77 Reed Block

[PCMAX]

I recently bought a 77 Maico 250. It has a reed block looking thing but I can't find any reference to it in any of the online parts manuals. I haven't actually pulled it off to see if there is a reed in there yet. Can anyone shed any light on it?

[Mick D]

I am pretty up on Maico.
You will not find that in any parts manual or otherwise.
Definitely post factory creation.

It appears to be a nice sort of a fit.
If you ever open it up and go in for a closer look?
I would love to hear more about it, see more pics etc.

Cheers, Mick.

[tony27]

It's a G.E.M part, you'll have a V-6 reed valve in there. Not 100% sure but I may have bought a complete NOS kit from this seller for a Maico loving mate, still sealed so I can't say whether it had the mounting plate like this or the type that uses a bolt on rubber spigot

http://www.ebay.com/itm/Nos-GEM-G5163-Vintage-Motocross-V6-Reed-Valve-spigot-Mikuni-INTAKE-MANIFOLD-1pcs-/161610403594?vxp=mtr&hash=item25a0bb0f0a

Seller has a 77 G.E.M catalogue for sale, I bought a 75 catalogue a couple of months ago from them

Have a look in this folder, it's a complete scan of the 75 catalogue
http://s788.photobucket.com/user/tony27_photo/CZ%20981%20random%20stuff/GEM%20reed/1975%20G%20E%20M%20catalogue/story

[Mick D]

Great work Tony, thanks

Peter is thinking of trying it without the reed arrangement.
Looking forward to hearing his comparison opinion if he does

[PCMAX]

Thanks Tony & Mick for your insights.
I plan on taking the block out (just to have a better look) later in the week. Bloody work is getting in the way of fiddling with my bikes.
I'll post some pics of what I find. As Mick mentioned I might even see what she goes like without it fitted.

Cheers
Peter

[tony27]

Guess it will depend on whether the holes were drilled in the back of the piston as to how it goes.
 
I know with the holes in the back of my CZ piston it wouldn't run very nice without the G.E.M reed fitted, unfortunately I've managed to lose the safe place I put the cage & mounting plate while having the exhaust port sleeved. Luckily I also have a 4V DH unit that I can fit with some work until I find it

The seller with the plate I put up has new reeds for not much if you need them, they don't need stopper plates so if there aren't any fitted when you pull it out don't worry

[jimg1au]

you cant just take the reed off and expect the engine to run.i have had a 400 cz with a reed valve and with all the extra porting it would never run piston port
also have a 1973 cr250 honda with a gem reed valve set up it also would never run with out the reed
if fitted properly extra ports should have been cut int the barrel and windows in the inlet side of the piston
jim

[Mick D]

Yes and yes.

I had already got a PM from Peter, where he mentioned he was thinking about removing the reed block.
Obviously if he looks down the intake and sees no holes it means the kit was just fitted without the mods.

As he has said he has only just recently bought the bike. He has reasons for thinking about removing it.
And has said to me, quote; "Im thinking of reverting to the original (no reed) setup depending on what I find when I pull it off."

So yes and yes fellas, we are all curious. I guess we'll just have to wait see if someone has just thrown it straight on or not?

[jimg1au]

at least he knows thats the main thing
jim

[PCMAX]

Thanks again for your replies and valuable insight. I pulled the block off tonight and noted that the piston has two lower and one upper hole in the inlet side of the piston so I guess it's been done properly. What bothers me is that the reed restricts the inlet volume quite a bit when you compare the size of the reed opening compared to the size of the inlet port.

[tony27]

Try it, I doubt it will be a bad thing having the reed valve conversion. I think I'd be correct in saying there has been quite a bit of welding done to give a good mounting/sealing surface around the intake port, do you have a standard cylinder to compare?
Quite interesting to see how the reeds protrude from the casting, on the CZ casting they are slightly recessed. Looking at the catalogue there was only 1 cage design with different castings to suit the different bikes, even the carb mounting plates were multi fit

[Lozza]

Thanks again for your replies and valuable insight. I pulled the block off tonight and noted that the piston has two lower and one upper hole in the inlet side of the piston so I guess it's been done properly. What bothers me is that the reed restricts the inlet volume quite a bit when you compare the size of the reed opening compared to the size of the inlet port.

The holes in the piston effectively do nothing. The conversion will work fine without the piston ports. First rule of two strokes is what 'looks' logical usually isn't so. Reeds don't 'restrict' anything (they limit hp but that is a different story) they open when the pressure in the crankcase goes negative and stay open until the pressure is equalised or inlet inertia can't hold them open any more. You can draw more air through a drinking straw than a 100mm conduit. The petals look short making them fairly stiff, experimenting with reed thickness and backing reeds would show really good gains in low end power and throttle response

[tony27]

Lozza, being the V-6 reed set up the reeds are 33.4mm long with the screw holes 3.2mm from the back, thickness is .34mm. 
Would you consider that to be a stiff set up?
The strangest part with the GEM V-6 set up is the assymetrical cage that was used, it makes sense with CZ's bent manifold but not where the cylinder is vertical. Makes me wonder if CZs were the first bike they developed them for

[Lozza]

Assymetrical cage is to bias flow one way more than the other. The shorter the petal the stiffer it becomes, 33mm is very short for a big bore engine

[Maico-Mac]

Hi, I tried the GEM reeds on my 69'er squarebarrel GS250. It runs greath
The reed cage has been milled out to fit the Intake port on the cylinder (see the pics).













I also use:
shorter piston (modell 1983-20XX),
crank from 1982 and bosch ignition,
exhaust pipe for 400ccm cylinder, because the 250ccm doesn't work well any longer on the reed 250ccm!