BSA Conrod in a 4G?

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leonc
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BSA Conrod in a 4G?

Postby leonc » Thu Dec 06, 2018 12:12 am

Is anyone familiar with a BSA conrod, possible A7, that can be modified to fit a Square Four?

I have been offered a brand new set that have had the small end rebushed and the tunnel machined for the Ariel. They are a very reasonable price so I am tempted to buy them before my engine tear down, but would like to be confident that it is all viable. I am aware that new Ariel ones are available but they are much more expensive than this option.

Thanks for any feedback.

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paul.jameson
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Re: BSA Conrod in a 4G?

Postby paul.jameson » Thu Dec 06, 2018 8:41 pm

I have never heard of a BSA conrod in a 4G. If it was a good idea, I think I would have heard of it by now. I do know of Carillo rods being used but they needed the cranks re-balancing and I know that the man who did that has since passed on to a better place. At present I don't know of anyone who can re-balance Square Four cranks and one of the whole points of the new Club rods was to improve the balance by going back to the original weight of the (early) rods.

Ask yourself why these rods are cheap.

Stripping and rebuilding a Square Four engine is not a job most people would undertake lightly. If you use Club rods, the outcome is pretty well guaranteed to be good. If you use the BSA rods - who knows?

But whatever you do, make sure the crankshaft sludge traps are cleaned out or else whatever rod you choose will next be seen through the hole in the crankcase.
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.

leonc
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Re: BSA Conrod in a 4G?

Postby leonc » Fri Dec 07, 2018 8:09 pm

Thanks Paul, exactly the reason I put the question out there.

I am assured by the seller, that they were a common replacement in the States where they came from, but if the Ariel community here does not support that claim with actual history, then I question the validity of this option.

Yes the sludge traps will be cleaned out as that is the main purpose of pulling the engine down, otherwise I would be tempted to fire it up and see how it runs.

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Re: BSA Conrod in a 4G?

Postby nevhunter » Fri Dec 07, 2018 10:10 pm

Unless any alloy rod you fit is fairly new they are a bit of an unknown. Back a while most builders of fast Triumphs twins always used new rods with a rebuild and the Alloy JAP speedway rods only ran one season and hung it on the wall with a hacksaw cut in it. Nev

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Re: BSA Conrod in a 4G?

Postby nevhunter » Fri Dec 07, 2018 10:10 pm

repeat deleted by poster Nev

john.whiting
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Re: BSA Conrod in a 4G?

Postby john.whiting » Sat Dec 08, 2018 2:01 am

the fact the rods are available means someone has had second thoughts after paying for the set an work......I have heard of the conversion before,but when parts wernt available.....if you can buy new rods from the club that have a good reputation......why gamble........unless the rod set was free ,I wouldnt even bother looking at them........as we know,resizing the tunnel is going to reduce the contact area of the caps,maybe even cutting into the bolt holes..........there is also the question of how the work was done,and to what standard of accuracy..........its quite possible to do this kind of job on a hobby lathe,and the result may be good ,bad ,or indifferent.

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Re: BSA Conrod in a 4G?

Postby TonyBaxter » Sat Dec 08, 2018 10:31 pm

Intrigued to know why re-balancing a square four crank is a problem? There are quite a few dynamic balancing companies around, the most well known in the South (West) at least is Bassett Down.

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Re: BSA Conrod in a 4G?

Postby nevhunter » Sun Dec 09, 2018 7:28 am

Deleted by poster. Duplication.
Last edited by nevhunter on Sun Dec 09, 2018 7:33 am, edited 1 time in total.

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Re: BSA Conrod in a 4G?

Postby nevhunter » Sun Dec 09, 2018 7:29 am

They don't run the same balance factor as many other motors as the opposing rotation of the geared cranks cancels out a lot of forces other engines have to address for smooth running. As with all engines though, The correct factor must be known and applied even IF you have the best dynamic balance equipment at your disposal. The square four is a very unusual configuration, which is potentially one of the best balanced engines out there. With engines like this and parallel twins also, suitable dummy weights have to be made and installed on the crankpins in the dynamic balance situation. Nev.


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