Weak links

Fast Eddie · Apr 15, 2018

Out of curiosity, what are the main known weak links on a Commando? Here’s the ones I know of, please adivise if different:

Starting from the head and working down and back...

Head: RH4s know to crack. All others OK?

Rockers and valve gear OK?

Pistons: Slotted 750 type known to break. All others OK?

Rods: have been known to break, but generally considered OK.

Cam: Some later cams found to be soft and prone to wear.

Crank: Flywheel known to break up. PTO shaft known to break where it meets the cheek.

Crank cases: Known to break under racing conditions and occasionally on the road. Combat issues with main bearings and oil return ?

Primary: Bronze clutch pack puts heavy weight on main shaft. Otherwise OK?

Gearbox: Case known to crack between bearings, mainshaft known to flex (causing the aforementioned?). Layshaft bearing weak on later models. Otherwise OK?

Rear wheel: Two piece wheel spindle known to break.

Please let me know if I’ve missed, or miss represented any know weak points.

JimC · Apr 15, 2018

Fast Eddie said:
Out of curiosity, what are the main known weak links on a Commando? Here’s the ones I know of, please adivise if different:

Starting from the head and working down and back...

Head: RH4s know to crack. All others OK?

Rockers and valve gear OK?

Pistons: Slotted 750 type known to break. All others OK?

Rods: have been known to break, but generally considered OK.

Cam: Some later cams found to be soft and prone to wear.

Crank: Flywheel known to break up. PTO shaft known to break where it meets the cheek.

Crank cases: Known to break under racing conditions and occasionally on the road. Combat issues with main bearings and oil return ?

Primary: Bronze clutch pack puts heavy weight on main shaft. Otherwise OK?

Gearbox: Case known to crack between bearings, mainshaft known to flex (causing the aforementioned?). Layshaft bearing weak on later models. Otherwise OK?

Rear wheel: Two piece wheel spindle known to break.

Please let me know if I’ve missed, or miss represented any know weak points.

Wet sumping? Judging by the machinations of some, it must qualify.

kommando · Apr 15, 2018

Why reinvent the wheel

http://www.billymegawatt.com/uploads/6/8/4/6/6846461/norton_750cc_service_notes.pdf

Fast Eddie · Apr 15, 2018

kommando said:
Why reinvent the wheel

http://www.billymegawatt.com/uploads/6/8/4/6/6846461/norton_750cc_service_notes.pdf

Cos I’d never seen the wheel!

Thanks for that. That’s my bed time reading sorted for a couple of days...

Fast Eddie · Apr 15, 2018

JimC said:
Wet sumping? Judging by the machinations of some, it must qualify.

Strewth, you’re persistent aren’t you ?!

JimC · Apr 15, 2018

In 1969, no one in his right mind would have chosen a Commando over a Honda CB 750. I will admit, I was not of right mind in 1969. Nortons have the allure of a beautiful, narcisstic woman. Great to look at, but extremely troublesome.

JimC · Apr 15, 2018

Fast Eddie said:
Strewth, you’re persistent aren’t you ?!

Sometimes the hole you dig to trap another being ends trapping yourself. As the engineer hoisted by his own petard, so to speak.

As they say in the south (U.S.), bless your heart.

Fast Eddie · Apr 15, 2018

Quite right sir.

auldblue · Apr 15, 2018

More like fausted by ones own p'eter, If it's a wet sumping thread! Not quite an idiom but give it a few hundred years and you never know ,it may well be. Probably by then wet sumping will be a thing of the past also ,never to be discussed again except by individuals with a wet towel wrapped around their heads talkin about the good old days and watching black and white PG tips adverts on utube, More tea vicar!

ashman · Apr 15, 2018

JimC said:
In 1969, no one in his right mind would have chosen a Commando over a Honda CB 750. I will admit, I was not of right mind in 1969. Nortons have the allure of a beautiful, narcisstic woman. Great to look at, but extremely troublesome.

Well when I was 17 years old buying my first road bike in 76 all my mates were into CB 750 4s but I didn't like the top heavyness of the Honda's and my mate gave me a ride of his hot 750 Commando in a Featherbed frame for the day while he rode my Honda dirt bike, well that was me I been hooked ever since and brought my new 74 Commando 2 weeks later well none of my friends have theire old Honda 4s now but I still own my Norton which I converted to a Featherbed in 82.

As for wet sumping not all Nortons do it mine has never done it in 42 years but then I ride it regularly, but maybe it will now that its sat for just on 12 months while doing other things to it and riding my Thruxtons.

Ashley

JimC · Apr 15, 2018

auldblue said:
More like fausted by ones own p'eter, If it's a wet sumping thread! Not quite an idiom but give it a few hundred years and you never know ,it may well be. Probably by then wet sumping will be a thing of the past also ,never to be discussed again except by individuals with a wet towel wrapped around their heads talkin about the good old days and watching black and white PG tips adverts on utube, More tea vicar!

I beg to differ with your definition. Here’s the definition I found:

Shakespeare in "Hamlet", used the phrase "hoisted on his own petard" to describe someone caught in his own trap. ... To be "hoist by one's own petard" is to have your plot against someone backfire on yourself.

Mr. Rick · Apr 15, 2018

Not sure who is plotting, or whose heart is being blessed, and this is sorta uncomfortable, like calling out your friend's faults, but to the original post, we might add:

Fractured oil tank bottom fittings
Chain oilers that "over-performed"
Mediocre non-serviceable rear shocks
Oddly designed front forks
Marginal charging system
Dim headlamp
Poorly plated spokes
Weak front brakes
Swingarm spindle problems
Carelessly placed timing marks
Air filter that scraped off frame paint with every service attempt
And how cd I have almost forgotten the bloody speedo drive!

I love my bike, and I'm pleased to address most of these "issues".

Fast Eddie · Apr 16, 2018

Hmmm, that’s quite a long list of extra, and valid, points Mr Rick!

Hobot · Apr 16, 2018

Add faulty functional forks to the fragile Commando fruit cake. Its a crazy making illogical cheap stop gap short cut contraption that appeals to hobot, which should give pause to others on their sense of judgment. At least Lucas smoke system is reliable, especially the bullets. oh yeah - Horn deserves honorable mention to me. Nortons were accidental/opportunist acquisitions to me, not sought out, so I deserve my ignorant fates, but rest of yo'all are the real nutz cases to volunteer for it.

SteveBorland · Apr 16, 2018

Gears tend to pit on the tooth faces
just about every bloody nut, bolt or stud is designed to be as inaccessible as possible...

oldmikew · Apr 16, 2018

But is wet sumping a bad thing ? It means that on start up plenty of oil gets throwen up the bores and over the cam ?

Onder · Apr 16, 2018

There is no logical reason to own any older brit bike at all. Well perhaps a few exotics as investments. Otherwise as idiotic
as running a 1920 gravity coal boiler in your basement.
And just for the record, I own four. Pathetic .

baz · Apr 16, 2018

Onder said:
There is no logical reason to own any older brit bike at all. Well perhaps a few exotics as investments. Otherwise as idiotic
as running a 1920 gravity coal boiler in your basement.
And just for the record, I own four. Pathetic .

Blimey four boilers !!! Must be cold out your way!!!

74ok · Apr 16, 2018

dunno about weaker but frame neck angle change for 850, yokes not compatible wth prior,
early frames 'widowmakers' & stll see them, but most are fixed,
rear frame loop weak, bends

early sidestands changed modified,
center stand itself upgraded (stronger) visually different, also went from frame to cradle mount,
- my 74 original still broke (weld) tho

3 type swingarm welded cross member supports near the pivot end i'm aware of,
early is tubular, then beefed up twice for 850,
next is rectangular with a pronounced v shape facing aft,
final 75 on, rectangular

early no cush, later wheel cush problematic, new for 75 way better but not an easy fix for prior

original left footbrake lever if the cable breaks,
original front brake master cylinder bore/piston size

primary cover oil seal, running oil also results in clutch slippage,
gearbox cover seals (o-rings mod fix),

proper oil filter introduced at some point

cylinder head exhaust pipe threads strip

afaik ^

Danno · Apr 16, 2018

The weakest point is the design of the crank and cases. Two outboard main bearings with all that flexible mass spinning in between is a recipe for disaster. I would not attempt to really power one up without uprated cases and crank. Then there's the non-unit construction......

Weak links

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