MB100 development

[koba]

looking at the pic i would say mine was actually wider.
Never actually had an issue and was surprised when i saw Mikes was a triple port. but i guess his was more area and the single would lose some area esp with the reed bars and outer area.
I tried to find the port map, it is somewhere, but it was within the "Bell specs" for width.
The pic is a std Cr80 ac which was around 49mm bore.
I are still gutted i never got around to running it with a decent size carb.
the CR80ac had a huge bridge port ex, with eyebrow windows and a tiny crankcase and huge transfers std.
same stud patern as the MB100 as well, only it has the MB50 stroke.

True, competition heritage makes it a no for buckets but would possibly be really good on a road bike if it's got enough in it to adapt to 100 stroke, bridged exhaust and all.

[datfreak]

Guys - as before thankyou for this info.
The idea of using solder to check dome/head gap is very clever. thinking of sanding the head down with w&d paper on a glass sheet then (very carefully!) reshaping the head outer rim with ----i will not do anything to a two stoke head with a dremel------so maybe, ill wrap the piston in sandpaper also and "spin it" in the head until the squish and the CC's were correct.
- i was going for about 13-14:1 C.R and using 98 fuel and a synth 2 stroke oil.

"bell rules" say I should have 35mm ish wide exhaust port and inlet - but im curious to this 3 window inlet idea.
Any idea on what a safe divider width would be? Its on the cold side of the motor so i think i should get away with a thin one
Just having a look and those side windows will be VERY close to the transfer runners.


EDIT : if I go with a 3 window design for the inlet, the side windows will go around the bore enough to be "open" even @ bdc (due to the shape of bottom of the pistons skirt), does this matter at all?



Here is a pic of the h100 barrel with alot of alloy(and steel) removed to fit the cr85 reed block. - this is still a work in progress, as i still have to take at least another 5mm off the one side and cut a 12mm piece of alloy plate for a spacer. oh and here is a inlet BEFORE pic

[husaberg]

repeat after me i will not do anything to a two stoke head with a dremel...... i will not do anything to a two stoke head with a dremel.

[speedpro]

Something like this.
Make sure the side of the reed petals don't scrape on the side of the cylinder inlet as they open and use devcon or similar to form a nozzle from the reed stops top and bottom into the ports. You don't want any sudden changes in cross section.

[Grumph]

i like the triple inlet setup. If i was to do another MB barrel that's how I'd go. I've had good results with the single port but it's eventually not big enough but too big for safety...Looking at the side ports on the triple, it may even be possible to squeeze in a couple of Boyesen ports through into the rear transfers. That's probably only possible as a 100 as when it's big bored there is NO room there...
With the better piston support of the triple, You could use a port in the piston too - these work really well to lengthen small end life but with the big single port piston life is too short.

[koba]

i like the triple inlet setup. If i was to do another MB barrel that's how I'd go. I've had good results with the single port but it's eventually not big enough but too big for safety...Looking at the side ports on the triple, it may even be possible to squeeze in a couple of Boyesen ports through into the rear transfers. That's probably only possible as a 100 as when it's big bored there is NO room there...
With the better piston support of the triple, You could use a port in the piston too - these work really well to lengthen small end life but with the big single port piston life is too short.

You can fit some tiny boysen ports in there, I think the area is possibly better employed making the side ports of the triple better though as the stud spacing is quite restrictive.

[koba]

Here is a pic of the h100 barrel with alot of alloy(and steel) removed to fit the cr85 reed block. - this is still a work in progress, as i still have to take at least another 5mm off the one side and cut a 12mm piece of alloy plate for a spacer. oh and here is a inlet BEFORE pic

Cool, looking good.
As part of that work in progress make sure you give it a nice radius from the roof of the inlet up in to the boost port.

[speedpro]

Make sure the end of the reed stops and the reeds themselves don't obscure the boost port.

[F5 Dave]

Which is why a spacer or better yet a new bit tack welded on is usually the go. I just ran ports either side of the main about the same time as I mentioned it to Mike he was apparently already but presumably Pete S had been going this way. It just seemed logical & easy to get way more area than you need from what your carb will flow.

I'm cheating now as I don't have an inlet port in the barrel. . .but its more than you could achieve with a dremel.

oh yeah, forget the glass & sandpaper for head. Get someone with a lathe to take a swathe off the face & cut an old piston in half so they can do the chamber to the right angle & di (+ a smidge). Then make a guess at a bowl shape. From there you measure with fluid & have to recut a couple of times.

trying to do the above by hand will result in you going crazy with boredom, but mainly, you might get it flat - but won't give you much hope of it being square once you bolt it up.

[speedpro]

couple more. In 0988 you can also see the adaptor plate and the spacer that the pretty big 6 petal reed mounts to.

[datfreak]

thanks guys the info-- and the pics are art! just beautiful

oh and i didnt think about the reed pedal covering the boost port , it is maybe 8-10mm past the reed cage tip.

[datfreak]

The cr85 carb and inlet pipe mounted.
no I havn't done the porting yet but I couldnt resist to see it together . Started easily but would not rev too high (? too small of jet? it has 125 mains)
The inlet pipe is slightly bent, and points the carb west - it doesn't get the carb level but close enough.

The 12mm spacer plate was more work then expected - honda has very tight spacing with the reed screws to outer edge. Hours of filing and grinding.

The other pic is the remains of the oil pump. it is my attempt to delete the pump. I was going to make up a plate to seal it, but i found it easier to cut up the pump and use that. I think i will work a treat.

re: inlet porting - I was thinking of doing a 2 port - ie taking the existing inlet port to one side to a total of 33-35mm , then have a bridge on the other side and a 20-25mm port. but maybe this will be too hard on the piston. So may go with the 3 port alike to what you guys have done.

[koba]

Started easily but would not rev too high (? too small of jet? it has 125 mains)

To small, or too big.

What pipe do you have?

[F5 Dave]

No body can predict what jet size you need, but a word of caution. Spend some time finding the right size or slightly too big. These bikes can be super reliable, but too lean of a jet will seize any 2 stroke solid. Heaps of jetting articles on web. Small steps.

[husaberg]

Which is why a spacer or better yet a new bit tack welded on is usually the go.

No body can predict what jet size you need, but a word of caution. Spend some time finding the right size or slightly too big. These bikes can be super reliable, but too lean of a jet will seize any 2 stroke solid. Heaps of jetting articles on web. Small steps.

When i mentioned the the reed at the start it sure looks like the later CR85 reed is deeper looking the Old aircooled reed was very short hence why no spacer for me.
I seen a real could jetting from scratch article the other day i will see if i can regoogle it onto the web.Its the neatest one i have seen.
http://books.google.co.nz/books?id=J...ameron&f=false

I do remmber why i never used the CR inlet thopugh because the angle was wrong even with the Downdraft TZR carb.
Make sure the Keihin isn't to steep that the float level is off and fuel comes out.
I used a RD250 inlet it was a simple job to fit. redrill two holes file the other two.

PS put a filter on it.