MZ/MuZ Riders

Hi,
Hope I'll be moderately welcome here. Do tell me to sod off if I'm not.

I've recently purchased on ebay, a ratty, hacked about Yamaha SZR660. Upon trailering it home I discovered that both fork seals had failed . I whipped the fork legs out, only shearing one 6mm mudguard bolt flush. I managed to weld a washer to it and then a nut to that to have something to screw it out with. Luckily it came out with a little patience. The fork springs need compressing to loosen the damper rod securing nut and I am currently knocking up a spring compressor.
It's not pretty, but should make a reasonable base for some tuning.





I am currently rescuing a cylinder head from a spare engine that needs a little bit of Tlc before I set to and big valve it.


As you can see it has 2 seized exhaust collars,2 broken exhaust studs an a broken cyl hd bolt

Some lateral thinking is required here methinks

Mark.

Welcome. We need all of the Yamaha 660 action we can get on this site.

I don't know what the previous owner of that head did to cause so much to go wrong with it but you might be better off buying a different head from ebay that looks a little less abused.

I bought it from a really nice chap named Dave who has a thread all about his experiences with his SZR on the Performance Bikes forum entitled Not-so-super-single. I had previously read his thread and then by chance ended up buying his old engine on ebay.

I was primarily looking for a spare cylinder head to rework and his engine came up at a price too good to miss. I intend to big valve it with 5 of these little beauties......

I have pictured the standard valves on the right as a comparison.

Of course, other performance enhancing parts will be added to the mix at the appropriate time. I do warn those of an impatient nature that this will be a very slow moving project . I still have other bikes to ride and tweak.

Mark

I ended up with +1's on my head too. The valve seats were bad enough that the extra machining was required any way. So far I've hit 60hp on the dyno but that was with stock carbs. My Mikuni TM34/38 B70 just got here this week and I'm trying to get it installed at the moment. Should put me over 65hp if the gain from moving to flat slides is as nice as everyone says it is.

Ok, strange that your valve seats were not great, all the 5 valver seats that I've seen were in really good condition even
after tens of thousands of miles.

Did you dyno before embarking on tuning work, probably the only way to quantify real gains.

My inlets are +2mm and the exhausts are +1mm. I intend to keep the ports (relatively) small but the valves as big as practical in my quest for torque . Carb chokes will be smallish at 33mm as befits a roadgoing engine. I'll be more than happy with 55-60 bhp but my real quest is for a broad spread of torque.

Mark.

It's hard to say what my gains were so far. I haven't been back to the dyno that I used to get a stock number. It was an eddy current dyno, and the operator said that you need to add about 15% to his numbers to get what most people would see at a Dynojet facility, although the second place that I went to had a newer Dynojet unit with an eddy current system. The stock numbers were 39hp, corrected to almost 45hp if you add 15% but I was having problems with fuel flow through the old petcock after more than 5 or 6 seconds at full throttle. The dyno it went to after doing the engine work gave me a result of 60hp @ 7400rpm. I'm pretty confident about hitting 65 with the flat slides and assuming I can keep the candle lit above the rpm it was breaking up at before.

Oh and the bike is down to just over 300lbs. It's fun!!!

Is that an aluminum frame on the SZR ?
Thanks.
Srinath.

Yes the Yamaha SZR660 has a beam frame very similar to a TZR 250 two stroke twin. It has been found that the SZR frame is actually wider between the frame rails though.

I never pay much heed to absolute dyno numbers only the change after performing the work, obviously using the same dyno for before and after.

Have had some success with the head. Turned up an adaptor for a slide hammer
It has a little spigot to centralise itself in the collar.

Welded to the collar and then pull out with a slide hammer.




So a little way to salvaging a head that many would have scrapped. I just want to get on with porting it now

Mark

I have removed 2 of the broken 6mm exhaust studs by welding a nut to the stud stumps. All four required removing and unfortunately 2 sheared off below the surface. I tried welding a nut to the cylinder head bolt stump and wouldn't you know it, that sheared off too, just below the surface. I have drilled out this bolt remnant and may "Helicoil" it or fit an weld in an oversize aluminium plug, re-drilling and tapping back to standard.

I feel confident of removing the 2 remaining exhaust studs later.

I have dressed the exhaust collar bores and may or may not enlarge them for some homemade collars and oversize headers. For now at least they will do.



Mark.

To someone who can use a milling machine,getting the two remaining stud remnants out without damaging the threads is quite an easy job.-Do you have a machine shop locally?

Yes there are shops locally, but this would be work that will eat into my budget. The exhaust stud angles are not straightforward relative to the head faces and would involve not insignificant set up time. I still have a couple of
options to carry out repairs myself.

I have distracted myself from the unglamourous repair work by the distinctly more exciting task of porting to accept my oversize valves.

Here I have made a small start on an exhaust throat. I need to make up some gauges to ensure concentricity with the valve guides.



Mark.

I managed to turn a couple of gauges/test plugs with stems that fit directly in the valve guides to ensure concentricity as I bore the valve throats manually with a Dremmel.


After some careful work opening out the exhaust valve throats to accept my test gauges, I have almost achieved my desired diameters.


I have used engineers blue on my gauges to mark the areas of the throat and port where material needs to be removed. Finally the plug gauge fully enters the port.


Mark

You are really going to town with your new project. Love it! Thanks for sharing it with us. I can't wait for the continuing adventures!

Cool. Hopefully I'll get to ride my bike soon and see what the Mikuni's have to offer. They sure made a difference in throttle response in the garage.