MZ/MuZ Riders

Timing is correct - good spark.
Carb has new jets / needle, float height is correct, air filter system all OK.
50:1 in the tank - with new petrol

Problem is that it is very hard to start, when it runs it will die after a short time and will not start again, if you take the plug out it is covered in oil.

If you clean the plug it wil sometimes start again, sometimes not.

I drained the gearbox oil thinking that if the crank seal had gone the plug would not foul, since doing this when it does eventually start it will die but the plug is clean.

My thoughts are that because it is hard to start, and the plug fouls when gearbox has oil, it is most likley to be the seal on the drive side that has gone, I also found out that the bike had not been used for about 10 years prior to me buying it so another eeason why the seals may be gone.

Being a 5 speed I believe that you do not have to split the engine to replace the seals.

What do you guys think - replace the seals?

Yes, it is very likely that the seals are bad.

No, the engine doesn't have to be split in order to replace the seals. But you will need a clutch puller and a torque wrench to properly install it back.

Yep - they will have gone for a reason.

I looked at the timing side seal today and that looks new, having problems with the drive side as I cannot get the cotter pin out of the kickstart, looks like is rusted in place.

Tried penetratig oil and heat and it will not move, only solution left is to cut the kickstart with a grinder to release the pin, so that will be a new kickstarter.

There was a small dribble of water came out when I took the rev counter drive off, so may be some corrosion in there, even though the oil was clean - I'll find out when I get it apart.

You do realise that the clutch cover can be removed with the kickstart left in place? Or do you have a reason for wanting it off?

Dave - I tried pulling the cover off with the kickstarter still in place, the cover comes away by a few mm but there is something stopping it going any further, should I just pull harder? all the screws are out by the way.

I assume that there is a seal in the case for the kickstarter, there is some oil leaking past the kickstarter shaft so it will be a good idea to remove it to replace the seal.

If the cover will come away with the kickstart in place I can then probably drill the pin out.

OK so with a bit of gentle tapping off came the case, then out with the clutch extractor to get the clutch off.

The crank seal looks pretty new - see the picture below, no signs of rust on the crank that I can see.

The one on thetiming side is the same colour seal and also looks new, but it is fitted the other way around to the one in the picture below.

My question now is which way round should they be fitted?

Both your seals are fitted the right way, ie flat side facing right.

Thanks for letting me know Dave.

Guess that now I have pulled it apart I had just as well renew the seal - it might look new but who knows.

Just been looking at an engine rebuild video on You Tube as I was wondering that if perhaps the problem is being caused by oil getting from the gearbox into the engine via the crankcase joint.

This looks unlikely to me because of the way that the cases join, and the joint looks pretty unlikley to leak unless jointing compound has not been used or the joining faces have been damaged by some idiot if the engine has been taken apart.

Anyway, I'll order some new seals at the weekend and see what happens when they are fitted.

Another update.

I pulled the drive seal out this afternoon, the rear of the seal facing the crankshaft was pretty discoloured, suggesting that there has been / is blow past the piston.

I have not checked bore / piston clearance so no idea about the bore / piston clearance. The engine is very quiet, and has plenty of compression if that is anything to go by.

By the looks of it the seal has been in there for sometime.

Looking at the seal there is no discernable lip on it, where it contacts the crank it is just flat.

No signs of rust / pitting on the crank - it looks perfect.

So I am optimistic that the seal is at fault, I'll know when I fit the new ones next week - not pulled the one on the timing side yet.

If I were you I would fit this new seal and see how it goes.

You've mentioned in YT videos about the possibility of seepage past the crankcase. This has come up before, and someone has found on this forum that they were missing the black rubber disc that can be forgotten that sits in a recess on the left hand crankcase at the top near the conrod clearance.

Though, like I say- i would just do this green seal first

Hopefully it is the seal - no way of checking the crankcase seal without splitting the cases, dont really want to have to do that.

Puffs.

Certainly no sign of any lip on the seals, as you say probably the source of my problems.

Never heard of your way of testing seals before, as you probably know the proper way of doing it is to carry out a leakdown test, but I am going for the easiest option for me at the moment - fit the seals and see if it runs.

If you google "2 stroke leakdown test" there are some quite innovative DIY ways of doing it.

I managed to dril out the kickstart pin while I have it apart - no way that was every comming out by tapping it, the flat side of the pin was pretty mangled, guessing perhaps and incorrect size pin had been fitted, or not tightened properly in the past, never had a problem with kickstart cotter pins before.