crankshafts

[olev]

Anyone know what crankshafts will fit what?
for instance will this ss lump fit my 52 star twin?
http://cgi.ebay.com.au/BSA-A7-CRANKSHAFT-500CC-SHOOTING-STAR_W0QQitemZ190322132479QQcmdZViewItemQQptZAU_Motorcycle_Parts_Accessories?hash=item2c501545ff&_trksid=p3286.c0.m14&_trkparms=65%3A1%7C66%3A2%7C39%3A1%7C293%3A3%7C294%3A50
I understand A50s and A65s can be fitted to some A10s and A7s.
Anyone got a definitive list, .. an undefined list,.... a theory?
wild guesses are good too.
cheers

[muskrat]

G'day Olev, It will fit but I'm not sure about the cush splines. I have a plunger and a s/a and from memory (not that good anymore) they (cush components) are different.
cheers

[A10Boy]

That looks to me like the later crank, the cush was indeed different on the early models.

[beezalex]

That looks to me like the later crank, the cush was indeed different on the early models.

Yes, but are the splines different?  I'm not so sure they are.

[trevinoz]

Olev,
          The splines are the same. All model shafts are interchangeable. A50/A65 have an Imperial size main bearing.
Trev.

[coater87]

 Trev,

 Then the only difference in an a50/65 crank is the bearing size? I sure think it would be easier to source one of those even if you had to have the rods redone.

 Lee

[olev]

Trev,
Does that mean I can drop an A50 crank into the old A7 plunger?
cheers

[cus]

G'day All,
On the crank subject, when I pulled my engine down, my bike had a big journal crank with the small bungs,
instead of the larger diam. bungs, I was told it was an engine set up for a sidecar, I think mid 50's,
has anyone heard of these, is also heavier than a normal crank,

regards, Cus

[beezalex]

Olev, the timing side bearing journal is also larger and, of course, the drive side shaft is longer to accept the alternator on the A65/A50 crank.  The drive end can certainly be modified on a lathe, or you could use this as an opportunity to add an alternator.  Then, of course you'd have to put a cush center on the clutch because the cush drive is gone.  The timing side is even more problematic, and I haven't quite figured out how to deal with that one.  There really isn't enough meat on the case to install a the larger bearing, so I'm leaning toward welding in some material to support the larger bearing.  I don't think grinding the journal diameter down is a good idea because it would bring the oil passage dangerously close to the intersection of the cheek and the journal.

So, while I think it can be done (and I plan on doing it for my A7 racer), it's not as straightforward as first impressions would have you think.  For a street bike, I don't think it's worth the effort.

[olev]

Thanks Alex,
I think you are right.
Its not worth the effort.
cheers

[trevinoz]

Marcus,
                The crank you have is a Road Rocket one from 1956 - 57. Some say it was in the earlier Rockets.
As far as I know, the Rockets all used the large journal radial bolted crank from 1958, along with the Flashes.

Olev,
         The A50/A65 stroke is different to the A7 so pistons may be a problem as well as the other difficulties.

[Rocket Racer]

I recently pulled apart a motor and came across a large journal crank that is much heavier than a "normal" large journal one. I'd be interested in knowing if this is a special or not. It has the smaller bungs and is very similar to the one in the haynes manual fig 1.3 (on page 30) as distinct from the one shown on fig 1.4 (page 33).
Seems ideal for a sidecar as mentioned.

G'day All,
On the crank subject, when I pulled my engine down, my bike had a big journal crank with the small bungs,
instead of the larger diam. bungs, I was told it was an engine set up for a sidecar, I think mid 50's,
has anyone heard of these, is also heavier than a normal crank,

regards, Cus

[mark]

My belief like trevor is that this crank is the standard one for the 54 to 57 road rocket. It is also clearly shown in the BSA parts catalogue for the 1956/57 road rocket. It also doesn't have the tube inside the sludge trap like the later ones or any visible bolts on the circumference. I have one for my 55 rocket that I removed from a 57 engine.
Mark

[Rocket Racer]

While you may be right, my own ex US '55 road rocket mtr which was still std shells and std size plain bush down below, was small jnl. I didnt think the bottom end had ever been touched. I understood small jnl was the standard until the '58 large journal cranks came out.
This heavy crank came out of a bitsa motor with '55 a10 cases 10.5:1 pistons, thin flange barrels, 357 cam and a twin port alloy head so I dont have a reliable lineage for it.
I'd just like to understand these two very different large jnl cranks. The heavy one is certainly built like a brick shit house and very different to the more common type.
 Are you able to attach a pdf of the '56/'57 parts list showing road rockets with large jnl cranks...
Cheers

My belief like trevor is that this crank is the standard one for the 54 to 57 road rocket. It is also clearly shown in the BSA parts catalogue for the 1956/57 road rocket. It also doesn't have the tube inside the sludge trap like the later ones or any visible bolts on the circumference. I have one for my 55 rocket that I removed from a 57 engine.
Mark

[Rocket Racer]

I see BSA do talk about heavy duty cranks being standardised for the '57 year, presumably these were the small button ones...