Oil pump driveshaft weirdness?

Assembling 1973 6V-engine. I'm aware that oil pressure is crucial to engine survival.
Now, I observe that the driveshaft + sprocket combo can actually disengage the oil pump drive.

Looking down the camchain path through the engine block cutout while turning the oil pump sprocket, I observe that the sprocket has free play left/right (most likely to allow alignment with the sprocket on the crankshaft). Unfortunately, when the two sprockets are in line, the driveshaft barely engages the oil pump.

Hmmm...

I've checked the engine schematics at http://www.cmsnl.com. I've checked my original workshop manual. Neither of these mention oil pump sprocket free play between crankcase housing and alternator plate nor any washers to aid in removing the free play

When looking down the camchain path while fiddling with the oil pump drive sprocket, I find that when aligned with the camshaft sprocket, a mere half millimeter is all that separates 'disengaged' from 'engaged'. Unnerving...

Am I missing something (a washer?) somewhere? Has the oill pump axle somehow shrunk? I'm confused!

Facts:

• 1973 6V short-stroke engine housing.
• 'Thick' oil pump axle to go with the original short stroke crankshaft.
• Original 1973 oil pump assembly.
• Paper-thin oil-pump-assembly-to engine-housing-gasket.

Explanations? Anyone?

Hi,
Un-nerving but normal I think.
When the stator plate is fitted it prevents the oil pump drive shaft and sprocket from moving (endfloat) and dissengaging.
If you still have the problem when stator plate is fitted then the shaft/oil pump is damaged.
There are no shims/washers fitted etc
I've just completed an engine assembly after complete stripdown and was alarmed by this myself,but if you look at the inside of the stator plate you will see were the sprocket has abutted against it to prevent this .
Hope this helps ?
Dave

Your explanation is spot on, Dave!

Thanks Waynus, its reassuring to know I havn't made a complete fool of myself by Waffling on and missing the point!!!!
Cheers,
Dave

Sure it helps

Now, I've measured stuff to make sure everything is under control. This is what I found:

No stator plate:
Drive sprocket distance to crankcase housing when in disengaged state: 2.1 mm
Then, I turn the sprocket to let the axle engage oil pump drive - this lets the sprocket move sideways onto crankcase housing.

Stator plate installed:
Now I move sprocket sideways to touch stator plate and measure distance to crankcase housing again. Distance is 1 mm.

From this I learn that axle engages oil pump drive with [1.1 to 2.1] mm overlap.

Enough to ensure a reliable and continuous pumping action.

OK. Alarm cancelled.

Next: Anyone who has anything to say about cam chains? What brands or types to avoid, and what to buy instead? I'm asking because I realize that cam chain is absolutely crucial to engine survival. Doing it right the first time may cost extra, but there's no telling what I'm going to end up doing with this old geezer. At the moment target is 72cc + aftermarket top with ball-bearing cam + advancing CDI ignition. I guess this means that 11.000 rpm is within reach. And this is new to ye olde engine

Ye olde engine has been withering away for nearly fourty years, denied its proper place in the sun by 49cc cylinder kit (moped), an actively retarding ignition and intake restriction featuring a 5 mm breathing hole. Gasping for air... Thus, what I'm intending to do to it is quite a change!

Just making sure that I'm not creating any weak links in the drive train.


Of course I'll run it in gently, once I get to that bit

All sounds good!
DID chain - top quality and not expensive,£10/15 should buy one

And make sure all sprockets are in excellent condition, and the rubber one in the cylinder is installed correctly.
Also, make sure you set the tension exactly right! + The rubber pad on top of the tensioner does not show any signs of damage.