Converting a 750 to an 850 engine, what does it take?

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kommando said:
True, but in this case the original poster never came back to look at any replies, which makes it even odder is he asked same question before and never went back then either.
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Maybe it was due to the first thread where it took 24 replies and page two to get something close to an answer then it turned back into 76 off topic happy hour replies at the rest home. :D
The dude must have tried one more time in this thread and given up. (nearly 100 replies in total)

Not to mention you do not need to sign in to read replies.

I could see someone if they wanted a little more torque while retaining numbers (matching bike) adding an 850 top end if doable within reason or if the 750 top end was worn out so why not. (go to the 850 upper)

I had taken for granted (incorrectly) the 1973 750 was all but a 73 mm bore 850.
 
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kommando said:
Which all comes back to the first answer he was given, sell the 750 and buy an 850 ;) .
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I always told people this with snowmobiles. "Sell the 600, buy an 800!"
It was always the NON-MECHANICS talking about "doing it" (extensive engine mods) meaning HAVING it done, angling for motorhead beer buddies to do it for free.
 
Time Warp said:
I'm not sure I would want to build an 850 on 1972 750 engine cases let alone earlier 20M3S 750 cases.
It couldn't be that hard though.

A 1974 case 73 mm x 89 mm 750 would be something else and could have been a factory bike with a smaller bore through bolt cylinder.

Perhaps even better would have been a kick start 1975 750 with the Mk3 cases, 3/8" bolt crankshaft and revised for bore RH10 cylinder head.
Lively and free revving within reason in candy apple red.

If if's and but's were candy we would all have a merry Christmas.
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Ive got one of those except it's green rather than red and a 920 rather than a 750.
Other than that, identical!

Glen
 
I'm confused... why does nobody answer the actual question, regardlless if the guy comes back or not. Isn't this site about technical information? Can it be done? Adding a 850 barrel to a 750 bottom? Different size studs? Different spacing of base studs? Can it be done? We know anything can be done, but what would it actually take? What about the difference between Commando and Atlas bottoms? Can a 850 barrel be fitted to both an Atlas and a Commando 750? What would it take? The discussion goes way off the original topic. Then posts of links to stupid non Norton videos.
Why does nobody answer the question in a technical manner? I'm confused.
 
YukoNorton said:
I'm confused... why does nobody answer the actual question, regardlless if the guy comes back or not. Isn't this site about technical information? Can it be done? Adding a 850 barrel to a 750 bottom? Different size studs? Different spacing of base studs? Can it be done? We know anything can be done, but what would it actually take? What about the difference between Commando and Atlas bottoms? Can a 850 barrel be fitted to both an Atlas and a Commando 750? What would it take? The discussion goes way off the original topic. Then posts of links to stupid non Norton videos.
Why does nobody answer the question in a technical manner? I'm confused.
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The crankcase stud pattern is the same form a 750 to an 850
You need to take some meat out of the 750 case to clear the 850 liner
The cylinder head bolt pattern is different between the 750 and 850 Although it can be altered the 750 head will not fit straight on
There's a difference in crank balance and studs etc but that's about it
 
YukoNorton said:
I'm confused... why does nobody answer the actual question,
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It isn't a case of nobody answering the question.

If sufficient time, money and energy are thrown at any project then it can often be achieved but the sensible argument here is that there's little or nothing to be gained by converting a 750 to 850 on what appears to have been no more than a whim or just do for the sheer hell of it.
If, however, the OP had said they had a 750 engine with a blown/worn out top end and a good spare 850 top end then I'm sure the responses would have been different.
 
It's also a bit odd to come on for one question (twice ) and not come on again for the answer !!
 
As we are on the subject year's ago I fitted a combat top end on an 850 bottom end with a 1mm spacer under the barrel on a mates commando and I have to say that was a superb bike to ride
 
YukoNorton said:
I'm confused... why does nobody answer the actual question, regardlless if the guy comes back or not. Isn't this site about technical information? Can it be done? Adding a 850 barrel to a 750 bottom? Different size studs? Different spacing of base studs? Can it be done? We know anything can be done, but what would it actually take? What about the difference between Commando and Atlas bottoms? Can a 850 barrel be fitted to both an Atlas and a Commando 750? What would it take? The discussion goes way off the original topic. Then posts of links to stupid non Norton videos.
Why does nobody answer the question in a technical manner? I'm confused.
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The answers were actually given in his first asking of the question which he also never read, no need for a repeat performance.

Post #24 gives all the info

Upgrading a 750cc Commando engine to an 850cc

Do a 45 mph roll-on in top gear and watch the 750 disappear in your mirrors. The 750 will want to downshift, and the 850 will just pull. Well, yeah, but why? Ain’t that what gearboxes are for ??
www.accessnorton.com
 
baz said:
It's also a bit odd to come on for one question (twice ) and not come on again for the answer !!
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It's also normal for a thread to follow OP. With no further input it is what it is & usually ends quick. I don't see any reason it must be & completely no less, covered for someone else, who even starts in by complaining along with a filibuster question.
 
baz said:
The crankcase stud pattern is the same form a 750 to an 850
You need to take some meat out of the 750 case to clear the 850 liner
The cylinder head bolt pattern is different between the 750 and 850 Although it can be altered the 750 head will not fit straight on
There's a difference in crank balance and studs etc but that's about it
Click to expand...
Thanks for the straight forward technical based answer baz. If you had replied first, it would have avoided all the 'chatter' that I would expect to find on a public facebook site, not The highly respected Norton site. Now I can share this with two others I know that have 750s as an option for their rebulds as compared to aftermarket kits, a 850 barrel fits the 750 bottom just use the matching head, thank you.
I come here often to read and learn, as those with the technical knowledge willing share their experience, and I don't log in as it is not necessary for learning... didn't know an answer will not provided unless the OP comes back on. I was out in the bush yesterday, saw your answer baz, but was not able to reply. I think, as with other technical forums I am on, if a question is asked, and I can answer, I do, regardless if the OP doesn't come back or if his question will take a lot of money, or time, or doesn't make sense, I just answer the question in a technical based reply, It doen't matter if he has the parts, or even has a bike, he asked a question... it makes sense to just provide a correct technical answer for sharing knowledge. I typically find off-topic replies to indicate they don't know the answer. Comments will be visible for as long as the site is accessible, and will be available for others in the future to learn, That's it, no suppositions, just technical based replies.
 
kommando said:
The answers were actually given in his first asking of the question which he also never read, no need for a repeat performance.

Post #24 gives all the info

Upgrading a 750cc Commando engine to an 850cc

Do a 45 mph roll-on in top gear and watch the 750 disappear in your mirrors. The 750 will want to downshift, and the 850 will just pull. Well, yeah, but why? Ain’t that what gearboxes are for ??
www.accessnorton.com
Click to expand...
post #24 just says to buy something else, not a technical reply that actually answers the simple question... what fits what.
 
Converting a 750 Commando into an 850 is easy. You just bolt in a replacement engine.
 
That would be an engine swap.

The question is way more complicated

'Converting a 750 to an 850 engine, what does it take'​

The problem right away tho, from an OP who doesn't participate is

'Converting a 750' could be referring to a 750 model bike or a 750 engine.

I think the wording implies converting a 750 engine to 850.

Don't have a clear question and then even worse, unwilling to elaborate, forget about a clear answer or dreams of a focused thread, or response.

No point also in harping about someone else's botched thread & expecting results.
 
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