Combat engine or not

hobot said:

L.A.B. I'm not sure of anything I say on anything Commando after you point out

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Thats OK, we've never been sure either.
Especially when you keep repeating that suff about breathers...

Cheers !

dynodave said:

My general description of the combat failing is first and foremost the crankshaft. The main bearing failure is a resulting symptom of the cranks flexing due to flywheel over loading the strength of the crank. Eventually the cranks breaks. Main bearing failure is remedied by "superblends" but crank breakage is not fixed by superblends....
However it is the cam and compression and porting/carbs that allows the engine to rev until destruction.

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A lot of Combats were cured, by the Factory, by fitting the Superblends.
They didn't break cranks after that....

??

Even the best of them can have engine gremlins...

Porsche, no less.
http://www.autoblog.com/2014/03/19/pors ... -official/

L.A.B. could you set others straight on the superblend myth as me and others have found prior issued 'flat' rollers in Combats in pristine condition 10's of 1000's of miles of full scope Combat enjoyment. Just stay out of lugging zone which of course on Combats is easy. Extra points if anyone can pick out the 1st and second reasons in Combat myth article concerning bearing life. Other other older list we recently discussed Frank Foster's 100K+ mileage Commando with same non superblend in them so mostly discuss how long this or that triplex chain or sprocket teeth last and ring jobs or rod shells. I spen pre-Peel's 'flat' rollers off with at least 40K miles on them before me, as was a famous area bike over couple decades & few owners before me, to have em checked both for wear and in fact NOT superblends. They were still good to go and Not Superblends. Something else caused Combat failure of bearings that wasn't bearing related. Norton PR and brochures are not good to base beliefs on.

Combats, it is my understanding that when the crankshaft turned at high rpm it also "whipped", which then caused the ends to rock in the bearings instead of turning true, the rocking motion would destroy the bearings

the "superblends" are better suited to cope with this rocking by having a slight taper so no digging in

the 19 tooth sprocket combined with the compression and cam encouraged higher rpm usage, boom

hobot said:

could you set others straight on the superblend myth

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As previous threads, the taper on the very ENDS of the rollers is so slight, its not even visible by eye.
You didn't read that ?

The BIG improvement was the EXTRA ROLLERS in the superblends - this gave the bearings an Extra dose of LOAD CAPACITY (the E in the 306E ?).

It has been suggested, before, that the bearings were simply underspecified for the extra duty they were being called on with the stronger cam.
The non-Combat 750 models don't have the reputation for destroying bearings and breaking cranks - and they used an ABSOLUTELY identical crank setup.
The hotter revvier cam, more compression and better breathing just stressed the bottom end beyond what is was capable of surviving.

Once the bearings start to break up, the crank gets a pretty rough ride.
Not having fillets intact in various corners doesn't do anything for retaining crank strength either...

It should perhaps also be mentioned that the pair of main bearings in the Commando are physically the identical same size as the bearings
fitted to the 1st Model 7 500cc early dommie twin for 1949. This put out a claimed 29 hp, and the crank was a few pounds lighter than a Commando crank.

So the basic bearing spec had barely been uprated from 1949 to 1972, when the Combat appeared.

It is therefore perfectly possible to fit a pair of Superblends to the earliest dommie twins.
One thing is for sure, its bearings won't then be underspecified !

L.A.B. makes a good point I and others overlook, the super-duper-blend's secret ingredient was extra rollers to take Combat power loads, not the slight barrel shape, [long used on flat rollers prior to special Norton name], for crank flex tolerance. I found bent crank in pre-Peel Combat cases which were stress-fatique cracked but the flat rollers were still essentially pristine. I ain't got nothing against Superblend load upgrade but when I did Peel I followed old world school and put ball bearing in TS with 11 balls instead of nine to help tolerate flex and fix crank shift w/o shims. To get any benefit form much engine development implies illegal behavior in public. Ordinary Combat is plenty for me on un-tamed isolastics and admit I tried Trixie to max a few times to test my rebuilt bravery but can't bring myself to anymore knowing what it'd cost again in long run. Btw I'd never seen info that mentioned 6800 Combat peak power but agrees with my glancing down as tach swung past and front got light as my head, then let down to let off or else.

So what does the original poster have and how would he find out short of valve floating or mic-ing the cam after crank dial degree'd?

Rohan said:

hobot said:

could you set others straight on the superblend myth

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As previous threads, the taper on the very ENDS of the rollers is so slight, its not even visible by eye.
You didn't read that ?

The BIG improvement was the EXTRA ROLLERS in the superblends - this gave the bearings an Extra dose of LOAD CAPACITY (the E in the 306E ?).

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Are you sure ?
The original Commando roller bearing was the R & M MRJA30 which was a 13 element bearing which was also used in Triumph engines,I think there might have been another a earlier 11 element MRJA30 (some have the engraved 6 after the stamped part number but forget which one,Triumph related perhaps)
The 'superblend FAG 306E replacement has 12 rollers of larger diameter so there is a load rating difference combined with different surface speed at the roller face.

The other difference is the rollers are caged on the inner on the MRJA30 and on the outer on the 306E.

Disclaimer... I am in no way any form of Norton *whatever the word is* this is just based on what I found inside the engines hands on since I was doing both a 750 and 850 crankshaft this afternoon.

"When the Commando main bearing problem started to occur the D.S roller bearing was a Ransome and Marles MRJA30 bearing but with a brass cage and a designation 8MRJA30.The roller elements were the std. shape for that time having 11 rollers 11.12mm in diameter"

The FAG 306E had 12 rollers.
And was a heavier duty bearing than supplied for dommies, that was the E bit.
Apparently they were cheaper....

A R&M 13 roller bearing was tried somewhere (?). Used in production even ?
It had a more visible taper at each end of the roller.

Going from memory and abbrev notes here.
There are thousands of pages of guff on this....

I came in the other day and asked the boss if I could heat the engine (850) cases in the oven so I could remove the bearings,her answer was "Can I do lunch first ?
I told her I needed to get them (cases) spotless first to avoid future Castrol flavoured roasts.

I got sidetracked with crankshafts but will do it tomorrow.
I suggest the main improvement with the so called 'superblend bearing,barrel shaped rollers or not is that the inner sleeve only was fixed to the crankshaft journal instead as earlier the sleeve with the caged rollers.
That had some beneficial effect when the crankshaft started to do odd things at higher RPM's.

Reading a bit, anything with 13 rollers is the fix to only having 11 rollers.
Before they went F.A.G. for cheaper fix...

Interesting about the cages.
Obviously its all part of it.
Some of them have plastic cages these days (but are they any good ?).

Put something with a trace of kero on it in the freezer once. (wrapped in a plastic bag even).
Wow was that a bad idea.
kero flavoured icecream, and everything else.
In the doghouse for a while...

My combat engine didn't blow up but needed new crank bearings at 4700 miles from new. (The drive side bearing was very noisy.) Whatever bearings the dealer put in back then have worked for the next 30,000 miles. (Supposedly "superblends".) The bearing races were completely destroyed. I was 21 years old and took it up to redline but not beyond if I could help it.

I could not get reimbursed for the work because the dealer said I bought the bike in England and so it was not covered under the US distributor's warranty. Bunch of BS.

My combat engine didn't blow up but needed new crank bearings at 4700 miles from new

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needing new bearings in less than 5000 miles IS "blowing up the motor" !

If ya read the Combat myth article its distinctly notes only 4-5000 miles out of bearing gotten UNTIL, wait for it * Until* they replaced the 1st version of the mechanical AAU then over double the bearing life gotten and way more like we get now after some other *non bearing* issues found and solved. IF really interested Don't stop with the fairy tale level of why Combats could go wrong even if not coming apart though their cases. My buddy Wes had a Combat that early blew up then took it too good shop that went through it and told me he had the fastest thing around up to 100 mph then some the newer bike could creep past. No bearing up grade yet no blow up showing what a Combat can do time and time again. Re-consider reflex fixation on failed bearings like most Dr.'s do only looking where it hurts but not often able to look beyond to deeper causes so mis diagnosis and mis treat for fun and profit.

hobot said:

Re-consider reflex fixation on failed bearings like most Dr.'s do only looking where it hurts but not often able to look beyond to deeper causes so mis diagnosis and mis treat for fun and profit.

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Non-Combats didn't notably wear out their bearings anything like Combats did,
and they had an IDENTICAL bottom end,
so the initial bearings weren't man enough for the job.

But it was a package of problems and fixes, like you say. ...

Non-Combats didn't notably wear out their bearings anything like Combats did,
and they had an IDENTICAL bottom end,
so the initial bearings weren't man enough for the job.

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Ugh, re-read what your wrote and consider that Combats don't make very much more power than a standard yet both Combats and standards rev to same range, so they experience very similar if not identical crank bearing loads. Its rpm that kills bearings not the big toque hits. So you just backed up what I say, > that it wasn't the bearings that were the real Combat Bomb issues and I repeat there used to be lots of reports of Combats opened up with standard bearings still fine. If ya made up your mind to stop thinking further about why same ole *bad* weak bearings as in prior spunky 750's caused Combats down fall, oh well, most folks always use superduperblends now to be safe anyway.

I didn't back up what you said at all.

Combats had a more revvy cam (than the std Commando),
and SOME Combat pilots used that to the max,
and the main bearings couldn't stand up to that for long.

The higher load-capability bearings COULD.
Thats rather black-and-white, in't it ??
Thats a bearing problem, pure and simple.

With a few side issues thrown in.
As mentioned here before, the Combats could rev past their 7000 redline.
Maybe all they needed as a part solution to the Combats exploding was a rev-limiter ??!!
Bit late to figure that out.....

So while we may be saying similar things, in places, we are drawing different conclusions.
And, while I didn't mention it ?, the Combat puts out more power than a stock 750,
so puts out more torque than the stock 750 EVERYWHERE above 4500 rpm, was it.
Thats where all the trouble starts...

Aw you are in denial Rohan - as Standards can easy rev as high to strain crank, bearings and cases with same rods and piston inertia, [but not the cases] so just not as quickly as a good Combat can. I gain nothing but bad feelings to try to point out - might be over looking something else like Norton did, so leave it at that. Don't care to make more waves either on how the 750 dragster guys got away with non superdupers till the cases and crank failed first.

The std Commandos didn't have the problems the Combats had,
so you are misquoting/misinterpreting/missing stuff.

Same as the earlier Atlas had the same bearings (?), and didn't have the Combat problems either ...