1972 750 Interstate Resurrection

Hammerski said:

I’ve been in a similar situation with the tariffs recently. Another option is to order from gregmarsh.com. He’s got a solid selection and very good prices. In most cases I’ve found his Andover parts to be cheaper than the same thing from the UK once shipping is factored in.

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That is good information right there. Will surely contact gregmarsh.com as soon as I get an idea of what I definitely need to buy.

On that note I am realizing I am in over my head presently. I currently cannot look at a part and say "oh yes, that's got to be replaced".

There are any number of parts I look at and think "that looks bad", but is it really? First example: I look at your camshaft pictures and then look at my camshaft. I lack the experience of seeing many good and bad examples.

And what of the followers? Again I see wear but is this a normal happening? Can they be 'cleaned up' by machine shop or are they simply too far gone?

The bike has 34000 miles on it. Maybe much of what I am seeing is to be expected at that mileage.





And the followers which came to me in 2 ziplock bags, drive side and timing side..So I don't know which was where but wear patterns seem to show they have been rotated about at some point in their lives. And one of them has an inexplicable pattern on it. 1st image towards the top of the image.




One more camshaft related puzzlement: I found marks on the cylinder(s) that seem to show two lobes of the camshaft made some contact with the cylinder barrel(s)??



Could this indicate worn camshaft bearings? I cannot fathom how this happened.

Bad oil or not enough oil flow.

Looks like the lifters were swapped left cylinder to right cylinder, and the barrels were not prepared correctly for an SS cam, which has more lift than a stock cam.

You can clean the lifters up by hand making them flat again with 600 grit wet/dry sandpaper on a flat surface and then finish them up with some 1000 grit. Well, I could anyway, and if I can do it anybody can. It does take a long time though.

ClassicBritishSpares in California resurfaces stock flat lifters at a reasonable price considering how long it takes to do it with sand paper.

Edit:
You can grind the bottom of the lifter bores where the cam is banging on it to get clearance. If this is a Combat engine I'm very surprised it left the factory like that. If someone (I used a different term initially there) put a SS cam in the engine without doing any prep work for the SS cam there could be other issues in the cases and the engine probably wasn't working all that well without higher compression. SS cam responds well with more than 9:1 compression.

As far as reusing the cam. It can be done if the surfaces are cleaned up, but I'd have to touch your cam to see how bad it really is. Pictures of the cam aren't that pretty, but close up digital photography makes everything that is not perfect look bad. If money is not an issue put a new cam in it. People here rave about the stock cams. I personally don't understand that, but they out number me.

kommando said:

Bad oil or not enough oil flow.

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I have to check something tomorrow. I was reading in the USNOA Tech Digest Version 2, (page 9) where they review changes over the years for cams & bushings. Clearly the cam here is non grooved. I haven't got good pictures yet of the bushes cleaned up. Maybe those are grooves there?

Schwany said:

the barrels were not prepared correctly for an SS cam, which has more lift than a stock cam.

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I am as certain as I can be that this is the original cam and barrels.

Schwany said:

You can clean the lifters up by hand making them flat again with 600 grit wet/dry sandpaper on a flat surface and then finish them up with some 1000 grit. Well, I could anyway, and if I can do it anybody can. It does take a long time though.

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I do the same treatment for lots of things. I keep 180, 320, 600, 1000, 2000 grit wet or dry on hand. I have a small piece of quarter inch glass mirror that I use for the flat surface. (WWII emergency signal mirror!) Just not experienced with such things as these lifters here.

Schwany said:

If this is a Combat engine I'm very surprised it left the factory like that. If someone (I used a different term initially there) put a SS cam in the engine without doing any prep work for the SS cam there could be other issues in the cases and the engine probably wasn't working all that well without higher compression. SS cam responds well with more than 9:1 compression.

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I will go out on a limb here and say this is as delivered from the factory. And it is a Combat engine. Early in it's life it did have the lower end opened up and some work done there. Main bearings and such. I think I have some paperwork on that from an early owner. It may even have been a Norton dealer who did that work. But I don't know why they were in there to start with. Serial Number (208482) is after the start of the superblend bearings according to what I have read so that shouldn't have been the reason.

Schwany said:

As far as reusing the cam. It can be done if the surfaces are cleaned up, but I'd have to touch your cam to see how bad it really is. Pictures of the cam aren't that pretty, but close up digital photography makes everything that is not perfect look bad

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I will be taking the frame to the machine shop/welder soon so I can also have them put me on the schedule to check several items such as the cam and crank and so on.

Schwany said:

If someone (I used a different term initially there) p

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It may be time for me to come clean here. Full disclosure and all that....

In my first post here I stated that "some idiot" took this bike apart like 40 years ago. Some may think that was a bit harsh. However, I believe I am uniquely qualified, and perhaps even justified in calling this fellow an idiot. You see, I have known him all my life. In fact, I see him every day,,, whenever I look in a mirror!!

Those are grooved bushes, even if they are worn they do not cause the cam and cam follower wear. The oil for lubrication of cam followers comes from the head and drained down the pushrod tunnels. You want a good oil with high ZDDP levels to protect the cam and cam followers.


and fit an oil filter in the return feed pipe if its not currently there, the factory did get round to fit one so just buy the parts. You may need to drill 2 holes in the cradle for the filter housing retention bolts.

The cam is starting to wear and either needs replacing or sending to someone like Webcam who can build it up and re-profile it.

Similar with the lifters, but all they need is a re-grind. Webcam will do that too if you wish.

Norton managed to make their cam designations a tad confusing. Dyno Dave did some excellent work plotting Norton cams. He wrote:

“650SS and later 750 Atlas grind with common X2 marking on the twin chain core, known as SS”

“The famous or "infamous" 2S combat cam. Note, this is MARKED "SS" on the camshaft, but it is not the 650SS grind”.
So, as your cam is marked SS, it is indeed the 2S / Combat cam.

Good spot ref the lifters fouling the block! I wonder if the barrel was changed at some point? Maybe someone fitted an even wilder cam at some point? Or the crankcase to barrel face machined? Mock it up by putting the barrel and cam into one case have, turning the cam and looking to see how close it gets. It’s easy enough to remove metal from that area of the barrel if required.

Now you gotta decide if you wanna rebuild it as a Combat or castrate the poor beast by building it to ‘standard’. Personally, I say let him keep his gonads intact and keep it in Combat spec !!

There are some suggested mods to the oil scavenge set up for these motors that would be worth researching.



Link to Web Camshafts:


Link to Dyno Dave’s cam info, worth printing out for posterity:

TJBaker57 said:

Serial Number (208482) is after the start of the superblend bearings according to what I have read so that shouldn't have been the reason.

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Where did you read that (ok it's in the INOA tech digest*) as it's incorrect according to the factory service release N2/9. Superblend bearings (the R&M 6/MRJA30 type) were fitted from serial 211891. The original roller bearings should have been MRJA30. If they're 6/MRJA30 (the 6 is etched on) or the later FAG NJ306E bearings then they're not the originals.

*207197 which I think you are referring to relates to the nominal increase in bearing housing diameter (service release N2/6 July 1972) so that number in the tech digest section 7 should be crossed out/amended in my opinion also what it says in section 1 is incorrect as the Superblend bearings were only introduced after the Combat series had ended (at 211110).

TJBaker57 said:

That is good information right there. Will surely contact gregmarsh.com as soon as I get an idea of what I definitely need to buy.

On that note I am realizing I am in over my head presently. I currently cannot look at a part and say "oh yes, that's got to be replaced".

There are any number of parts I look at and think "that looks bad", but is it really? First example: I look at your camshaft pictures and then look at my camshaft. I lack the experience of seeing many good and bad examples.

And what of the followers? Again I see wear but is this a normal happening? Can they be 'cleaned up' by machine shop or are they simply too far gone?

The bike has 34000 miles on it. Maybe much of what I am seeing is to be expected at that mileage.




And the followers which came to me in 2 ziplock bags, drive side and timing side..So I don't know which was where but wear patterns seem to show they have been rotated about at some point in their lives. And one of them has an inexplicable pattern on it. 1st image towards the top of the image.

One more camshaft related puzzlement: I found marks on the cylinder(s) that seem to show two lobes of the camshaft made some contact with the cylinder barrel(s)??

Could this indicate worn camshaft bearings? I cannot fathom how this happened.

Click to expand...

Clean and oil the tappets and pushrod tunnels. Put the tappets back in including the separators and see how well the tappets move. If not smooth or you can feel rocking, then you need to determine if it is the cylinders, tappets or both. If smooth without rocking, then you only need to surface them.

With care and a small surface plate, you can surface them yourself.

A new set of tappets is very expensive - cost a lot more than a cam.

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.

These days, I almost always change the timing side cam bushing and I use the MK3 type (06.5428). A pair of them eliminates the problem inner thrust bushing and adds much better outer thrust surface than the edge of the bushing - yours is gone. They also provide better oiling.

Fast Eddie said:

Mock it up by putting the barrel and cam into one case have, turning the cam and looking to see how close it gets.

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Too close! Actually in contact. I fitted up the drive side and barrel with what remains of the paper gasket that was there. With the worn out bushings the cam wobbles a good bit with only the drive side engaged.

Fast Eddie said:

Now you gotta decide if you wanna rebuild it as a Combat or castrate the poor beast by building it to ‘standard’.

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I would prefer to keep it as I remember it.

As for what it was to begin with that's looking harder to say with certainty. Registration info says it was first sold in March 1973 and I know of 2 owners before I bought it in November of 1975.

Just a couple months before I bought it the crank main bearings were replaced along with some other things like a camshaft bushing and thrust washer!

L.A.B. said:

If they're 6/MRJA30 (the 6 is etched on) or the later FAG NJ306E bearings then they're not the originals.

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I knew they had been replaced I just didn't know why. It currently has the FAG bearings.

Debating replacing those. They have like 28000 miles or more on them I think.

marshg246 said:

Clean and oil the tappets and pushrod tunnels. Put the tappets back in including the separators and see how well the tappets move. If not smooth or you can feel rocking, then you need to determine if it is the cylinders, tappets or both. If smooth without rocking, then you only need to surface them.

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Not sure how tight they should feel. There is movement laterally for sure. Is there a specification for the bore the tappets ride in and/or the tappets themselves?

If I check lateral movement when dry without the keepers in I see as much as 0.14 mm movement.



If the cylinders are worn too much is there a resolution other than repacement cylinders?


The keepers themselves are worn also. In the neighborhood of 0.003 in (I can't seem to stick to one unit of measurement)

marshg246 said:

A new set of tappets is very expensive - cost a lot more than a cam.

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I am quickly becoming aware this project will be costly.

TJBaker57 said:

Not sure how tight they should feel. There is movement laterally for sure. Is there a specification for the bore the tappets ride in and/or the tappets themselves?

If I check lateral movement when dry without the keepers in I see as much as 0.14 mm movement.

View attachment 121205

If the cylinders are worn too much is there a resolution other than repacement cylinders?


The keepers themselves are worn also. In the neighborhood of 0.003 in (I can't seem to stick to one unit of measurement)

I am quickly becoming aware this project will be costly.

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I'm not sure your first picture is a valid test. Try the same thing with them in upside down. I don't know of a specification on the tappets and tappets bore, but they are not a tight fit. Also, I would worry much more fore and aft than side to side.

Also, the keepers are inexpensive so I would change them - most likely there is little wear on the tappets where the keepers ride.

Provided the tappets, and bores, are not visually worn and / or scored, they should be fine.

TJBaker57 said:

With the worn out bushings the cam wobbles a good bit with only the drive side engaged.

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With the cam in only one bush it will wobble at the far end as the bush needs clearance and the length of the camshaft amplifies this at the outboard end. Factory spec is 1.5 thou clearance but running spec would be nearer 3 thou between bush and cam journal.

Fast Eddie said:

Provided the tappets, and bores, are not visually worn and / or scored, they should be fine.

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Well thats the concern . They are visually worn/scored to my eye at least. I can catch a fingernal in several of these scores.

marshg246 said:

I would worry much more fore and aft than side to side.

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With the tappets protruding just enough to get a dial gauge on I read as much as 7.5 thousandths free play in the fore/aft direction with or without oil. With oil it just takes a little longer to drift up to the same reading.

kommando said:

With the cam in only one bush it will wobble at the far end as the bush needs clearance and the length of the camshaft amplifies this at the outboard end. Factory spec is 1.5 thou clearance but running spec would be nearer 3 thou between bush and cam journal.

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It's not so much a question of whether or not these bushings are bad. It's more a question of how bad are they. That may be a useful indicator of how bad the rest of the motor is??

I was seeking to learn how much wobble should exist at the far end based on clearances at the captive end. Using your given specs of .003" and a measured bushing width of about 0.865" I calculated the free end should move about 0.0225".

I measured free end movement of about 0.048" in the horizontal and about 0.075" in the vertical.


I also directly measured (using a digital caliper) the camshaft journals and as well as I could the bushings. In this I found roughly 0.006" difference in the (mostly) horizontal orientation. That seems to correlate with the free play wobble measured in the horizontal. I could not get access to the bushings in the vertical orientation using the caliper.


I noticed the manual I have does not deal with replacing these bushings stating they have an extrememly long life (??) and replacement requires extensive machinery or something to that effect.

marshg246 said:

With care and a small surface plate, you can surface them yourself.
https://a.co/d/21Sllto https://a.co/d/3g3N3td

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Have these on order, even if my tappers are shot these items seem good to have around.

Are these connecting rods toast?

Connecting rods can be reamed and bushed with brass.

marshg246 said:

Try the same thing with them in upside down. I don't know of a specification on the tappets and tappets bore, but they are not a tight fit. Also, I would worry much more fore and aft than side to side.

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Does this qualify as "rocking"? Turn audio up to hear the sounds.

TJBaker57 said:

Does this qualify as "rocking"? Turn audio up to hear the sounds.

New video · Thursday, Aug 14 🎬

Tap to view!

photos.app.goo.gl

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Will it run - I think so. Are they looser than I'm used to? Yes