Fly wheel taper

[Tony Betts]

I know some of you out there are fantastic with data and dimensions.

Could any of you help me with the taper angle on the flywheel end of the crank.

Thread size and pitch for the flywheel nut.

Bearing jernal sizes and tolerances, I think the front is 1 1/8 exact. There is no plus tolerance. And I think the rear is 1 1/4 plus 2.5 though. But I don't know if thee is a plus or minus tolerance.

Also what is the exact crank stroke.

Any help is well apreciated.

I'll let you know why in time. I have an exciting project in the offing 

Thanks Tony.

[Charles P]

Taper is 1 in 8
The thread will be whitworth form (55degree and rounded nose/root)

Not sure on the bearing tolerances. I was certain that I have a crank drawing somewhere but I can't find it.

Charles

[Bob Culver]

Someone published a 1929 factory dwg some time ago. Front -1/4 thou, rear + 1/4 But these chosen with convenient assembly in mind.  Machinerys Handbook, bearing catalogues, or Tony in OZ will give recommended fits..

For special cases there seems to be scope for using a cheaper and more readily avilable metric rear bearing. The biggest problem is finding a truly circular housing to turn out! And acheiving the precison necessary for bearing housings.

[Colin Reed]

HI Tony,
            The crank stroke  3 inches  76.200mm.

Also are the new 26mm valves Exhaust quality
Cheers
Colin 
NZ

[Henry Harris]

Here's a print of the factory drawing...

https://www.flickr.com/photos/henryharri...5/sizes/o/

[Chris KC]

Taper angle 1 in 8
Flywheel thread 7/8" dia x 12 TPI
Front journal 1.12475 - 1.125" dia
Rear journal 1.250 - 1.25025 dia
Big ends 1.312 - 1.3125" dia
Stroke 3"
For a 3-brg I believe the centre journal is 1.75 - 1.7505

[Tony Betts]

Thank you for the Replies.

The areas im struggling with are with the blue print. Are the bearing jernals. The 1/4 isn't clear what it relates to.

A 1/4 relates is .250 of anything.

When I used to have original cranks reconditioned. The good rear main jernals measured 1 1/4 plus 2.5 thou. Ie 1.2525

So does the 1/4 refur to 1/4 of a though. Or as ive measured in the past 1/4 of a tenth. 2.5 thou ive measured.

Could anyone with Good cranks confirm this.

Also with the front, the 1/4 doesn't make sence. I've seen other crank blueprints that have no tolerance at all, Ie no 1/4

the front bearings don't need to be pressed fit like the rear. As the dog clamps the bearings.so the jernal can be size or slightly under.

If a 1/4 is what in tenths on the rear, 2.5 thou. On the front as an undersize. This would be baggy. So is the front tolerance a 1/4 thou?

Please help to make some sence of this.

Colin, if you meen the valves I'm supplying. Then yes. All valves are exhaust quality. As I'm trying to supply as high quality as I can. AND DO THE PRICE CHECK TEST. I'm keeping prices below everyone else. I can't coment on other suppliers, you will have to ask the same question.

The quality to price is a part of what I'm trying to do for the future, but I need to restrict the range I supply. So I can keep both quality and price in hand.

Check my new head gaskets and see the difference.

This is the same reason for asking some of these questions, quality in the world has to be lifted.

Thanks Tony.

[Bob Culver]

hi Tony B

The current tolerance for inner rings of bearings is 0 to 10 microns under,  .0004 inch.
Cranks just to size may explain why so many bearings loosen.
Half of  .0025 interference fit is defined as a force fit so .0025 would need brute  force to assemble and the separate bearing parts would be unlikley to then fit together.
But it would cure the Seven rumble.
(Quarter of a thou is .00025, the factory tolerance, and probably the figure you recall?)

[Tony Press]

The SKF Manual suggests for a Cylindrical Roller Bearing on an 1.25" shaft in an Internal Combustion Engine an interference fit of +0.0003" to +0.0007" which is a little more than 1/4 of a tenth or 0.00025" on the drawing or the quoted Rear journal 1.250 - 1.25025 dia.

EG- 1.2503 - 1.2507 dia.

A fit of +0.0025- (two and a half thou)  would be quite difficult to install and most likely overload the inner ring.

Sorry +0.0007 corrected.

Yes a little tighter than Austin's tolerance would be useful.

[Chris KC]

Yes, 1/4 thou.

1.25" min to 1.25"+1/4 thou max on the rear - should be tight. You'd never get the bearing on at +2.5 thou. Though I'd agree with Tony Press (if I'm understanding him correctly), a tad tighter say +1/2 thou would do no harm.

1.124"+3/4 thou min to 1.125" max on the front - shouldn't be nearly as tight as the rear (or you wouldn't be able to build / dismantle the engine).

I agree it's a bit confusing but take a look at the big ends and keyways, they are dimensioned the same way e.g. 1.312" to 1.312"+ 1/2. If you look up big end diameters for Reliant side valve engines, 850 Minis etc. (which are published figures) +1/2 thou tolerance tallies exactly.