Scooterotica

Hi chaps, need some help please.
couple of years ago i bought a spare engine (spanish S3 200) to strip and re-build mainly so i could learn. When i rebuilt it with new crank and electronic ignition etc the crank web was catching on the oil seal retaining plate. I changed the plate and still had the same problem. I did a bit of reading and its mentioned in the manual that MB sell shims that fit between the crank and the drive side bearing to solve this problem so i got one and it seemed to do the trick.
Put it all together and it almost immediately starting burning oil. Took it out of the scooter and stripped it again, nothing obviously amiss so just rebuilt it and got exactly the same problem. Threw it to the back of the garage and left it.

Since then i've done a few jobs on my scooters, including re-fitting a crank with new seals etc without problem. Also invested in a leak test kit. Just started looking at the problem engine again and before i stripped it did a leak test and sure enough there's a big leak from the drive side bearing. Stripped it all down and cant see anything wrong. I really dont want to just re-build this and end up with the same problem.
Am i doing the right thing using this shim or could this be the cause of the problem? When i pull the crank through I use the bolt and the front sprocket pillar thing and pull it until it wont go any further. This is ok with the shim, but without it the crank locks solid, If i re-build it and do a leak test will that prove the seal etc is all ok?
I'm getting frustrated because I cant see what I'm doing wrong. I'm reluctant now to go any further until I find out whats causing the seal to fail,
any suggestion gratefully received.
thanks Steve

First check that the drive side seal plate is flat and concentric - is it alloy or steel?

Alloy are more prone to warping if overtightened.

Make sure the drive seal plate compresses the halite washer too.

also check the bearing is fully seated as the gap from oil seal plate to crank web is only 0.5 to 1mm so tolerances are tight

Also worth checking that the drive plate screws and not bottoming out before tightening the plate itself.

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GeorgeS wrote: ↑Fri Jul 28, 2017 4:50 pm Also worth checking that the drive plate screws and not bottoming out before tightening the plate itself.

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often appens if you Loctite em; loctite makes a plug at the bottom of the threaded hole clean threads with a 7mm bottoming tap

6mm

Thanks chaps
been checking more stuff......
I think the bearing is seated correctly but,,,,,,
When I put just the retaining plate on without any oil seal or halite washer and pull the crank through fully without the shim it locks solid against the plate. Plate is 5mm thick and the shim is 0.9mm.
Does that tell me that the bearing isn't fully seated? I'm reluctant to try driving it in further.
Cheers steve

Also checked the screws aren't bottoming out, and the plate is steel and flat.

You

I would either try a different plate or linish or get 1mm machined off because as you pull the crank in the shoulder on the crank stops against the bearing and also the oil seal and should automatically set the gap so it's either the shoulder on the crank or the plate

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Looked at this the other day, and as Garry ^ says, the shoulder on the crank stops against the bearing. Work from that. I'd be inclined to put bearing (loose) onto crank (make sure you have a method of removing the bearing!), and measure. check you've correct bearing, and that crank is correct. I've had to machine the seal plate on a few, but rare (up to 1.5mm). Try your seal plate without bearing too, flush with casing? I've not come across a crank with the shoulder wrong, (but then, we also found the GENUINE PX gear selectors to be wrong??).
You could also put in bearing, no seal plate (again, make sure you've a method of removing bearing from crank), and pull in crank against casing as opposed to the bearing. Does it still lock/ rub. This will tell you for certain its a crank or casing issue, or not as the case (lol) may be. From that, you'll get your fault and rectify. I would not be looking to use a shim between the bearing and seal to move crank away from seal plate, something is amiss there.
Just because shims are sold, if it wasn't used originally, it is probably to overcome mis-matched components (bad tolerances during aftermarket/ poor/ worn production).