Crank cases
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lcrken
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When Norton came out with the 850 ('73 or so?) they used the same crankcase for both 750 and 850 engines, part no. 604045. No differences there between 750 and 850 cases, except for the MK3 850, which had significant differences in the crankcase from earlier models. Prior to the introduction of the 850, there were several variations of the 750 crankcase. Unless you are looking for a period correct set of cases for an earlier 750, the 604045 will work just fine for either 750 or 850 engine.
Ken
Ken
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I would have thought that the cylinder sleave would have been larger on the 850, requiring a larger hole in the top of the cases where the cylinder attaches. Hope that makes sense. BTW, I have never held a set of 850 cases or cylinder, just thought there would be a difference.
jug
jug
lcrken
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illf8ed said:
It's that dyslexia again. Quite right about 064045 vs 604045. That part number applies to all 850 except MK3, and all 750 after serial numbers from 212278. They are sort of interchangeable. You can use the later crankcases on the earlier 750s, and you can convert the earlier crankcases to fit the 850 with a bit of work.
Ken
lcrken
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jug said:
The 850 cylinder is, as you thought, larger at the bottom, but the bolt pattern is the same, and because the case mouth is large enough to clear the 850 cylinder, the 750 cylinder will bolt on with no problem, so Norton used the same cases for 850s and for 750s built after the new cases were developed. That's why I said you can use the later cases (064045) for earlier 750 engines. It doesn't work the other way around. Some of the earlier 750 cases will not take the 850 cylinders without machining the case mouth larger. I don't know about the 750 cases used just prior to the 850 introduction (for early '73 750s prior to serial 212278).
Ken
Fast Eddie
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Its interesting that there is very little price difference between all of the options mentioned (driven by the fact they all have basically the same manufacturing input, I presume). Which makes the Maney crank cases something of a bargain to my mind.
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OK, now I get it. LOL
My bad on the dyslexia, typo on the engine #.
Thanks for clearing things up. How much wriggle room between the 850 case and the sleave on a 750 barrel? Most cylinder base holes are not a close fit on the studs, or at least the ones I've had in my hands I would have thought that would create an alignment problem, or am I over thinking it.
jug
My bad on the dyslexia, typo on the engine #.
Thanks for clearing things up. How much wriggle room between the 850 case and the sleave on a 750 barrel? Most cylinder base holes are not a close fit on the studs, or at least the ones I've had in my hands I would have thought that would create an alignment problem, or am I over thinking it.
jug
Fast Eddie
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jug said:
The barrel mounting studs are shouldered Jug, ie the plain part close to the case is a larger diameter than the threaded part. So the 'stud to barrel fit' provides the location datum, not the 'liner to case fit''. This is pretty standard thinking on most engines I believe.
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lcrken said:
Previous discussions have shown the '72 - '73 750 models had the 063334/063786 '750' cases with the "rear" case breather and no sump strainer and that is what is shown in the 1973 parts book, there's no evidence the factory switched to 850 cases for the late 750s except for the 750 'short-stroke' engines.
http://bigdcycle.com/tempbooks/nor/1973_1974.pdf
N
nortonspeed
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lcrken said:
As far as I know none of 750 cases will take the 850 cylinder without machining the mouth backwards (the 750 short stroke engine used 850 cases). In fact only the later beefier Combat cases are useful to machine the case mouth larger because the earlier 750 cases will leave a critical thin wall in the left top rear corner of the case after machining.
lcrken
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My mistake. LAB and nortonspeed are correct about the late 750 engines having a different part number for the crankcases, and I'm guilty again of passing on incorrect info. Sorry about that. No real excuse, just getting fuzzier in the head in my old age (seriously, not in jest). I was quite sure from memory that the later 750 and 850 cases were the same, and when I checked the parts list to verify the part number, I didn't go past the 850 illustrations. My bad, and I apologize for misleading anyone. I need to spend more time in the shop and on the bike, and less on the computer.
So, the only thing left from my post that might still be helpful is the statement that you can retrofit the 850 cases to a 750 with no problem. I've done it myself several times. I also have a friend who races a Rickman with Commando engine, and he used to regularly swap 750 and 850 top ends on the same cases, depending on the class he was going to race in. I've also bored out earlier 750 cases to take 850 cylinders sleeved to 920. As nortonspeed pointed out, it does get pretty thin in one corner, but I've never had one fail there. That doesn't mean it's a good idea, but it worked for me.
Ken
So, the only thing left from my post that might still be helpful is the statement that you can retrofit the 850 cases to a 750 with no problem. I've done it myself several times. I also have a friend who races a Rickman with Commando engine, and he used to regularly swap 750 and 850 top ends on the same cases, depending on the class he was going to race in. I've also bored out earlier 750 cases to take 850 cylinders sleeved to 920. As nortonspeed pointed out, it does get pretty thin in one corner, but I've never had one fail there. That doesn't mean it's a good idea, but it worked for me.
Ken
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nortonspeed said:
You mention that the "later Combat cases" were beefier, any idea from what serial # the beefier cases started at, Ken. Or what part # they would be. Got a line on a set of NOS Combat cases for about half of what a new set is going for at any of the suppliers.
JUG
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jug said:
I think 06-3786 are the cases which have the large (unused) starter motor (not 'magneto' as it's sometimes referred to) hole in the rear of the timing chest cast-over instead of blanked off by a steel plate, and this particular c/case was introduced around mid-'72 but is otherwise basically the same as 06-3334 although the '73 parts book still lists the 06-3334 part number for the 750.
Around 206000 to 208000 they improved the machining processes.
This was to address stress fractures around the mounting.
I swapped out my 200xxx cases for a set of 210xxx during my motor build up.
See this,
http://atlanticgreen.com/engcases.htm
This was to address stress fractures around the mounting.
I swapped out my 200xxx cases for a set of 210xxx during my motor build up.
See this,
http://atlanticgreen.com/engcases.htm
