Skorpion 660 Lightweight Build

[breakwellmz]

Hi

I has assumed the same in metal would be a lot more expensive. Your nylon one will be fine i`m sure and will be be less thermally conductive which might be useful.
3D printing is such a brilliant technique, if someone came up with this in years past they would of been accused of witchcraft!

If my `Heath Robinson` single carb system works fine (and several said it couldn`t) you don`t need to worry too much about `flow` with your setup by comparison!

Looking forward to more posts.

Cheers

[Puffs]

Some more comments from my side:
- the cross sectional area of 2 carbs vs. 1 carb can easily be compared (¼πD²), yet even if the summed area of the 2 carbs is bigger, the drag for 2 smaller carbs might be larger than for single bigger one, see https://en.wikipedia.org/wiki/Drag_(physics). In summary, if you compare 1×ID=40mm pipe with 1600×ID=1mm pipes, depending on the velocities, the drag in the 1600 small ones is bigger, so that at the same ΔP the flow through the single big one is more. Yet they have an identical xsectional area (40²=1600).
- at room temperature nylon should be strong enough, and for a water cooled engine a 160°C upper limit should suffice. But of course conventionally welding something from alu is also possible.

[jpmsteadi]

Some more comments from my side:
- the cross sectional area of 2 carbs vs. 1 carb can easily be compared (¼πD²), yet even if the summed area of the 2 carbs is bigger, the drag for 2 smaller carbs might be larger than for single bigger one, see https://en.wikipedia.org/wiki/Drag_(physics). In summary, if you compare 1×ID=40mm pipe with 1600×ID=1mm pipes, depending on the velocities, the drag in the 1600 small ones is bigger, so that at the same ΔP the flow through the single big one is more. Yet they have an identical xsectional area (40²=1600).
- at room temperature nylon should be strong enough, and for a water cooled engine a 160°C upper limit should suffice. But of course conventionally welding something from alu is also possible.

That all makes a lot of sense. Plus the drag from the butterfly in the CV carb is most likely fairly significant vs the flat slide FCR. It will be interesting to see how it all works. Waiting on a couple more seals and parts for the FCR and dialing in the prints. I am going to test it with a foam clamp on filter and trying to put it through the airbox. It will all be fun experimentation while I'm stuck at home!

[jpmsteadi]

In addition to the FCR, I also found an ordered a radial brembo master cylinder for the front brake off of a Ducati Multistrada (I think 2015-2017). It has a 14mm piston and is lighter and smaller and MUCH nicer than the nissin that was on there. I understand that at some point someone took the OEM master off and replaced it.

Here is a picture of it fitted:

I rode it around for about an hour this morning and am very pleased with the feel and stopping power. Good initial bite then building linearly to full stopping power. A HUGE improvement. And only 130 bucks on ebay. It required a litle 3d printed bracket to fit the reservoir but that was knocked out this morning quickly. I think I will try and find a smaller reservoir; the one that came with it is huge.

[jpmsteadi]

Another update: got enough of the FCR parts in to do a test fit with the pod filter. I got the bike started, but quickly realized there were enough other things going on that I need to slightly redesign the intake manifold. Since I am going to kind of commit to either using a pod filter or at some point designing my own airbox, I can push the carb back a bit to get straighter intake runners and to gain a bit of clearance for the throttle cables. The angle they come out of the FCR isn't ideal and leads to them being slightly squished by the fuel tank.

But! that is simple enough and I will be redesigning it this morning.

The current other big problem is the seat. Boy is it uncomfortable. I have an email into the uk supplier for MZ parts to see if they can source the full tour seat.

[Berniecal]

Looks like a very effective boredom killer! The Skorpion was already a minimalist design and was built with economy in mind, so lots of weight-loss opportunities with lighter metals and plastics. Good Luck with the project and hope you get to a conclusion before things open up again. (You probably have a busy day job!)
Off-topic: Is that an i3 in the background? The electric revolution is just around the corner.

[jpmsteadi]

Looks like a very effective boredom killer! The Skorpion was already a minimalist design and was built with economy in mind, so lots of weight-loss opportunities with lighter metals and plastics. Good Luck with the project and hope you get to a conclusion before things open up again. (You probably have a busy day job!)
Off-topic: Is that an i3 in the background? The electric revolution is just around the corner.

I think the movie industry is going to be awhile longer before we open up, so I am not particularly pressed for time. It is an i3! I think its the best bang for the buck for an electric vehicle right now; the used ones are very cheap, but still really nice cars to drive. Plus with the range extender and a simple flash to the computer it is drive-able pretty much anywhere. I drove to chicago in one day.

[jpmsteadi]

I realized that I just wasn't getting the print quality I needed in terms of bed adhesion and flatness to make a good seal with the head. Because of that I think I had a small intake vacuum leak. I order the grizzly manifold and will be going down that route of converting and adapting in order to mount the FCR. 3d printing is great, but it does have some limitations. Honestly even if the part had fit perfectly and worked, I probably wouldn't have been super keen to ride it a long way without worrying about the part breaking.

Just another one of those times I wish I had a full machine shop. At the next place I live I will have space for that, for sure!

[jpmsteadi]

I had gone through a bit of a phase of not having a bunch of motivation to work on the MZ, but this past week I came at it again and have made some progress. With the Grizzly manifold, a very poorly made adaptor bracket, and a 3d printed part I got the FCR carb on an running. I have a couple of small issues with the carb that I am going to work out, but I went for a small test ride and damn its smooth. pulls so well from basically idle. I haven't gone full throttle, but so far it is an incredible improvement. I am excited to get it running perfectly.

Does anyone know what the stock springrate on the MZ is? I am fitting an R6 shock and would love to have a reference point. The shock fits and is very close to the right length and stroke, but the spring is insanely soft.

I will post some pictures tomorrow if folks want them. I think the carb swap could be a good solution to get rid of those awful stock carbs and get a fantastic carb in place.

[breakwellmz]

Hi.

Would love to see how you adapted the Grizzly manifold to fit the MZ head, go on give us a picture! Have you come across this? - viewtopic.php?f=3&t=5332
Your positive test run sounds similar to mine in terms of outcome, that`s always good for motivation!

Cheers

[Puffs]

Yes, metal might be better.

The R6 has a hard, short-stroke racing suspension, so if an R6 shock feels soft on your 660 it means the 660 has another transmission ratio (more movement rear wheel per movement shock). Is the shock's stroke compatible with the 660's suspension construction? And also, if you fit a stiffer spring on the same shock, you may find it is underdamped.

I don't know details of the original spring on the 660, but you can estimate the spring rate using:

Or search for 'spring rate calculator' on the web.

[droy]

I running two different shocks

07 CBR 1000RR and BMW S1000rr with stiffer spring. 07 GSXR 600 will also work. All need some spacers on the top and some need the lower bolt hole expanded 1mm.

My stock Replica WP shock is 12.5 kg if I'm not mistaken. The CBR 1000 spring is also about 12 KG but on the stiffest setting it still feels soft and I cant get rear sab under 40mm so I need a stiffer spring there also.

[jpmsteadi]

Yes, metal might be better.

The R6 has a hard, short-stroke racing suspension, so if an R6 shock feels soft on your 660 it means the 660 has another transmission ratio (more movement rear wheel per movement shock). Is the shock's stroke compatible with the 660's suspension construction? And also, if you fit a stiffer spring on the same shock, you may find it is underdamped.

I don't know details of the original spring on the 660, but you can estimate the spring rate using:

Spring rate formula.jpg

Or search for 'spring rate calculator' on the web.

Interestingly it seems that the R6 actually has about the same stroke as the MZ shock. It does seem as though the linkage is slightly different, which is accounting for the difference in spring rate observed.

I actually used that formula yesterday and estimated a spring rate of 145-155 N/mm on the stock spring (depending on the alloy of steel being used, which is an unknown). This is in line with the aftermarket shock I saw on the internet being advertised as 175 N/mm. It seems that the stock spring is just about perfect for my weight. In talking with a suspension guy it seems that because of the slightly less overall length of the R6 shock it would behoove me to shorten the dogbones slightly in order to get the same ride height as stock. I am going to play around with making some dogbones that are slightly shorter.

Re: the under-dampened: I fully expect it to be. My goal was to find a nice-ish inexpensive OEM shock for cheap that is rebuild-able, make the spring work, then play around with the shim stacks inside and get it optimized for my riding. Seems that it will be a little cheaper than just buying a custom shock, AND I get to learn about valving and shock internals and suspension in general. Every little project I do I like to learn something. The R6 shock from those years really fit the bill: very close to the same size, very cheap (I got this one for 60 bucks), and a nice shock (triple clicker adjustments).

[jpmsteadi]

Hi.

Would love to see how you adapted the Grizzly manifold to fit the MZ head, go on give us a picture! Have you come across this? - https://www.mzriders.com/viewtopic.php?f=3&t=5332
Your positive test run sounds similar to mine in terms of outcome, that`s always good for motivation!

Cheers

Here is some pictures. This is not an ideal setup yet. The adaptor plate from the head to the manifold needs to be thicker to allow for the passages to widen to the correct width from the head. This is a down and dirty setups until I get the machine tools in to do a better, more precise job (I sent my check off for a mill and lathe monday!!! Been interested in it for awhile and finally bit the bullet).

So because of that the adapter plate is acting as a slight restrictor. Again, not ideal, but I had some spare aluminum sitting around and wanted to get the MZ back on the road.

The adaptor plate is just plate aluminum cut to rough shape with a jigsaw then cut holes in, the gasket is 1/16" gasket material from mcmaster car. There is that PETG 3d printed part that converts the angle of the grizzly manifold to the proper angle to keep the carb clear of the gas tank. It is a press fit part with some RTV on it to seal it from air leaks.

[jpmsteadi]

In inspecting the FCR more I have discovered the issue with the hanging revs after throttle close.

I took the side cover off and confirmed that the hanging revs was indeed a slide sticking issue: I could take my hand and force the throttle cam closed and it dropped fast. The FCR normally has a push-pull throttle cable setup, but I have been running pull only (mostly for clearance with the gas tank, but also just for cleanliness. I have been running pull only on the FCR on my DR650 for two years now with no issue).

Well, taking the FCR apart I discovered that the interior bore of the slide chamber has some serious grooving from the slide wheels. Must have had poor filtration some point in its life

This allows the slide to twist slightly and bind, giving the rev hang issue. This has been documented on other forums as something that CAN happen, but doesn't happen often.

As can be expected, the ebay seller said the carb was in "perfect condition save for normal wear". I don't account this as "normal wear", but I doubt anything will be done. Once I get the machine tools in I will attempt to fix the bore (you can put jb weld in the bore, then machine it flat again, or machine a section out and press-fit a stainless steel insert).

In the meantime, I have another FCR body I am going to put all the parts and jets into and try and get this thing running!! (this body is off of a different bike, so alas it doesn't have the air cut valve. some decel popping will occur)

I appreciate you all's interest in the project!! Nice to know more people still both appreciate these bikes AND are crazy enough to do weird stuff to them!