Heart Transplant

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The difference is from the machined pad where the crank throw bolts to to the edge of the top portion of the flywheel where you have the yellow marker.
It is deeper on the drive side.

A air heat gun is plenty, and will never produce enough heat to damage the crank but will expand the inner. It is not just the interference fit on the crank journal but the seal surface to watch out for at bearing removal and installation.
It takes very little expansion to make it an easy job.
 
Time Warp said:
The difference is from the machined pad where the crank throw bolts to to the edge of the top portion of the flywheel where you have the yellow marker.
It is deeper on the drive side.

A air heat gun is plenty, and will never produce enough heat to damage the crank but will expand the inner. It is not just the interference fit on the crank journal but the seal surface to watch out for at bearing removal and installation.
It takes very little expansion to make it an easy job.
Click to expand...

If there's a difference I can't tell.

Heat gun, check!
 
Heart Transplant
 
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Hi Thomas... Both my 750 cranks have that variation as dose the Mk2a 850 (Dec 73 build tag) ... Crankshafts from the 1974 build year or MkIII I do not know.
 
Although marking which is the drive and timing side regarding the crankshaft centre section is a good idea,not all is lost if not done as the pad depth is different so easy to identify original position side to side. (Deeper on the T/S)

May be reading this wrong but the pics show the D/S being deeper which is at odds with the text, be good to have a definitive way to ensure the flywheel is the right way round, you can never be sure it has not been tampered with before ;)
 
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You are absolutely right, I thought I had a picture but could not find it so did that one to hastily.... yes the larger depth is on the timing side so will need that incorrect picture removed.

I am 100 % sure the crankshafts out of both my 750 and 850 were as they left the factory and the other crank I checked was the '1800 mile one which also looked as it left the factory. ??

Edit
Wrong one deleted and a correct one uploaded to replace it, thanks for the pick up.
 
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I can confirm my 72 crank matches your text ie deeper recess on timing side and still has the marks I made, but as it is at -20 on the big ends before it came to me and so has been apart before I cannot be 100% sure its correct, only that I put it back the way I got it when I cleaned out the sludge trap.

I removed the pics from my post so only the corrected ones will show.
 
cyclegeezer said:
I'd want to know the thickness between machined surfaces and if it was consistent among engines of the same displacement.
Click to expand...

I'd need to find my micrometer for that and I haven't seen it for 30 years... doesn't mean I don't have it. :confused:
 
comnoz said:
Most cranks are about even on both sides.
If they are different it is not consistently to one side or the other.
Click to expand...

Would this have been done for better balance with each set of cheeks? I can't imagine it was just random.
 
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swooshdave said:
I'd need to find my micrometer for that and I haven't seen it for 30 years... doesn't mean I don't have it. :confused:
Click to expand...

I will post some numbers tomorrow after I fix this thing but don't want to push your thread to far off course.

Heart Transplant
 
Just had a look at my crank and flywheel, its is a set of cases so can't measure the thickness of the metal on the flywheel between the 2 machined faces. However one journal is definitely looks offset to one side until you look closer, the flywheel has a thinned area on the flywheel at TDC, it is this that is offset to one side on my flywheel, the machined area on the OD of the flywheel at the full width is centralised between the 2 sides of the barrel hole and the journal webs look central too. So it looks like the first datum cut on the rough surface is not taking certain features into account or a machining operation was set up on a wrong datum.

Even if your flywheel has this offset feature the flywheel will fit both ways and the journals will sit in the same place, but suspect the balance will be off if its turned round accidentally from when it left the factory.
 
Hortons Norton said:
Would this have been done for better balance with each set of cheeks? I can't imagine it was just random.
Click to expand...

It's not done for balance. It wouldn't affect the balance.
It's just how the flywheel was setup in the jig when it was machined..
For some time in the early 70's they were normally off center, but I sure would not count on that as a sign as to which side that is supposed to be on.
It just needs to be put back as it was taken apart to maintain any balancing that was done at the factory.
 
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