JAP 750 v twin ,type MTS

[john.k]

I have a JAP 750 to rebuild,and I m wondering about the drive side  mainbearing........the shaft is OK,but the outer race is chewed,and been turning in the case..............My old fallback of using INA races and rollers has hit a snag....SKF.......seems Skf have taken over INA,and prices are now astronomical,as in 2.FN.DR!...........inner race +caged roller +outer race..(need to be trimmed) is over $200.............but big advantage is it all fits in the case.......which case IMHO is a bit weak to be enlarging bearing bores.........However ,a 62/22 ball is 50mm od,needs about 4 mm enlargement,say 2mm  cut from the housing.(original bore is oval ,and needs skimming anyway,at 46-47mm........but a 62/22 is 22mmID,fits the shaft ,and costs around $20 depending on brand............one other option considered is tapered rollers with 22mm bore /44 mm OD,but obviously needs two opposed bearings ......not impossible,.....but.

[33d6]

It’s concerns like this John K that remind me why I find ancient Villiers engines so attractive. A 300mm length of bronze from which I can turn up a set of main bearings costs mere chump change in comparison. Then again, I’d rather be pulling a chair with your 750 J.A.P. engine than a small two stroke.
Cheers,

[chaterlea25]

Hi John.K
What is the housing depth, maximum bearing width? and ideal bearing O/D ?

I recently got some NOS bearings and there are some likely looking bearings for such an application in there
I have not measured up what actual size they are or cleaned off the protective grease to see any numbers

Last year I rebuilt a HD model F engine, I machined a metric double row self aligning bearing (52 x25) to imperial
2in. x1in.dimensions, rather than to wait another month for bits and then try and sort out roller sets to 0.0001 to make it work 
I read an article that mentioned the early racing engines used the self aligning bearing
I posted a bit about the job here
https://madmodder.net/index.php/topic,12588.msg149940.html#msg149940

John

[R]

A 300mm length of bronze from which I can turn up a set of main bearings costs mere chump change in comparison.

Didn't all early JAP engines have bronze main bearings anyway ?
As did plenty of the other makers.
So you'd probably get away with this, at a pinch.
Never mind that it probably needs a trickle of oil through them,
so it may be difficult to make them oiltight.

[john.k]

Ive looked at all the options ,main problem is the case is  not very strong..........same as the rest of it.......Anyhoo,Im thinking the cheapest option is to make a new outer race,and skim the case bore just enough to round it up........fortunately the 22mm mainshaft is good......looks like it was replaced....................the rebuild with INA bearings is probably the best,but  too costly........The main bearing is somewhat similar to a WLA part,similar dimensions ,and I could use WLA cages ,but the JAP alloy cage is still good........................I suggested to the owner to rebuild the whole motor with new WLA parts,including flywheels,rods, shafts ,bearings..........but cost is an issue ..... and its only a sidevalve................the conrods are also problematic,but the owner wants the JAP system retained..........in fact the outer forked rod is completely wrong since day one,and machining out the centre rod space has made part of it paper thin ,and its cracked.......every non racing JAP ive ever worked on had serious issues with poor quality and bad design.

[33d6]

Sounds like the owner is standard motorcyclist. Needs a Rolls-Royce job but only has Villiers money.

[john.k]

The owner is a millenial.......and if he says "cool" one more time ,he will be walking funny,with Jap parts inserted.