650 Triumph Pre unit cases

madass140

madass140

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Alt cases were always preferred for Tritons etc mainly I think because you could have 12v electrics, but with these new
6v generator replacements which look like the old generators but are 12v alternators, wouldnt that be as good if not better option than the much preferred? generator case are certainly a lot cheaper to buy. certainly less dramas around the end of your crankshaft.
 
I am surprised the generator cases are cheaper. There seem to be lots of the alternator ones around. I think you could use the generator cases and still fit an alternator. You would need the alternator type primary chaincase and also the alternator type crankshaft. You would be best off to use the one piece crank from a unit construction bike. You would want the later cases that have the bigger bearings. I am not sure at what number or date those cases started.

The three phase Lucas alternators put out a lot of power at low revs. They must be a lot cheaper than an Alton. You can easily find used single phase Lucas alternators that are good. Get a new rotor though, the old ones generally are low on magnetism now.
 
yes I'm not sure if the generator cases have the big bearing, but for a Triton etc I think it would be nice to only have the sprocket or pulley at the end of the crank.
 
tricatcent said:
You would be best off to use the one piece crank from a unit construction bike. You would want the later cases that have the bigger bearings.
Click to expand...

Do you know if there is a optimum one piece crankshaft that would go into 1957 generator cases. ?
 
I don't know all the part numbers, but there are light and heavy flywheels. The engine will feel like it has more acceleration in first gear with the lighter ones.

I don't think you can notice the inertia of the alternator rotor. I had a race bike where I removed it and I never noticed any difference.

The other thing you have to be careful about is the size of the shaft on the timing side. Any of the earlier cranks will fit, but sometime in 1971 or 1972 there was a change to the size of the timing side bearing. They switched to a metric one. That later one and the ones from the 750 will not fit.
 
Thanks for that.
It will probably be a 2014 project so plenty of time to do some homework.

650 Triumph Pre unit cases
 
The light one piece shaft out of the saint is not worth using. The one piece shaft out of post 58 650s are great. The big journal three piece shafts out of the mid fifties 650s don't usually break, however you must be sure to use the strong OEM bolts which hold it together. If you only have the cases which accept the small timing side bearing, it is possible to get a bearing to fit the bigger mainshaft, however you might have to use spacers to make up the width - not a good option. Or you could get the mainshaft reground to fit the standard bearing which suits the cases. .Do not use an early small journal shaft, even in a 500.
 
The alternator that replaces the generator is expensive,and less reliable than the Lucas type alternator.I don't think it even produces as much power as you can get from a Lucas alternator;you can get 180W @ 5000 rpm thesedays,single-phase or 3-phase.
You can still use a Lucas alternator with generator cases,you just need the alternator primary cases.You just need to plug up the generator hole in the crankcase,if it's not being used.
T100 and T110 got big bearings in '54 model.5T and 6T got the big bearings in '55.T110 used generator and magneto until about '59.5t and 6T used alternator and distibutor,since about '54.

A light crank might be fun when you first accelerate in the low gears.It will make more vibration and less power.The crank used by Johnny Allen at Bonneville weighed 10 lbs more than standard.If you use a unit crank,you need to trim some thread at the timing side,so it doesn't interfere with the bush in the timing case (or shorten the bush).

Use a clamping washer between the timing side bearing and crank pinion.There's a narrower pinion gear for this.That allows you to use a roller bearing on the drive side.Check that the conrods are central in the cylinders,and shim the crank if necessary for rod alignment and end-float.

The lightest flywheels were '66-'68,and even some in '69.Rods got heavier and stronger during '67,and more crank counterweight was used to keep 85% balance factor.You only want about 71% for a pre-unit.Rod bolts changed to UNF after June '69,and these only get torqued to 22 ft-lbs dry (or still 0.004"-0.005" elastic stretch).

Cranks made after mid-'71 have a bigger metric bearing on the timing side (30 mm vs 1-1/8").You can grind down a metric bearing to fit the pre-unit big-bearing case (about 0.020" to grind off the O.D.).They also used UNF flywheel bolts,instead of 3/8" x 26 BSC.That means it's easy to find better grade-8 bolts.
Cranks '73 and later have a longer alternator snout to clear a triplex chain.You would need to shorten the snout to clear the primary case;not difficult.
 
There was a factory Tacho Drive that fitted at the generator position , for 55 to 58 Triumphs . The Big Bearing case is from 55 odd , the bump under the timing cover being the visual I.D. , assembled .

This isnt quite standard .
650 Triumph Pre unit cases


Pre Unit RIDGID ALTERNATOR Primary Chaincases , arnt to common , particularly the inner . If someones getting all createive again . :wink:
 
Time Warp said:
tricatcent said:
You would be best off to use the one piece crank from a unit construction bike. You would want the later cases that have the bigger bearings.
Click to expand...

Do you know if there is a optimum one piece crankshaft that would go into 1957 generator cases. ?
Click to expand...

When a Triumph crank breals, it is (nearly) always through the sludge trap.

3 piece bolt up cranks don't have sludge traps.

It is a fallicy that the one piece cranks are stronger.

Stick with the stock crank in yer '57 cases would be my advice.
 
I know the person that get them Donny cases made he also make and run Norton cranks in them he runs them in his 1/4 mile dragsters and sells a few, not cheap but.

Ashley
 
My dealings with Triumph pre unit crank cases,that as they get older the main bearings spin in the cases,and when tuned can break at the drive side housing some time breaking start at the holes where the alternator goes,or the base flange breaks off.
Yes the cranks can break at the sludge trap,where Triumph put punch marks on the threads to stop the bung falling out,but creates a stress fracture.One piece or three piece they can all break,take the time and fit a norton one using my next advice.
If you are going to race these or take them out to 750,I sugest that you purchase New Pre Unit crankcases from Thunder engineering Leicester England,(Steve Cambell)they are a straight swop for the pre unit,but are a lot stronger,and will take 8 Valve top ends no problem.His Con rods are also super strong ,even SRM BSA have copied his rods,and he does AMC gearbox casings also super strong ones especially around the final drive sleeve gear bearing housing.
 
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