A65 Engine rebuild

[Wilf2019]

Hello all, I have a 1969 A65 Thunderbolt which i am restoring, and I am some advice please. I have just joined the group so first time posting.

I have decided to strip, inspect and rebuild the engine as the rest of the bike is being fully rebuilt.  I have stripped the engine and had all of the casings vapour blasted, and barrels powder coated etc.

The one cylinder is heavily pitted and will need boring out and oversize pistons fitted.

After measuring the main crank shaft bush and crank shaft journal, the clearance is over the tolerance stated in the manual at approximately 0.0045". Manual states 0.001" / 0.002" clearance.

The camshaft bush on the primary side is also over tolerance at 0.004" - 0.0045". Manual states 0.001" / 0.0025" clearance.
Both of the bushes in question and the journals are visually in good condition but have obviously worn over the years.

I have removed the sludge trap for cleaning. But would like to have the crankshaft balanced if it would be beneficial to do so at this stage.

Is there any recommended machine shops around the Worcestershire / Midlands area that have experience in carrying out this type of machining work and balancing?

Any advice or recommendations would be greatly appreciated.

Thank you in advance.

[geraldhattrick75]

Sorry I can't help Wilf but, given how helpful this site has bee to me, I'm sure someone will be along shortly to offer suggestions.
Good luck with the rebuild.

In the meantime, these people seem to know their stuff:  https://www.srmclassicbikes.com/services

[chaz]

have a look through the forum recent posts, there was a discussion and recomendations ony a couple of weeks ago. one or two around the Oxford area

[DAVE BRADY]

Finding places to get dynamic balancing done is getting quite difficult.
Basset Down Engineering near Newbury may be the nearest to you that I know of.

Dave.

[Wilf2019]

Thank you all for the comments.
SRM seem to be the ideal place. However, it would be a 7 hour round trip for me to take the bits to them, and then again to collect. I don't think I would be too keen posting.

I have spoken to a couple of places locally. But they either have never done this kind of work before, or would rather avoid doing it if they can. Possibly not their run of the mill work.

The re boring of the cylinders should be no trouble.

I've heard conflicting views on the crank balancing. Is it really worth it?

Thanks again.

[DAVE BRADY]

Hi Wilf,

Our BSAs are renowned for vibrating and indeed the parallel twin will always suffer from some vibration.  Bearing in mind the way that our bikes were produced it is inevitable that more vibration would occur than was 'designed' in.
A blue printed engine would probably be quite smooth.  Also over the years regrinds and rebores have altered the original balance.  Dynamic balancing not only restores the design balance but goes further to make the engine even smoother.  The only thing I can compare it to is balancing a wheel.  If we balance our bike wheels we spin the wheel and put weights on to counter any heavy spots but a modern wide wheel on a bike or car is balanced in all planes to make it smooth in use.  This is what happens with the crank.  All elements are balanced and if done properly it transforms an engine.  Riding becomes far more enjoyable and bits do not fall off your bike.

Dave.

[JOHN KAY]

  HI WILF I ONCE HAD THE SAME CRANK BUSH TO REAM OUT AND AS I HAD NO MACHINING SERVICES NEAR ME  , I USED A SMALL SET HONING TOOL GRINDING STONES FITTED IN A DRILL WORKING WITH CENTRIFUGAL FORCE AND SPRING TENSION > A BIT UNORTHODOX AND MAYBE NOT RECOMMENDED BY OTHERS BUT IT WORKED AND YOU HAVE CONSTANTLY GOT TO CHECK THE FIT OF THE CRANK AND MAKE SURE NO GRINDING DUST IS EMBEDED IN THE BUSH >MY CRANK WAS SLIGHTLY WORN ON STD SIZE SO I GROUND OUT 0.010 SIZE BUSH TO FIT > WORKED FOR ME BUT NOT SURE HOW ACCURATE IT WAS  > REGARDS JOHNBOY