660 engine questions

[riversbikes]

Hey all, more of a szr660 question here, but the muz guys and gals, esp. Bill, might be able to help. Being in Canada, the szr660 never made it here. That engine only exists in the form of the raptor 660 atv, which comes complete with reverse! However, the tt600, xt600, and 500 versions of yamaha;s aircooled engines are far more plentiful. Simple, robust, and tuning options are available from our flat track friends. So, after successfully getting a cagiva mito frame shipped to me from Germany, my bright idea is to keep our dhl friends busy, import a szr660 frame, swingarm, linkage and tank, and have fun finding the rest of the running gear, after putting in an aircooled yamaha 600 engine in it. So the question is, will the tt or xt 600 engine fit into the szr frame with minimal fuss? I seem to recall reading that the cases of the aircooled bikes and the liquid cooled engines were the same. If Bill put an aircooled engine in his mz where a liquid cooled lump once was...?

Thanks in advance for any and all help.

james

[mincehead]

Pretty much anything CAN be done, the bike Bill showcases is in fact an XTZ660 (Skorpion) bottom end with the XT600 air cooled top end fitted from memory so not a full XT600 motor.
I expect the engine mountings to be pretty close if not the same between the SZR660 and XT600 motors but I`m sure someone will be along to confirm that one way or another.
I can tell you the front wheel for an SZR660 is the same as the TZR125 front wheel and I believe the back wheel the same as one of the TZR250 models too.
By the way, those Cagiva Mito frames happily accept (with the correct plates made up) an XTZ or SZR660 motor too, you`ll find a few on Youtube if you look for them.

[Bill Jurgenson]

mounting points for XT 600 and SRX and XTZ 660 are the same as are many many other parts.
Mine is not the first example of a XT600 E motor in a Skorpion; a friend has been riding his for several years now and that is a completely stock XT motor, unlike mine. The only XTZ parts of my motor, since broken up for parts, are the two crankcase halves. Cylinder is XT600 with 660 sleeve bored to 101, head late SRX modified and ported and with RD springs and Megacycle cam, crank with Carillo and timing gears etc one-off by us, cluster originally OVER, then 4SU with 1 tooth shorter 5th. Too much for here and all in my blog.
this year wiil see a new motor with shorter stroke, no balancer, 4SU cluster again etc but same cylinder and head.
Anyhow, it is no problem to put a XT600 motor in a SZR(4SU) frame except for the kickstarter for which clearance is a real issue if it is not a 600E. I do see serious cooling problems in the case of the 4SU/4DL if it is run with full fairing for an aircooled engine. Full fairings are always an issue for aircooling but the shroulding of the box frame and nearly closed top and back are not all good for the purpose.
Mito no different or better, BTW.
I would opt for a Skorpion frame amyway if track days/racing is the primary goal.
I've got both and can judge.
SZR 3" front is the same as one of the TZRs (4FL) and a couple of late TZs and the 17" FZR 400.
5" Rear wheel is a relatively rare "real" Brembo ( the others are stamped MP = Motoparts, a subsidiary of Brembo, both of which belong to Yamaha anyway) found only in the SZR and 17" FZR 400.
The TZR 4FL has a 3.5" rear which I use in my Skorpion and think the much better choice.
The late TZs had 4.5" and then 5" Brembos with typical 2-stroke-type cushdrives that don't cushion anything. These are fine for racing aa 4-stroke but not for a normal heavy handed sreet rider.
Except as an excercise I do not see any advantage of either a MITO or a SZR chassis. Get a Skorpion, any model. Then go from there, either with the water cooled XTZ (3YF) or a XT600E motor.
The Skorpion frame is much better than either of the others and is lighter as well. The 41mm RSU fork is better, too, than the Paioli of the SZR unless you serious invest.
The only real justification for buying a SZR is to get the Brembo wheels and brakes and the Minarelli motor which is better made. Put all this in a Skorpion frame and sell the Yamaha frame with registration. That's what we did.
And I have a SZR in daily use, it is a great bike, much better than the MZ for almost anybody both in quality and safe handling but not in the hands of a really good rider. the MZ is neutral to a fault. It does what you tell it to do but YOU have to tell it. Both the MITO and the SZR are typical italians, nervous at low speeds and stoic at speed, keeping the chosen line like a railway train. It is much easier to ride for a beginner and he will be riding decent hang off with an hour, something nobody but a pro will do right off on a Skorpion. the backside of the coin, you can change lines in the middle and get away with it on the MZ, but not with the Yamaha.

For track use, it ends up as a personal choice, unlike recreational riding, because nothing but the bare frame is left of the production bike. The Skorpion frame is lighter, it is steel and thus more easily modifed, It is easier to work on the engine in the frame and easier to get the motor in and out of the frame, too.

[samandkimberly]

Bill, I have a few questions RE doing an SRX/TT/XT motor swap in to a Skorpion, so I thought I'd resurrect this thread. I'm seriously thinking about getting rid of the whole liquid cooling system as you did, but I'd prefer to go the whole 9 yards and put a kickstart SRX/TT/XT motor in there. Looking at where the kickstart *would* go on my (half faired) MZ it would appear that it would fit, barring for possible problems around the rearsets, which I'd redo anyway. Do you happen to know if it will fit on the Skorp? How close are the 600 and 660 exhaust ports to each other - will the exhaust cross over, or should I expect to do a little welding there? I'd be changing over to a larger, AL oil tank and a oil cooler, likely with some sort of thermostat.

Any other issues you think I'd run in to?

Thks,

Sam

[Bill Jurgenson]

everything is pretty close.
Like I wrote above, I would go for a XT600E engine, keeping the starter. Th eearlier engine versions have some issues with the cluster, especially with 5th gear which is notorious for breaking down in the srx. The redesigned bottom end of the 600E has a different gear spacing in the cluster and wider gears. Since it has a starter, it also has a different primary drive ratio and this is one important improvement in the design: there is less torque applied to the mainshaft in real use so the surface pressure on the gear teeth of the cluster is less and they hold up much better, add to that the wider gears. You see the redesign was less to get a starter for the lazy (which is what all those would-be he-men think!). The starter is only an additional comfort, the main reason was to get rid of the torque issues connected with the 3:1 primary drive ratio which was necessary to kick start the beast. A couple of Skorpion XTZs have been modified for kickstart. It is no problem; all the housings etc are there in the crankcase. You only have to bore the hole for the kick start shaft itself. You also have to modifiy the kickstart lever to clear the frame. And of course you have to instate some kind of decompression unit. All no problem. It has been done. One guy who did laid himself up for half a year when the beast kicked back. That stettled that matter and that engine was sold.
Like I said, there are very well founded technical reasons for not using the kick start bottom end having less than nothing to do with kicking or not kicking. there is no virtue in kicking a big single. There is also no need.
The XT600E fits plug and play, all 38hp, no problem. Or one builds up a special unit like I did using the XTZ (better 4SU) bottom end.
there are also good reasons for using the 4SU bottom end or at least the 4SU mainshaft; the longer 1st gear means that the two shafts rotate at more similar speed which makes shifting smoother and wear less.

The exhaust ports of the aircooled 4-valve heads (these are all the same) are different to the 5-valve head; they are parallel pointing straight forward and the 5-valve are splayed to the outside. This difference is due to the cooling; the water-cooled head does not need fins close up. That said, I bent the Skorpion L&W headers together to fit the air-cooled head

until I found the Devil TT system I now use. Sorry I don't have any decent shots but it was always only temporary.
Kosta uses the 2-2 Replica system on his XT600E Skorpion.

Most important is the oil tank in my opinion and I did not waste as much time as I did with this topic for no reason. If you get the oil tank right, you do not need a thermostat or oil cooler at all. Perhaps for racing but definitely not on the road. I have been down that road with the oil cooler and it is not a good road. do not rely on the oil cooler, thermostat or not, to make up for a crappy oil tank like the MZ has. and the SRX, too. It is definitely even worse. For the oil tank, read up on the subject of dry sump oil tanks with cars. there is a lot to be found. You sill soon see that , if possible, they are always round and tall and that for very good reason.
But enuf said, I have written this before and it is on my blog.

[samandkimberly]

...so could I put the crank and transmission from the original Skorp in the XT cases? I may end up with a MZ 660 short block with a bad set of cases and would transfer as much of that over to the XT cases as I could. E start is nice and I'll adapt it if I can, but I'm plenty familiar with kickstarting big high compression singles.

I didn't know that the 660 had a different primary drive ratio; the benefits of that aren't lost on me, though I can see how it might make a kickstart less effective. Neither are the benefits of a real catch tank that both cools and does a better job defoaming. I appreciate how well you documented your own tank construction; thanks.

[Bill Jurgenson]

no.
well, yes you can put the crank in but it is too long on the left side for the side cover.
The cluster will fit but I am not sure the forks align correctly.

[samandkimberly]

One way or the other I think I'll be using the 660 bottom end; sounds like its the safer bet as far as fit/strength. Regarding that - I'll be splitting the case to do some repair work, so it seems to make a lot of sense to order up and install a higher SZR first gear per Bill's suggestion:

Mainshaft: 4SU1740100
1st. gear: 34K1721100

...but I don't think these came on any bike made in the US, so I doubt my local dealer will be able to get them. Barring someone happening to happening to have an SZR gear cluster they want to part with, any recommendations on a non-US dealer who might be able to get these and (economically, if possible) ship them to me in the US?

Sam

[Bill Jurgenson]

Well as chance would have it, I have those parts on order at my dealer's and they have been waiting for me to pick up for weeks. since I will not be using them at the moment, I can order them again and send you these if you want. I don't know the present price since I have also not yet paid for them. Somewhere around 120€ for the shaft and 30 for the gear if I remember right.

[samandkimberly]

Bill, you are a saint! I'll PM you with details. and if I can ever return the favor let me know. Maybe send you some American beer?



Sam