Trevor recons: "While BSA could produce bushes to a fine tolerances they could not allow for crush when the new bush was fitted to the cases thus the need for dealers to hand ream the bushes after fitting to the cases."
There is no mention of the need to ream a replacement TS bush in the factory workshop manual which gives comprehensive instructions on how to do the job intended for the average semi skilled owner....You can allow for crush (within limits) which is what tollerances and clearnces are for.
Mr Mike recons: "I disagree with the BSA idea of grinding the crank to fit the bush. It may be easier for the repair shops to do this, but one ends up grinding away precious material on an expensive crank instead of machining an inexpensive replaceable bush."
when these bike were new 40 years ago that is exactly what was done....you dont ream big end shells you grind the crank to specified sizes and fit the shells in! so why would the TS main require any diffrent treatment....obvioulsy I am talking about how it was done back in the day,,,,since then they have exceeded there design life by a lot , had all sorts of hammerings, and been worked on by guys with masonary bolisters.....they have also been worked on by clowns in reconditioning shops who rave on about "line boring" but dont seem to be able to expalin the process when asked.
Anyhow back in the day cranks were expencive but not totaly prohibitively priced, you got 3 undersizes on your TS bush and that was it ....reconditioning a motor has never been a cheap job....We cant just go down to the local BSA dealer and do the job how the factory said anymore so thats why things are done diffrently now.
The alloy the original bush is made (similar to white metal but coppery colour) of is a very difficult material to work with ....sure after stuffing up a few bushes you will have the tooling, method, lubricants and feeds right and will be able to do lots with a nice surface finish (and maybee even hold a size if you are lucky and dont sneeze) ....but well ya know im not going to scrap a few bushes you cant get readily anymore to reinvent the weel....the replacemnt solid bronze bushes are a diffrent matter...i would size on of those on my clapped out 50 year old lathe and get it spot on first time. Bronze is a breeze to machine accuratley.
Last edited by Ignoramus; 08/25/122:03 am.
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
The factory original timing bush is VP-23 copper lead on a steel strip backing that is rolled circular and pressed into another steel shell. It is not to be reamed.
The factory reamer that was issued to dealers is for the early pre-unit twins when they were fitted with a white metal bush that discontinued around 1953. The A50/A65 is a different bearing and has never had a reamer tool available or recommended
I would have thought that the center seam of the cases was parallel with the timing side joint and the primary side joint.
No,they are machined in 2 separate operations.There is plenty of room for error.Even the force needed to clamp the part causes distortion,let alone swarf between the already machined surface and fixture,or fixtures that aren't set up dead square to the spindle. It didn't mattter if the primary case surface or timing case surface weren't dead parallel to the parting line of the crankcases.
You'll find the same thing with Hepolite pistons.The bottom of the piston is bored so it can be mounted on a mandrel for final machining of skirt and ring grooves.Their mandrel (fixture) must have sometimes been running out 0.010" off centre and 0.010" off square.I've had to duplicate this to check ring grooves and see if they're parallel to the gudgeon and square to the skirt.It didn't matter when they made these parts.
One thing you can bet on.The main bearing housings would have been bored in the same operation where the crankcase parting line was faced.At that time,the bearing axis would be square to the case parting line.Things can move after 40 years.They can move at the time of manufacture.If you remove metal that has residual stress,the areas you've already machined will move.
"Things can move after 40 years.They can move at the time of manufacture.If you remove metal that has residual stress,the areas you've already machined will move." I'm trying to strengthen some cases and expect welding any sort of strengthening to them will cause distortion, and maybe the heat involved will also weaken them. So am thinking I'll add thickness right across and beyond the weak area with shaped alloy plate epoxied on, plywood is made up of thin sheets glued together that becomes very strong, I don't see why it wouldn't be the same with alloy cases. I'm pretty sure the inner T/cover on an A65 is matched to the C/cases, so when buying C/cases its good if you can also get the timing cover so you get good alignment for the idler gear. How the t/gears mesh makes quite a difference to how quiet the motor is, a spring loaded split gear would be nice in there to change the gear clatter to a wizzing noise, which at least sounds more healthy even if it works no better.
Welding aluminum will loose its temper, you will have to heat treat it afterward if full strength is required. Welding T6 aluminum will bring it back almost to T0. On low strength parts the added material is sufficient. Why not use carbon fiber plate? The weak point is going to be the epoxy adhesion to the aluminum. I once saw a gearbox made with aluminum end plates and carbon tube in between. Plating a steel strip and inserting it in a shell is a simple, cost efficient way to make a bearing. I made a TS bush using a Caterpillar tractor wrist pin bush. I have never seen a white metal TS bush. I would be interested in a picture of one. Ever look at the wrist pin bore if a piston? You do not get that type if finish with a single point cutting tool on a lathe or mill. That is what a hone is for. Accuracy is in 10,000ths inch, more if you are doing precision work.
Things can move after 40 years.They can move at the time of manufacture.If you remove metal that has residual stress,the areas you've already machined will move.
We'll never know if a set of cases changed in 45 years or were never right in the first place unless we check alignment. That is why I don't subscribe to putting a pre-sized bushing in and grind the crank journal. If is isn't straight it will never last. Grinding the big end journals to fit undersize bearings is different. You only have to deal with rods that may need truing which is easily fixed are journals which is out of round or tapered and that is fixed with the grind. Alignment is not an issue with rods but it is with the main bearings.