MZ/MuZ Riders

I have a 2001 Baggy which I have ridden for three years with minimal maintenance (oil, filter, plugs). It is now time for a serious going over.

It has always used a lot of oil with no sign of a leak and no smoke from the exhaust, so god where it’s going. It has had, for the past couple of years, an annoying clanking noise from the engine, intermittent (not every stroke) but frequent. Hasn’t affected performance or starting though.

So the first of what I suspect will be a number of questions.

I have the carb and rads off, the two side covers and the rocker cover. Can I take the head and the barrel off with the engine in the frame?
The main drive nut on the crank on the clutch side is lose (the cog can move in relation to the crank. Should this be tight?

Any tips on progressing? I am nervous about the timing particularly.

All assistance appreciated.

Stuart

Hi Stuart.

Yes the nut should be tight this is quite a common problem with this engine,
Do a search on here for woodruff key, Bill Jurgensen has a comprehensive article (warning) on this.

DO NOT run your engine or you could face a bill for hundreds of pounds.

Thanks, I make sure the nut is tight with a shim and new key as suggested.

I now have the head off, not much sign of anything major wrong but I will take it apart and give it a good look. Does anyone have experience of the valve seals. Would wear in these account for my use of oil?

Can I take the barrel off with the engine still in the frame?

I have removed the exhaust side cam chain guide but the manual appears to show the inlet guide held by a bolt at the base. Do I need to take the flywheel off to get at this?

The bore looked in good condition with no scoring. Is the piston prone to wear? Having got this far I feel I should take it out and consider a replacement. Any thoughts?

Thanks
Stuart

I’ve now taken the engine out and given it to my local engineering shop. They are going to measure the cylinder/piston clearance to see if a new piston. They will also give the head a quick refurbishment.

I am somewhat confused by the decompression gubbins in the cam. There is comment on the site about removing this but does it actually do anything? The only decompressors I am familiar with are those operated by a handlebar lever and the solenoid activated arrangement I had on a big Suzuki. This was a right pain and I eventually replaced with a trusty lever.

The text in the MZ manual is a little vague on the position for the decompressor. It seems to refer to some marks but there is no picture. Can anyone advise?

Thanks, Stuart.

A little lost here, hard to understand (unless one's experience ist based on KTMs) what the uproar is. You shouldn't need a new piston until at least 50000mls = 80000km.
Unless that shop is more than a little versed in big bore singles, I am not awfully sure what they are measuring. Of course, they can confer with the shop manual. So can you and you should download the official Yamaha SZR manual (Same engine and thus same data for all important questions). Or get a XTZ handbook.
Same goes for the head. Yamaha valves and guides are good for at least 100000km (not a typo). You can clean out the carbon deposites if you want. With proper usage, there should not be much at all.
Re: deco, it is really very simple, so simple the manual need not go into it. Just put it back together as it was. Inside the cam, there is a slender secondary cam with actuates the small plunger in the lob of the left exhaust valve.

This is the hole for it.This cam has been modified for use without the deco. The weights on the cam sprocket turn that slender shaft as RPM pick up, just like an oldfashioned distributor. At rest and up to about 600RPM the plunger protrudes, thus not allowing the exhaust valve to close, above the ±700RPM the weights swing out, turning the shaft and allowing the plunger to retract and the valve to close. It is that simple. No voodoo, no gimmick mechanics like on the XT, SR and SRX to couple the deco to the kickstarter, no hand trigger and no need for it. Drawbacks? For a civilized street engine few. It can break and has. You cannot check the compression. Given that the engine is nearly indestructible, no need to for a street engine, either. For more extensive tuning, tho, it is a good idea to remove it and some racing cams have no provision for it.
So, that ain't no marks for it, cause there ain't nothin to set. You can only bolt on the timing gear two ways, the right way and - 180º off - the wrong way. There is nothing in between. Use a GOOD torque wrench for the those M7 bolts and be careful of them.



The 3YF is the next best thing to a an old John Deere. It is not a Ferrari. Leave it alone until it makes itself known.
One thing you ought to do, tho, when you have it apart, is to replace the gear for the balancershaft.

You'll find losts on the subject in the archives and some here in my blog:http://cembalobill.blogspot.com/2010/03/update-sp-2010.html
Yamaha parts number for that gear: balancer gear Raptor: 1S31153600

Thanks for the info.

Bill, I agree that things are best left alone if they are working well but I think something is “making itself known”.

I am using about 200ml of oil for each tank of fuel, which is more than for my two stroke. I can’t see any evidence at all of where al this oil is going but I don’t think its right.

I am getting the shop to check tolerances against the manual just in case this points me in the right direction.

Any thoughts?

Stuart

I’ve had the barrel and piston measured and the results are good. Although the bore is wider at the bottom than the top it is all still within tolerance. The head has been de-coked, and as Bill predicted it is in fine condition.

I will put it all back together with new rings and gaskets.

Following Bill’s advice I have ordered the replacement cog from Grahams. £50.00 !!!!!.

Once back together I will try with a thicker oil to see if this improves consumption.

Does anyone have experience with 20/60? I have seen this recommended on the forum.

Stuart

Stuart109 wrote:I’ve had the barrel and piston measured and the results are good. Although the bore is wider at the bottom than the top it is all still within tolerance. The head has been de-coked, and as Bill predicted it is in fine condition.

I will put it all back together with new rings and gaskets.

Following Bill’s advice I have ordered the replacement cog from Grahams. £50.00 !!!!!.

Once back together I will try with a thicker oil to see if this improves consumption.

Does anyone have experience with 20/60? I have seen this recommended on the forum.

Stuart

I ran 20w50 in a car that called for 5w30 because I was making power, and had issues with contamination. I don't like a cylinder that isn't right. If it's out, it's cheap as hell to fix or replace it and you can always go with an oversize piston! single pistons are super cheap and worth it if you can find specs!