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
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.
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
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
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?
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.
Karl,
I'ld like a copy of it.
Thanks,
Teddy
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.
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.
Karl,
we would like one also.
John D.
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
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.?
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!
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.......
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
Due to the large investment necessary for developing a mold for these items, would there be any value to create a "blank" part that had applicability to more than just the KTM engine; for example, with final machining, could fit Buls or Huskys or Maicos, etc., so a larger market would be out there to justify the cost, time and effort?
Glenn
My brother in-law owns a small aluminum foundry, he does a lot of small runs and one offs. If someone comes up with some designs I could have him run them by his moldmaker and get some prices or if someone comes up with a mold I'm sure I could get a small quantity made for cost of materials.
Steve
I'm thinking the same thing. The other vintage MX brands that are plentiful and non-reeded are Honda Elsinores, CZ and Bultaco. Seems to be a bunch of Elsinore reed setups already being produced from something similar. But CZ's are like Pentons--everyone's chasing aftermarket DH reeds for the 250s and 400s and the demand could be strong enough to warrant. Not sure about the Bul's. Husky's went to reed in '74 and earlier are probably not valuable enough bikes when made race-ready to warrant cost of reed setup, to still get smoked by a Husky Mag.
I believe Charlie Richardson of CR Highperformance uses a later model Honda reedvalve setup and machines CZ's to match, for around $300. Haven't seen too many in action.
Thanks for the info, Mac.
Are there any AHRMA restrictions on reproducing to correct era specs that we need to worry about?
Glenn
Hey guys,
The GEM 250/400 reed valve kit works well on the 250's but we have not gotten around to trying one on the 400. With this setup on a stock 1974 250 engine, Kevin Brown won the AHRMA Sportsman 250 Expert National Championship both times we contested it - 2001 and 2002. Each weekend this engine outran the healthiest CR's, YZ's, CZ's, Bultaco's, and Husky's around and had 0 DNF's while doing so.
A properly designed reed valve setup is almost always an enhancement to a 2-stroke engine. A reed valve is, in essence, a check valve that allows the air/fuel mixture to flow into the engine but prevents it from flowing back out (reversion). When retrofitted to a stock piston port engine they can be used to increase low end and mid-range grunt, while sacrificing some airflow on the top end. In our case, the Gem reed made our bike's powerband more linear, smooth, and forgiving, which, with Kevin's skill and throttle control, allows him to really maximize speed in the corners and rough stuff. Realistically though, the 250 has an excellent powerband to begin with, so I don't think the reed setup is that important on it.
More frequently, reed valves are used by engine designers to enhance mid-range and top end power because they allow more radical cylinder/port designs that would otherwise be flat on the bottom end and too pipey. This is the reason you see reed valves on all modern 2-stroke's. Reed valves are also most helpful to smaller, higher revving engines like 125's and, conversely, less helpful to torquey open class bikes.
While you've got me going, I need to preach a little bit about horsepower. Peak horsepower wins when you have ideal conditions i.e. drag racing, where you have excellent traction and no turns. For anything else I would gladly sacrifice a few peak horsepower for a smooth, linear, predictable spread of power. I've witnessed hundreds of dyno runs in my life and can easily say that the engine that has the most peak horsepower doesn't always win. Engines tuned only for peak power typically give away some lower end power and are more prone to funky power curves as well. A good race engine designer first considers the engine's application and then attempts to yield the ideal combination of horsepower, torque, "area under the curve", and the shape of the curve.
As far as the KTM 250 goes, I personally think it was KTM's best design from that period. With a fairly elaborate porting scheme and good crankshaft flywheel weight, the 250 made tons of power yet was very smooth and tractable. The 250 is such a well designed engine that it can win races in its stock configuration. If you really need more power, then the Cranke porting and a better pipe are worth considering. Ultimately, a reed valve can be added but I don't think it's really necessary.
In contrast, the early 400's had fairly radical port timing and compression ratio, and too little crankshaft weight. The result was a pipey, explosive powerband like a 125 on steroids. As a result, on a tight or slippery track our 250 will beat our 400 any day. To improve the 400 you should use the heaviest ignition flywheel possible, reshape the combustion chamber like a later 400 (or use a later head), use a better pipe, or even use a bottom end from a later 400, which had extra weights bolted to the crankshaft flywheels. This engine would also be a good candidate for a reed valve. The GEM 250/400 kit (not to be confused with the small 175 kit) will work but may prove too restrictive based on its design. To design a reed kit that replaces the stock intake manifold you must work within the confines of the existing 4 bolt pattern on the cylinder, which doesn't leave much room for the added area of a reed cage and petals. Unfortunately, I have not used the GEM kit on a 400 so I can't really say how it would perform. The ultimate way to add a reed valve to the 400 would be by fabricating a large reed block and welding it to the cylinder. This would allow a larger cross sectional area that could house a reed cage and still maintain adequate flow. I have heard this is what J.P. Morgen does with his KTM 400's and I know that some of our competitors do this to their Maico's and CZ's.
For more info on this type of modification go to Replika Maschinen's web site and look at the article entitled "Big Reed Maico". They discuss their modifications and the related AHRMA rules. Also, at the top of the article there is a link to an AHRMA article with pictures of the conversion.
Whew! That's my .02 worth. Let me know what you guys end up doing.
Kent Knudson
Kent,
i agree with you on reed kitting that generation KTM motor.
the Gemm 175 kit is too small for the 175, its too restrictive. the ones i did for customers i did not like at all.
the early 400's power stock was like pulling the trigger on a gun. the 79 400 GS i had was a dream to ride in the tight woods with a stock Bing carb. the early 400 would probly work much better with weight added to the flywheel and some work on the pipe.
the key i believe to adding the reed kit and not looseing reliability is how much you modify the piston and ports.
where you cut the holes in the piston and any changes to the intake boost port area of the cylinder..
the way the piston is designed would limit where and how large you could go with the holes. same with the intake area where the bridge in the intake port is located. it would be better for anyone doing it to get the measurements from someone like you who has done it and tested it.
we reed kitted a lot of engines back then with Gemm kits.some designs did not work well at all with the gemm kits designed for that specific engine .
just my 2 cents chuckle chuckle!
JOhn D.
Hey John,
That's great info. I always enjoy hearing what dealers did back when the bikes were new. Were you ever able to tame down the 400 back then?
Well, I'm off to the Dealer Show in Indy. I'll catch you guys Monday.
Kent
Kent,
On taming the 400, we put a smaller carburetor and retarded the timing. This was mainly to help out of the turns so that the explosive power was more trackable.
Ron Carbaugh
Ron,
Did you guys tame the 400 by using a 36mm Bing from the 250 or did you use Mikunis?
Glenn
Glenn,
You can use either, but I used a Bing(36mm). I normally used carburetors that I had the most selection of needles and jets. Again this was out personal preference for keeping horsepower to the ground on tight tracks. I changed gearing for the long tracks. I don't consider myself a expert on the big engines since my real love was the 100/125 class.
Ron Carbaugh
Ron,
On the old 400, what did you retard the timing to? If you used a Mikuni, would you use the 38mm or 36mm? I am preparing two 400s for this race season. The first is a rebuild of my Mint 400 vintage bike which broke a cylider stud and sucked in enough dirt during a national to completely wear it out. THe cases were never very good so I have two lower ends to replace it, a '74 and a '77. I thought I had decided to use the '74 because it was supposed to be hairier than the '77 figuring that the people who didn't like the '74 were woods riders, and for MX it might be just great. I do have an aftermarket torqueier pipe for it and I'm putting on a PVL ignition so the most flywheel I can get is 17 oz. I wouldn't mind going to a Mikuni, they seem to work so much more reliably and parts are so much more available and cheaper. Should I use the '77 lower end or do you think I'll be happier with the '74 with pipe, timing and Mikuni changes?
The second 400 is going in the 1980 MC80 I'm building. I wanted a 420, but there just isn't enough parts available to race them I believe. So I opted for sending a '77 400 clyinder to J.P. Morgen to do his magic reed valve conversion and porting work on. I got it back and I am still trying to get everything else together. I can't wait to try it out. His porting work was beautiful. It uses a late '70s 6 pedal Yamaha reed cage which is then AHRMA legal. He supplied a 38mm Mikuni with it. I have less than 2 weeks before we take off for Florida for bike week to get both these ready. It has been so hard working in an unheated barn in sub 20 degree weather. I can't really try them out anyway because of the snow on the ground!!! I hoping I get one running by the end of this weekend and that all the snow melts!!!!
Thanks for your input.
Teddy
Teddy,
The Mikuni is probably a better choice, but I just had so many Bing parts(and it looked stock) is why I used a Bing. On the timing I don't have my original notes(went with the bike when my friend sold it), but it was very little. I retarded it to stop such explosive hits on coming out of slow turns or sweepers.
The pipe sounds interesting especially if it is a real torquer.
The other area to address (and I was visiting with Larry Perkins about this subject just the other day) is the flywheel. With a regular flywwheel we were discussing how we used to glue weights to get it under control.
This all may sound funny to some that read this as if we are trying to slow this bike down. But my point is trackable or useable horsepower.
The second engine may also be a candidate for trying the torque pipe on after carburetion is sorted out.
I guess the last thing after I sorted out the engines was to tune the gearing for the rider to get the most of bottom to mid range out of the bike. Any one can go fast down the straights according to Kenny Roberts[:p].
I final analysis I again state I am not a expert on these big engines in that there are too many years gone by since played with them. Now I won't sleep until I remember the setting for the timing.
TEDDY may I ask you for the frame number off you 125 Sachs with the lay down suspention. I'm trying to keep up with these bikes for hopefully future POG project;).
Keep them in line Teddy,
Ron Carbaugh
Ron,
I wrote a note to myself to remember to get the frame number for you. Thanks for your input. J.P. Morgen recommended 2.2mm advanced for the new set up. I was using 2.4mm for the Mint 400. Last year, I took off the 17oz weight on the PVL because I wanted more accelleration. I think the bike was just not running right all year long and I think the carb was a major part of it. I will order a Mikuni.
Teddy
Teddy,
One last comment before I'm banned from the message board for using up too much space. Timming is a good and bad thing for making horsepower. It is like Nitro for our big engines if a little helps, a little more should help it that much more[:0]. I have a set of $1500 pistons that prove that theroy wrong. What I am saying is each engine has a sweet spot and when I build a strong engine, with tricks some people will never know about(I'm not being funny), I start stepping it back to save it..and timing is one way to keep from burning up pistons(heat). I believe in the old numbers of 3600 ft. per second(piston speed) is when normal pistons start melting or go into stage one of fatigue. Understand these are just my thoughts and are probably worth what you are paying for them:).
When it comes to ignition and timing Dane is THE EXPERT period. I am honored he takes the time to contribute to this Forum.
Teddy when I grow up I hope to be a racer like you[8D].
Ron Carbaugh