750 vs 850 Commando Crankshaft

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Dec 24, 2003
Does anyone know the difference between the 1971 - 1972 750 & 1973-1974 850 Crankshafts ?

Can the 750 crankshaft be used in 1973 850 cases without problem ?

Another question is, Why does the 1972 Combat engine have the extra Tabbed Thrust Washer on the Camshaft ?

Thanks in anticipation of the answer/s.
nortonfan said:
Does anyone know the difference between the 1971 - 1972 750 & 1973-1974 850 Crankshafts ?
Can the 750 crankshaft be used in 1973 850 cases without problem ?
physically will bolt in, but different flywheel so balance and total mass is off unless you are putting the 750 top end on the 850 cases

Another question is, Why does the 1972 Combat engine have the extra Tabbed Thrust Washer on the Camshaft ?
Factory screwed up for 72-73 combat breather cases, do not use this style bushes/washers.

suggest you buy a INOA tech digest most of this stuff was documented a decade or two ago.

Thanks in anticipation of the answer/s.
Thanks for your response dynodave.

A lot of these questions I post are asked of me by owners of commandos.
Because of my website , I get questions/requests fired off at me on a regular basis, Like you probably do also.

It would be very easy for me to just tell them to phone any of the norton mechanics around here, if I wasn't sure of the answer. I am not a qualified mechanic, just a bloke that plays mechanic with my own engines.

Instead, I post them here knowing it may help others who may have asked the same questions.

Apart from the crankcases being about 1lb weight difference, the actual bolt holes are 5/16" instead of 3/8", I believe.

Please correct me if that is incorrect.

You didn't really tell me why the extra thrust washer was inserted though, you just bagged the 72/73 cases ................

I have compared the std, combat & 850 camshaft & see no difference in length/layout, so have yet to understand why the extra thrust washer.....

Maybe the answer lies in the INOA digest as you have suggested buying.

With Thanks,
cam bushes

the combat 06 2600 bush and (2) 06 2601 washers make up the same length as the 73/74/75 bushes though all 3 are different PN, they are flanged on one side only, and they stick out of the cases on the sprocket side.
You only really need one thrust surface because the cam thrusts to the right only, for that reason, IMO precise end float control is a pointless persuit. 73/74/75 bushes can and should always be substituted for the combat style. you should groove the cam or bushes for lube.
68-71 cam bushes are larger diameter and can't be used in late case.
Go to Fred Eaton's Old Britts site (http://www.oldbritts.com) and find the technical articles. Under "cam bushing information" is a great pictorial explanation. There are six different cam bushings, some with thrust faces, some without. As Combat cams usually had no scrolling on the bearing surface, the bushing needed oil channels. The bushing used, (062600) had no thrust face. The two tabbed spacers were used to compensate.

If you are using a scrolled cam in '72 cases, I would replace the bushing with either 063020 or two 065428 and use thrust washer 061086. If you are using the the unscrolled cam, then use the 062600 and two tab washers, but remove the tabs first. These tabs can fracture and circulate through the engine.
cam bushes

I guess each unto his own...
It might not have been clear to some....The 061086 beveled steel thrust washer is used in ALL inboard tach drive engines 20M3S thru 75, right next to the cam's tach drive gear and functions as the cams thrust surface. The flanged bushes function as the stationary thrust surface. Except in 72/73 when the 062601washer, with tabs removed, can sometimes spin in the case making the case the wearing part. That's why I always recommend against the 72/73 cam bush system. It is just a real bad system in my book. I have brand new 2600/2601 bush/washers sets that I wouldn't give away. They hang on my "wall of shame" display.
Thanks for the tips & taking the time to answer.

I have actually put a "Norris" 2S cam with scrolled surfaces in my Combat bottom end. It has the scrolled bearing surfaces.

I have not fired it up yet as I have pulled the bike to pieces & am in the process of putting it back together after powdercoating the frame.

Breaking off the "tab" on the end thrust washer has been suggested to me by a Norton mechanic, for the same reason RonL has stated, which I did.

Then another person who builds/races Nortons told me I should not have done so, like Dynodave has stated, as it may then wear into your cases. This also makes sense.

This sort of thing makes you wonder what is going to be "right".

I have since been told that the reason for the "extra" tabbed thrust washer was put in to stop wear on the crankcase caused by pressure from the tacho drive.

I guess if I start to see aluminium filings in my oil, I will replace the tabbed thrust washer pretty quickly.

Have had a look at the Old Britts site, it would appear that the reason for the tabbed washer is beacause of the removal of the cam bushing "shoulder" in the 72-73 750 cases.
Actually, I think that I would rather see how long the "tab" stays put & the washer doesn't spin into my case.

Having that larger piece lying in my bottom end, rather than lots of small filings & a possibly ruined crankcase, is preferable to me. Assuming it does break off one day that is.

I will pull my cases apart in the morning & replace the tabbed washer & leave it on this time.

Some will agree, some may disagree.

To fix the problem correctly would be to put the later cam bushing in with the flange as DD suggested, seeing as the Norris cam is scrolled.

Are there any agreements with that conclusion :?:
blowing engines

The reason the 2601 washer is so bad is "when" it breaks off, you don't just wear the cases, you put a rather large hole in then where the rod comes out. The tab goes in the oil pump, locks it up, and you loose oil pressure, then ka pow. I've seen it way to often....
If it was a motor I owned, it would come out, be torn down, and bushes replaced.

"I have since been told that the reason for the "extra" tabbed thrust washer was put in to stop wear on the crankcase caused by pressure from the tacho drive. "

Whoever told you this is wrong.
You MUST have the thrust washer inside the cases, ALL Norton Heavy Twins have that thrust washer in one form or another. The EXTRA one is on the NONTHRUST side behind the sprocket. and fill the gap since the 2600 bush is short and the extra washer makes up the remaining length equivalent to a non combat bush system.

"Have had a look at the Old Britts site, it would appear that the reason for the tabbed washer is beacause of the removal of the cam bushing "shoulder" in the 72-73 750 cases."
Yes a bronze lined, steel backed bush can't be made with a flange, so serperate thrust washers were made.
Thanks again Dyno, I have learned new stuff from you all !

I will be replacing the bushes for a better bottom end :idea:
Dyno Dave,

Thanks for clarifying that the chamfered washer (061086) should be used with all cams. I agree that the flanged bush should be used whenever possible, but if the cam's bearing surface is not scrolled, I would be concerned about proper oiling.
That being said, I personally have never had to make that decision, as all the '72/'73 bottom ends I've built have either had scrolled factory cams or scrolled aftermarket, so out cam the original bush and in went the flanged one.
So, the tabbed thust as well as the chamfered thrust was put into the 72-73 cases as the cam bush was changed & had no flange, I understand.
Thank you.

While we are on the subject of bottom ends then..............

The crankshaft end float should be .005" - .015" according to the manual.

It has been suggested as little as .003" should be ideal using the FAG bearings ? This is supposedly to stops whip/lash & prolongs the bearing life ?

Have you guys any thoughts on that one ?

Then, back on the 750 vs 850 crankshaft differences.

It would appear that the 850 crankshaft is a lil wider than the 750 apart from the bolts holes being 3/8" in the 850 as opposed to 5/16" in the 750.
The balance factor, I have no clue to yet....................

Would it be ok to bolt the 850 flywheel up to the 750 journals & have them properly drilled out to 3/8" & fitted with new bolts. The extra width may be in the flywheel width ?
I have been told that this is quite ok to do, BUT ?

The reason for this question is that I have a complete 850 engine now except for a crankshaft, I do have a spare 750 crankshaft though & would like to use it if possible to do so.

I have been offered an 850 flywheel that is stock for $50 AUS.

Thanks in advance for any help on this one also.
After some research, it would appear that the 1972 -1974 crankshaft complete setup is the same for these years.

I am finally basing this assumption on information provided at the NOC England website & speaking to people.

Under the "technical" section at NOC England, all the part numbers are the same for the above years.

Does anyone disagree with my conclusion ?
1968-1973 750

Complete crank assembly - 063106
TS crank cheek - NM.23262
DS crank cheek - 060542
flywheel - 060731

1973-1974 850

Complete crank assembly - 064254

1975 850 (e-start)

Complete crank assembly - 065660

Individual crank components were not listed for the 850's. It would be safer to say that there were three Commando crank assemblies, 750, 850, and 850 e-start. Certainly the flywheel was different between 850 and 750 and the drive side crank cheek is different between e-start and early 850 and 750.
information sources.....

You are a big boy so I needn't tell you of the perils of the internet.
Captain Nortons web site is excerpts from the BI list, I used to be on it but got tired of the BS. Good entertainment yes, technical resource NO.
NOC website technical files are in many cases just excerpts from the NOC list or RH magazine. Not technically authenticated information as far as I remember.
HUGE HUGE HUGE innaccuracies on these lists and websites, since they are all just reposting of peoples opinions.
I cringe when I hear some of those sources quoted for technical info.

Even the INOA tech digest, which I have been involved with, originated as Norton News excerpts. In volumn 3, many of the older inaccuracies have been deleted or corrected, but it is by no means "perfect", or thorough on all topics.

Ron's version above is pretty good, as far as I remember, except I should add the E-S crank has the 850 flywheel, maybe moded for the bigger dowel pin, and both ES crank cheeks are WIDER than any earlier commando crank cheeks so they will NOT fit in NON ES cases.
Thank you both for responding. I have a feeling you guys are no doubt correct & appreciate the input you provide to this forum.

I have one more question then on this subject.

Can you bolt the 73-74 850 flywheel up to the 72 750 right & left cheeks/journals & does that make a 73-74 850 crankshaft ?

With Thanks.
What is a BI list?

I would like to point out that the rotor shaft on a '75 electric start 850 crank is longer than the rotor shaft on a non electric start 850 crank in order to accommodate the sprague clutch and other electric start clap trap that lives within the primary. This is another reason why an e-start 850 crank and a non e-start 850 crank shaft are not intechangeable.

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