Author Topic: Crank shafts  (Read 1916 times)

Offline pato08

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Crank shafts
« on: 05.02. 2013 19:21 »
Hi Guys

I have started on my project A10 Plunger, and have found the crank is flogged out on one side, I have been following a thread about building them back up, but it seems most are not in favoure of that process.  Andy who posts on this forum has a few for sale, and my question is. will the cranks from a swing arm (latter model) fit my enjine ?
picture attached







 
1957 Plunger, one of the very rare collector's items ;-)
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Online trevinoz

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Re: Crank shafts
« Reply #1 on: 05.02. 2013 20:59 »
Pato,
                   The swinging arm cranks will fit but make sure you get the correct big end journal size, small or large.
For that matter, Ariel Huntmaster cranks are the same.

Trev.

Offline muskrat

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Re: Crank shafts
« Reply #2 on: 06.02. 2013 19:01 »
 G'day Pato, just be careful if you go for a LJ crank and rods. When I threw them in the '57 I found the con rod nuts just fouled on the cases, took a bit off the nuts to fix but the clearance is very minimal.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline pato08

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Re: Crank shafts
« Reply #3 on: 07.02. 2013 04:39 »
Thanks musky, I'll keep looking for a small journal. Or ask my engineer about building it up

Pato
1957 Plunger, one of the very rare collector's items ;-)
Australia

Online Brian

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Re: Crank shafts
« Reply #4 on: 07.02. 2013 05:21 »
Pato have you measured it to see just what size it is, or was ?

You can go to -.060" on them.

Offline pato08

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Re: Crank shafts
« Reply #5 on: 07.02. 2013 19:16 »
Hi Brian,  I have taken measurements and will post a detailed drawing and photo's,  here to see what others think
1957 Plunger, one of the very rare collector's items ;-)
Australia

Online KiwiGF

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Re: Crank shafts
« Reply #6 on: 11.02. 2013 05:53 »
Hello, im also interested in this as my SJ crank is on -040, and I have a spare at -040 that needs a regrind that I thought was door stop material! I thought -040 was the limit but had heard triumph rods could be used to go more...I'm not sure of the details though.

The sucesful building up of journals must be possible I reckon, as some UK bike tuners use that method to stroke cranks on modern guzzis.  The difficulty would be finding the person who has experience of doing the bsa crank and won't make a hash of it. I for one would not want to be the "guinee pig"......
New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, project missing parts, mission impossible?

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife

Offline muskrat

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Re: Crank shafts
« Reply #7 on: 11.02. 2013 08:41 »
G'day Kiwi, I think you will find that it's the LJ crank that can be ground down further to use trihard rods.
I shortened the A7SS crank by grinding off the outside of the pin and just touching the inside and used -60 shells. Did silly things like that when racing. *problem*
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline KeithJ

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Re: Crank shafts
« Reply #8 on: 11.02. 2013 22:50 »
Have a large journal crank which I hammered the journals and years ago had the journals "metalsprayed".  Worked OK but could convince myself they would last as well as normal journals.  Recently, I enquired about having the journals reclaimed by, I think, submerged arc welding.  I think it should be fine but as it is used on commercial vehicles and for stroking.  However, managed to pick up a "standard" crank for not much more than having the crank repaired.  Also could have done with the splines being re-built. If it was cost effective, I'd give it a try.  Just my thoughts.   
'59 A10RR + Second engine

Offline pato08

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Re: Crank shafts
« Reply #9 on: 12.02. 2013 04:31 »
I have found one in what looks like good condition on Ebay  Item number: 281061685649

Will I have any problems fitting this in my plunger engine ??

Pato
Below is an attempt to draw my crankshaft all measurements are accurate

1957 Plunger, one of the very rare collector's items ;-)
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Offline muskrat

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Re: Crank shafts
« Reply #10 on: 12.02. 2013 08:39 »
OMG left side is 75 under and right side is 112 under. *eek*Would have to be built up. Not a real fan of that. I'd be looking for another crank.
Commiserations.
Yes it'll fit, it's an LJ so you need the rods. Doesn't say what size the big ends are but not a bad price.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online KiwiGF

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Re: Crank shafts
« Reply #11 on: 13.02. 2013 03:22 »
That's quite an achievement to grind a crank that much and still be able to get shells to fit, as -040 is smallest ID shell readily available to fit std rods (as far as I know).

BSA originally recommended to grind to -030 but suppliers like DraganFly/SRM can supply -040 for SJ cranks.

I would check you have standard rods? Do you have a pic of the rods and shells? I suppose it's possible (but unusual) to machine "custom" shells to fit std rods!

As per Muscrat's "EEK" post the SJ crank big end journal is 1.460 dia as std, so your crank has been ground to well under the accepted min size.

The rh main is 1.374 as std, so that's well under the std size on your crank as well, but's relatively common to grind off the minimum to make that round again, and then get a custom bush made to suit the resultant journal size.
The lh shaft just needs to be a slight interference fit inside the std roller bearing. It's not used as a bearing surface of course.

BE journals do not wear much before an obvious "knock" occurs so it's unlikely the BE journals have worn to that size, from a std size, so they almost certainly have been ground to those dimensions to suit non std big end shells.

To assess the "state" of a big end journal it's notrmal to measure how OVAL it is as well as it's diameter, as nearly all the wear occurs on the top/bottom of the journal and very little on the journal sides.

Others may disagree but 002 ovality would indicate to me the need to regrind to the next size down. Any ovality adds to the "normal" clearance needed between rod and journal and of course fitting new (round) shells without grinding the journals will not remove that "extra" 002 clearance, so new shells fitted to an oval journal will not last very long.

For my BE journal regrind I asked for 0012 clearance between rod/shell and journal. In my case if/when the ovality has reached 002 there will be 0032 clearance on the top/bottom and that would almost certainly cause a noticable "knock".

As regards buying a used crank, you need to know it's undersize, and you then probably need to assume it will need grinding to the next size down AT LEAST, as it will probably be worn and have oval journals. Effectively this means that a crank already ground to max undersize is not worth buying, one on the next size up is stil a risk, especially if it's rusty or was used well after the knocking started.

Another risk with used cranks is that they are bent or cracked. The seller may be unaware of these faults, either of which might have caused the crank to be "put on the shelf" in the first place. Splines can be worn as well of course. Another fault is that  either too small or no radius was ground on the crank during a prior regrind, and this cannot be fixed with a further regrind, once the metal in that corner is gone...it's gone.

A problem I encoutered with fitting -40 shells is that being thicker wall compared to the std shell they take quite a few foot pounds of torque on the rod bolts to make them go round in shape, not so much a problem for me as I was using billet rods which take a higher torque on the bolts than std rods, but it makes me  wonder whether (even) if -050 or less shells WERE available for standard rods I wonder if there would be problems fitting them?

Anyone got any experience of buying and fitting BE shells smaller than -040?
New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

1949 C11 rigid, but why!!! (cos it was cheap)

1937 B21, project missing parts, mission impossible?

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife