Project Cafe Rocket 686 begins. Finally!

[Geoff7yea]

Haha yea probably for the best you havnt heard from them yet! Unless they did rush...and broke something...lol only kidding

Well its only if its cool with you to throw up some pics. i can only find pics of the raptor head. i have a spare head off the above ruined engine but id rather not make a mess of either!

[den]

im about ready to do the gear mod myself and now you have thrown another spanner in the works ,
please explain what you mean by this ,
"remove the two vented washers and the thick solid washer when doing this mod."
Didnt know i had to do this aswell , replace with what , more new parts??

[edfmaniac]

The solid gear replaces the sprung gear and all three washers in the picture. Don't forget to put a new key and lock washer on when you reassemble. They are cheap. My key had the slightest evidence of wear but I bet they go south quickly once you can start to see the damage. One other thing to remember is that the marking on the balancer gear won't line up with the one on the solid gear. You'll have to count how many teeth away from the key way that the dot is on the original gear and orient the solid gear in the same position.

[den]

Thanks for the reply,,

[edfmaniac]

Just got off of the phone with the machine shop and had an interesting conversation. Evidently, the MZ Skorpion head isn't an exact match to the Raptor head. The tech said that a lot of the work he would do for a trail port on a Raptor, and he's done hundreds, was already cast into my head. He spoke of short sides mainly, and said that my head was like a cross between a Raptor and a Rhino and needed very little work. After asking him if it was possible that it had already been ported, he was fairly confident that it was a stock casting, as was my observation. He even said something about either Tim Barker or Gailen telling him it might be a good idea to think about experimenting with the MZ heads on the Raptors. Very interesting.

Got +1 valves whether I wanted them or not since my stock seats were beat to hell. CHECK YOUR VALVE CLEARANCES FOLKS! It only cost me an extra $90 since all three intakes needed to be replaced anyway. I may have to think about the rod now since I already planned on matching or surpassing that 60hp mark that seems to be the danger zone.

[edfmaniac]

Now that the flywheel is off, I'm debating on whether or not to do the machine work on it. After comparing pics of lightened flywheels with mine, it appears that very little material is removed, and only from the middle of the three distinct sections. Anyone out there have more info on modding this part? Is it worth it? I know that adding weight on my 2 stroke woods bike gave it a little more grunt when plucking the clutch but it definitely wasn't night and day.

[Bill Jurgenson]

at the risk of bring a bore, I suggest reading the relavant sections of my blog carefully.
Http://cembalobill.blogspot.com/

All the questions, especially concerning teh balancer gears but also lighten freewheel are covered there. I can supply more detailed info about lightening the rotor/freewheel assembly off list if desired. there are many other pointers there such as the quick-release tank latch and seat fairings and especially the Skorpion specific solution to the oil tank problem. And I would definitely consider removing the cross-tube from the frame.

The projected weight/performance are entirely within reasonable limits (although the wire wheels will not be light- in terms of performance and handling a bad choice and maintenance):

My air-cooled Skorpion SP weighed in last at 148kg = 326lbs with 1/2 full tank and has about 60hp. This year (?) it will be a bit less without balancer shaft and I hope with much smaller and lighter generator. My blue engine had 59hp at the rear wheel, the bike itself 342lbs with not much effort. The SOS racer weighed it at 270lbs with 80 rear wheel hp. Obviously something like that is not viable for the street. None of these had a stroker crank, not even the 80+hp race engine and my newest project has 4mm LESS stroke. The statement made about increasing bore only with a stroker crank is utter nonsense. In my book a stroker crank itself is utter nonsense. The Winner of the supermono championships two years ago had both a stroked engine at his disposal and one with the normal stroke. Although the stroker engine had more umpf on the dyno, he preferred to ride the shorter stroke engine. On the race track, RPM are of more use than brute guts in a narrow, low rpm band. My race engine delivered from about 4500 upwards and turned well past 9000. We kept it between 6500 and 8500. Mostly just shy of 8000; the OVER cluster had only 800rpm overlap.
I would definitely use a 100mm Wiseco in the stock bore (honed of course) until the cylinder demands reboring. Then go to a 101mm Wiseco in the bored and honed OEM cylinder. Sell the after market thing to some unsuspecting Raptor rider.
The envisaged budget is too optimistic from my experience but as he says, it is a hobby. The racer devoured well over 20k$ when time is taken into account - which I must since I am self-employed.

[edfmaniac]

Thanks for responding Bill. I've read most of the stuff that you've posted on the Skorpion and try to follow your advice when I can remember it. Any info on the flywheel/freewheel would be greatly appreciated.

[Bill Jurgenson]

to disassemble the flywheel, heat it up on a hotplate to break the Loctite on the three bolts, then remove them with an impact driver.

The flywheel itself can be turned down as far as you want as long as you leave the center section reasonably intact for bolting the freewheel on.

I usually leave about 1mm standing to center the freewheel but you can go further down. Then you must assemble the entire thing on the crankshaft to get it centered, then taken it back off as an assemble and reinsert each bolt separately with Loctite 242 and finally peening the end of the screw. With the lip left, you can assemble the thing and be done with it. Whether the addition few ounces are really that important is questionable Admittedly, My own private use flywheels were done that way.

The freewheel is another matter. It is casehardened and so can only be turned with tungsten carbide cutters at low speed. It is time-consuming.

You can see the difference in hardness. You can turn this part down to the shoulder that fits the recess on the flywheel. You cannot leave like that, however.

This is not one of mine, but it show what happens when the ring is left that thin.
I will continue with the ring on the next posting since one is limited to three attachments.

[Bill Jurgenson]

with the ring turned down, turn a ±140mm OD ring from suitable aluminum 11-12mm thick. Turn it out inside to -0,35mm and heat that to 250º C and let it drop over the steel ring. After cooling, you can turn the thing to its original size (always assuming you made a dimension sketch beforehand!).

Bolt the parts together as described and install exactly like the OEM part. Don't forget the Sprague clutch! And before bolting up, check to be sure that the clutch turns freely in the flywheel. Otherwise, carefully grind out the freewheel ring revolving at high speed in the lathe with an airgrinder and fine stone. Only just skim it. Usually it is not necessary but sometimes the condition of the ring inside is already soptty so a bit of smoothing does no damage.
All in all, doing the job properly is quite a bit of work, time consuming for which reason it is either not done at all or it costs money to have it done - or is it improperly done with the results shown above. Such burst rings are not so uncommon.

My personal opinion is that it is money and/or time well invested. HP on the dyno will not be affected but engine response in real-life is definitely improved and so is mileage. The fact that mileage does imporve it proof that the flywheel is using less power for itself. Dyno ratings are not the be all-end all. There was talk in a different thread (about the TDM box which is a definite no-go) that there is no use in pushing the limiter farther up.
Humbug. The SRX has no limiter at all. Same basic engine. I ran both my nearly stock red Skorpion Sport (lightened flywheel, tampered-with Denso box, Tm34-B65s, SZR wheels) and my SZR (lightened flywheel, Ignitech-limiter at 9500, but OEM carb and airbox and otherwise stock engine never opened BUT with the very fine Termignoni racing exhaust and SR-Racing can)


for 100-200kms at a time on the Autobahn between 7 and 8000rpm, keeping close to 7400-7500 all the time. Running 15/43 and a 140/70 BT090 rear tire on both. Neither exploded, neither needed 20km to get up to speed and both would accelerate from the constant 170kmh to well over 180 right off. Mind you both were stock engines inside, never opened, the Yamaha even with the Teikei carb. I routinely revved the SZR to 8500 in the lower gears.
So much for the would be limits of the stock engine. 7200 is simply nuts, too low for real use. Basically the engine needs no limiter at all.

Same thing goes for the balancer shaft. Again, max on the dyno will remain unaffected, but in accelerating and decelerating, the balance uses up to 5hp( in words FIVE) all by itself. Anyone seriously looking for real getupandgo on the track must look into this option.
http://cembalobill.blogspot.de/2007/12/balancer-shaft-and-myths.html
I rode my blue toy for 50000km of its 80000km useful life (in my hands - it is still running without serious rebuild)

Without a balancer shaft and lived to tell about it and without all of my teeth dropping out.
The race engine, likewise, had none.

[edfmaniac]

Thanks. That's the first time I've seen the entire process posted anywhere that I'm aware of.

One question on the balancer if you have the time. Is it possible to remove the stock shaft, cut it down to a fraction of it's original weight and then reinstall it? It seems like that would be easy for the average mechanic if it will work.

Good to see you back on this forum sharing your valuable knowledge.

[Bill Jurgenson]

yes, that is the way to go. Slipstream among others offered different lightened balancers and I have turned down some myself. I use one turned round, the weight completely removed.
I learned the hard way that you should not completely remove it; I did.
The shaft, weight or not, should be there and it should turn. I is part of the oil/vent system and in turning it fills the function of a centrifugal oil trap. it is not just a tube as I once incorrectly thought. The turning, not the weight itself, is the important part. With only a static tube, the crankcase vent pumps far too much oil. adding a much larger vent like OVER did does help but a healthy catch can is necessary. I emptied this after every run and sometimes there was a cup of oil in it.
with my present oil tank, finally sufficient very unlike that plastic thing, and revolving shaft, the catch can remains virtually empty. I have given up even checking it. There is no discernible oil consumption.
check my blog on proper dry sump oil tanks (and other better informed sources). Check catalogues as well for images of typical dry sump tanks.

[basser23]

Yea Bill! Great to have ya back .....as a side note to all..READ his posts..READ and re Read...he explains things in easily understood language,with much detail///
Thanks Bill!

[Bill Jurgenson]

I blush
seriously, I forgot to add that without the weight, there is no reason to replace that gear. There is no possible danger and practically no wear to the keys of either shaft.

[edfmaniac]

Already planning my NEXT build. Hopefully I can make it through the first season of riding on the new engine with no major failures, as I don't want to split the cases this time around. Next year comes crank/rod work, balance mod, and the flywheel if I don't get to it this time. Need to make friends with a machinist.