The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: trickytree on 18.06. 2010 17:06

Title: A10 sidecar crank
Post by: trickytree on 18.06. 2010 17:06
Has anyone had experiance of one of these monsters? There is one on ebay at the momment, chap reckons it is very heavy and was used for sidecar work. Cant get my head around wether this would be a good idea in a solo bike or not. Obviously it would make for a pretty lazy engine, which is what I am after, but would it offer any advantage over a ordinary A10 crank?

My guess is that if it is properly ballanced then it should be quite smooth but if it isnt then it is going to give the main bearings a hard time. Apparently quite rare so was it not popular becouse of cost or was it just not nessesary?

Cheers, Paul.
Title: Re: A10 sidecar crank
Post by: A10Boy on 18.06. 2010 20:51
That guy breaks and sells parts, he doesn't know much about BSA's so its probably a guess.

My view is that you dont need one so heavy.

There is a topic on here about the extra heavy crank if you search.
Title: Re: A10 sidecar crank
Post by: bonny on 18.06. 2010 21:01
never heard of any manufacturer making a crank specifically for side car work, specific bikes yes eg. m21, but cranks no. how much heavier is it ?
Title: Re: A10 sidecar crank
Post by: muskrat on 18.06. 2010 21:18
I think the heavy crank came in at the time they were going from small journal to large. They would have found that it didn't rev as quickly and re-designed it to the lighter one.
A heavier crank will give you more torque, which is why it would suit a sidecar.
Cheers
Title: Re: A10 sidecar crank
Post by: A10Boy on 18.06. 2010 22:13
Sorry to disagree, it wouldn't give more torque. The engine would accelerate slightly slower and have more momentum or stored energy, that's all.
Title: Re: A10 sidecar crank
Post by: trickytree on 18.06. 2010 22:40
Thanks very much guys, reckon I'll knock this idea on the head.
Title: Re: A10 sidecar crank
Post by: muskrat on 18.06. 2010 22:45
G'day Andy,
                   I may be wrong, but I was under the impression that momentum is torque. A heavy weight is slower to accelerate but also slower to slow down.
I'm not an engineer just a lowly fitter & turner. *respect*
Cheers
Title: Re: A10 sidecar crank
Post by: bonny on 19.06. 2010 00:35
G'day Andy,
                   I may be wrong, but I was under the impression that momentum is torque. A heavy weight is slower to accelerate but also slower to slow down.
I'm not an engineer just a lowly fitter & turner. *respect*
Cheers
oi muskrat i'm a fitter and turner too , and a crank thats heavier being slow to accelerate and decelerate is my understanding too. 
Title: Re: A10 sidecar crank
Post by: trevinoz on 19.06. 2010 00:46
As far as I know, the billet crank was made for the RR in 1956 - 57. It was the original large journal crank.
According to my mate who had a couple of these early Rockets, the acceleration was a bit slow but once the engine was revving it pulled like a train.
Definitely was not made for sidecar work exclusively.
Trev.
Title: Re: A10 sidecar crank
Post by: bonny on 19.06. 2010 00:53
i know in stan stentons "triumph tuning" he recommended using a heavier crank for racing .
Title: Re: A10 sidecar crank
Post by: Rocket Racer on 19.06. 2010 01:36
I have one of these and a normal LJ crank, am currently building them into two race engines, am very interested to see how they compare. There will be differences in piston o/s and compression though and one will be twin carb...
No help in making your decision to buy this one on ebay though as my completed builds are still months away (for both). Should have the heavy crank motor done first.
In my case they will be hauling a chair, so not concerned about the weight too much!
Title: Re: A10 sidecar crank
Post by: trickytree on 19.06. 2010 09:31
Be interesting to see how much it goes for, last few big journal cranks on the bay have gone for £300 ish (similar price to a set of thick flange barrels) so not something I'm willing to have a punt on at that price.

Wonder what ballance factor would be used? (My) logic would sugest that it could be made to run smoother than a lighter crank as the same rods and pistons make up proportionaly less of the overall weight??
Title: Re: A10 sidecar crank
Post by: A10Boy on 19.06. 2010 13:29
I may well regret posting this, opening a can of worms, but faint heart never - well you know the rest.

For practical purposes, I think of momentum as the flywheel effect of energy stored in the flywheel, crank etc, and torque is the turning force of the crankshaft caused by the engine being produced at that time.

F1 engines have almost no flywheel effect, kill them at 10,000 rpm and the stop almost instantly, while your old Lister which runs at only 400 rpm with huge flywheels takes about 3 days to stop. For our old beezers, we need somewhere in between.

In theory, stored energy in the crank helps when starting off or hitting a hill, but that's partially used up and then its over to the engine producing power and that's where you feel its torque.

I've never ridden an A10 with one of these super heavy cranks, but I would imagine its quite smooth. Although, BSA must have had a reason to make the lighter one we all know.

Anyhow, they weren't made for sidecar use.

BTW, that seller is ok, hes got a breakers in Bromsgrove, and hes ok to get random bits from.

I just find it frustrating that his adds are always only one pic, and hardly any description.  Just been reground- Yeah, what to ??

Title: Re: A10 sidecar crank
Post by: trickytree on 19.06. 2010 15:37
.........Just been reground- Yeah, what to ??.....

-20 thou!! Spoke to him this week, going down next Saturday for a look around, suposed to be a real Aladins cave so thought I would have a day out. Of course I will undoubtedly return with a boot full of "projects" *conf*
Title: Re: A10 sidecar crank
Post by: A10Boy on 19.06. 2010 18:12
I've been there many times, its just down the road from me. You will be amazed at the stuff hes got there, literally many tens of tons of British bike parts. Good luck.
Title: Re: A10 sidecar crank
Post by: Rocket Racer on 20.06. 2010 00:20
my other cranks are sadly not to hand today, but putting a bare "heavy" crank on the bathroom scales shows 13kg of ballast.
I can weigh the other cranks in coming weeks or does someone else have a bare SJ or the '58 onwards common LJ type to weigh and report on ?
Title: Re: A10 sidecar crank
Post by: A10Boy on 21.06. 2010 12:09
I tried to weigh one of my spares but her kitchen scales only go upto 8 KG and it was much more than that.
Title: Re: A10 sidecar crank
Post by: Rocket Racer on 23.06. 2010 01:25
I've retrieved my later type crank and it weighs in at 10kg on the bathroom scales.
Certainly in the heavier crank the extra weight is not carried in the flywheel but in the centre section inside the flywheel.
Title: Re: A10 sidecar crank
Post by: Rocket Racer on 25.10. 2010 09:55
I had my "heavy" crank motor at the track in the weekend for the first time. Nice light bsa pistons fitted. Med comp 8.x:1 road rocket type.
yes on methanol, a 357 cam and a twin carb head with 10TT9's fitted. Pulling 2 people round a track. She was no slug! I was impressed with the legs she showed. The track is also quite hilly (hampton downs for those with utube) . We were reining in the white 750cc triumph kneeler shown behind us on the picture on our humble sitter.
The crank may weigh a bit but the bike flies 2 up with a chair! As a solo this would still be a stunning motor for the road wink2
Title: Re: A10 sidecar crank
Post by: A10Boy on 25.10. 2010 12:09
Thats brilliant well done. Have you compared it to a std LJ crank in that motor / combination?

Title: Re: A10 sidecar crank
Post by: Rocket Racer on 25.10. 2010 20:23
Thats brilliant well done. Have you compared it to a std LJ crank in that motor / combination?



sadly still broke from building the chair, but have most the parts for a similar second motor, albeit single carb super rocket head. But likely to be some time off yet.
But I would have no hesitation in recommending the "heavy" crank