Gem Reed Setup

[Big Mac]

Anyone have any experience with the correct setup for a Gem Reedvalve on a KTM 250 motor? Bought a reed kit that came with a "windowed" piston for a pattern, but not sure if it was cut right in the first place. The left window is wider for some reason than the right. Also, not sure what is recommended for modifying booster ports in the cylinder, if at all?

On a Husky 250 cylinder I have that was adapted with a D&H reed, the booster port transfer (runs between the intake ports)was modified and opened to allow breathing through the intake area....not sure what KTM mods might work. Any ideas? Any old Gem install instruction around? thanks a lot.

Mac

[Auto5guy]

Jon

I didn't look at the check until we were on the road home.  That was not the price I asked for!!  I will get even I promise!:D

Good luck with this project.  I am interested to see what you can do with it.

Congratulations on your win saturday.  That CZ really flys.

Matthew

WARNING: The Surgeon General has determined that castor smoke can be hazardous to your health.  It is highly addictive and causes delusions of grandeur.

[Big Mac]

Gem Reed and windowed piston was courtesy of Matthew "Auto5guy" above...No, he does not have any others, unfortunately...was able to scrounge this one only with very green cash (small tip for delivery service) and lots of invaluable Penton knowledge combined with unbridled raceday fan support. My apologies for flogging a CZ on Saturday---the Penton was just so clean and shiny I couldn't bear to take it out to grind in the mud.

So Gem Reed experts...any advice? I saw on a Hodaka website, someone posted complete instructions from back in the day on mods for a reed setup--Promise I'll do the same if I can get my hands on any info. Thanks,  Mac

[imported_n/a]

Matthew and all who have a G.E.M. reed block for the 250/400 KTM engine, could you measure and develop some specs for future use in having these remade?  A dream maybe, but they are legal for Vintage Sportsman 250 and 400, and remakes may be an item that would justify the investment.  

Glenn

[Big Mac]

Glenn- I'm on the project, unless someone else out there has done more legwork and can advise. I have a moldmaker providing a price to cast and machine replicas. Will take someone sticking their neck out for a pretty sizable up front investment.

First, I'd like to see for myself what the performance gain is from going to a reed. So I'm thinking the right info on cylinder modifications and piston setup are a vital piece of info for all Poggers. Anyone?

[metalkfab]

Ive got a NOS Gem REED for the 250 KTM here.I can fax the instruction sheet to anyone and I'm willing to loan the Reed assemble out for repop's if needed.

[tlanders]

Karl,

I'ld like a copy of it.

Thanks,

Teddy

[Big Mac]

Karl - Can you fax the instructions to me at 503-684-7440? If you can put JON MCLEAN on it or with it somewhere, it will make it to me. I met with a shop today that machines aluminum aftermarket parts for ATV motors, they are to work up a cost to produce duplicates. Thanks a lot! Will let all know what comes of it.

[Gavin Housh]

I had one of those GEM reed valves and was going to put it on my 75 250 and my friend / machinist told me it was not big enough. Teddy Landers I believe you know about J.P. Morgans reed conversion on KTM motors. These machines become monsters after he works his magic on them. If your still going with the GEM setup check out Dirt Bike Mag. issue July 1976. This article covers instalation, pros/cons, diagrams of where to drill the piston and such.

[john durrill]

Karl,
 we would like one also.
John D.

[JNOYES]

The Gem reed valve questions keep popping up, but I don't remember anyone reporting that it made a big difference.  Anyone out there that has one on a race motor?  I keep hearing that the early reeds like the Gem were too small and verified this by talking to a noted vintage engine builder.  If significant money is to be spent on developing a Gem knock-off, why not spend it on newer technology.  Shops such as Replica Mechinen (spelling???) are grafting big reed cages to Maicos, etc.  Perhaps the Gem is not the way to go for racers. I'd love to have a reed on our race motor because they do work, but I'm not convinced the Gem is the final word in performance.  Can someone be found that can design one for the racers in our group?  Just my two cents on this subject.

Jon Noyes

[rob w]

I believe you would start by designing it around an already made/easy to get reed CAGE, that way you'll be able to use modern and easy to find reeds, also opting for a larger block than what GEM had made. Remember the GEM reed set-up was designed 30 years ago, if you're going thru the trouble to make new ones, why copy something that was'nt all that terrific to begin with.

The man to ask the questions about how the old GEM's performed would be Knute.

Glenn, Yes they are vintage sportsman legal.

Who know's the old Carl Cranke quote about reed-valves, M.L.?

[Big Mac]

Kent Knudsen's performance tips in Still Keeping Track says that the GEM works, even though it looks small and restrictive. Article says he runs on both 250 and 400 AHRMA winners. Don't know him personally, so can't vouch for it.

I'm volunteering to research performance, cost for both GEM repro or alternative bigger volume repro, and report back. I have a DH Reed setup made for Husky 250s sitting unused on the bench now, it's significantly bigger and adapting design for KTM motor doesn't look that far off. Will talk to a sharp performance guy here on it. Reality is someone's going to have to spend a couple thousand bucks to get a first simple repro made, probably 2-3 times that much to invent a new high-zoot version from scratch. First estimate from a mold maker for aluminum casting method I've got is $3500 --then about $40 each to mold and machine from there, then add reed petals, gaskets, etc.

So how many do you have to sell at what price to break even for all the effort? Probably 20 at $200, plus cost of reed petals and all--probably take 2 years. Getting real, the least expensive repro of a simple already-designed system that works is probably the best option unless someone has their own CNC machine, a lot of spare cylinders to experiment on and a lot of time.

Gavin/Karl- Copies of the info for piston and cylinder setup would be greatly appreciated. I can scan and post too. Fax 503-684-7440 or [email protected]. Thanks a lot!

[DKWRACER]

Silly question...Maybe one can help! Doesn't engine reliabilty have a question hear? Performance breeds heat, heat fatigues parts, then what!!! Geeze they are only 30 years old you know.......

[Big Mac]

DKW- All I've ever read and experienced is that addition of a reed valve allows for smoother powerband, more low rpm torque and slightly higher hp on top, not higher revs. Probably less heat, since less need for slipping the clutch out of corners to get back on the pipe, and maybe even less rpms to get to same power.

Husky put reeds on all CR250s from '74 on and still tons of those bikes holding up just fine. I have aftermarket reeds on a CZ and a Husky and both run smoother with more usable grunt than stock. Anybody else have good/bad experience with reeds on KTM motors? Mac