again.

Offline edboy

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Re: Crank end float and bush clearance problems
« Reply #14 on: 31.05. 2016 19:15 »
o.k. muskrat . i m normally wrong. with my present rebuild i ve put the shim behind the bearing as you suggested, but it was 0.060" thick so no problems. its extreemly difficult removing the inner race without damaging the bearing and that is even with a bearing puller.i was told years ago that thin shims can spit out and since have gone along with that. however it hasnt happened to me yet.
in defence of the outer bearing method ; the bearing outer is normally easy to remove and therefore easy to shim and when satisfied i put locktite on the bearing outer to go into the cases when straight out of the oven. gas mark 7 x 30 mins.  the outer race will not spin if correctly applied when cases 100 c. i only use thread lock 222 and avoid smearing the lip end or it can get behind the bearing seat where the shims are. i have read others use this method as well so dont shoot i m only the messenger.