rh10 head

Did all 1974 850s, whether MK2 or MK2A, get the RH10 head?


Glen

My understanding was that late 73's and all 74's got them. But I could be wrong.

Good, thanks snort. I have found a 74 for sale, a couple hundred miles aways but might be worth the drive.
Jim has got me all RH10!

Glen

My December 1973 Mk2a (3110xx) has a RH10.

NOW that was easy ; finally found it . :x



If these blokes just stuck to Triumphs , they wouldnt have these sort of troubles . :lol: :lol: :lol:

Time Warp said:

My December 1973 Mk2a (3110xx) has a RH10.

Click to expand...

Mine is from December 1973 too (3120xx) with a RH10.

The document listing the different model heads has a July 73 date at the bottom, for whatever that's worth...

I've also got an RH10 on my 11/73 manufactured 850. Actually, I bored out the intake to 32mm right through, so I've re-stamped it an RH10-4.

From the NOC website
NORTON COMMANDO CYLINDER HEADS
Identification
Number Part
Number Capacity Compression
Ratio Inlet Port Remarks

RH1 060988 750cc 9.0 : 1 30mm Standard up to 1972
RH2 061427 750cc 10.25 : 1 32mm AMA racer
RH3 063327 750cc 10 : 1 32mm 1972 Combat
RH4 064038 850cc 8.5 : 1 32mm 1973
RH5 064048 750cc 8.9 : 1 32mm 1973 low compression
RH6 064097 750cc 9.3 : 1 32mm 1973
RH7 064845 750cc 10 : 1 32mm 1973 short stroke
RH8 064884 750cc - 32mm 1973 short stroke race kit
RH9 065013 850cc 10:5 : 1 32mm 1974 high performance
RH10 065062 850cc 8.5 : 1 30mm 1974

A suffix S, e.g. RH6S, indicates a 750cc head fitted with 850cc guides


Will a 750 head fit onto an 850 motor? Has anybody ever tried it? Also, the identifier code over the exhaust rocker is absent, but I believe the head in question is a 1972 Combat. Has anybody else run into heads with no identifier before?
750 and 850 heads are different
The 750 and 850 heads are not easily interchangeable; they have different bolt patterns.

illf8ed said:

From the NOC website
Will a 750 head fit onto an 850 motor? Has anybody ever tried it? Also, the identifier code over the exhaust rocker is absent, but I believe the head in question is a 1972 Combat. Has anybody else run into heads with no identifier before?
750 and 850 heads are different
The 750 and 850 heads are not easily interchangeable; they have different bolt patterns.

Click to expand...

I have used 750 heads on 850's several times. The bolt holes need to be bored and plugged and moved outward, The chamber needs to be bored larger. A 28mm port 750 head makes a good head to start with for a port job. More work than a rh10 though.
A 750 combat head is not much good for anything. Jim

comnoz said:

I have used 750 heads on 850's several times. A 750 combat head is not much good for anything. Jim

Click to expand...

Hobot will love that statement :mrgreen: But seriously Jim why is a Combat head no good for using on an 850 barrel :?:

A 750 combat head is not much good for anything. Jim

Ugh, when I put a Combat head with 6 mm K/W Dreer kit on 750-2S Peel instead of the plain stock standard 28.5 mm head, it knocked the crap out of power band off idle to mid red zone, ugh. I'm money-time limited like many so had Ken Canaga modifiy Combat head for the 920 engine, with hopes the bigger displacement would tend to over come the big bent ports somewhat w/o blower and just get blown past with boost. Ken over sized drilled the bolt holes for interference plugs, redrilled to 920 cylinder and widened the head chambers which made a good bit of extra wider squish band appear. Swain coated inside and out.

nortonspeed said:

comnoz said:

I have used 750 heads on 850's several times. A 750 combat head is not much good for anything. Jim

Click to expand...

Hobot will love that statement :mrgreen: But seriously Jim why is a Combat head no good for using on an 850 barrel :?:

Click to expand...

Because a Combat head does not flow any more than a standard head so the larger port ends up flowing with less velocity.
And since the ports are large to begin with there is not enough metal to reshape into a good flowing port. Jim

comnoz said:

nortonspeed said:

comnoz said:

I have used 750 heads on 850's several times. A 750 combat head is not much good for anything. Jim

Click to expand...

Hobot will love that statement :mrgreen: But seriously Jim why is a Combat head no good for using on an 850 barrel :?:

Click to expand...

Because a Combat head does not flow any more than a standard head so the larger port ends up flowing with less velocity.
And since the ports are large to begin with there is not enough metal to reshape into a good flowing port. Jim

Click to expand...

Why doesn't the larger port flow more? Kinda like electronics, wider port equals more band width. Of course the amount of draw from the engine is limited, but with combat spec cam and compression I would expect the engine to draw more than a standard spec. Or is the problem due to porting shape only? With just seat of the pants opinion, a combat spec engine seems more powerful than any of the other factory specs I've ridden.

hobot is on a mission put some teeth in The Unapporachable Norton Commando moniker any way I can get away with. I do know that the Combat head finally comes into its own about 6800 rpm to feel like a 3rd piston kicks in, which is just a few 100 rpm short of factory kit valve float/clash. I felt this transition in both my 1st and 2nd factory Combats but learned my lesion and only did that a few times on my 2nd Combat, just to make sure it was really Combat spec. On the eve of Y2K end of the world I took no name 1st Combat out to try to break it as planned to go through soup to nuts >>> and had tasted the benefits of moderns on and off tract so pretty disgusted with my clunker but damit those moderns didn't pull like the Combat lifting its front in red zone through 1st and 2nd dive bombing into and out of turns in nice surface Mt hwy.

So have I shot Peel in head for next 920 10.5 CR engine with what I call a 'CHO' big port head with 6mm stem stock valve sizes? If I have would there be much trade in value of this CHO 920 head + a good spare 28.5 mm head [that gave Ms Peel her name as a terror for the poor unresponsive liter bikes up the ton towards a FullAuto with the slick seat contours?

I've messed with forbidden women and injected illicit drugs and am as Experienced as Jimmy Hendricks and have time in stunt air craft to tell ya I got similar hi's on Ms Peel for most a year til the stuck throttle event. My P!! topped Peel for pure pull though so she's got some proving yet to do for me. Only Tunnel Hull race boats and water skiing behind race boats have topped the G's in turns Ms Peel delivered so hope to match that before I die.

A combat engine is more powerful but it is not because of the ports. It is because of the higher compression and the cam.

The ports flow poorly because the shape of the port where it enters the bowl is not good. Plus a 32mm port is a waste on a longstroke 750 motor. It does not have the ability to generate good velocity in a 32mm port except maybe at very high rpm where friction will take about any increase you may get.

You can mill a 750 head to Combat specs and use it with a Combat cam and tapered manifolds and it will outrun the same motor with a Combat head. [and be more fuel sensitive due to higher cylinder pressure]
When I tested that I found several more horse at 4000 rpm with the standard head and about the same at 6500 rpm.
Of course the steep rise in power from 5500 to 6000 with the Combat head gives you an exhilarating ride. Jim

I have a Combat motor in my 750. And enjoy riding it. But it is not a numbers matching bike. The gearbox matches but the frame is from an 850. So I have considered more than once building a 750 motor. Start with a crankcase that has a sump plug in it for one, and then go ahead and get the Fullauto head for the flow. I suspect by increasing the compression ratio a bit and selecting a cam with a nice mid range that the over all effect would be a much nicer bike to ride and probably faster.

Truth be told, I don't spend enough time in the RPM range that matters for the Combat. And in street riding probably wont.

Russ

I didn't feel my 2 Combat's 32 ports get really effective till over 6500, or just normal 750 Commando spunk. I did not ever find a point after that the power fell off just got stronger till I got scared for the engine. The plain Jane standard head literally kicked my ass off the seat onto tail lens once I got the exhaust opened up, until i developed dragster planting white knuckled grip reflex prior to lower gear throttle snaps. I only let Peel's rpm get to 7500 with the standard spring head as afraid of valve clash but very hard to back off in time as power spiking enough to lift front out of effect. After Peel accidental combo I don't feel my factory Combat is worth pressing much over 90 mph- 6000 rpm so never try contests with hot shots, just a nice quaint smooth tourer with caution handling turns.

So want to hear your opinion JIm > that my 920 'CHO' early factory hogged out ports will work a treat in 20% bigger displacement with more draw in volume per stroke with Norris D cam, even w/o boost. I believe if Peels dual Amal stuck throttle event had occurred with the standard head it would of choked down or valve floated to save bottom end but I will never ever forget what happened with the hogged out head near end of red zone RPM INCREASE SPIKED!!! w/o a hint of misfire or other noise but megaphone jet ROAR.

Think of trying to drink a milkshake by using a vacuum cleaner hose and compare it with a normal straw.
You'll get the picture.

Fullauto said:

Think of trying to drink a milkshake by using a vacuum cleaner hose and compare it with a normal straw.
You'll get the picture.

Click to expand...

So, what I am hearing is bigger is not always better.
It is my experience with a tweaked RH1, milled face and opened to match the carb manifolds, that it seems better thant my old RH3, particularly in the mid and upper regions.