JAP Model 6 help needed

What sort of main bearings are they? Ball, roller, or taper roller? I'm not familair with the internals workings of a Model 6. Assuming some sort of roller bearing, I normally run a ring of weld round the inside of the outer race, this causes enough contaction to make it fall out. For the inners, if you don't have a suitable puller, cut the cage with a Dremel or similar, and remove it plus the balls/rollers. Again using the Dremel, cut a V shaped notch in the edge of the inner, and give it a sharp tap with a chisel. This should casue the inner to crack across when it can easily be pulled off the shaft. Hope this helps. P.T-E

According to the A C Fenner book, "The JAP Engine", the Model 5 and 6 have taper roller bearings, and the books says " It is a most difficult job to get these parts off the shaft..." so I guess a bearing puller of the split variety with the thin edge to go behind the cage is the only way. The outer races as per Philip's suggestion, or as per his article on restoring his Petter Atomic, drill a couple of holes in the bearing housing and punch it out, fill holes with epoxy afterwards.

The others, including the Model 55 have deep-groove ball races.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

Probably a daft question Alan, but if they are taper roller races, they

*should* have the slightest amount of slop in the bearing & the end of the crank can be moved up and down *very slightly* when they are correctly shimmed.

Extracting the outers can be easily achieved with aluminium crankcases by just heating them in a domestic oven. Gas Mark Nine, make yourself a coffee & sit on a kitchen chair to await the "CLANG!" from the oven as they drop out. Done.

Velocettes have TRB's on the mains & many a happy hour I've spent taking hot cases in and out of Hazel's oven in order to add or remove another bloody shim!

If the races are not pitted, shimming is your answer - fiddly, but cheap!

Inners can be a LOT harder to shift, but I'd at least try a thinned cold chisel twixt track and flank. If they are scrap anyway, nothing lost & they may readily move along the mainshaft with little effort. Be prepared to give up though & resort to crueller methods.

Finally, have you priced the new bearing? Bearing prices vary widely & it might be a help to say that many cars use TRB's as wheel bearings & some work poring over parts books at a motor factors might make a big difference to cost.

Regards,

Kim Siddorn

Remind me to avoid JAP 6's (and Velocettes, though one could forgive them almost anything for the way they look and sound). Unless your bearings look like any of these leave well alone.

Beats me why taper rollers are ever used for main bearings, thier main 'feature' is the ability to handle as much axial as radial load, not something which is generally required to support a crank shaft, and you pay for that with tricky setting up to get the clearance or preload (depending relative running temperatures and expansion coefficients of shaft and case) just so. Petter got it right with the later M's - a cylindrical roller bearing on the drive side and a deep groove ball on the timing side for axial location.

inner races can ALWAYS be shifted dead easy by also running a penetrative root weld across the race in line with the shaft, when the cooling weld contracts it will crack the race which will just slide off... not tried it with mig, nut any electrode with the current turned right up does the job a treat, apart from splatter you can NEVER damage a shaft this way.

Many thanks. I wasn't in the kitchen to hear the clang, but when I returned there was the outer race sitting in the oven dish :) I can't do the same with the other side as I don't think the whole engine would fit in the oven, and I don't really want to strip it down any more, but I should be able to press that one out OK.

I have to change the bearing because at some time it must have had water in the crankcase......very rusty bearings. The engine ran OK, but the noise was unbelievable. It's fitted on a nice old 2 stage compressor complete with air receivers so it is worth doing.

I never had to do the main bearings on any of my velos, but do remember reading about it. In those days you just went out and forked over £10 or so for another bike. I wish I had them now.

However, every success is a step to teh next problem, and like an idiot I left the leather oil seal in the bearing housing. It seems a bit charred. I haven't been able to make a full inspection as it is still too hot to touch, but I expect a replcaement will be required. Anything special about them? or do I just cut a suitable ring of leather and soak it in oil?

Thanks for all the help.

Regards

Al

Cut from a piece of used shoe sole leather. It is compacted from walking & survives better than ordinary leather.

Regards,

Kim Siddorn

Well, I've priced the bearings, and they aren't cheap. I will look around on the net and see what I can find. I have the dimensions and part nos now so it should be easier.

I was very surprised. Does anyone have any idea why a British engine made in the 1950's fitted with bearings made in england use metric? 80mm x 40mm x

21mm. Very strange.

Al

Price, metric sized bearings have always been more common hence cheaper. If you want a shock, price some similar sized bearings in Imperial measurements.

Tom

*** Posted via a free Usenet account from ***

I was similarly suprised when the mains (deep groove ball) in my Stuart-Turner 'N' turned out to be metric. What is the part No. of your T-R's, 344A/332 seems a candidate with a list price of over £86, but most places sell brgs at a fairly hefty discount!

Our local guy reckons he could do it for £20-£25 plus VAT if that is any help.

Not a stock bearing but still on his price list so still available.

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

Thanks guys. I managet to get some standard bearings that are 1.25mm narrower. Shouldn't be too much of a job to turn a spacer for the cone. I can make a modified housing for a standard oil seal too. I have to build up the keyway on the shaft as it is somewhat damaged but a quick spin on the lathe and the judicious use of a file should sort that out.

That just leaves the really hard thing to do......deciding what colour it should be. At some stage in the past it has been painted a sort of pinky primer red all over. There is no clue as th the original colours. I am thinking something like compair blue for the compressor and tanks, but the engine I have no idea. I suppose i will get some inspiration from somewhere.

Thanks to all of you......I'll be back. :)

Al

You might find the whole thing was one sprayed colour so what you paint the compressor will do for the engine also.

Martin P