Lay Shaft

Gday all, not wanting to hijack another thread but!, Ive purchased a Barnett clutch thinking its a good product. Can someone tell me why they are crap.Im assuming they are too grabby? Once again a student of this fabulous forum and looking forward to being edjumakated!

FOXY

Hi Foxy,

Probably should start a new string to talk about Barnet plates. I tried them and they are "grabby" as you mentioned. Have heard stories of excessive gear bush wear when using them. They're actually too good - a little slip is a good thing for these gearboxes under the output of a Commando engine.

Regards,

David

Foxy I have been using a Barnett clutch for 2 1/2 years now on my Commando and have used them on other bikes as well. I think If you are to ride like Bill and dump the clutch at 7,000 RPM maybe you should use something that slips. I guess some of it has to do with how you use your clutch and just how fast you let it out. I just stripped a box to change the layshaft bearing that had a Barnett clutch in it for some time and didn't see any abnormal wear. But remember these gearboxes were not designed for this much H.P. so in a way we are all living on borrowed time if we abuse them, They can't take it. And once again this is just my opinion.

I'd have to agree with Chuck here. A Barnett clutch can work fine if you don't ride like a sixteen year old. When I first had a Commando I rode it hard and a slipping clutch was a constant battle. However, I never did have much gearbox trouble. This is certainly an under designed gearbox for the amount of HP a Commando can put out.
It seems folks often don't notice that beefing up one area often causes the next weakest link to snap.

As always ,the replies recieved are informative and much appreciated to boot. Ive checked out Old Britts theory on Barnett clutches and it says that the rumours dont hold any merit relating to layshaft failure. So I guess with mine, time will tell. I know that the box is a boy doing a mans job, as originally it was designed for some 30 odd Hp instead of perhaps 70 to 80. Theres also a big difference between use and abuse and Im hoping that when Im finished my Commando Manx will be to beautiful to flog! Im yet to rebuild the gearbox so I will be doing the recommended mods mentioned previously. Also I recieved in the mail today Mick Hemmings DVD,s on engine and G/box rebuilds, so something worthwile to watch on TV at last!
Rgds FOXY

Sometimes I just pop one of the DVD's in just for fun, The kids love it and even know what some of the parts of the transmission are now. My brother in law thinks I have gone nuts and so do the other grown ups, At heart I guess i still am a kid. Oh well.

You can perform limited work on your gearbox in the frame, but any serious work like replacing the lay shaft bearing, which is recommended for all pre-MK3 gearboxes,

I just found the above quote on the Old Britts web site. That would tend to make one believe the Lay Shaft Bearing is not as much of a weak point on the MK III's.

Any comments?

Foxy said:

I know that the box is a boy doing a mans job, as originally it was designed for some 30 odd Hp instead of perhaps 70 to 80.

Click to expand...

If you are getting 70 to 80 HP out of your Norton, first of all, congratulations, and secondly, HIH are you doing it?!?!

I do thank this thread for reminding me, I still need to do this! I just bought a spare gearbox and rebuilt it with new bearings, bushings, springs, seals, and gaskets, and it's sitting on my shelf. Meanwhile, I'm riding a bike with an unknown-quantity gearbox. So I'll tackle that job soon (I was waiting for winter, but you guys have reminded me how foolish that may be - 'twould be a shame to die from a defective Portugese bearing with a newly rebuilt gearbox sitting on a shelf in my workshop, twouldn't it?)

What I could use is any tips on removing the gearbox from the frame. Remove the primary/alternator/clutch, and gearbox mounting bolts, rotate box counterclockwise, and ....? What? Am I likely to get it out that easily, or is more involved?

Gday Brian, OK Ive opened myself up here, but I did say "perhaps" 70 to 80 hp. I believe there are Commando derivatives racing and producing hp in this range, 920 cc up to now 1007 cc Steve Maney kitted machines. My project is currently being built, a 74 850 Commando motor now with an RGM 920 kit installed.( Incidently done by Martin Adams formerly of SERCO in the UK, now Australia). Ive also invested in an 90 degree offset crank (balanced) by Ed G Collins in Ontario Canada, with a Newman cam to suit. Hopfully this will run smooth as silk. Head is yet to be ported and oversize valves fitted but its ready to go as soon as I make up my mind who is going to perform this surgery for me. I also have 35 mm FCR Keihin carbs and Steve Maney CNC machined manifolds to fit, as well as JimC-CNW style crank case vent. When its all buttoned up it will live in a 64 featherbed frame supporting a John Williams TANK SHOP manx 5 gal alloy tank and seat etc etc. Anyway back to the issue of hp producing this its still a fair old screw on a lay shaft especially when reved to 7000 rpm and the clutched dropped! Something eventually has got to give and its probably the wallet! My Commando Manx wont be getting this treatment when finished. Rgds FOXY

Thanks Foxy. Your HP is beyond my wallet, methinks, but at least now I know I wasn't leaving power on the table with me poor pre-allthatgoodstuff build.


Would love to see some results (dyno, track, etc.) when you get 'em! Make us all proud, mate! Thanks - BrianK