My flywheel seems to be having some major issues.

It is at a local machine shop, one of the only places in the area that will take on these kinds of jobs.

Tony here is following Dave Plumb's instructions on the technical page, but is finding that he doesn't think it will aver be within the tolerances described there. At one point he had it to where it was 5 thou out, but then when he went to tighten it, things popped back out and it was much farther out than that. He is thinking that where the big end attaches to the flywheel is worn out.

Please take a look at these pictures, and let me know what you think of these flywheels. Are the welding marks correct or a [further] sign that this thing is a lost case?

Also, I bought an 'm20' flywheel off ebay years ago, but through this saga, it's clear that this is not for an m20. Can anyone ID the flywheel and/or numbers form the conrod?

Thanks,
nt

how the rod bearing wandered (or was never in right):





How the halves 'line up' Also, please note the weld marks--are they correct???:







Mystery flywheel, one side looks like its M20, the shorter shaft is shorter though:





And a number from the conrod of the mystery flywheel, to me it looks like: A7 | 524 6733 XXXX:



There are a couple other photos in that photobucket if interested.

email (option): nicktog at gmail com

Nick,

Your mystery flywheels are Ariel no idea of model, you will have to measure the stroke for this.
Re your M20 flywheels, i had the same problem with a so called set of M33 wheels. Ended up odd wheels and i had to find a match set.
Your pics are not clear where he has the straight edge. If he has them at 90 degrees to the big end pin then all you can do is get them the best you can then tighten the nut up hard the tap them into line. The guy who is doing your work will know what he is doing if he has done a few of these. Dave's notes are a very good guidance and i have followed these in the past.
If you have a rough set of wheels you may still be able to recover them by doing them up really tight even though when you do this it drags them out of line, then knock them up into line. it can take a long time but its a satisfying job. Just make sure everything is clean and you are not pulling the pin up against a ridge in the flywheel pin hole.
My odd wheels i could get them bang on 90 degree to the pin but they were out when measuring over the pin, so this was a case of odd flywheels. Shame as they were steel ones not the iron type.

Best of luck

Tim W

email (option): t.j.walker@btinternat.com

I gather from Ian that it's possible for wear to take place (or at least distortion) in the holes for the big-end, and then no amount of tightening them can cure it properly.

Also engineers like Ian, Dave Plumb and my own engineer have a proper heavy jig that clamps the flywheels for initial tightening of the nuts, so that they can't spin out of true.

Yes Ariel flywheels from the 'Qualcast' foundry same as the brake drums on my W/NG.

Ron

email (option): ronpier@talk21.com

Run out for the flywheel assembly should be .005" max. at the flywheel faces and, more importantly, .002" max for the main shafts..

Failure to achieve these figures will result in more vibration due to misalignment and a lot more mechanical noise as the clearances between the crank pinion and cams will vary between too tight and too slack....

This is made worse by valve spring pressure at certain points as the assembly revolves...

The big end assembly is designed so that its rigidity relies on two features.
Firstly the fit of the pin into the flywheel taper and secondly,locking the pin against the flywheel face...If the pin is fitted into the flywheel by hand there should be a .010" gap between the shoulder on the crankpin and the face of the flywheel...

When the nut is fully tightened it pulls the pin into the flywheel, forcing it into the taper and it also locks the shoulder on the pin against the flywheel face...

If the tapers are worn and/or the holes in the flywheel are stretched/worn the fits will be insufficient and the assembly will be difficult to true up and prone to movement even after tightening of the nuts...

For that reason having the correct gap between the crankpin shoulders and the flywheel faces is critical...

Worn flywheels can be 'resurrected' by grinding back the shoulders on thr crankpin on a cylindrical grinder...

This allows the pin to drop further into the taper (in effect increasing the pin diameter) and will result in restoration of the correct .010" clearance described previously...

It should be noted that grinding the shoulders to solve one problem can create another...

That is a reduction of the gap between the flywheel thrust faces and a consequent reduction in side clearance for the conrod in the built up assembly...

That clearance should be approx. .010" and if necessary after grinding the pin shoulders, it may be also be necessary to grind both sides of the conrod at the big end eye (using a surface grinder) to restore that dimension to the right tolerance...Ian

email (option): ian@wright52.plus.com

email (option): Jomichael@aol.com

The flywheel edges are only a guide it is the "truth" of the main shafts that is important thus mounting between centers and using a DTI is the only accurate method to use. Check everything and check again and again.....
Richard

Thanks for the replies, I will keep you posted.
nt

email (option): nicktog at gmail calm

I agree with Michiel on this one...

Mounting the crank on the bearing surfaces most accurately replicates the way the crank actually runs under operating conditions...

I made a jig that supports the crank on the main shafts using a pair of cam bearings at each side for checking purposes...
Knife edge rollers or V blocks (with the bearings fitted to the shafts) would work equally well....Ian

email (option): ian@wright52.plus.com

agree with Ian & M - i use a pair of old (mismatched) V blocks - fit a pair of bearings on the shortest main shaft - use V blocks to clamp into a vice.

Then use a DTi to measure run out of the unsupported mainshaft.

Usually better to clam the shorter main-shaft in vice as it then allows you to DTI along the full length of the unsupported shaft.

Its relatively easy to get the two main shafts running within a few thou at the f/wheels (in the pix i see some 'bruising' from a big hammer used to line things up - a lump of lead on a stick is better) but when you measure them at the extremity of the main shafts - they are substantially out!

Rough lining up the flywheel with a ruler is the first stage - when the shafts are lined up, don't be surprised if the flywheels no longer line up.

Many taper + shoulder cast iron flywheels are worn so its no longer held on the taper - just the friction on the shoulder.

Easiest I've ever done were 750WL Harley - worst Nortons - any of the early ones (suspect its why they moved from the 2 bearing crank!) !!!

Thanks again for all the replies. Tony at JM machine shop in San Leandro got it!!!

First of all, it was the folks who put the bike together that had been beating on the flywheels--NOT Tony!

Issues it had (now fixed):

A woodruff key was keeping it from sitting in the flywheels correctly--He was able to reshape it.

A couple of the rivets that hold the shafts to the flywheel had loosened up--once tightened, things were much closer to tolerances than before.

And everything else--I now have a gudgeon pin bushing that fits perfectly, etc.

If anyone in the US is looking for machinists who are willing to take on projects like our bikes, and who will really keep after it until they feel they have it right, I HIGHLY recommend JM machine shop:

212 San Leandro Blvd
San Leandro, CA 94577

Phone number (510) 562-0400

I have run out of time to work on the bike this week, but hope to have it back together within the month.

email (option): nicktog at gmail calm

Not blaming anyone specific ...... its +60 years old so it will have seen life!

My Norton (and my Dougie) have some seriously non standard, but entirely period mods - which i cherish, as someone loved these bikes enough for them to be personalized (as we say now) ..... some 'mods' however are luckily hidden away!

A bit of 'bruising' wont harm anything - mind you an XT600 crank (bob-weight type) i recently had to try and sort out was more than bruised - it had been ASSAULTED & BATTERED.
Never did get it acceptably straight!