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[HELP] Crankshaft pre-unit questions *photos* #567510
10/13/14 8:08 pm
10/13/14 8:08 pm
Joined: Aug 2013
Posts: 14
Italy
lollo85 Offline OP
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lollo85  Offline OP
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Posts: 14
Italy
Hi, I have a pre-unit 650 engine of 1952 with small journal crankshaft (70-1460).

unfortunately the crankshaft is worn-out, it measures 36,33 on both sides.






The con rods are without shell and i can't increase the measure.






I'm considering to change crankshaft with a post 54 (big bearing) and post 54 conrods with shell; but I should change also the crankcase because the timing side bearing is too small among post 54 cases.

Another alternative could be use a post 54 crankshaft with a small bearing cases, reducing the size of crankshaft joint.





Which do you think about alternatives? are there better solutions?
Thanks

Last edited by lollo85; 10/14/14 5:42 am.
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Re: Crankshaft pre-unit questions [Re: lollo85] #567520
10/13/14 8:58 pm
10/13/14 8:58 pm
Joined: Jul 2009
Posts: 3,549
Vic. Australia
P
Pete R - R.I.P. Offline
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Pete R - R.I.P.  Offline
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Joined: Jul 2009
Posts: 3,549
Vic. Australia
Fit a later 650 crankshaft and rods. You can get a bearing for the timing side that will make it fit. Adjust the balance factor to 71%.

Re: Crankshaft pre-unit questions [Re: Pete R - R.I.P.] #567565
10/14/14 5:37 am
10/14/14 5:37 am
Joined: Aug 2013
Posts: 14
Italy
lollo85 Offline OP
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lollo85  Offline OP
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Joined: Aug 2013
Posts: 14
Italy
Originally Posted By: Pete R
Fit a later 650 crankshaft and rods

Which later 650 crankshaft do you advice? for example I have considered a 70-3296 crankshaft.


Originally Posted By: Pete R
You can get a bearing for the timing side that will make it fit.

Which kind of bearing do you advice? I know only 70-1591 (for big bearing) and 70-2877 (for small bearing).


Originally Posted By: Pete R
Adjust the balance factor to 71%.

Is that balance factor at 71% valid for only for late 650 crankshaft? or for all crankshaft?

Thanks for helping smile

Re: [HELP] Crankshaft pre-unit questions *photos* [Re: lollo85] #567573
10/14/14 7:07 am
10/14/14 7:07 am
Joined: Dec 2004
Posts: 9,543
Scotland
kommando Online content
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kommando  Online Content
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Scotland
Quote:
Is that balance factor at 71% valid for only for late 650 crankshaft? or for all crankshaft?


Its the frame that determines the balance factor so 71% applies to all cranks when fitted to your frame.

Re: [HELP] Crankshaft pre-unit questions *photos* [Re: kommando] #567578
10/14/14 8:17 am
10/14/14 8:17 am
Joined: Aug 2013
Posts: 14
Italy
lollo85 Offline OP
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lollo85  Offline OP
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Italy
Quote:
Its the frame that determines the balance factor so 71% applies to all cranks when fitted to your frame.


mine is not the typical triumph frame, but it is handcrafted by an austrian old factory; how can I determinate the balance factor?


Last edited by lollo85; 10/14/14 8:17 am.
Re: [HELP] Crankshaft pre-unit questions *photos* [Re: lollo85] #567579
10/14/14 9:09 am
10/14/14 9:09 am
Joined: Dec 2004
Posts: 9,543
Scotland
kommando Online content
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kommando  Online Content
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Posts: 9,543
Scotland
Quote:
how can I determinate the balance factor?


You are snookered then, the factory ran bikes with difference % ages and picked the one that seemed to work best, today you would do it on a computer using a model of the frame and then test the output to confirm. Suggest you find other people with the same frame and ask them what % they use and if it works..

Last edited by kommando; 10/14/14 9:10 am.
Re: [HELP] Crankshaft pre-unit questions *photos* [Re: lollo85] #567580
10/14/14 9:12 am
10/14/14 9:12 am
Joined: Sep 2005
Posts: 5,963
NL
G
Ger B Offline
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Ger B  Offline
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G

Joined: Sep 2005
Posts: 5,963
NL
Machine shops specialised in this technique can burn material onto the journals and increase the diameter.
Flame Spray Technology, I think it's called.
The journals are then ground back to round and true.

I have seen this on marine propeller shafts and rudder shafts.
I'm not sure if it's done with smaller shafts, but It may be something to investigate.

PS

A mate of mine here at work mentioned a shop which sprays pump shafts 50mm (2inches).


Ger B

Re: [HELP] Crankshaft pre-unit questions *photos* [Re: lollo85] #567582
10/14/14 9:51 am
10/14/14 9:51 am
Joined: Jan 2014
Posts: 2,176
South cone
R
reverb Offline
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Posts: 2,176
South cone
...I do not understand why not to fill (I do not know the name in English) then ground back to STD and also put super sized shells?
This was done couple millions times...

Re: [HELP] Crankshaft pre-unit questions *photos* [Re: lollo85] #567622
10/14/14 3:16 pm
10/14/14 3:16 pm
Joined: Feb 2008
Posts: 4,496
New Jersey USA
Tridentman Online content

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New Jersey USA
Metal spray or plasma metal spray the crankshaft then grind back to standard size.
Common industrial reclaiming process.

Re: [HELP] Crankshaft pre-unit questions *photos* [Re: Tridentman] #567733
10/15/14 9:29 am
10/15/14 9:29 am
Joined: Oct 2012
Posts: 3,991
Running from demons in WNY
Hillbilly bike Online content
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Running from demons in WNY
Originally Posted By: Tridentman
Metal spray or plasma metal spray the crankshaft then grind back to standard size.
Common industrial reclaiming process.


The connecting rods shown have babbit on the steel rod cap..Once worn ,new babbit will need to be applied,specialist work done by very few in the USA ,I have no idea about elsewhere.Perhaps there's a conversion to bearing inserts available??
I had a 53 Triumph with the same problem.I fitted a later crankshaft and connecting rods. At first I was just going to turn down the timing side main journal to fit the early small bearing. Then I decided it would weaken the crankshaft...A local very eccentric machinist welded up the right side case under the timing cover to look like the later pre unit cases. The case was bored out to accept the later bearing...
It worked out well after a lot of machining to correct distortion caused by the welding...but I believe just turning down the main journal of the later crank would also have worked out for normal riding...


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