As I now have the facilities, a bigger hotter funace :D, I am tempted to cast up some new barrels for the BSA unit twins in cast iron or aluminium alloy, with sleeved liners.
I can make these from 500cc upto about 810cc using the original form of barrels, as they are sand cast using a set of patterns I am making. The bore size is purely down to machining and it would be possible to change the barrel height to give different engine characteristics.
Anybody interested in new barrels for their beloved bike? Just an expression of interest at this stage would be useful. Price and availablity would be forthcoming once I get further on with the project.
I've already done some alloy barrels for my big singles, using modern modified pistons.
I have a number of sources for new pistons and no, not those nasty cast rubbish parts from the Far East.
I would certainly be interested in a set of barrels, especially a big-bore set - do you know of a piston source for a big bore ? I'll keep my eye on your post and if you decide to go ahead let me know. Regards Kev
68 bSA , i want a set of 750 short stroke barrels, why ? I have lomg and short stroke versions, the short stroke I want to live on, pistons are lighter than stock nad the motor is torquier and smoother than stock. new jugs , yes please. Can you get pistons as well.?
71 Devimead A65 750 56 Norbsa 68 Longstroke A65 Cagiva Raptor 650 MZ TS 250 The poster formerly known as Pod
will the cam followers running in the block be an issue with alloy ? i know some triumphs run alloy cam follower blocks but there not the same alloy as the cast barrels, nice idea tho, a65 barrels are heavy
im a bit thick tonight (no one say "What do you mean tonight") well i am most nights, but tonight a little more cotton filled than normal.
How do you follow - off set studs?
From memory, the centre studs are located slightly differently for the 5/16 stud and 3/8 stud cylinders. SRM used to list studs for fitting the big bore kit (3/8 studs) to early cases. The studs mostly had 2 diameters, but a couple were also offset. There's not much in it; just enough to be annoying.
I could well be totally wrong, in which case Kevin or Rich will sort me out
Re: New BSA A65 & A70 barrels.
#383754 07/11/1110:33 am07/11/1110:33 am
Cost. This a a variable at the moment, until I can get view on the quantites involved. The more I can make per batch, the cheaper they get.
Cast Iron sets. I'll need to make a chill piece for the castings to ensure the material around the tappet area is cast correctly.
Alloy sets. I will probably go for a cast in steel tappet block, although I could look at other materials offering good wear properties. Treated alloy may be possible, but longevity of the wearing surfaces is a big consideration. The muff will probably be linered, making reboring un-nessecary, as the muff can be re-sleeved. Larger bores can be accomodated purely by boring the muff to fit the liner, providing there is enough material in the muff not to weaken the casting.
Bore sizes. This is governed by the design of the head and crancases and any dimensional limitations, like fixing locations and crank strokes. It is possible to make a near 750cc barrel using the standard crank, using pistons that are sqatter than the stock sizes and a shorter cylinder muff with a larger bore. I've done this before, as this is what Les did at Devimead.
Cubic capacities. As there are limitations to the maximum bore size, any increase in capacity has to be done by modifying the stroke. Not difficult until you try to sqeeze in a Norton crank to get to 900cc. The whole motor gets really stressed and rather fragile. Time to think about a whole new design. Fitting an A10 crank to get a bigger CC is quite common, I've done a few of these over the years.
Pistons. I have a number of sources for these, although I do have two prefered UK based manufacturers. If I can use stock castings from them, with a few bore variations, that will make them affordable, but not cheap.
As this project is not high on my workload list, it will be months before it gets completed, but I will post up information as it progresses.
I cannot post up photos of the singles barrels I have made as they are currently in use and I have no intention of stripping down the lumps just yet.
As for larger 3/8 studs fitted on to earlier cases and boring early cylinder muffs to take the larger size studs, I have sets of jigs to do this. It is only a drilling and tapping exercise.
The triples use aluminum tappet blocks, unknown if these are a different alloy than the barrels. Presumably they are since the barrels are cast and the tappets are machined round stock (no point in casting). You could use valve guide sleeves in the aluminum tappet block. The front and rear wall are only to prevent rotation. The early A65 cylinder front centre two studs are farther apart than the later 3/8" studs. The cylinder would need a different drill pattern. I had to make a drill plate for both cases so I could find the bore centres. I doubt you will be able to make a 750cc using the stock stroke and liners, not enough material between the bore and head bolts.
Handyman, I'd recommend alloy cyls rather than cast iron. And I wouldn't use liners, Nicasil makes it one piece and gives a good ring seal. I tried a set with thin liners which pressed down against a step at the bottom of the bores, problem is with a long stroke crank the lower bores need slotting a little to clear the rods, it would probably be ok if the liners didn't move or turn in the block, mine did. With a 79.5mm bore the lower bore is getting a bit thin even with the casting oversize and needing the case mouth opened, when that thickness is half sleeve half alloy neither is very strong, mine cracked a sleeve. A thicker sleeve stepped at the top is a bit problematic because of the limited room from bore to bolt/stud holes. Which needs reduced H/bolt dia so as not to distort the bores. So the second set I made are all alloy with Nicasil plated bores 79.5mm and they seem to work very well esp with Ed V's forged B44 pistons and high spec chrome rings. I just use a cast tappet block, the cyls are heat treated to T6 and I expect the tappet block to last, although I've not had it apart to look. When I build a short stroke motor I'll still use a std length cyl but with B44 pistons and longer rods, that way I can use the same cyl for long or short stroke motor. These are my cyls before plating.
For those of us who have owned the same A65s for many years, which have undergone one or two rebores with no rebalancing, it would be nice to go back to a standard bore, and pistons that weigh the same as the originals, so that the engine would be balanced at least as well as it was when it left the factory. (Is that laughter I hear?).