Combat differences
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Hi all,
What is the difference between an RH4 head and an RH10?
I thought the Mk 3 had strengthened crankcases, is that so?
Did the change in tyre size improve handling/ adhesion?
At what point in production are Nortons considered to have achieved best reliability and performance?
With thanks
Alan
What is the difference between an RH4 head and an RH10?
I thought the Mk 3 had strengthened crankcases, is that so?
Did the change in tyre size improve handling/ adhesion?
At what point in production are Nortons considered to have achieved best reliability and performance?
With thanks
Alan
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RH10 has 30mm inlet ports with inlet manifolds that tapper from 32mm carb end to 30mm, Mk3 cases are different to Mk1/2 850,
standardising the tyres was a cost cutting measure, my Mk3 has a slightly narrower front tyre and therefor "points better", when I first built my Mk3 I had 100/90x19 Roadriders Front and back it was a bit like riding a " freight truck" I changed the front to a 325x19 which makes it point a lot better!
standardising the tyres was a cost cutting measure, my Mk3 has a slightly narrower front tyre and therefor "points better", when I first built my Mk3 I had 100/90x19 Roadriders Front and back it was a bit like riding a " freight truck" I changed the front to a 325x19 which makes it point a lot better!
Thank you Pssm, just to enquire a little further, what inlet size does RH4 heads have, are they the same carbs etc, what was the change for, does one perform better than the other?
I presume the Mk 3 is considered the ‘ultimate’ crankcase. Did it solve existing weakness problems? Is it considered substantially better than the Mk 2?
With thanks
Alan
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The RH4 heads had 32 mm ports. But they also had cracking issues at the intake guide areas on a lot of these heads.
That is why Ken developed the Fullauto head and how it all started. It became cost prohibitive to continue to manufacture the Fullauto heads in Australia so he sold the works to a US company. These heads are newer technology in casting and materials and flow bench developed by Jim Comstock to improve the OEM design.
That is why Ken developed the Fullauto head and how it all started. It became cost prohibitive to continue to manufacture the Fullauto heads in Australia so he sold the works to a US company. These heads are newer technology in casting and materials and flow bench developed by Jim Comstock to improve the OEM design.
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marshg246
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Combat and non-Combat used the same bearings. Except for the cam and cam bushings, the bottom ends are identical between Combat and Non-Combat. Also, although not "Combat", in 73 there were four different heads available: RH5, RH6, RH7, RH8 (look on top of the head near the timing side exhaust rocker access and who knows what head it has now without you saying.
I gave you a link that had links to all four services releases. I don't remember you giving us your serial number so we keep having to give complete info rather than specific info. If your engine is 211891 or later, it left the factory with at least the 3rd version (first "SuperBlend"). If it was built or had the bearings changed after Jan 73, it has/had the final version unless the dealer had old stock. "73" is almost worthless info. Serial 220000 is the "beginning" 73 but built in 72 or 73. Norton had NO official model years.
Assuming it was built in late 72 or in 73, it is very likely that it has at least the 3rd version and they are OK for non-race IMHO.
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It's a '235' (Jan. '73) Hi-Rider, therefore, I would expect it to have a standard or RH1 (28.5mm inlet) head and 930 (30mm) carbs.
1972 750 Hi-Rider
Yes, I suspect that the hunting tooth is much more important on timing gears than sprockets and chains. Glen
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marshg246
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OK, serial in post #97 of a different thread. 235187 makes it even more important to say the head or at least the carb size since from the parts list it could be RH1, RH5, or RH6. Even though not listed in the parts list, RH7 and RH8 are also possible (235576 & 235713 were short strokes). If he said it somewhere I missed that too.It's a '235' (Jan. '73) Hi-Rider, therefore, I would expect it to have a standard or RH1 (28.5mm inlet) head and 930 (30mm) carbs.
1972 750 Hi-Rider
Yes, I suspect that the hunting tooth is much more important on timing gears than sprockets and chains. Glen
Of course, I don't know the accuracy of any available documentation, but so far the list below has not been disputed before your post as best I can tell. Do you have better info that this?
Although I don't really care what head is on my engine, except out of curiosity, I've been out to the shop and looked (closely) at the head where marshg246 said it should be marked (stamped?), on top of the head near the timing side exhaust rocker access. I see no mark of any kind. Should you be able to see it with the head stay in place, or may it be under the head stay. I did see that the carbs are 930s. As I think it's already been established from earlier posts, my bike serial is 235187 and has a date stamp of 1/'73.
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Short strokes were 850 engines with a shorter stroke crank (different rods etc.) so the RH7 and RH8 heads should be 850 type.
On a 750 if it's marked then I believe it's likely to be under the head steady.
As I posted above, I don't really care what head is on my engine, so I won't be removing the head steady just to find out if or how it is marked/stamed
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Hi Greg,
I believe RH7 & 8 would fit 850 barrels as the short stroke engines used that type…right? As far as I know standard stroke 750 “MkV” used RH5 and RH6 heads. Then again a 235xxx is anyone’s guess.
marshg246
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Since 30mm, LAB is correct that it is a RH1 head. RH1 heads were not marked.
Since it has a stamp of 1/73 it left the factory with either the 3rd or last iteration of the main bearings, so, IMHO, there's no main bearing issues assuming that they are still good.
marshg246
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Ok, I'm confused. What was the displacement of the engines with RH7 and RH8 heads? Were they standard 750 or 850 cylinders? Were the cylinders shorter? Where the head chambers 750 or 850, or something else? Were the crankcases 750-type or 850-type (cylinder through bolts)?
In my survey, I have:
235576 From AccessNorton - 750 Short stroke engine
235713 From AccessNorton - 750 Short stroke engine (72/73 750 crankcase?)
This came from your post: https://www.accessnorton.com/NortonCommando/235xxx.24272/post-357469
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If I was designing a Commando engine in the 1960s, the Combat engine is the sort of thing I would have built. All of the old theories pointed in that direction. Bigger ports used to be associated with better performance, and so were extreme cams. However it turned out that there are better ways of getting performance. Even with 30mm ports and a mild cam - with fine tuning, I need to feed the throttle on in a controlled fashion, when using my 850 engine. I suggest a Combat engine could be good fun. I like that sort of stuff, it usually comes on song with a rush.
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77 x 80.6* I make to be 750.7cc
*Brochure says 80 but I believe it was 80.6.
850 (If you short stroke a 750 then it wouldn't be a 750).
No, the (steel) rods were longer.
Must have suited the 850 77mm bore size.
Should be 850 type.
I can't explain that.
short stroke 750
L.A.B. need your historic knowledge. I took this photo of what the owner said was an original short stroke 750 engine on his '71 production racer. In case you cannot see it the engine number is 235713. I don't see how it is possible this engine could have been original to a '71 proddy racer...
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marshg246
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OK, so 750s built with 850 parts but short-stroke and they are called 750cc engines - see the brochure.
77 x 80.6* I make to be 750.7cc
*Brochure says 80 but I believe it was 80.6.
850 (If you short stroke a 750 then it wouldn't be a 750).
No, the (steel) rods were longer.
Must have suited the 850 77mm bore size.
Should be 850 type.
I can't explain that.
Do you agree with this re-written chart:
luckyed
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I’ll add a little something to the lore and also have a question. I’ve got a 750 roadster, serial #211407, build date August 1972. So, just post Combat. The original black tank, not currently in use has the “D” stripe. The instrument cases are polished alloy. The barrels are painted black which looks to be original. Front disc there from new. 32mm original Amals ( little slide wear, I rebuilt the internals and they run fine) 19,000 miles and I’m the 3rd owner. I’ve had it 10 years. The second owner had it sitting around in a collection for 15 years or so and rarely, if ever, road it. From the data provided by Greg Marsh it appears that it would have been built just ahead of getting the factory installed “Superblend” bearings. And it would have been fitted with either the RH5 or RH6 head with the 32mm intake ports. My question: The head has almost no material below the bottom fin, and the gap between the bottom head fin and the top barrel fin is noticeably less than the other fin spacings. Would that be an indication that it is the higher compression RH6 head? (I’ve never had the head steady off to see if it’s marked)
Deckard
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Well, you've gotten the gist of the differences and what happened to Combats when they were revved to the moon by Norton neophyte owners. Most were not mechanics, so suffered accordingly. That all happened in '72, so ancient history now.
