Another bit off BSA but maybe of interest

[Mike Farmer]

 

Greetigs, once again as said this is not specific BSA but may be of overall interest. As previous post so not going to repeat too much.

I have an old dry lined international 4 cyclinder engine that has been full of water and one liner is pitted beyond rescue.  The proper replacement liners are not available because the later engines had slightly larger bored liners

The newer liners are about 1/16" ID larger, and the new pistons are Aluminium rather than cast iron. So we have a greater displacement and a lighter piston. Essentially its max revs about 1200 and the comp ratio is about 5.5:1. These points would not change.

I wonder what the general thoughts are about fitting the later liner whether it would be radically different and whether it would completely unbalance the engine and cause catastrophic failure. If it had 5 main bearings I would just go for it.

In truth I am inclined to do it but thought I would run it by you all to garner opinion and wisdom. So your thoughts please.

Mike

[chaz]

Mike

dont know if of any help, but when I started out restoring bikes, I was told to hunt out cast iron down pipes.
these could be used to make liners , but, in those days there were plenty of small machine shops and back yard machinists.

as for the question, I dont think it would make much difference. its acceptable to rebore +0.040" or even 0.060", but then, this was to limit the overboring and making a thinner wall thickness of the liner. +0.060 is close to a 1/16 so I wouldnt worry as 1/16 oversize engines still run at anywhere to 10krevs

[Mike Farmer]

 

Hi Chaz.

Thanks for that, perhaps I wasn't completely clear but we only need to change one liner. Only one is damaged. hus the Q. Had it been all four then not a prob.

Mike

[John Dynostar]

so what is the weight difference of the piston out of interest 

[BILL NELSON]

Mike
Why not give Westwood a call & see what they can do for you.
https://westwoodcylinderliners.co.uk/

[Mike Farmer]

 

Piston weights----At this stage dont know.

Have spoken to westwood, and others. Always a possibility. But trying to get International part first.

Thanks for input.

Mike

[chaz]

Mike
have you tried Cox and Turner?
https://www.coxandturner.co.uk/engine-machining/

[Mike Farmer]

 
Chaz

Yes with no luck.

Mike

[Maddog226]

IMHO, I don't think the increase in bore dia will be a significant factor here.  The issue is the change in reciprocating mass, however at 1200rpm max, it may be that you could just get away with 'giving it a go'.  Your crank will have been designed to counter the forces generated at TDC and BDC (v=0, a=max) - using Newton's 2nd Law F=ma gives the force on the conrod and the crank.  In this instance the change in mass of the piston is the driver.  As it is lighter, the force on the conrod will be less, but the force on the crank will remain the same, accelerations will remain the same, so I would anticipate that the engine will be a bit rougher as the opposing forces will be different.  You could always get the crank, conrods and pistons dynamically balanced, but that might be OTT for an engine that revs to 1200rpm.

Maddog226 CEng MIMechE

[Henry10]

You could always get the crank, conrods and pistons dynamically balanced, but that might be OTT for an engine that revs to 1200rpm.

Maddog226 CEng MIMechE

Can you show me a video on how to do that?