Hi, I have a pre-unit 650 engine of 1952 with small journal crankshaft (70-1460).
unfortunately the crankshaft is worn-out, it measures 36,33 on both sides.
The con rods are without shell and i can't increase the measure.
I'm considering to change crankshaft with a post 54 (big bearing) and post 54 conrods with shell; but I should change also the crankcase because the timing side bearing is too small among post 54 cases.
Another alternative could be use a post 54 crankshaft with a small bearing cases, reducing the size of crankshaft joint.
Which do you think about alternatives? are there better solutions? Thanks
You are snookered then, the factory ran bikes with difference % ages and picked the one that seemed to work best, today you would do it on a computer using a model of the frame and then test the output to confirm. Suggest you find other people with the same frame and ask them what % they use and if it works..
Machine shops specialised in this technique can burn material onto the journals and increase the diameter. Flame Spray Technology, I think it's called. The journals are then ground back to round and true.
I have seen this on marine propeller shafts and rudder shafts. I'm not sure if it's done with smaller shafts, but It may be something to investigate.
A mate of mine here at work mentioned a shop which sprays pump shafts 50mm (2inches).
Metal spray or plasma metal spray the crankshaft then grind back to standard size. Common industrial reclaiming process.
The connecting rods shown have babbit on the steel rod cap..Once worn ,new babbit will need to be applied,specialist work done by very few in the USA ,I have no idea about elsewhere.Perhaps there's a conversion to bearing inserts available?? I had a 53 Triumph with the same problem.I fitted a later crankshaft and connecting rods. At first I was just going to turn down the timing side main journal to fit the early small bearing. Then I decided it would weaken the crankshaft...A local very eccentric machinist welded up the right side case under the timing cover to look like the later pre unit cases. The case was bored out to accept the later bearing... It worked out well after a lot of machining to correct distortion caused by the welding...but I believe just turning down the main journal of the later crank would also have worked out for normal riding...
650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...