New low miles combat, should I worry

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joshtjeerdsma

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I just purchased a 72 commando with just over 4k miles. The serial # is 206xxx and it has the c on the head. I do not know the previous maintenance history. Is there any way to tell if the crank bearings have been upated without tearing the engine down? Should I worry about how hard I ride it. I wouldnt have bought a combat commando without knowing the maintenance hiatory, but the price was right. Been wanting a norton for awhile, and excited to get out and ride it. Thanks
 
Bowtoy70 said:
I do not know the previous maintenance history. Is there any way to tell if the crank bearings have been upated without tearing the engine down?
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No.
If the previous owner cannot say, then the only way to know for sure is to open it and have a look.

With only 4k miles, has it been standing for the past 40 years though. ?
That alone could be enough reason to get inside it, to inspect bits that may not have travelled too well.
Rubber bits and seals often don't survive prolong non use - and if the oil pump seal in particualr has perished, the oil delivery/pressure may suffer.

If, on the other hand, only the speedo has been changed to give that '4k' miles,
it may all be in good order and well maintained and good to go...
 
And if it truly is only 4k miles, does it still have the original tires on it ?

If it does, it may truly be the genuine mileage.
If they have been changed, maybe it has been maintained along the way.

The original tires would not be safe to ride on....
 
I've see bikes that are said to be 4K miles and the trans is trashed, the rings are broken, etc. At least take the engine apart and replace all the bearings and seals, at this age it will need it and then you will have a pretty good idea of what you have. It shouldn't cost more than $5K. Kidding (about the $5K). Unless you just want to thrash it and see what happens. Then it will be $10K.
 
Given the unreliability of speedo's, cables and drives along with how easy it is to replace a speedo and the fact that many people zero them when having them rebuilt I would take any low mileage on an old Brit bike with a grain of salt unless I had some sort of other evidence it was correct.
 
I'm sure you are all right about the mileage. The engine ran well with no knocks or odd sounds. There where no oil leaks or stains on the jug or head. I have not ridden it yet as the points cover seal was leaking oil into the points and out the hole where the ignition wire leaves the case causing it to not idle well. I have a seal and electronic ignition on the way though. The previous owner put new tires, fork seals, and supposedly rebuilt the carbs before the sale. I was mainly wondering if it would do any harm to just ride it and not worry about whether or not the bearings have been changed out. I'd hate to tear the engine down and realize they had been changed. But, I'm fairly mechanically inclined and could probably stumble my way through an engine rebuild if need be.
 
If its running OK (and you don't thrash it within an inch of its life every time you ride it)
whats the worst thing that pre superblends are going to do
- just grumble a bit to warn you they are wearing out.

If this bike has been ridden and maintained over the years, it may well have had all the fixes anyway,
so just ride it and see how it goes.
Last time this was discussed, some Combat owners said they'd ridden their bikes normally for years, no problemo..

One of the problems that Combats did have a bit was the auto advance unit sticking fully advanced.
Since you have to go in there to cure the oil leak, have a good look at that aa unit,
and make sure its in good condition.
Check that the little springs still have some spring to them.
Being well oiled may well cure any tendency for it to stick !
 
Bowtoy70 said:
Is there any way to tell if the crank bearings have been upated without tearing the engine down?
Click to expand...

As you will most likely be removing the timing cover to replace the points housing oil seal (and check the pump and crank seals) if you were to remove the oil pump, crank pinion nut/oil pump worm(LH thread), backplate and washer (see manual, section C) then it might be possible to identify the timing side bearing-even if the inner race isn't marked on that side-as I think you should at least be able to tell if it's an 'NF' or 'NJ' bearing.

Fast Eddie said:
New low miles combat, should I worry
Click to expand...

New low miles combat, should I worry


If marked 'MRJA30' or if it's NF type (with the rollers captive on the inner race) then it's unlikely they have been changed?
However if there is a '6' etched ahead of the marking thus '6 MRJA30' then it would be the R&M/RHP 'Superblend' or if NJ (FAG NJ306E with no lip at the outer end of the inner race) then the bearings probably have been changed.

Manual: http://www.classicbike.biz/Norton/Repai ... mmando.pdf
 
Check the bolts and nuts that hold down the head and cylinder barrel. If it has been apart there is typically wear on them. My combat showed 16k on the speedo with original bearings before I rebuilt. They can last if the owner is gentle.

If you take the timing cover off, service your oil pump as described in the shop manual. Mine had a piece of piston ring but far more common is the camshaft retainer tab.
 
While I'd actively seek an opportunity to fit Superblends to any Commando engine, the historic reputation for Combat bearing failure needs some research.
The biggest issue was the oiling system not scavenging correctly under sustained acceleration, which can only be properly remedied by a total tear-down and mods to the crank case - great article here...

http://www.oldbritts.com/n_c_case.html

There seems to be a consensus that once the mods are done the motor is as strong as it needs to be. The Combat spec motor performs very well, but mine had a poor idle compared to my 850... a very small price to pay for the benefits gained IMHO :lol:

I wouldn't hesitate to buy another Combat, and the initial hassle of getting the case mods done is well worth it, and also is a great opportunity to get rest of the motor 100% sorted.
 
B+Bogus said:
While I'd actively seek an opportunity to fit Superblends to any Commando engine, the historic reputation for Combat bearing failure needs some research.
The biggest issue was the oiling system not scavenging correctly under sustained acceleration, which can only be properly remedied by a total tear-down and mods to the crank case
Click to expand...

I'm not sure if you're linking the main bearing failure to the reputed scavenging problem? There isn't a link. The main bearings failed at very low mileages, mine at 4K miles. I have never made any scavenging mods to my Combat and it's survived ok without drama, including many sustained high speed runs. So I don't think the oiling is the biggest issue. I'd be much more worried about it having the slotted pistons still fitted. They last longer than the main bearings but the tops of them do become detached and it is definitely dramatic when they do.

I'd suggest to the OP to run the bike as is and see what happens. If the main bearings haven't been replaced you will get warning that they are going, they don't fail dramatically. I'd be very surprised if it has only done 4K miles in 43 years and if it's done more then the main bearings have probably been changed. If you really want peace of mind take the head & barrel off, check the pistons aren't slotted and look how worn the cam is.

Ian
 
Nortoniggy said:
I'd be much more worried about it having the slotted pistons still fitted. They last longer than the main bearings but the tops of them do become detached and it is definitely dramatic when they do.
Click to expand...


Could be wise to check although the stronger 063348/9 'Combat' (later, all 750) pistons were supposed to have been fitted from 204166 (according to Norton Service Release N2/4), so hopefully, Bowtoy's 206xxx serial bike has them.
 
Nortoniggy said:
I'm not sure if you're linking the main bearing failure to the reputed scavenging problem? There isn't a link. The main bearings failed at very low mileages, mine at 4K miles. I have never made any scavenging mods to my Combat and it's survived ok without drama, including many sustained high speed runs. So I don't think the oiling is the biggest issue. I'd be much more worried about it having the slotted pistons still fitted. They last longer than the main bearings but the tops of them do become detached and it is definitely dramatic when they do.

I'd suggest to the OP to run the bike as is and see what happens. If the main bearings haven't been replaced you will get warning that they are going, they don't fail dramatically. I'd be very surprised if it has only done 4K miles in 43 years and if it's done more then the main bearings have probably been changed. If you really want peace of mind take the head & barrel off, check the pistons aren't slotted and look how worn the cam is.

Ian
Click to expand...

You make a good point, and no, I wasn't linking the 2 issues; merely that the scavenging problem was a more serious issue considering the consequences. As you say, the mains are likely to fail 'gracefully', whereas starved big-ends generally fail catastrophically, and with no prior warning. I know of guys in the NOC reporting big mileages with no issues, but it remains a known issue with lots of evidence, and one which cost Norton dear back in the day.
From what I can tell, Combat mains were the same as the preceding models, but were not previously prone to premature failure?

My Combat had a lovely ding in the gearbox cradle where the RH rod had opened a window in the crank case :(

I think it was more to do with hard acceleration preventing oil getting to the forward-located scavenge port (and the oil being forced out of the breather), rather than sustained high speed running?

Still no harm in running the bike as-is to see if there are any unfortunate rumblings or not, but I'd be wary of riding it hard... which is when they are the most fun :|
 
Combat mains were the same as the preceding models, but were not previously prone to premature failure?
Click to expand...

correct

in theory Combat main bearings are not necessarily bad, the problem mostly came from the fact that a 19 tooth sprocket was fitted stock and as such it could be
easily revved to redline, which caused the crankshaft to flex and its ends to dig into the main bearings and cause failures

this was fixed by fitting bearings that had the rollers tapered at the ends thus being better able to handle the higher rpm flexing

and so if your bike was ridden sensibly and not revved to that point of flexing then your bearing may well still be just fine

personally I would just ride it now and have fun but would not subject it to wide open throttle acceleration over say 5000rpm

and you could have a number of years good usage without taking it all apart to replace the bearings which may still be fine
 
Thanks for all the great info. I think for now I will just replace the seal and put the EI on so I can get a chance to ride it before the weather changes. If we have a long winter I may tear into it deeper. It will be hard to not get after it when my friends on thier old yamahas taunt me though.
 
Bowtoy70 said:
Thanks for all the great info. I think for now I will just replace the seal and put the EI on so I can get a chance to ride it before the weather changes. If we have a long winter I may tear into it deeper. It will be hard to not get after it when my friends on thier old yamahas taunt me though.
Click to expand...


One thing you should do before you put any miles on it is pull the camshaft sprocket. Behind it you will find a thrust washer with a tang that fits in a hole in the case.

Cut the tang off and reinstall the washer.

If you do not cut the tang off it will break off by itself and will end up in the oil pump which will cause severe damage. If the oil pump locks up the next thing that will happen is a rod will exit through the case. No warning.

The mains will fail eventually but they will give some warning. Jim
 
I would like to get at that washer, but I dont have the necessary puller to pull the crank side timing gear(pinion gear?).
 
Bowtoy70 said:
I would like to get at that washer, but I dont have the necessary puller to pull the crank side timing gear(pinion gear?).
Click to expand...

You will not need to pull the crank pinion gear. Just unscrew the oil pump drive gear and then the intermediate gear will slide off it's shaft along with the cam sprocket. Jim
 
I don't know if it has been mentioned and I'm not going to read through to find out, but if you find a ball bearing on the timing side doesn't mean there is not an updated roller on the drive side particularly on later combats.
It is not uncommon to put a good ball bearing on the TS and the high dollar roller bearing on the DS.
 
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