1972 750 Interstate Resurrection

[marshg246]

50 years after I first encountered the following issue, but I finally figured out the cause!

Every time I had to install the cylinder barrel it was a struggle. The thing wouldn't align right so that it would simply lower into place. Always had to rock it this way and that and even after getting it down it never seated fully. The timing side rear always sat high.

So this afternoon I took a real close look at this. Set it in place with no studs present and measured the gaps with feeler gauge. Only the forward drive side made good contact. The timing side rear stud location had 11 thousandths gap!

View attachment 122148


The question was what the hell was holding it up? No portion of the flange other than the forward drive side made contact at all. I could push down on the high side and it would sort of rock, the timing side went down and the drive side lifted.

Took the cases apart (there's nothing in them right now) and had a look setting them separately on the inverted barrel one at a time.

The timing side was first and by itself it sat down nicely. Little to no gaps.

The drive side however, even by itself resisted. Had to rock it around a bit to get it down. I noticed there was no play at all between a point over the cam location and the rear left of the cylinder bore skirt. The case half still rocked a little around these points, apparently it was enough of a bind to prevent the case half from dropping flat to the barrel.

There's scratch marks inside the case half where the skirt has been draging during installation.

Similarly the forward point also had scratch marks from contact with the cam follower bore skirt.

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I dressed up that front location some and now the barrel lowers on nicely onto the assembled cases and sits down flat without a struggle. Will need to recheck this with studs in place of course.

Look at the bottom rear of the cases. Each side should have an identical 3-digit number. If at some time in the past someone replaced one side of the crankcases it may be your whole problem.

A new/different set of cases might be a better solution but then you lose the matching numbers. I do have a new set of cases in a bike I'm parting out and they have no serial - I'm assuming they are 06-4045 from AN. I also have a complete engine Combat engine I'm going to part out.

 

[MichaelB]

Good point Greg. To further clarify, the OG case are machined in pairs and then stamped on each
with matching 3 digit numbers.

 

[grandpaul]

Well this doesn't look good at all. I was cleaning up my cases a bit before taking them to cNw for cam bushings and a cleaning service. Then I discovered this.... timing side by the tach drive.

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Saw this post that sounds like it was the same place??

Post in thread '750 cylinder head measurement ie standard/skimmed'

Apr 14, 2023

Front crankcase stud, over the cam on the timing side. The whole piece has been welded, not a bad job but when you heat the case on the inside, it bubbles from under the weld. Cleaned it up & you can see a crack in the case. It also has a weld repair to the bottom of the case. Might be alright on the road but then again.
Just got the rear hub back (Triumph conical) from the welder. He's built up the sprocket mounts. It looks awful lol. Off to dress them back & try & get the sprocket mounting faces level.
Frames being coated this weekend. Telsport is making a new stem for the bottom...

• Fast Eddie

Given that I doubt I will put more than a couple thousand miles on this in my remaining lifetime after I get it back together I am hopeful there is someone who can weld this.

BAH!

Squirt half a tube of red RTV silicone in it, use the cheapest you can find, like Harbor Freight.

Squirt the other half in various oily places like the rocker covers, no need to trim up the mess!

 

[TJBaker57]

Look at the bottom rear of the cases. Each side should have an identical 3-digit number. If at some time in the past someone replaced one side of the crankcases it may be your whole problem.

I think we covered this before ?? Maybe over the phone,,, but yes, they are matching numbers. Noticed a little "x" on each case half yesterday also down there nearby.

new/different set of cases might be a better solution but then you lose the matching numbers. I do have a new set of cases in a bike I'm parting out and they have no serial - I'm assuming they are 06-4045 from AN. I also have a complete engine Combat engine I'm going to part out.

I want to keep all original as I can. If it wasn't "this" bike I would have no interest in motorcycles at this stage of my life. These things are just little bumps in the road of getting it back together and running.

Edit: And when the drive side case half didn't seat fully to the barrel by itself that cannot be the fault of mismatched cases as the timing side isn't even there then !!

 

[marshg246]

I think we covered this before ?? Maybe over the phone,,, but yes, they are matching numbers. Noticed a little "x" on each case half yesterday also down there nearby.





I want to keep all original as I can. If it wasn't "this" bike I would have no interest in motorcycles at this stage of my life. These things are just little bumps in the road of getting it back together and running.

Edit: And when the drive side case half didn't seat fully to the barrel by itself that cannot be the fault of mismatched cases as the timing side isn't even there then !!

Fair!

Slightly lost - are the stud holes in the wrong place(s) or is crankcase/barrel interference the problem (or something else). You keep having different interference problems and I keep focusing on how that can be and probably missing the fine details of what you say.

I assume two things:

1) The two crankcase dowels are in place
2) You are being sure to knock the cases into perfect alignment. The dowels are supposed to do that, but often the two case halves have a slight misalignment and a small bang on the high one is needed to get the tops of the crankcases in perfect alignment front and back.

The barrel to crankcase studs should be very close to precise for the barrels to drop on correctly. The cylinder head studs and barrel studs must all be precise for them to mate correctly. Anything that is crooked or doesn't mate correctly is likely to break/crack something.

 

[TJBaker57]

Fair!

Slightly lost - are the stud holes in the wrong place(s) or is crankcase/barrel interference the problem (or something else). You keep having different interference problems and I keep focusing on how that can be and probably missing the fine details of what you say.

I assume two things:

1) The two crankcase dowels are in place
2) You are being sure to knock the cases into perfect alignment. The dowels are supposed to do that, but often the two case halves have a slight misalignment and a small bang on the high one is needed to get the tops of the crankcases in perfect alignment front and back.

The barrel to crankcase studs should be very close to precise for the barrels to drop on correctly. The cylinder head studs and barrel studs must all be precise for them to mate correctly. Anything that is crooked or doesn't mate correctly is likely to break/crack something.

Agreed, I keep coming up with these off-the-wall, never before seen anomalies !! I actually kind of like the challenge of figuring out these puzzles.

It doesn't help when I get mixed up with drive side vs timing side when posting here. The write-up I posted last night was done from the house while the items are in the shop. I swapped drive and timing sides in the write-up which I must now edit. It is the timing side case half that was the problem, not the drive side.

Anyway, this particular thing has been diagnosed and resolved. The write up was just for documentation' sake.

For the test fitting I did yesterday there were NO STUDS in place. I sought to eliminate them from the equation when looking for the trouble.

In the image below, the distance between the two circled points was greater on the barrel than the same points on the case half. An interference fit if you will. The case half pinched on the barrels' cam follower tunnel skirt and piston cylinder bore skirt with enough force to prevent the case half from getting flush to the deck without using studs & nuts to pull it down. Or vice versa pulling the cylinder barrel down to the case deck.

There was a small raised area on that case half that pressed hard against the cam follower tunnel bore skirt, drawing the case half in to press tightly against the pistons cylinder bore skirt. Zoomed in you can see the single point of case to barrel contact at the cam follower bore skirt. A close up of that raised area is the last image in the write-up posted previously.

I relieved the interference at the small raised area of the case half.

All fits together now with relative ease, even with the studs in place (excepting the front center stud for which I have no stud since doing the Time-Sert there).

 

[TJBaker57]

Does this logo look familiar to anyone?

Not important, just curious.

 

[Saber]

Is it on the barrels?

 

[TJBaker57]

Is it on the barrels?

Not on barrels.

This is on a camshaft bushing sold at a Norton dealer in 1975. Listed on the receipt as a 06-2600.

Just curious who the logo belongs to.

These are the bushings in my cases.

 

[TJBaker57]

Another insignia, this on a pair of 06-2601.

 

[CanukNortonNut]

If you are going to reuse these cam bushing washers, I would break off those tabs where you see the cracking as these were notorious for breaking off in the engine and getting sucked up in the oil pump and locking it up, and shortly there after grenade the engine with a con rod blowing out of the casing from a locked up oil pump. Or better yet use the later style on the 850's. Or the earlier type before 72 models. They are basically the same. Camshaft thrust washer needs the bevel to face the tachometer worm gear.
does your camshaft have scrolls on the bearing races where the bushing would be in the case halves?

Old Britts, Cam Bushing Information

Cheers,
Tom

 

[TJBaker57]

If you are going to reuse these cam bushing washers, I would break off those tabs where you see the cracking as these were notorious for breaking off in the engine and getting sucked up in the oil pump and locking it up, and shortly there after grenade the engine with a con rod blowing out of the casing from a locked up oil pump. Or better yet use the later style on the 850's. Or the earlier type before 72 models. They are basically the same. Camshaft thrust washer needs the bevel to face the tachometer worm gear.
does your camshaft have scrolls on the bearing races where the bushing would be in the case halves?

Old Britts, Cam Bushing Information

Cheers,
Tom

No scrolls on my original 2S cam. Scrolls were in the 06-2600 bushings, all but worn away now.


All the rest is being taken care of. Got new 2S profile cam and recommended bushes etc. from Greg Marsh and the cases are at Jim Comstocks now having some welding etc. done.

I just have nothing better to do than pick at these old parts and wonder what those markings were.

 

[mdt-son]

Well this doesn't look good at all. I was cleaning up my cases a bit before taking them to cNw for cam bushings and a cleaning service. Then I discovered this.... timing side by the tach drive.

Given that I doubt I will put more than a couple thousand miles on this in my remaining lifetime after I get it back together I am hopeful there is someone who can weld this.

Try to find someone who does laser welding. It will limit the HAZ greatly and you may get away with limited to no heat distortion and loss of strength.

- Knut

 

[TJBaker57]

Not much progress to report here. Still waiting for my crankshaft to be ready after a regrind. And no word on my cases yet either.

And although I have a space to work in it is neither heated nor insulated so whatever the outside temperature is that's what I have to work in. This morning it was 11°F here.

 

[marshg246]

Not much progress to report here. Still waiting for my crankshaft to be ready after a regrind. And no word on my cases yet either.

And although I have a space to work in it is neither heated nor insulated so whatever the outside temperature is that's what I have to work in. This morning it was 11°F here.

View attachment 122752

My heatpump is out so I'm back to this: https://a.co/d/3DuhQfI Heats 24'x36' shocking fast. Insulated ceiling, not insulated walls, 6 windows. Yes, I run it with everything closed and have for years - my carbon monoxide alarm always shows none detected: https://a.co/d/3DuhQfI as does my fire/CO alarm.