250 Monza Engine set up questions

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Cucciolo - the Lil Pup
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250 Monza Engine set up questions

Post by [email protected] » Mon May 24, 2010 5:13 pm

I am attempting to help my son resurrect a basket 67 250 Monza. The motor was unassembled. Two primary questions.
1. If the bottom end gears alignment dots are lined up is that supposed to be TDC? Someone has made marks on the case and flywheel that correspond with those marks but it is NOT TDC.
2. The top end bevel gear alignment dots do not line up. There is no indication of the assembly being apart and there is staining consistent with the engine having been run this way. Is there any reason the marks should be 4 or 5 teeth out of alignment?
Thanks in advance for any help you can offer.

bobnorton
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Post by bobnorton » Tue May 25, 2010 9:58 am

I suppose its possible you have some parts from a different motor,I would reset all the gears as per the manual and then turn over slowly to check nothing hits, you should also do a cam timing check and spark.

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Cucciolo - the Lil Pup
Posts: 12
Joined: Mon May 24, 2010 5:02 pm
Location: Atlanta, GA

250 Monza Engine set up questions

Post by [email protected] » Tue May 25, 2010 11:47 am

That is essentially what I am doing.
I figured out the Cam bevel gear mystery. (question 2) By disassembling the gear drive bearing housing and removing the oil line you can mess up the gear alignment without removing the lock tab and nut from the cam.
As the saying goes, the problem with making anything foolproof is that fools are so creative.
Now I have to find a source of piston rings. I discovered a crack in one of the oil rings.

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DesmoDog
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Post by DesmoDog » Wed May 26, 2010 9:34 pm

I'm assuming the '68 is set up basically the same as an earlier bike?

On an earlier bike the cam gear has 28 teeth, the top tower shaft gear has 20 teeth, the lower tower shaft gear has 30 teeth, and the crank gear has 21 teeth. If you do the math you'll see the final ratio between crank and cam is .5 but the dots will only line up something like once every six revolutions. Basically you haven't turned the engine over enough times to find the spot where they line up, but everything is/was likely synched correctly. Which is all a long way of saying that what you were seeing was most likely perfectly normal.

By using different size gears they keep the same teeth from coming in contact all the time, which helps the gears live longer.

I also seem to remember that the piston is not at TDC when the dots line up, but that's pretty easy to check and really doesn't matter anyway. IMHO you need a degree wheel to set everything up so the marks on the gears won't come into play other than the initial set up.

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