850 head in 750 engine
- Thread starter pierodn
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Different bolt patterns.
http://atlanticgreen.com/nhth.htm
http://www.nortonownersclub.org/support ... tification
http://atlanticgreen.com/nhth.htm
http://www.nortonownersclub.org/support ... tification
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I read of a 750 head being welded up, new bolt holes bored and used for it's smaller ports on a set of 850 barrels and cases, but it sounds like more trouble than it's worth. I think if you went the other way, you might be infringing on the combustion chambers.
Piero, there are some 750 heads on US E-bay at the moment at less than $200, some that are listed as G15 ot Atlas are actually Commando because they have the rocker oil feed ports on the side of the heads rather than in the middle. You can expect to do some work on them, but at that price there is some room for repairs.
htown16
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I picked up a good 750 core on ebay a couple of weeks ago for 200$. The guy had a "buy it now" price of almost 500$ but under the "make an offer" option I offered him 200$ and he accepted it. Don't be afaid to make a low offer if they give you the "make an offer" option. I've bought some other things lately at a pretty good discount to the "buy it now" price that way.
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Piero you should read the links I posted above.
pierodn said:
Combustion chamber size, head bolt pattern is a bit closer on the 750, that is, the two bolts on either side of the spark plugs.
Various porting differences, which wouldn't be of much consequence.
That's really about it. I think Jim Comstock has done a conversion before.
That head chart shows a variety of head number types, and various compression ratios.
That says to me the chamber volume is all over the place.
And, if you (could) then used a high compression ratio head for a 750 on an 850, the compression would be higher again.
So yes, the chambers MUST have different volumes....
That says to me the chamber volume is all over the place.
And, if you (could) then used a high compression ratio head for a 750 on an 850, the compression would be higher again.
So yes, the chambers MUST have different volumes....
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The diameter of the squish counter-bore is larger on the 850 head than it is on the 750 head.
The differences in combustion chamber volume was often due to how much material was left on the deck although the counter-bore diameter does figure into this.
I have plugged and redrilled and enlarged the counter-bore on 750 heads for use on 850's but I have never used an 850 head on a 750.
The 750 head is better, both for performance and durability. Jim
The differences in combustion chamber volume was often due to how much material was left on the deck although the counter-bore diameter does figure into this.
I have plugged and redrilled and enlarged the counter-bore on 750 heads for use on 850's but I have never used an 850 head on a 750.
The 750 head is better, both for performance and durability. Jim
comnoz said:
Just explain that "how much material was left" a little bit more ?
Is this how much was shaved off the head - the gasket surface - in manufacture ?
(like the combats had 0.040" shaved, to get higher compression).
So all different RH head varieties have different pushrod length requirements ??
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Rohan said:
Yes, it is how much was shaved off the head. From the squish band up the combustion chambers were all pretty close to the same -750 or 850.
The standard pushrod length was within the range of adjustment until the cut got really severe -like the combat head.
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