The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Rocket Racer on 29.06. 2009 22:57

Title: Small Journal Crank
Post by: Rocket Racer on 29.06. 2009 22:57
I?m currently in the process of building a 1955 Road Rocket for sidecar racing and intending to retain the small journal crank (its what I have) and plain bush, but using an SRM oil pump and fresh SRM SJ rods. Do any members have any experience regarding the reliability of these cranks when used under duress?
Title: Re: Small Journal Crank
Post by: trevinoz on 29.06. 2009 23:40
The old literature recommends using a large journal crank for racing.
A mate broke a large journal crank in his sidecar racer.
Title: Re: Small Journal Crank
Post by: Rocket Racer on 30.06. 2009 00:35
Thanks, I guess I asked for that response, yes large journal (LJ) cranks are obviously better and most cranks can be broken if not well maintained or over revved (commando cranks snap over 7k).
The SJ cranks are however still sturdy one piece cranks unlike bolt up norton and triumphs. Certainly Eddie Dow stated LJ cranks were ?preferable? for tuning, yet Gene Thiessen did 143.54mph on his ?51 gold flash at Bonneville and there are other examples like Erle Culver in NZ who raced a gold flash outfit in the mid 50?s with a genuine 358 cam for several years very successfully  (both on SJ).
I?m focused on the rolling chassis currently, so have some time to consider engine options, but if I move away from the original crank that I already have, start to open up significant options like using a commando crank or even doing a 90 degree motor with twin carbs. LJ cranks are equally difficult to source as the A65 owners love them.
Is your mate still racing? I?d love a photo of his outfit.
Title: Re: Small Journal Crank
Post by: trevinoz on 30.06. 2009 01:10
Rocket Racer, no he is not racing now but I think he still has the outfit. I will see if I can get a picture.
Is the SJ crank original from new? I know the parts list for the pre '56 RR has that one but a mate reckons that they used the one piece billet crank, bloody heavy thing.
I have the bones of a '54 RR which is a long way off starting to restore and I was going to use the SJ crank.
The mate offered me a one piece item but I am a bit short of LJ rods.
Interesting that you mention the 358 cam. The fellow I mentioned before is the only person I know who has ever had one. He fitted it to a Rocket back in the late 50s or early 60s. He reckoned it was no good at all on the road and swapped it away. He's sorry now. He also said it had a smaller base circle than the standard cams and I think he machined the rocker box to suit.
I don't know , obviously, whether you have seen the one piece crank, I think they were fitted to the '56 and '57 RRs.
In '58 they all used the LJ crank with the radial bolted flywheel.
Title: Re: Small Journal Crank
Post by: Rocket Racer on 30.06. 2009 08:41
Sadly I don?t have a 358 cam, my engine a 55 road rocket is typical thick flange, but has a SJ one piece crank that I understand was used for all the road rockets from 1954 to 1957.  I can only guess it?s the original although a lot can happen in 54 years! The crank still looks pretty sturdy. Its an ex US motor and still std big ends and main bush, albeit in need of a full reco. The top end was running +1/2mm pistons (+20), it had a 356 cam fitted but big valves. I?ve got a 357 for it. Was hoping to put some 10.5/1 pistons in it and keep it fairly stock. I can supply a pdf copy of the article on the NZ 358 based A10 racer if you?re interested.
Title: Re: Small Journal Crank
Post by: BSA_54A10 on 30.06. 2009 11:45
essential if you are going to use the small crank .
Get it carbo-nitrided or nitro-carburised ( same process) .
Sort of like case hardening but you used Nitrogen rather than Carbon.
Should cost about $ 20.00 and make the crank about 3 time tougher than it was when it left the factory.
Note I said TOUGHER, not harder, not stronger.
So it will fail under the same excessive loads as the standard crank but will be far less prone to cracking & breaking at sub critical stress levels and will have a much higher fatigue limit.
Title: Re: Small Journal Crank
Post by: olev on 30.06. 2009 12:40
If you are going racing, I strongly suggest you get a copy of
"Four Stroke Performance Tuning" by A. Graham Bell and spend a bit of time reading the section on 'The Bottom End' in particular 'Main Bearing Alignment' & 'Cylinder Boring'. actually read the whole damn book.
This takes over from 'Tuning for Speed' and is the best thing to come out of New South Wales for years.
NZ is chock full of mad petrol heads, I'm sure you will get this thing to fly.

Title: Re: Small Journal Crank
Post by: chaterlea25 on 30.06. 2009 13:18
HI Rocket Racer,
I would be very interested in the article on the 358 racer,
 if you could send me a copy I would be very grateful, email address is in my profile
John O R
Title: Re: Small Journal Crank
Post by: beezalex on 30.06. 2009 14:24
Sounds like a fun project.  If it were me, I would find a large journal crank and get some MAP or carrillo rods.  Either one of these pieces failing is just potentially too destructive to machine and your person to compromise.  And yes, get the crank nitrided, though I don't know of anyone who will do it for $20.  Trev, is there a place in OZ that will do it for $20?  If so, I'll ship some cranks down there 'cause I looked around here in the US and $250 was what it cost me.

Other Trev: What is this one-piece crank?  A friend here has what looks like a billet SJ A10 crank with the flywheel a part of the crank.  What's the origin of this?  Was it a racing item?

Anyway, Rocket Racer, as far as cams are concerned, the Megacycle 544-x3 is just phenomenal.  The same profile in my A65 is, anyway.  Doesn't give anything up on the bottom end but just builds incredible power and torque through the midrange up to as fast as you want to rev.  I imagine for the A10 it will do similar things...probably much better than the 358 cam.
Title: Re: Small Journal Crank
Post by: A10Boy on 30.06. 2009 20:06
Not sure about retaining the plain bush for a racing motor, but I'm sure those with more experience will have a view.

Title: Re: Small Journal Crank
Post by: trevinoz on 30.06. 2009 22:30
             The crank I mentioned is one piece, that is , the flywheel and crank are not bolted together but a single forging. They are large journal and were standard fit to Road Rockets at least '56 and '57. They are much heavier than the radial bolted LJ crank.
Title: Re: Small Journal Crank
Post by: beezalex on 01.07. 2009 14:03
Trev, that's interesting.  I never knew about these things until about three weeks ago when I found one at my friend's shop.  He had no idea what it was.  I thought it was SJ, but we may have to check again.  One thing's for sure.  It IS heavy.  I wonder what the motivation for this animal was.

As far as the timing side bearing: While I haven't raced A10's, I've had good luck with them on my A65 racers.  I still run the stock setup, though with increased crankshaft endplay (.005") since the crank seems to grow faster than the cases when pushed hard.  The result is this:
Title: Re: Small Journal Crank
Post by: Brian on 02.07. 2009 03:19
Alex I have seen that happen in a few A65's. I dont think it is because of expansion or anything similar, I think it is caused by the bearing being fitted. When you fit the bearing in the case you have to heat up the case until the bearing drops in by itself, if you try to drive the bearing in or give it a few taps when fitted to make sure it is full seated then this is the result. The last two motors I have had apart, a A65 and a A50 where both broken like this. I had them welded and both were fine. The bloke that welded them for me left an old bearing outer in place and then welded the piece back on with a TIG. After he finished I heated up the case and the bearing outer fell out and I fitted the new bearing. Actually I think they were better after the repair because there was a lot more metal around the thin section that breaks. The bad new is that its a total dismatle job to do the repair.

Title: Re: Small Journal Crank
Post by: Rocket Racer on 30.09. 2009 04:12
I did think I had tracked down a decent LJ crank but was not to be, hope to obtain one in the new year. But by then I intend to have my initial race motor together. which will be kept fairly humble so it can cope. It will be plain bush/sj with a 357 and a nice 10TT9 carb (30mm). Am also intending to run tele's but will alter the trail probably by putting a leading axle on the sliders

I have some images stored on my kiwibiker profile my account being named after the norton atlas I raced for the last 6 years but have now sold to build a proper A10 sidecar. There are also pictures there of my double sided beesa brake. The hubs are off being laced up at present to 16" rims (2.5" wide). The frame is BB32R replica a la daytona replica/Erle Culver tribute. So much to do...
Title: Re: Small Journal Crank
Post by: chaterlea25 on 30.09. 2009 21:45
Hi Rocket Racer,
The link you gave only accesses the front page of
us non members dont seem to be able to get at the interesting stuff!!!!
Title: Re: Small Journal Crank
Post by: Rocket Racer on 30.09. 2009 22:42
Sorry my link didnt quite work, if you search for threads there involving my user "atlas" you should be able to get to my profile and access my public album.
Title: Re: Small Journal Crank
Post by: Rocket Racer on 30.09. 2009 22:48
One of the main things I'm intending to do is keep the reciprocating masses as light as possible, so will avoid heavy rods and pistons, if you look at the original BSA pistons they are lovely and light unlike many modern ones. I'm guessing that most modern manufacturers make too many different sizes from one mould so piston wall thickness can be  pretty clunky if the piston happens to be at the wrong end of a size range. Everytime you go up an oversize the piston wall thickness gets greater and the piston heavier.
Title: Re: Small Journal Crank
Post by: muskrat on 01.10. 2009 14:29
G'day RR, if you use the SJ keep the comp under 10:1 and revs under 7000. I snapped a few SJ's in my 57 A7SS racer. 357 is good on petrol but 356 is better on Methanol and will run on 10:1. I used roller conversion in mine with no probs there, if useing bush do not use white metal go for solid PB. Lighten push rods (alloy), rockers (replace springs with shims) and valve spring collars. For sidecar work do not lighten flywheel. I also through bolted the head & barrels (thick flange). Tuning for speed is my bible. Good luck.
Title: Re: Small Journal Crank
Post by: RichardL on 01.10. 2009 15:15
Not that I am tuning for speed or intentionally built for it, but my '55 A10 has been 9:1 with a 356 since I bought it in 1973. Can I assume, from your use of a 356 with 10:1, that my cam/compression match is a good one, even if a later Super Rocket with 9:1 came from the factory with a 357?

Richard L.
Title: Re: Small Journal Crank
Post by: olev on 01.10. 2009 15:53
Gday rocky,
A month or so ago there was a pile of A7 and A10 parts for sale on 'Trade me"
There were a few cranks in the pile.
I didn't see the end of the auction so he might not have sold them. There is no feedback on the sale anyhow.
He seems to be flogging off a lot of BSA stuff from a deceased estate.
He currently has an ad in Trade me for 'BSA B31 Parts' so you may be able to contact him through that. He is in Timaru, Oamaru and his seller name is AKD11.
Just thought it was worth pointing out in case you missed it.
lots of sheep down there
Title: Re: Small Journal Crank
Post by: muskrat on 01.10. 2009 20:50
G'day Richard L,
                     the 357 gives a stronger top end and coupled with the SR's bigger valves it comes "on" at about 5000 - 5500 rpm. The 356 gives better torque down low which would suit RR's racing chair.
RR will you be using petrol or methanol ? Either way a long inlet tract ( from valve to end of velocity stack 11" ) and a smallish ( 1 1/8" ) carb will work.
Title: Re: Small Journal Crank
Post by: Rocket Racer on 01.10. 2009 22:20
I was planning to stick to race gas to keep it simple for carb set up, with a 357, but do have both a 356 on the shelf which was what was in the early road rockets and came out of this one.
Was hoping to run 9:1, but realistically the well used pair of BSA stamped 8.5:1 which came out of this motor may well get reused as they have some life left in. Seems easier to find 10.5:1 in hepolites but not too keen to overload the crank.
I've got an 1 3/8" (30mm) 10TT9 with two float chambers (was planning to run a swill pot to offset any fuel bias on corners), its slightly bigger than I wanted, but should do the job and a nice bit of bling for the bike.
The solid plain bush sounds like the business, I'll get one through Mike who is mentioned in one of the threads as soon as I've checked the state of the crank which was still standard but well used when stripped down.
I have an article (avail in pdf 4mb) on a NZ A10 sidecar racer which mentions briefly that the BSA technical department in 1954 (David Munro) recommended that a new location hole be drilled in the timed breather to give a 30 degree retard. I'd be interested to know if any competition A7/A10 users have modified their timed breathers...
Title: Re: Small Journal Crank
Post by: muskrat on 02.10. 2009 08:14
G'day RR, I would go the 357 with a 30mm feeding two pots with moderate comp. I used 2 X 32's on the A7 on methanol with very short intake (7"), it wouldn't pull the skin off a rice custard under 4500 rpm, but from 6000 to 8000 hold on.I did away with the timed breather all together and vented out the inner timing cover to where the dynamo should be with 1/2" hose to the oil tank then to the catch bottle, also vented the rockers.
Are you going to use the mag or electric ignition ?
Title: Re: Small Journal Crank
Post by: Rocket Racer on 02.10. 2009 22:24
The k2f mag that came with the motor is missing some bits and obviously not been used in quite a while. I'm not a fan of old mag's, well most things lucas that the british bikes put up with in the day. So will probably be leaving it on the shelf. If my budget can be extended that far I'd like to put one of those new BT-H electronic mags on it, I've got one on my B33 and its been worth its weight so far, unlike a brand new joe hunt I ran on my norton a few years back that gave me nothing but grief. The BT-H  mags arent cheap but are at least new and appear well made.
I was planning to put an oil filter where the dizzy went. I like your idea re the breathing, have also yet to decide whether to run twin pipes or a 2 : 1 which would reduce weight.