1972 Interstate Question

Can someone answer a couple of question RE: a 1972 Interstate Commando please.

I am currently rebuilding a a 1972 Interstate that has 30mmm carbs with 32mm manifolds. The carbs may have been replaced at some stage, I guess. Did some 1972 models come like this ?

The head has RH5 stamped on the top in the middle where the "C" would normally be on a combat head. The 5 overlaps the H, therefore I am curious as to whether or not this is a factory stamp or someone else has stamped it. The head is appears to be a low compression head as it does not appear to be "decked/shaved" as the combat heads were. Did some RH5 heads come like this ? The head has 06-#380 cast into it.

The engine # is 207525 & the ID plate is stamped 1972 OCT.

The bike has a 20 tooth gearbox sprocket which may have been changed also.

The bike seems very original otherwise. The tank colour is the "blue" that came out in 1972 & averything thing else seems right for 1972.

I have yet to split the crankcases to see what the camshaft is, but will let you know soon enough.

Thanks in advance to any of you that can shed some light in this question.

This is from Dave Comeau's site

This is a RH5 73 low compression 32mm port head. NO birco or part number of any kind is remotely visable. The side profile is indistinguishable from the 71/72 head. The RH6 would be the semi high compression head with .020 cut off the head.

Here is the link to his page on Norton Heads

http://www.britiron.com/dynodave/nhth.htm

Remember late 72 was when all the warranty work was being carried out and fully built Combats were being de combatted, you should have 32 mm carbs though, be interesting to see which cam is in there, might still be a combat.

'72 cylinder head

Your '72 would have come with a combat head originally stamped "C". The RH5 head was likely a replacement. Both RH5 and RH6 heads were for '73 model year 750s, see below from the NOC website. RH6 would be a good alternative for your engine if you want the compression back up. If you're happy with the performance, go as is. At least your won't have to worry about high octane rated fuel.

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

just a quick question to this theme......does anyone else have a head on their motor that has NO stamping? Mine is a 72, and I've never found any marks on it to tell me what headI have. Think there are numbers cast faintly in somewhere...but this stamping you all mention...I've never seen it on mine.

Nortonfan,
Sounds like you have a very late '72 model. Do you have the short, unpainted clock holders or the deeper, black ones? Large taillight or small?

Your engine number is definitely a '72 build model, but the October '72 build date is rather late in the build year. I have a 1973 model MkV which was also built in October 1972.

Your manifolds should be 32 mm at each end, as should the inlet port to the cylinder head. Your head is what was listed as the low compression model for the '73 model year, possibly used due to the late build date.

Hewho..
Most non-Combat and all pre-72 cylinder heads were not stamped with a designation. The RH1 and RH2 designations were never stamped, the RH3 was stamped with a "C" and all heads after 1972 were stamped with their model designation.

Ron L said:

all heads after 1972 were stamped with their model designation.

Click to expand...

There's no 'RH' number on my 850 MkIII head that I can see! At least not where it is supposed to be (above the R/H ex. rocker cover)! I don't remember there being any stamp markings anywhere else.

Interesting... I have never seen an 850 head without an 'RH' stamping. (And there are three RH4's and two RH10's out in the shop now). I guess the guy with the stamp was on vacation!

Ron L
Thanks...having only one machine that I use, and 2 that are sort of not in a condition/location to check such things....means I can only say what is on the one I drive. I searched for a stamping last year when I did the valves and found none. Now, at least, I know why.......

Hewwho,
I have had stampings hidden by the head steady. They are sometimes stamped near the valve cover and sometimes at the base of the "V" formed by the exhaust rockers and sometimes under the head steady. It can be difficult to find it unless the tank and the headsteady are off.

I concur with Ron on this. My 850's have been stamped over the left exhaust rocker. My Combat is at the base of the V and 73 RH6 is stamped under the head steady. The head steady has to be removed to see it.

'72 head without mark

Hewho,

Defining "year" can be different than what the registration states. What most of us are using for year is model year. The '72 range started with engine number 200100. There were several engine differences from previous model years. If you have an engine number prior to 200xxx it would not be '72 range. It would also have a timed engine breather at the left end of the camshaft rather than at the lower back side of the crankcase. If you do have the '72 engine, I read somewhere that the early combat heads were not marked. If you have a non combat '72 the head would also not be marked.

Thanks for all the replies.

I was curious about the RH5 stamp being under the top engine as I have not seen an "RH#" stamp in that location before this one. The RH# stamps, that I have taken any notice of, have always been over the right rocker cover & usually only on the 850s. After sandblasting the head yesterday, the casting/part # is more clearly visible, it is 06- ?383. I did have a look at "DynoDaves" very good nrotn head site & he states that the RH5 heads had no discernible birco or part #, that is another reason I posted this question RE: this particular head. That was when I started to wonder if someone other than norton had stamped this head I have.

This bike has the early tailight & early clock holders. But it does have the 73 "basket weave" seat cover, which may have been replaced I guess.
It also has the original interstate exhaust system, a bit worse for wear unfortunately.

Also, It is not my bike, I am rebuilding it for someone & I was very curious about the differences on the bike, thanks again for all the responses.

The "basketweave" cover is also correct for the 1972 model.

So does that mean, the 1972 models could have had either the pleated or the basket weave?

I do remember my first Commando, a 1972 Interstate did have the basket weave pattern seat, come to think of it.

Re: '72 head without mark

illf8ed said:

I read somewhere that the early combat heads were not marked. If you have a non combat '72 the head would also not be marked.

Click to expand...

Boy...

This leaves me sort of up in the air. Not that I really NEED to know which head I have. Mine is though, a 72, on the data plate, and the motor number, and I've had it since it was nearly new, this is the motor out of the machine I was stupid enough to crash, as mentioned early on in the blog I have been plagueing everyone with. It might be "Combat", might not. All I know is that the motor has lasted now over 120 thou with only changing rings out and doing the valves a couple of times. Never had the bottom end apart. That may tell us it is a non combat, as I haven't been all that gentle on it either. The fellow who had ridden it before me, had said it had over 10 to 1 compression when I bought it, and I remember this because it was a good thing to use in bragging sessions, but that doesn't mean that it was true...he liked a tall tale too.
Maybe I should ask the NOC, i think they have a good list of what each machine was, when it left the factory, and I know mine can't have been sent back for warentee work...so it is still sort of "Original".
Somewhere on the head are numbers cast in, and I seem to think I looked them up when I had the head off last year, and that they said it was a combat, but I didn't note them and they are very faint and hard to read...have to look again. In the meantime, that can wait.....we have had snow again overnight......greetings from Schnitzelland :wink:

Hewho..

Measure the intake ports. The standard compression '72 came with 930 concentrics, 28.5 mm (thanks Dave Comeau) intake ports, 30 mm intake manifolds, and silver barrels. It would be relatively easy to change the carbs and intakes and paint the barrels, but a porting job is a little more involved. The Combat version had 32 mm intake ports, 932 concentrics, 32 mm manifolds, and black barrels.

If you have 32 mm ports, you either have a Combat or somebody went to a lot of trouble to make it one. In either case, you have the "benefits" of a Combat.

Hewho,

Notice the spacing between the head and barrel. Because of the shaved head, a Combat is noticeably thinner hear than the rest of the fins on the head and barrel.

combat or not

Hewho,

I believe all the non-combat crankcases were as the '71 and previous type with timed breather and sump filter. If you have an engine breather at the lower back of the crankcase "combat breather", your engine was likely a combat from the factory. In the US most '72 model year Commandos (roadster & interstate) were combats. Don't know about German exports.

I worked on the factory records project for the NOC. The Commando factory records don't indicate combat or not, only body type and color.

illf8ed said:

I believe all the non-combat crankcases were as the '71 and previous type with timed breather and sump filter.

Click to expand...

All the information I have says the timed breather was discontinued from engine number 200000 ('72 model). There doesn't appear to be any timed breather parts shown in the 1972 parts book?
Although I am always interested to hear more information.

Well...
Quess the way to get to the bottom of this is to take the manifolds off. Truthfully, I won't be doing that soon, even to satisfy my curiousity about this. It's about 15 degrees F, minus 10C, out there in the garage, and who wants THAT badly to know if the machine is a Combat or not. Not me, not for a while. The carbs have always been 32s, and I've never noticed any difference in size between the ports and the manifolds...but honestly, who, without really wanting to know, would eye-ball these items and see a difference? Not me, again. Have enough trouble seeing the keyboard here, never mind a difference of 2 mm. The machine may also be non combat, if what is said, is true , due to the barrel color, seem to think mine was a rusty silver and I thought it looked better black, so I painted it...but I'm not sure. Such a long time ago.
If the weather warms up, I will take a look, at the port size, and at the fins on the point where the barrel and head come together......in the mean time, I will just assume it is a standard type motor and let it go at that....Thanks for all the tips and greetings from the land of cold garages......