Fast Eddie
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They’re simply to ensure that the correct cap goes on the correct journal and in the correct orientation.
1972 750 Interstate Resurrection
- Thread starter TJBaker57
- Start date
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.
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.
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.
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.
Fast Eddie
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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.
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.
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.
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.
concours
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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.
grandpaul
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Most of my bikes (ALL of the ones I've worked on) have meticulously detailed spreadsheets with every last bit of info, ziploc plastic baggies or manilla folders with receipts, and (many) hundreds of digital photos documenting everything ever done to them.
I think 3 of the 22 in my possession right now have only had oil & filters so far.
So it's been a minute or so as the current US slang goes.....
Query: if you were replacing the intermediate gear bushing and you found the replacement bushing could be pushed nearly all the way home by hand with no heating of the gear or any other such preparations, would you trust that bushing or get another and try again?
Only the final 3/32" or so required tapping in with a composite mallet. The rest I could push in with a pair of strong hands and a block of wood.
The original and a previous replacement ruined by a machine shop require significant force in a vise to remove/replace so I expect the gear bore to be OK.
Query: if you were replacing the intermediate gear bushing and you found the replacement bushing could be pushed nearly all the way home by hand with no heating of the gear or any other such preparations, would you trust that bushing or get another and try again?
Only the final 3/32" or so required tapping in with a composite mallet. The rest I could push in with a pair of strong hands and a block of wood.
The original and a previous replacement ruined by a machine shop require significant force in a vise to remove/replace so I expect the gear bore to be OK.
marinatlas
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If you are speaking about the third gear layshaft bush it should be a sliding fit , see above ...
If you are speaking about the third gear layshaft bush it should be a sliding fit , see above ...
Not referencing any gearbox bushing. Talking of the intermediate gear driving the camshaft.
This fellow here....
Currently wondering about taking it back out and reinstalling with Loctite 609 retaining compound?? I don't think I want to try reaming it as it sits, it may spin?
marinatlas
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Sorry , my bad ....
I think there is about .0015" or slightly more interference with the bush OD and the gear bore ID as they sit. Does that sound about right? EDIT/CORRECTION: I misremembered the interference, there is actually almost none depending on where one measures.
To ream it before installation it sounds like I would need to devise some means of holding the loose bushing. Hmmm. I have never used a hand reamer before. I ordered an inexpensive adjustable reamer. I do have the old bushings to practice with.
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Not to worry... I eventually will also be replacing all the gearbox bushings so your linked thread was helpful.
Richard Tool
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I second this - I bought a complete set of them from Harbor Freight a few years ago. Now instead of having one worthless reamer I have many worthless reamers .. ( I should have known)
Well my plan is to have a go at it. If I'm not happy with where I end up Greg Marsh has a new gear with bushing available.
I made a few practice runs last night on a sacrificial bushing. On one pass I did see the result of attempting too thin of a cut.
Before getting into it myself I took the gear and a new bushing to a machine shop to have them do the replacement and reaming. I left the shaft with them as well for them to judge the fit. What I got back looked very much like what I saw last night when I tried to make a thin cut. Looked pretty horrible to my eye.
I am replacing the bushing because there was greater than .004" clearance. There is a mark on the crankcase behind the gear, mostly on the one side nearest the camshaft. I figured the gear was tilting with the excessive clearance and the cam chain pulling the gear over that way? The bore in the crankcase doesn't show ovality and the pin checks out straight.
Elsewhere online someone pointed out that the 68-70 750 had a thrust washer behind the gear. But I see the gear, pin, and bushing are different part numbers there. Andover Norton shows no thrust washer for the 1972 750. Does this seem correct?
kommando
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The thrust washer is the case, you can see the marking the gear/sprocket has made on the case. There are no helical gears so no side thrust and they must have dropped the thrust washer as a cost saving.
This is the Andover listing of the drawings the thrust washer is on
Which shows it does not last beyond 1970.
This is the Andover listing of the drawings the thrust washer is on
Which shows it does not last beyond 1970.
