Crank timing mark 75 mk3

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Commando75

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I am trying to confirm the accuracy of the timing scale inside the primary case. I removed the crank case inpection cover on the timing cover side. My question is, what should I see in the hole that would indicate propper position (28 before TDC) for timing? I suspect that my primary scale is not accurate due to an over advance condition when I set timing by it. Any help would be much appreciated.

Andy
 
Do you have or can borrow a degree wheel in order to set the motor accurately at 28 degrees BTDC and then put the cover on and verify if it indeed does read 28?

I need to do the same with my motor, and I need to get educated on how exactly to do this.
 
No I dont have a degree wheel but I believe that with the Mk3 we should be able to confirm the accuracy of the primary scale by looking into the inspection hole on the timing side. I just don't know what I should see in there!
 
There should be a notch in the flywheel that accepts a bolt with a "pin" shape on the end that indexes into the notch and fixes the crank in position.
 
You should see a groove or slot machined in the crank cheek. It's about 1/8" wide so you can't miss it...but, of the three Mk111 cranks that I've had, not one has had a slot in it !

It will show you where 28° BTDC is but it's not accurate enough to time the motor with.
 
Commando75 said:
I removed the crank case inpection cover on the timing cover side. My question is, what should I see in the hole that would indicate propper position (28 before TDC) for timing?
Click to expand...


Crank timing mark 75 mk3
 
Last edited:
Commando75 said:
Here is what I see with the primary scale set at 28 before TDC.
Click to expand...

Yes, that certainly looks like the 28° BTDC slot.
 
Thanks L.A.B. My mark is not lined up with casting line as your pic shows. Perhaps the primary scale is in fact off by a few degrees as has been mentioned on the forum.
 
Commando75 said:
Thanks L.A.B. My mark is not lined up with casting line as your pic shows. Perhaps the primary scale is in fact off by a few degrees as has been mentioned on the forum.
Click to expand...


The primary scale could certainly be off (the MkIII scale is adjustable) and as others have said, it could be worthwhile verifying the positions of the primary scale and slot are correct with a degree disc as I found that the slot on my own MkIII was accurate to within a degree.
 
SWEET!!!!!! Sure enough the scale in the primary was off. After an engine, primary, clutch, gearbox rebuild everything was sort of a variable in terms of being dialed in. As soon as I got the bike started after all this work it was pinging (pre ignition, pinking, detonation...call it what you will) under load. I was positive that I had timed it by the numbers. Problem was that the whole procedure hinged on the primary timing scale being accurate. It was not. I have learned alot during this project but it usually falls on basics to get things correct. Start with the obvious and work towords the unusual. Thanks for all the help guys.
 
Why the he'll didn't they make the timing scale extend to tdc. Then you could find tdc w/ a dial indicator and verify accuracy of scale?
 
I much prefer a fixed static timing mark with a non-variable index (TDC). After all the timing mark on the rotor is still relative; they should have two marks, one static, and one fully advanced to strobe-check.
 
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