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Positioning unit crank in PU cases #720899
01/02/18 9:40 pm
01/02/18 9:40 pm
Joined: May 2006
Posts: 302
Scotland
Bry Offline OP

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Bry  Offline OP

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Posts: 302
Scotland
While taking measurements on the engine (T110 big bearing crank cases and unit crankshaft) that I am assembling for my Triton project, it looks as if I need to remove 0.010” from the face of the crank where the TS bearing sits against, to get the con rods central in the cylinder bores.

The crank end clearance is currently 0.011”.

Has anyone come across this before?

Thanks
Bry


1946 Velocette MSS
1955 Triton
1959 Velocette Venom
1966 Triumph T120
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Re: Positioning unit crank in PU cases [Re: Bry] #720914
01/03/18 12:48 am
01/03/18 12:48 am
Joined: Nov 2012
Posts: 680
Isle of Wight, UK
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koan58 Offline
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What I would say here Bry, is measure 10X, think 20X.
It is so easy to jump to a mistake.
Are you confident of your measurements? Based on your bores? The bores are perpendicular to the crank?
There's always a first time, but Triumph cranks usually fit comfortably in varied cases, with shimming, not skimming, usually.

Re: Positioning unit crank in PU cases [Re: Bry] #720929
01/03/18 6:54 am
01/03/18 6:54 am
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Skudeneshavn Norway
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Stein Roger Offline

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You're thorough Bry, but I'm with koan here. Think long and hard before skimming the crank. But I'm also a little confused, you have clearance where? When the crank pinion is done up, there shouldn't be any perceptible axial clearance at all.
Personally I don't worry about centralizing the crank and bores either, but then I build road not race engines.
On the TSS they deliberately used off-set small ends and pistons, and that was never one of its flaws.

Then again, a few much better engineers than me advocate centralizing, like Pete R, and maybe John Healy. I hope the latter will chime in so we can all learn something.

Re: Positioning unit crank in PU cases [Re: Stein Roger] #720971
01/03/18 7:18 pm
01/03/18 7:18 pm
Joined: May 2006
Posts: 302
Scotland
Bry Offline OP

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Bry  Offline OP

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Originally Posted by koan58
What I would say here Bry, is measure 10X, think 20X.
It is so easy to jump to a mistake.
Are you confident of your measurements? Based on your bores? The bores are perpendicular to the crank?
There's always a first time, but Triumph cranks usually fit comfortably in varied cases, with shimming, not skimming, usually.


Thanks, sound advice. I'm pretty sure about the measurements, the bores are perpendicular to the crank and after I checked the con rod centre locations with the big bore kit barrels that I am using, I fitted the original barrels and got the same measurement.

Originally Posted by Stein Roger
... But I'm also a little confused, you have clearance where? When the crank pinion is done up, there shouldn't be any perceptible axial clearance at all.


Thanks for the reply. The clearance I measured is the crank end float with the pinion nut removed. When the pinion nut is tightened securing the crank against the TS bearing this clearance would be the gap between the crank and the DS bearing. This measured 0.011", if I remove enough material to centre the rods, this would increase to 0.021", exceeding the 0.003" - 0.017" range specified by Triumph.

I am taking these measurements with the existing bearings installed, I will install new bearings and measure again. Assuming there is no change I suppose I need to decide if it is better to keep the end float within spec and live with the rods being off-centre, or centre the rods by skimming the crank and either accept the 0.021" end float or possibly shim the DS bearing against the case (Velocette style) to bring the end float back within the specified range?

As I bought this engine as a bits from eBay and don't know the history is it possible that I have a T140 metric crank that has had the TS bearing journal OD turned down to 1-1/8", is there a way to tell? I see that the metric bearing is 19mm wide and the imperial bearing is 13/16" (20.64mm), could this difference explain what I am seeing?


1946 Velocette MSS
1955 Triton
1959 Velocette Venom
1966 Triumph T120
Re: Positioning unit crank in PU cases [Re: Bry] #720994
01/03/18 11:17 pm
01/03/18 11:17 pm
Joined: Dec 2004
Posts: 9,551
Scotland
kommando Online content
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I would only be worried about excessive endfloat in an engine with a fully floating crank, however even if you take 10 thou off the timing side of the crank you can reduce the endfloat on the driveside by shimming the bearing inner out to get to the 3 to 5 thou I try to aim for. There is an alternative which is to move the roller bearing outer inwards by fitting shims in the housing before the bearing outer is inserted.

Re: Positioning unit crank in PU cases [Re: kommando] #720996
01/03/18 11:34 pm
01/03/18 11:34 pm
Joined: May 2006
Posts: 302
Scotland
Bry Offline OP

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Originally Posted by kommando
... There is an alternative which is to move the roller bearing outer inwards by fitting shims in the housing before the bearing outer is inserted.


Thanks kommando, that's what I mean when I say "...shim the DS bearing against the case (Velocette style) to bring the end float back within the specified range."


1946 Velocette MSS
1955 Triton
1959 Velocette Venom
1966 Triumph T120
Re: Positioning unit crank in PU cases [Re: Bry] #721001
01/04/18 12:11 am
01/04/18 12:11 am
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Posts: 680
Isle of Wight, UK
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koan58 Offline
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Hi Bry,

I have no direct knowledge of the differences in the crankshaft/crankcase machining when the metric bearing was introduced, hopefully Mr Healy will be able to provide definitive info.
Until then, my best guess would be that the only crank change would be machining the journal to the metric dimension. I think the shoulder would still be left at the same distance from the end of the crank, to preserve the relations in the timing case, eg gear alignment.
I would expect that the crankcase bearing housing would have been machined to the shallower metric bearing depth, so the inner bearing face is in the same plane as the imperial bearing (again preserving timing case alignments). I would suspect a different, thicker, thrust washer would have been the only other necessary change.

If this is anything close to truth, then I wouldn't expect any difference in crank location, irrespective of whether he crank is pre-metric, or post-metric machined to adapt it to imperial.

I do agree that 10 thou is worth correcting. So where could this 10 thou mis-alignment come from?
Of course we are assuming the rods and big-ends are are good. And that you are taking measurements with the rods pushed to one side and then the other, giving an average, and that the averages come close to the 10 thou for both bores?
If both cylinder blocks (650 and 750) give close results, it is quite convincing that the problem is downstairs. Before concluding that, I would want to convince myself that the barrels reliably sit in exactly the same position each time on the studs/dowels.

Only then would I consider the following 4 possibilities:-

The crankshaft may have been mis-machined, in which case your solution is the right one, and fairly simple.

The bearing housing may have been mis-machined (not deep enough), more work to correct.

The bearing is a freak.

There is something stopping the bearing from going fully against the crank shoulder, or, more likely, the bearing is not fully seated in the housing. As you'll be replacing the bearing anyway, I'd be tempted, after measuring its depth in the case, to heat the case and see if you can press it in further.


I then would get the new bearing and do it all again

I'm sure you will get to the bottom of it, I look forward to hearing what you find.

With regard to the possible 21 thou clearance (not float, unless you assume the timing bearing is free in its housing at temperature), I don't think it matters at all. I've never understood why a maximum figure was given, but a minimum is crucial. This assumes you are using a ball timing side and a roller driveside.

I don't know what primary drive you are using, if simplex then sprocket alignment is pretty accomodating. If duplex, then you'd be best checking that after moving the crank.

Dave

Re: Positioning unit crank in PU cases [Re: koan58] #721019
01/04/18 3:18 am
01/04/18 3:18 am
Joined: Oct 2012
Posts: 4,008
Running from demons in WNY
Hillbilly bike Offline
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What actually happens if the crank is right of left of center line by .010 inch ? Will it reduce power or engine life? Will it increase vibration? has anyone "centralized" a crank and said it fixed an existing problem ? And what's more important, the crank central in the cases or the rods exactly center in the cylinder bores? Do you actually check the rods being central in the bores with the cylinder bolted down ?


I ride dinosaurs that eat money
Re: Positioning unit crank in PU cases [Re: Bry] #721042
01/04/18 1:12 pm
01/04/18 1:12 pm
Joined: Sep 2014
Posts: 755
Naarfuk, UK
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Tigernuts Offline
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The length of the drive side shaft will tell you whether it's a T140 crank or not (longer for triplex chain)


If anything other than a blank space is visible here, something's wrong.
Re: Positioning unit crank in PU cases [Re: Bry] #721082
01/04/18 5:35 pm
01/04/18 5:35 pm
Joined: Sep 2008
Posts: 871
Skudeneshavn Norway
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Stein Roger Offline

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I have used roller bearings with no lip on the outer ring, that's perfectly acceptable of course, and makes the term "end float" or clearance irrelevant. If clearance is a worry, this could be a solution.
I agree that a minimum clearance needs to be observed if there'a a lipped outer race, some Norton dignitaries likes to see .015" as a minimum to allow for flexing, even if the cases grow apart with heat, more so than the crank. For some reason Norton people seems to enjoy this "fully floating" situation, instead of using the same type timing side bearing as Triumph used on the late T140. Something to do with the "Superblend" myth I presume. To be fair, the Norton oil pump will pull the crank over to the timing side with considerable force, effectively locating it to the TS.
I haven't yet seen a Triumph with too little end clearance in the lipped bearing, nor have I heard of it, but I suppose it could happen.

If you'd feel better with the crank centered, machining it .010" should be safe enough I think, if you avoid creating a stress raiser at the shaft radius.
Even if I'm happy with the crank "centered by eyeball", I do secretly admire those who will go the extra mile. But then I'd also expect you to make sure the cylinder base is parallel to the crank, that the cylinder flange is parallel to the cylinder top, and that the bores are square to either and centered over both big ends... bigt

Re: Positioning unit crank in PU cases [Re: Bry] #721088
01/04/18 7:03 pm
01/04/18 7:03 pm
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Posts: 871
Skudeneshavn Norway
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Stein Roger Offline

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Here's an old thread about the opposite situation, might be of interest: http://www.britbike.com/forums/ubbt...;Main=58041&Number=531031#Post531031

Re: Positioning unit crank in PU cases [Re: Bry] #721135
01/05/18 9:13 am
01/05/18 9:13 am
Joined: Sep 2008
Posts: 871
Skudeneshavn Norway
S
Stein Roger Offline

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An old thread again, discussing your exact situation. As a bonus you get a couple of engineering terms explained...

http://www.britbike.com/forums/ubbt...;Main=58309&Number=533659#Post533659

Re: Positioning unit crank in PU cases [Re: koan58] #721402
01/07/18 6:07 pm
01/07/18 6:07 pm
Joined: May 2006
Posts: 302
Scotland
Bry Offline OP

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Bry  Offline OP

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Posts: 302
Scotland
Originally Posted by koan58
Hi Bry,

I have no direct knowledge of the differences in the crankshaft/crankcase machining when the metric bearing was introduced, hopefully Mr Healy will be able to provide definitive info.
Until then, my best guess would be that the only crank change would be machining the journal to the metric dimension. I think the shoulder would still be left at the same distance from the end of the crank, to preserve the relations in the timing case, eg gear alignment.
I would expect that the crankcase bearing housing would have been machined to the shallower metric bearing depth, so the inner bearing face is in the same plane as the imperial bearing (again preserving timing case alignments). I would suspect a different, thicker, thrust washer would have been the only other necessary change.

If this is anything close to truth, then I wouldn't expect any difference in crank location, irrespective of whether he crank is pre-metric, or post-metric machined to adapt it to imperial.

I do agree that 10 thou is worth correcting. So where could this 10 thou mis-alignment come from?
Of course we are assuming the rods and big-ends are are good. And that you are taking measurements with the rods pushed to one side and then the other, giving an average, and that the averages come close to the 10 thou for both bores?
If both cylinder blocks (650 and 750) give close results, it is quite convincing that the problem is downstairs. Before concluding that, I would want to convince myself that the barrels reliably sit in exactly the same position each time on the studs/dowels.

Only then would I consider the following 4 possibilities:-

The crankshaft may have been mis-machined, in which case your solution is the right one, and fairly simple.

The bearing housing may have been mis-machined (not deep enough), more work to correct.

The bearing is a freak.

There is something stopping the bearing from going fully against the crank shoulder, or, more likely, the bearing is not fully seated in the housing. As you'll be replacing the bearing anyway, I'd be tempted, after measuring its depth in the case, to heat the case and see if you can press it in further.

I then would get the new bearing and do it all again

I'm sure you will get to the bottom of it, I look forward to hearing what you find.

With regard to the possible 21 thou clearance (not float, unless you assume the timing bearing is free in its housing at temperature), I don't think it matters at all. I've never understood why a maximum figure was given, but a minimum is crucial. This assumes you are using a ball timing side and a roller driveside.

I don't know what primary drive you are using, if simplex then sprocket alignment is pretty accomodating. If duplex, then you'd be best checking that after moving the crank.

Dave


Thanks, good advice. I'll certainly measure again with the new bearings fitted.

I am using a BNR belt drive with the narrower 1" belt, so sprocket alignment within this range is not an issue.


Originally Posted by Hillbilly bike

What actually happens if the crank is right of left of center line by .010 inch ? Will it reduce power or engine life? Will it increase vibration? has anyone "centralized" a crank and said it fixed an existing problem ? And what's more important, the crank central in the cases or the rods exactly center in the cylinder bores? Do you actually check the rods being central in the bores with the cylinder bolted down ?


Yes, I bolt the cylinder block down before measuring.


Originally Posted by Tigernuts
The length of the drive side shaft will tell you whether it's a T140 crank or not (longer for triplex chain)


Thanks, good to know. Looks as if I have a crank from a duplex chain bike.


Originally Posted by Stein Roger
An old thread again, discussing your exact situation. As a bonus you get a couple of engineering terms explained...

http://www.britbike.com/forums/ubbt...;Main=58309&Number=533659#Post533659


Thanks for the links and advice.


1946 Velocette MSS
1955 Triton
1959 Velocette Venom
1966 Triumph T120
Re: Positioning unit crank in PU cases [Re: Bry] #721407
01/07/18 7:17 pm
01/07/18 7:17 pm
Joined: Sep 2008
Posts: 871
Skudeneshavn Norway
S
Stein Roger Offline

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Skudeneshavn Norway
With two Velos in your stable, I'm sure you have a firm handle on this anyway! But a good discussion, thanks.


Moderated by  John Healy 


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