1972 750 Interstate Resurrection

T

TJBaker57

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First time poster here. A couple of weeks ago I got hold of a basket case. A 1972 Intertstate Commando with the Combat engine option. Almost entirely disassembled. Only the gearbox remains assembled.

40 years ago some idiot took this thing apart. 10 or so years later it was given to an auto mechanic / motorcycle enthusiast. It was stored untouched for like 20 years until he passed away. At that time his stepson took possesion. He had it for another 10 years or more. No real progress was ever made towards getting this thing together.

I knew the stepson through a friend. So I drove a couple days to load up all that he had and a couple days drive back home. I like to travel anyway.

I have been unloading, taking inventory of what is here, cleaning some stuff, maybe fitting together a thing or two just to see how it goes together and just generally assessing the present state of things.

Have already noticed some missing stuff, mainly small items and hardware. But the major components seem to be here.

Looks like everything will need a full going over. I wouldn't say I am looking at this as a "restoration" but more like a resurrection. Not destined for a showpiece.

I'm retired so I have the time and I also have a good workspace.

The frame has had some work done at the upper rear shock mounts. In checking dimensions against a workshop manual it appears the rear u-shaped loop still is a bit lower than it should be. Maybe a half inch at the rearmost point.

The literature I have has an error in the frame dimensions. I just now searched this site for frame dimension talk to see if an error I see in the service literature is well known or not. I found no confirmation of this error. It drove me batty for quite a good amount of time before I saw the error.

The manual uses two holes in the middle of the frame as a horzontal basis to make other vertical measurements from. The two holes they use are a bit too close for my liking as far as a reference so I set about calculating a vertical distance between the two isolastic mount holes based on the data they do provide.

Since they have a horizontal measurent between the two isolastic mount holes and the straight line distance between the two a little basic geometry should give me that vertical distance between the two isolastic mount holes.

Once I had my distance I set about checking things but my calculated distance was quite a bit different than what I was seeing on the frame.

After battling this for some time I eventually saw that the stated 452.12 mm is wrong. The 17.075 inches is correct. Looks like the conversion to millimeters was incorrect? When I redid my calculations for the vertical separation of the two isolastic mount holes using 433.705mm (17.075 x 25.4) everything checked out, except of course for the aforementioned tail droop.
 
Welcome, you have your work cut out for you there. There's a lot to know. The first time I rebuilt my commando, there was no internet or forums to do research. Luckily, I had a friend was a pro mechanic so he guided me on some decisions, but looking backward I just got lucky too. IMO, go from the center point outward, meaning inspect and renew the crank journals and rods, empty the sludge traps in the crankshaft. Inspect the camshaft and cam followers for polished even wear marks and replace or repair. Inspect the crankcase, bearings and bushings. Once you have all that renewed you have the deepest part of your engine taken care of. As you go along, make sure you inspect the oil pump because that protects your engine guts. Best of luck to you. People will respond usually the same day if you ask questions here.
 
TJBaker57 said:
First time poster here. A couple of weeks ago I got hold of a basket case. A 1972 Intertstate Commando with the Combat engine option. Almost entirely disassembled. Only the gearbox remains assembled.

40 years ago some idiot took this thing apart. 10 or so years later it was given to an auto mechanic / motorcycle enthusiast. It was stored untouched for like 20 years until he passed away. At that time his stepson took possesion. He had it for another 10 years or more. No real progress was ever made towards getting this thing together.

I knew the stepson through a friend. So I drove a couple days to load up all that he had and a couple days drive back home. I like to travel anyway.

I have been unloading, taking inventory of what is here, cleaning some stuff, maybe fitting together a thing or two just to see how it goes together and just generally assessing the present state of things.

Have already noticed some missing stuff, mainly small items and hardware. But the major components seem to be here.

Looks like everything will need a full going over. I wouldn't say I am looking at this as a "restoration" but more like a resurrection. Not destined for a showpiece.

I'm retired so I have the time and I also have a good workspace.

The frame has had some work done at the upper rear shock mounts. In checking dimensions against a workshop manual it appears the rear u-shaped loop still is a bit lower than it should be. Maybe a half inch at the rearmost point.

The literature I have has an error in the frame dimensions. I just now searched this site for frame dimension talk to see if an error I see in the service literature is well known or not. I found no confirmation of this error. It drove me batty for quite a good amount of time before I saw the error.

The manual uses two holes in the middle of the frame as a horzontal basis to make other vertical measurements from. The two holes they use are a bit too close for my liking as far as a reference so I set about calculating a vertical distance between the two isolastic mount holes based on the data they do provide.

Since they have a horizontal measurent between the two isolastic mount holes and the straight line distance between the two a little basic geometry should give me that vertical distance between the two isolastic mount holes.

Once I had my distance I set about checking things but my calculated distance was quite a bit different than what I was seeing on the frame.

After battling this for some time I eventually saw that the stated 452.12 mm is wrong. The 17.075 inches is correct. Looks like the conversion to millimeters was incorrect? When I redid my calculations for the vertical separation of the two isolastic mount holes using 433.705mm (17.075 x 25.4) everything checked out, except of course for the aforementioned tail droop.
Click to expand...
Tail loop "frame droop" is very common, simply tweak it back up! Perhaps a well-fed pillion, or overloaded camping gear is all it takes. Welding in a support triangle helps, they're available pre-fabbed.
 
grandpaul said:
Tail loop "frame droop" is very common, simply tweak it back up! Perhaps a well-fed pillion, or overloaded camping gear is all it takes. Welding in a support triangle helps, they're available pre-fabbed.
Click to expand...

This one already has an added reinforcement. Not store bought for sure. 1/8" triangular plates slapped on the outsides. And something added inside the tubing. I inverted the frame, secured the tail loop to an elevated sturdy flat surface for support so the entire frame was inverted, supported by the tail loop and elevated so I could push down at the steering head. No dice. That sucker ain't movin' !!

Since the existing repair looks like hell I have concluded the best approach is to remove the previous 'repair' and have it reworked/welded professionally. Called my local Airgas welding supply and asked who is the go-to-guy for such work around here and they did not hesitate to name a local machine shop/welder.

This is not destined to be a showpiece so I will forego purchasing a new loop and will use the existing loop.

I talked to the shop and will bring it over early next week so he can see it before I grind off all the previous crap. I want to do as much of the job as I can personally so I will do the removal of the existing junk.

Here is a question or two about frame dimension tolerances:

I have a strong background in sheet metal layout and fabrication. About 40 years in HVAC with maybe 20 years in field measurement, layout, and fabrication. Had a 5' x 10' plasma cutting table and drew up blanks in CAD softwares.

I read somewhere here the other day where someone suggested that even new these frames may not have been spot-on with the published dimensions?

I find my tail droop to be in the neighborhood of say 7 millimeters maximum. Part of this is due to a very slight bend in the rear downtubes where the added 1/8" plates end. This is about 4.5 inches down from the tail loop. I suspect this happened after the plates were added and excessive weight was likely carried by the tail loop with a luggage rack or the like. Downward force at the rear of the tail loop was transferred by these 1/8" plates to produce a forward force at the rear down tubes. Thats my working theory at least.

One other variance with dimensions is the vertical distance between the rear isolastic mount hole and the forward isolastic mount hole. I come up with about a 2 millimeter discrepancy, my forward hole being ever so slightly lower than calculations would indicate it should be.

Given that the horizontal reference line holes are only like 4" apart and are different sizes this makes establishing the horizontal reference line a bit of a PITA.....

So my feeling is this small discrepancy in the forward Isolastic mount hole is likely OK and some of it may be due to minute errors in establishing the reference line.

With this in mind how accurate should the tail loop elevation be? Would we want to favor any variance towards the upward side vs the droop side?
 
Welcome to the best Norton forum on the planet! 😁

It’s generally accepted that the rear loop should be parallel to the lower frame rails.

Here are the dimensions of the 750 frame.


You will find the search function is invaluable when researching. For example I searched “Frame dimensions” and found the image above.

Please post Lots of pics. ( as a VIP member you can just copy & paste).

Good luck 👍
 
cliffa said:
Welcome to the best Norton forum on the planet! 😁

It’s generally accepted that the rear loop should be parallel to the lower frame rails.

Here are the dimensions of the 750 frame.


You will find the search function is invaluable when researching. For example I searched “Frame dimensions” and found the image above.

Please post Lots of pics. ( as a VIP member you can just copy & paste).

Good luck 👍
Click to expand...


Thanks for the replies folks!


I do have what I believe is the 'factory' workshop manual and one other publication, "USNOA Tech Digest Version Two". Both of them show the same frame dimension error I mentioned earlier BTW. 452.12 mm is not the metric equivalent of 17.075 inches.

My question should have been phrased differently. I meant to ask more about tolerances rather than the actual dimensions. More like "how far off is too far off?" If a rear frame loop was 3 mm low is that worth chasing? 8mm low? 20 mm low?

As it turns out as I got into removing the old repair it got ugly in there as I ground down old welds. I uncovered a handful of cracks in the area above the upper rear shock mounts. Solid rod had been welded into the loop and slid up into the main frame members but those stubs didn't get far enough in. Plus the old repair welds did not get proper penetration.

At any rate I have ordered a new rear frame loop and the associated plates from Andover Norton.


As for pictures I am one of those that take an absurd quantity of pictures. It helps jog my memory of what I have done or how something goes together as I take it apart.


Here is a shot as I was checking frame dimensions with various instruments. A crossline laser is seen centered on the rear Isolastic mount hole.


1972 750 Interstate Resurrection
 
TJBaker57 said:
Thanks for the replies folks!


I do have what I believe is the 'factory' workshop manual and one other publication, "USNOA Tech Digest Version Two". Both of them show the same frame dimension error I mentioned earlier BTW. 452.12 mm is not the metric equivalent of 17.075 inches.

My question should have been phrased differently. I meant to ask more about tolerances rather than the actual dimensions. More like "how far off is too far off?" If a rear frame loop was 3 mm low is that worth chasing? 8mm low? 20 mm low?

As it turns out as I got into removing the old repair it got ugly in there as I ground down old welds. I uncovered a handful of cracks in the area above the upper rear shock mounts. Solid rod had been welded into the loop and slid up into the main frame members but those stubs didn't get far enough in. Plus the old repair welds did not get proper penetration.

At any rate I have ordered a new rear frame loop and the associated plates from Andover Norton.


As for pictures I am one of those that take an absurd quantity of pictures. It helps jog my memory of what I have done or how something goes together as I take it apart.


Here is a shot as I was checking frame dimensions with various instruments. A crossline laser is seen centered on the rear Isolastic mount hole.


View attachment 120932
Click to expand...
Nice setup!

"a whiff of overkill"
 
have you checked whether the steering head is pointing straight ahead ( not to one side) relative to the pair of ISO mounting points?
I checked two frames recently, and both were out of true. Also, the ISO points were nearly all out of position relative to the other side of the bike, and spacing between front and rear also out.
My theory is that bikes had been dropped heavily on their sides, and lower parts of frames knocked sideways relative to top spine tubes.
 
TJBaker57 said:
In 5th grade of elementary school a teacher watched as I was doing something with a compass or maybe protractor?

She said to me " Whatever you do in life, you are going to do it with precision."
Click to expand...
Now THAT is cool.

Inspiration goes a long way...
 
jan nelder said:
have you checked whether the steering head is pointing straight ahead ( not to one side) relative to the pair of ISO mounting points?
Click to expand...


Spent much of the day checking that out. All looks good there.

Here is a rear tires view of a laser line passing through the centerline from the rear. Stuck a 3 foot or so long piece of tubing through the steering head bearings and marked centers of the IsoLastics on rods with bits of white tape. Zoomed in a bit the center marks show.

1972 750 Interstate Resurrection


hmmm, well that went sideways!!

I also shot the laser from above and from the front plus above and from behind the frame. Extended my steering head reference tubing above and below.

I'm satisfied that I only need to deal with the tail loop issue.
 
I'm sure you will but check your swinging arm. Often twisted so the wheel is not vertical wrt frame and front forks. Also check the top shock mounts on the frame are directly above the mounts on the swinging arm when fully assembled.

Interesting pickup on the inch to mm conversion. I'm going to check my manual when I get home.

I'm impressed by your careful work. I owned my bike almost 50 years and it always pulled left and tried tankslappers at around 90 mph. 7 years ago I stripped it and had a very good local guy go over it just as you have done. He found a twisted swinging arm and also a misaligned rear sprocket and gearbox sprocket. Even with all spacers correct. I never did totally solve the misalignment but made new spacers to get it correct. Bike tracks perfectly now.

So I think you are definitely doing the right thing if you want a nicely handling bike.
 
Last edited:
johnm said:
I'm sure you will but check your swinging arm.
Click to expand...

That's a whole 'nother issue! It was fairly well frozen in place when I got it about a month ago. I soaked the thing inside and out with PB Blaster for several days then screwed a 2x4 to it, parked a vehicle on the 2x4 so I could then see about getting it moving!!

Of course the whole thing will need to be overhauled but just getting it moving should help with getting the business apart, I hope.

1972 750 Interstate Resurrection
1972 750 Interstate Resurrection
 
TJBaker57 said:
That's a whole 'nother issue! It was fairly well frozen in place when I got it about a month ago. I soaked the thing inside and out with PB Blaster for several days then screwed a 2x4 to it, parked a vehicle on the 2x4 so I could then see about getting it moving!!

Of course the whole thing will need to be overhauled but just getting it moving should help with getting the business apart, I hope.

View attachment 120979View attachment 120980
Click to expand...
Just edited my post.

Your definitely on the right track. 👍👍

Oh and by the way check the rear axle very carefully. They can snap at the run out of the thread into the stub axle. I and many others replace them with a one piece axle. Available from Don Pender in the Philippines
 
Last edited:
Still fiddling about with the frame. I have taken it about as far as I can so it will be off to the welder soonish.

Looks like I should place an order for a bunch of things that will be needed eventually. I was going to order as I went along but the email I got today from Andover Norton regarding tarriffs makes me think I should order now to beat the phase out of the de minimus exception.
 
TJBaker57 said:
Still fiddling about with the frame. I have taken it about as far as I can so it will be off to the welder soonish.

Looks like I should place an order for a bunch of things that will be needed eventually. I was going to order as I went along but the email I got today from Andover Norton regarding tarriffs makes me think I should order now to beat the phase out of the de minimus exception.
Click to expand...
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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