Ariel Owners Motorcycle Club

Can anyone comment on the VHA cylinder breaking off at the base flange when high compression is used and how high does the compression have to be to break the base flange. The early HS models clearly used this cylinder at 9 to 1. Was the only problems with the HS or was 7.5 to 1 a problem with the VHA as has been suggested to me. I am planning on using 8.5 to 1 and do not want any problems.
I am considering through bolting the cylinder. The through bolting shown in Cheval some time ago used ½” rod that was turned eccentric to 3/8 at the top for the head. This set up would have to be angled slightly as the offset between head and cylinder bolts is greater than this.
I am considering a ¾” (or possibly larger) steel bar turned eccentric for an integral 3/8” stud into the crankcase and drilled and tapped eccentric on top for the long through head bolts. The ¾ adapter would finish about the top of the base flange. The cylinder base flange holes would clearly need enlarging for the ¾” crankcase to head adapter. Has anyone got any photos of a VH that has been through bolted. I want to have something that is original in appearance to at least a casual glance.
Alternately I am considering a head steady/fixing to the frame as it would not be noticeable although it may not be as effective. Any comments there.
David

I have never seen a broken barrelbase with VHA, you will distroy a lot of money with bolting trough.

At a club Long Distance Run many years ago, Dick (Chopper) Henry was heard to remark that he had never known any one who had broken a cast iron VH flywheel. Both Bob Brassington and I instantly replied "I have". Bob also broke a VHA barrel at the bottom flange. He went to HS barrels after that. So if you use it hard enough for long enough you will break it. With gentle use the chances are it will see you out.

Didn't Bob ride home from Moscow with that broken barrel, Paul? I seem to remember he wedged it with wood and made up some form of jacking system with a couple of nuts and bolts under the frame tube...

I've seen Rudges break the bottom flange off in grass track racing, but this is at 7000rpm at 9:1 plus compression ratios. I've never seen a road bike fail this way.

Perhaps I'm just not trying hard enough!

I too have been looking into through bolting to use VB crank in a VH, enclosed pushrod type. I am away from my workshop just now, but as I remember it the PCD of the c/case holes is larger than the head. I was thinking along the lines of drilling out the c/case cylinder mounting holes to a larger size on a smaller PCD, and enlarging the mounting holes in the cylinder, also on a matching PCD, to such an extent the cylinder may need cleaning up in that area. Small eccentrically drilled and taped adaptors used to offset the cylinder studs even further to a smaller PCD. If that does not give the necessary PCD to line up with the head bolts, then drilling these out on a slightly larger PCD might, and turning up some special sleeve head bolts to match. All in all it will be a fiddly job. I also have thought about a head steady. Most bikes of the era had these. You should see the size of the one on my HD. It once came loose, so did my fillings until I realised what was going on. So I would be looking to add a steady too, possibly mounted off the head bolts adjacent to the spark plug and the bolt between the push rods, on an alloy head. Whatever way you choose, it will be difficult, and some parts are going to be irreversibly altered.

There was a through studded Hunter on Oz ebay a while ago,The studs were bent to suit and it looked horrible.Despite the vendors cock and bull story about racing,the thing didnt get a bid.Incidentally,unless you have sleeve nuts onto short studs you wont get the head off in the frame.This means large holes in the head.Or you might just use long bolts and trust your luck that the crankcase threads didnt pick up in the alloy case and strip.Long steel studs with alloy parts is asking for trouble from differential expansion rates.Regards John.

I understand where your coming from John, with an all alloy engine, it may well be a problem.Years ago I ran Royal Enfield Bullets. The iron barrel was very deeply spigoted to the crankcase mouth. The head and barrel are thro bolted on those machines, 5/16 or 3/8 dia studs. The last one I owned was a 'big head' 500. I remember that the studs had a small square machined on the end to tighten them into the c/case and I made a tube wrench to suit. They did have a very substantial head steady, which was a turnbuckle arrangement off a lug cast into the rear of the head. This, I guess, was to limit the rocking moment of the engine, and certainly triangulated it in the frame. Never blew a head gasket!

These are the through bolts I once made.
Somewhere on a cd disc I have pictures of them in the engine, I'll see if I can retrace them.

here it is :
The new holes for the M14 thread in the crankcasemouth are milled offcentred, towards the centre of the engine.
This new thread just cleans up the old thread.
Engine was sold, I still have the rods.