1972 750 Interstate Resurrection

grandpaul said:

Connecting rods can be reamed and bushed with brass.

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True, and I'm thinking the Triumph Small End bushes might be the close to the right size. Triumph 70.1511:





Keep in mind that a used set of good conrods is often available for way less than machining cost. the last time I had a "machine shop" replace Triumph bushes in Triumph rods, they screwed them up so bad that I bought a used set of rods, two more bushings, the proper reamer and ball and did it myself.

This seller is excellent and most things he says are good are. If you get something from him that is not usable, he gladly refunds fully an doesn't have you send the things back. I've bought from him MANY times. https://ebay.us/m/TL67UA

marshg246 said:

It's possible that the cylinder was installed without a gasket to increase compression - not sure if that could make the cam touch the pushrod tunnel bottoms.

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At your suggestion I assembled the case halves, cam and barrel to check for interference.

At first I put the barrel on with what was remaining of the last gasket used (1978). I did not use any nuts to pull the barrel tight but it seemed to sit down well enough. Nothing hit.

Next I scraped off the old gasket. I salvaged a piece or two and checked the thickness with a dial caliper. Read .0145 for the compressed thickness.




When I assembled the business with no gasket I could not rotate the camshaft due to the intake lobes contacting the barrel as indicated by previous images of the contact markings. The cam rotated freely up to the point where a lobe hit the barrel cam follower bores.

So how I ended up with the barrel Cam follower bores being marked by a rotating cam will seemingly remain a mystery.

I have had this barrel off at least 3 times in the mid to late '70s. Seems like if ever it was assembled without a base gasket there would have been significant damage based on the severity of contact I saw tonight. Perhaps I re-used a base gasket to the point of crushing it too much and there was some level of contact then? I will likely never know for sure what happened.

TJBaker57 said:

At your suggestion I assembled the case halves, cam and barrel to check for interference.

At first I put the barrel on with what was remaining of the last gasket used (1978). I did not use any nuts to pull the barrel tight but it seemed to sit down well enough. Nothing hit.

Next I scraped off the old gasket. I salvaged a piece or two and checked the thickness with a dial caliper. Read .0145 for the compressed thickness.

View attachment 121265View attachment 121264


When I assembled the business with no gasket I could not rotate the camshaft due to the intake lobes contacting the barrel as indicated by previous images of the contact markings. The cam rotated freely up to the point where a lobe hit the barrel cam follower bores.

So how I ended up with the barrel Cam follower bores being marked by a rotating cam will seemingly remain a mystery.

I have had this barrel off at least 3 times in the mid to late '70s. Seems like if ever it was assembled without a base gasket there would have been significant damage based on the severity of contact I saw tonight. Perhaps I re-used a base gasket to the point of crushing it too much and there was some level of contact then? I will likely never know for sure what happened.

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Any chance inn your youth you had the crankcases decked for more compression? Next text, relieve the spots where it's hitting on the tunnels and install without a gasket until not hitting, then put in the tappets and install without a gasket. If still hitting install with one gasket and test. If ok, then you'll probably need to install with two gaskets.

This is very abnormal. It's also possible it has an aftermarket cam, not a 2S. I've never seen a Std, 2S or 4S cam with clearance problems to the cylinders and the camshaft bushing cannot be causing this. I have seen 2S and aftermarket cams interfere with the cases, but not the barrels.

marshg246 said:

This seller is excellent and most things he says are good are. If you get something from him that is not usable, he gladly refunds fully an doesn't have you send the things back. I've bought from him MANY times. https://ebay.us/m/TL67UA

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He sure has a lot of rods!

(and great prices, for the most part)

grandpaul said:

He sure has a lot of rods!

(and great prices, for the most part)

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Ya, he parts out a lot of bikes. fastback_inc does too and he usually has good parts but he is WAY more proud of them and not as forgiving on returns: https://ebay.us/m/wX9WED

marshg246 said:

Any chance inn your youth you had the crankcases decked for more compression?

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Me? No way. I am one of those "stocker" fellows..Would never consider such a thing.

The records I have from the previous owner(s) don't directly suggest that sort of modification either. However, the records I have are of course incomplete. I have receipts showing parts purchased when the superblends were installed but no shops labor ticket for installing same. Only have a work order for the assembly of top end to lower end and miscellaneous related work.

marshg246 said:

Next text, relieve the spots where it's hitting on the tunnels and install without a gasket until not hitting, then put in the tappets and install without a gasket. If still hitting install with one gasket and test. If ok, then you'll probably need to install with two gaskets.

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Relieving the interference has been on the agenda ever since discovering it. I have been leaving it as is in order to fully investigate/document the condition. This evening I am going to try to document the existing dimensions of the barrel/tunnel as best I can before relieving the interference. I would do it sooner but I have to replace a clothes dryer heater element for a friend this afternoon.

I seem to remember seeing in a parts listing somewhere talk of a "spacer" gasket at the base?? Am I remembering this right? Was there ever such a thing?

marshg246 said:

This is very abnormal. It's also possible it has an aftermarket cam, not a 2S.

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Is there a way to determine if this is an original 2S cam? I will recheck this but previously I had measured the max lift of each lobe and saw values of 0.340" and 0.384". I remember seeing two "S" marks and a single "X" marking.

marshg246 said:

I have seen 2S and aftermarket cams interfere with the cases, but not the barrels

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There is some closeness to the cases but no contact. Tightest spot is like 0.020". I think I want to give this a little breathing room and open these spots just a little as well??

TJBaker57 said:

Me? No way. I am one of those "stocker" fellows..Would never consider such a thing.

The records I have from the previous owner(s) don't directly suggest that sort of modification either. However, the records I have are of course incomplete. I have receipts showing parts purchased when the superblends were installed but no shops labor ticket for installing same. Only have a work order for the assembly of top end to lower end and miscellaneous related work.





Relieving the interference has been on the agenda ever since discovering it. I have been leaving it as is in order to fully investigate/document the condition. This evening I am going to try to document the existing dimensions of the barrel/tunnel as best I can before relieving the interference. I would do it sooner but I have to replace a clothes dryer heater element for a friend this afternoon.

I seem to remember seeing in a parts listing somewhere talk of a "spacer" gasket at the base?? Am I remembering this right? Was there ever such a thing?




Is there a way to determine if this is an original 2S cam? I will recheck this but previously I had measured the max lift of each lobe and saw values of 0.340" and 0.384". I remember seeing two "S" marks and a single "X" marking.

View attachment 121269


There is some closeness to the cases but no contact. Tightest spot is like 0.020". I think I want to give this a little breathing room and open these spots just a little as well??

View attachment 121271View attachment 121270

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It's called a "compression plate" https://andover-norton.co.uk/en/shop-details-2/20527/compression-plate-028-750-commando-atlas They are still available and are to reduce the compression ratio. If someone did deck your crankcases, then this would fix it.

Your cam to crankcase clearance is normal - no need for more.

Camshaft measurements - need to use a micrometer, caliper probably not accurate enough. Combat = 2S The numbers are confusing and I don't have them straight in my head. I normally replace them with Hepolite and they come with clear info on the type (Std, 2S, 4S). I've got quite a few used cams that I cannot identify - there were/are many aftermarket. @L.A.B. probably has a document that identifies the markings - maybe he will chime in.

marshg246 said:

there were/are many aftermarket. @L.A.B. probably has a document that identifies the markings - maybe he will chime in.

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I don't think I do so I wil refer you back to Fast Eddie's post #27. However, it says the following on the Norvil website in Tech Talk "How

To Tell If You Have A Combat Engine".
"The camshaft on a combat is stamped with SS, this is called a 2S camshaft and not actually an SS camshaft"

L.A.B. said:

I don't think I do so I wil refer you back to Fast Eddie's post #27. However, it says the following on the Norvil website in Tech Talk "How

Norvil Motorcycles - Tech Talk

To Tell If You Have A Combat Engine".
"The camshaft on a combat is stamped with SS, this is called a 2S camshaft and not actually an SS camshaft"

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Thanks, @Fast Eddie made it clear enough - I was pretty sure an "SS" stamp meant 2S but not sure enough to say so!

The unscrolled camshafts are also supposed to be Combat.



"The top cam shaft does not have oil scrolling on the journals where the bottom cam does have the scrolling. The un-scrolled cams were mainly the SS cams, but some other grinds were also un-scrolled."

Because the Combat bushes were scrolled.

What does a cam with not one marking of any kind mean. Is that common. I measured the lobes and they seem close to stock.

marshg246 said:

need to use a micrometer, caliper probably not accurate enough

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My lifts were measured with my admittedly inexpensive dial indicator while the cam is installed in the cases. I noted the difference between my measurements and the posted graphic are both right about 0.13 mm. (the values I posted were converted from mm (.865 and .977)

Assuming this cam is original it has seen 34000 miles with very likely little maintenance with regard to oil changes etc.

There was a disturbing amount of grey sludge in the oil tank. The engine had no oil filter.

TJBaker57 said:

The engine had no oil filter.

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The spin-on filter was only fitted from serial 208754 so 208482 was too early but still worth fitting the oil filter kit.

marshg246 said:

Next text, relieve the spots where it's hitting on the tunnels and install without a gasket until not hitting, then put in the tappets and install without a gasket

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Got my measurements done after the dryer heater element replacement this afternoon. I wanted to know what was the radius/diameter of the arched bottoms of the tunnels. That and the height of this arch off the base of the barrel.

No particular use for this information excepting comparison with other barrels perhaps.

I then removed material from the offending tunnel bottoms (intakes) and left the others (exhausts) as they were. Leaving the exhausts alone provided a place for me to bridge a straightedge across to eyeball gauge how much material I removed.



Assembled the pertinent items and had a peek with a small LED lamp and a mirror. Not easy to get a good look and even harder to get a decent image. I'll show some representative pics:






Cannot really get any sort of measurement of what clearance I have now but I'm hopeful it is adequate. With no gasket and all surfaces clean the cam now rotates freely.

That said, when it's time to put this engine together with a replacement 2S cam I will again check the clearances in the same fashion. If I need to further adjust the clearance I can go at it again.

Addendum: I noticed there is what looks like a single "S" on the bottom of my barrel. Any significance to this?

I would have those followers refaced.

grandpaul said:

I would have those followers refaced.

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I certainly have concerns with these followers and will consider the options.

Greg and I had a conversation the other day about my intentions with the bike and so on. As greg posted the other day it would probably run with these followers, but I think I'd like to improve the situation in some way at least. I did just get a surface stone and related abrasives for the faces but that won't do anything for the scoring on the sides.

Here's a noob question: I haven't found a clear illustration or comment about which side of these followers faces forward? When paired together one side makes a V groove and the other side does not. I can see by my wear patterns these have been installed both ways but I can't seem to find out which way are they supposed to go. And is the purpose of this V groove to allow excess oil to pass down to the crankcase?

TJBaker57 said:

I certainly have concerns with these followers and will consider the options.

Greg and I had a conversation the other day about my intentions with the bike and so on. As greg posted the other day it would probably run with these followers, but I think I'd like to improve the situation in some way at least. I did just get a surface stone and related abrasives for the faces but that won't do anything for the scoring on the sides.

Here's a noob question: I haven't found a clear illustration or comment about which side of these followers faces forward? When paired together one side makes a V groove and the other side does not. I can see by my wear patterns these have been installed both ways but I can't seem to find out which way are they supposed to go. And is the purpose of this V groove to allow excess oil to pass down to the crankcase?

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Bevels ("V" Groove) towards the front of the bike. This may also help you: https://www.nortonownersclub.org/support/technical-support-commando/tappets

TJBaker57 said:

Greg and I had a conversation the other day about my intentions with the bike and so on. As greg posted the other day it would probably run with these followers, but I think I'd like to improve the situation in some way at least. I did just get a surface stone and related abrasives for the faces but that won't do anything for the scoring on the sides.

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If there is anything higher than the overall surface, carefully get rid of it. If the scratches are inwards, quit thinking about them.

When refacing, I usually start with 800, then 1000, then 1500, then 2000 and then go through the papers I recommended. When finished you'll be able to see yourself clearly in them and you are taking off no ore than .001"-.002". It's critical to keep them flat and use the surface plate. They would probably be fine after the 2000 but I go the extra mile - does not take long.

marshg246 said:

Bevels ("V" Groove) towards the front of the bike. This may also help you: https://www.nortonownersclub.org/support/technical-support-commando/tappets

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This is very helpful and reassuring to see a clearance mentioned. I'm on the loose side but within that range.

marshg246 said:

If there is anything higher than the overall surface, carefully get rid of it. If the scratches are inwards, quit thinking about them.

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Makes sense.

marshg246 said:

When refacing, I usually start with 800, then 1000, then 1500, then 2000 and then go through the papers I recommended

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I bought the surface stone and papers you linked to previously. Working on the tappet faces is exactly the sort of slow tedious project I need to keep me busy while I occasionally fiddle with other items.


Just now I got the gearbox shifter loose. It would not move previously. When I found it locked up, the shafts rotated fine, just the shifter was locked up. I put ATF in there and let that soak for a month or so. Most leaked out of these old shaft seals of course. Today it still wouldn't budge. I put a wrench on the shift cam retaining bolt head and very carefully applied a little force this way and that and it began to move. So a lot of back and forth action and it attains all gears now. Naturally the whole thing needs to come apart for inspection and whatever but it is nice to see it move again.

I had already removed the gearbox outer cover when trying to get the shifting mechanism loosed. So after freeing the shifting mechanism I went after the inner cover.

Decades ago I previously had the outer cover off for some reason or another but I have never gone deeper in the gearbox. Not too much trouble getting that off there now that my Ko-Ken Whitworth sockets arrived. Those a big set of pliers..




In washing the sludge out of the innards before I try to get them out I found this little bit... hmmm..