1972 750 Interstate Resurrection

They’re simply to ensure that the correct cap goes on the correct journal and in the correct orientation.

Bear in mind that I am not a machinist and don't have a firm grasp of how a new engine is machined, built up/assembled.

For context; In this particular engine there are only two times these marks could have been made. The factory, or the one time it was previously opened up to replace the main bearings before I acquired it in October 1975.

Fast Eddie said:

They’re simply to ensure that the correct cap goes on the correct journal and in the correct orientation.

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Would that suggest the caps were somehow different??

Regarding orientation,, given that the cap is mated to the rod and the rod has an oil hole that faces outwards the orientation is already known once the cap and rod are mated. Further marks would be unnecessary.

And if the purpose was only to mate and orient the rods to cheeks why mark the timing side in the awkward location it is marked at?



These are the thoughts that bounce around in the grey matter here. I have that curse of desiring to know why things are as they appear and what was the reason for them to be so.



It seems like these marks were made while the rods and cheeks were assembled, either mated to the flywheel or some machine fixture that allowed the rods to hang from the cheek.

If it were a complete crankshaft assembly being disassembled why would they then mark the caps and cheeks and not the flywheel.


I like the notion that they may have something to do with the factory balancing procedures. Now that may be because I don't have an idea of the step by step balancing procedure at the factory.

The engine rebuilder wanted to ensure that the same parts went back in exactly the same place and orientation. He punched them while they were assembled (as you say).

Common practice with the more fastidious engines builders. Some will even mark fasteners so that the same faster always goes back in the same hole, etc.

They are most definitely not anything to do with the factory balancing process. If they were, all Commandos would be similarly marked.

Fast Eddie said:

The engine rebuilder wanted to ensure that the same parts went back in exactly the same place and orientation. He punched them while they were assembled (as you say).

Common practice with the more fastidious engines builders. Some will even mark fasteners so that the same faster always goes back in the same hole, etc.

They are most definitely not anything to do with the factory balancing process. If they were, all Commandos would be similarly marked.

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It makes sense what you say about these marks not being on other engines.

I have never thought this engine was touched by an engine rebuilder.... I suppose it is possible though.

I have thought the teardown to replace main bearings was done by an owner in his garage. I have receipts for the parts and a dealer work order for the top end reassembly and startup.

Whoever put this crank together struggled with it. The timing side cheek locating dowel was tapered down for the outer half of it and the cheek has hammer marks on it from where it was beat down over the dowel !! That doesn't sound like a good engine rebuilder to me.

Fast Eddie said:

The engine rebuilder wanted to ensure that the same parts went back in exactly the same place and orientation. He punched them while they were assembled (as you say).

Common practice with the more fastidious engines builders. Some will even mark fasteners so that the same faster always goes back in the same hole, etc.

They are most definitely not anything to do with the factory balancing process. If they were, all Commandos would be similarly marked.

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I do have to accept that perhaps it has been apart more than once. I am 3rd owner. I have receipts etc from 2nd owner. I suppose it is conceivable the 1st owner had the engine rebuilt then sold to the 2nd owner who also rebuilt the lower end himself.

Perhaps the 1st owner had a shop do it and that's when the marks were made and it was the 2nd owner who hammered the crank cheek.

Previous owners are deceased so I will never know.

TJBaker57 said:

I do have to accept that perhaps it has been apart more than once. I am 3rd owner. I have receipts etc from 2nd owner. I suppose it is conceivable the 1st owner had the engine rebuilt then sold to the 2nd owner who also rebuilt the lower end himself.

Perhaps the 1st owner had a shop do it and that's when the marks were made and it was the 2nd owner who hammered the crank cheek.

Previous owners are deceased so I will never know.

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"People lie, machinery does not"

If I had a dollar for every time I've heard: "it was all rebuilt before I got it" I'd be rich.

I ask: "do you have receipts for the work done? Can I see them?"

"Well, uh, um..."

Believe what you can verify, dimensionally.