1962 CB72 Rebuild Thread

B15605 said:
Best suggested place to buy the engine gasket set from? Scrambler cycle has one for the 305, but not the 250...imagine the gaskets with the cylinders would not be right. I see a few random ones on ebay, but wanted to ask the group if there is a better place to look?
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AFAIK, other than the cylinder sleeve size the top ends are the same. You should email Kevin at Scrambler Cycle and ask him, Scrambler Cycle is one of our sponsors. [email protected] or send him a PM here @ScramblerCycle
 
Hi folks,

Been a while as havent had time to work on things due to family illness, but had some time this past weekend to begin putting the engine back together. I have a question as I simply dont understand it (probably because I dont know how to ride a motorcycle): is there a certain position the shift drum needs to be in before layong the transmission gears into the shift forks and case? Also, how does one verify it is correct when all mocked up? Photo of end of shift drum below for reference:
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Also, here is pic of things in the build process - any glaring issues that yall see?
IMG_4678.jpeg
 
Best sealant between the engine case halves? I used Gaskacinch to put beetle engine casss together. Any reason this wont work on these engines?
 
I use MotoSeal, available from auto parts stores. I suppose the engine is back together now. One of the gears looks like it may have been replaced with one from an early model.
 
B15605 said:
Best sealant between the engine case halves? I used Gaskacinch to put beetle engine casss together. Any reason this wont work on these engines?
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I've used *manufacturer*-bond' or Threebond 1104 since early 80's.
Before that I used Blue Hylomar, it was 'invented' by Rolls Royce in the 40's
All 'older' British bike mechanics used Red Hermatite as it was cheaper and easily available, it was also non-setting but would eventually 'cook' and become brittle.
It got quite a bad reputation due to 1960's leaky Triumph's
Hylomar and ThreeBond were designed to be 'non-setting' so it won't block passages or damage oil pump when it breaks away if/when too much is applied.
Working in shops I saw too many top ends burned out from silicon blockages in pick up or oilways
 
I am now resuming working in this project after a loooong time away (life gets in the way and all that). Anyway, I was installing the drive gear on the gearbox and it is more wobbly than I expectes or remember. It could be because of all the crud that it wasnt wobbly, but wanted to ask and see if I had missed something hereIMG_5178.jpeg
 
Seems like this looseness would cause problems, but perhaps it is normal? Or am I missing a shim of sort? The bolts are tightened snug so there is no more takeup to be had from the fasteners.
 
B15605 said:
I am now resuming working in this project after a loooong time away (life gets in the way and all that). Anyway, I was installing the drive gear on the gearbox and it is more wobbly than I expectes or remember. It could be because of all the crud that it wasnt wobbly, but wanted to ask and see if I had missed something here
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As Jim noted that is normal and necessary. Just a quick question on the transmission reassembly. Did you verify it will change through all the gears correctly with the shifter lever installed, or by rotating the shifter detent in one of your above pics with your question on transmission assembly? You need to rotate the output shaft that the small chain drive gear is attached to in your last question to assist the selection. Better to find out if there is a problem now vs after the motor is in the frame.
 
I was actually able to get the shifting sorted this atternoon. Not sure what the problem was before (probably me) but no troubles today so I honda bonded the case and bolted it up. That is when I started on assembly of the rest. Thanks for letting me know there should be intentional slop. Will move on now
 
Another question as I proceed. I installed the generator rotor. Upon tightening the bolt ‘securely’ per David Silver’s guide the crank is now pretty tight to rotate. It will rotate, but it is not free like before I tightened this bolt. Is this correct?
IMG_5187.jpeg
 
Well. As suggested by crazypj, there appears to be something wrong - looks like the wrong seal. The new seal I installed wraps around the shaft whereas the original seal has a lip that rides on the sprocket lip…see below:

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So, question is - can that seal be removed without splitting the case? I loathe the idea of splitting the case again and now that it is honda-bonded I assume all sealing surfaces would have to be cleaned again…all to change a seal. What are my options?
 
Hmmm. That looks like another undocumented change from the older 305/250 motors on the starter clutch sprocket. I ran into a change on the clutch outers and thrust washer arrangement on my early 64 that wasn't very clear in the parts catalogue and numbers. That oil hole in the crank spindle would not seem compatible with the seal that is installed, where would that oil be returned to? The spirals on the sprocket in your hand make sense, but would there then be another smaller outboard seal on it, that rides on the crank spindle? There looks to be a thin darkened line on the spindle, a centimeter or so, out from that oil hole on the spindle.
On the upside, fresh Hondabond does clean off a lot easier, I think.

Maybe Jensen can shine some light on this older variation.
 
If seal doesn't have an outer lip or flange you can just pull it out and fit new one.
It doesn't look like it was in crankcase deep enough?
If that is a machines angle groove at top, it should be at minimum level with inner edge, there is probably a specification for insert somewhere in manual not always easy to find though
 
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