The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: jachenbach on 23.11. 2014 21:55

Title: Crankshaft identification
Post by: jachenbach on 23.11. 2014 21:55

Trying to identify a bunch of parts. I have 4 crankshafts with 2 different types of flywheels and can't find numbers on any of them. Three of them were marked as A10 by the previous owner. The lighter ones weigh 25 pounds and the heavier 29 pounds. Rod journal diameters both measure 1.66". Didn't think to measure journal width. I'm wondering if maybe heavier ones were Golden Flash and lighter ones Road or Super Rocket? Look familiar?

Title: Re: Crankshaft identification
Post by: WozzA on 23.11. 2014 22:45

the one on the LEFT is a LARGE Journal
& the one on the right is a small journal 

Title: Re: Crankshaft identification
Post by: jachenbach on 24.11. 2014 03:23

I'm confused. I thought LJ and SJ referred to the rod journal diameter. These cranks both measure the same 1.66" rod journal diameter.
I've got a lot to learn about these bikes.

Title: Re: Crankshaft identification
Post by: Rocket Racer on 24.11. 2014 07:42

Yes the concept of LJ/SJ refers to the big end diameter. So both are LJ !
The crank on the right is a transitional crank, not particularly well mentioned in the english literature but used in the (if I remember this correctly) in the 56/57 american road rockets (road rockets were rarely seen in the UK) as they were snapping cranks with their 356 cams and 8:1 compression. The transitional crank is lovely and heavy and makes for a lovely smooth motor and has so much meat in it I can't imagine it flexing. It also has a different smaller sludge trap. The more common LJ crank on the left covered by all the literature came out in 58 and is much lighter.
I ran my race sidecar on a transitional crank for several years and it was extremely good, plenty of flywheel, nice for drifting. It was also very smooth. I've swapped this into my road bike and now racing on the later crank which does rev slightly quicker having much less weight. It should be noted the heavier cranks weight is central so they are one stiff sucker, but I suspect the later type were cheaper to make.
In practice use whichever is less worn and clean the sludge trap very thoroughly

Title: Re: Crankshaft identification
Post by: WozzA on 24.11. 2014 12:15

Well...  live & learn...  *eek*   I thought the one on the right was a small journal..  ::hh::

Title: Re: Crankshaft identification
Post by: trevinoz on 28.11. 2014 05:33

As RR said, definitely a 56-57 RR crank.
I've seen quite a few of them here in Oz.

Trev.