Pre 1975 reed valved CR125M

[Momus]

Guys, I know the commercially available GEM reed  kits are being used on 125 Elsinores but is there a consensus, or not, on the legality of home brewed set ups?

If there are precedents for yes, are they stand alone, and/or do they involve welded cylinders?

Thanks, Marcus

[motomaniac]

If you can fit Reeds without external changes its in , if you weld (external changes ) its out , as the book states . But that could change under pressure as it is now , history gets rewritten to get more bums on seats .

or less bums on seats.

[Lozza]

Just make a copy of the GEM housing.

[FourstrokeForever]

I had a CR250M with a GEM reed valve set up on it. The cylinder still requires machine work to fit it. The inlet tract gets removed altogether and then the flange face needs welding and machining in order to mount the GEM reed block. It did pass scrutiny at Connondale in 09 but as has been said before, you can't rely on precedents as proof of eligibility. It is well known however that the GEM reeds were available prior to 30/12/1974.

[tony27]

Bit strange to read that major work was required to fit a GEM to Hondas, they made units specific to each model & I assumed they were all straight bolt-ons with the only work required being to the piston like the 1 I have for my CZ

[bazza]

Tony 27 i thought so as well on 250M.
Great track at Aria.

[JohnnyO]

There is no machine work required to fit a GEM reed to a CR250M,  I had 2 bikes set up with them and they are bolt on. The only machining required is to the intake side of the piston

[Momus]

There is no machine work required to fit a GEM reed to a CR250M,  I had 2 bikes set up with them and they are bolt on. The only machining required is to the intake side of the piston

I have a spare 125 barrel with a square ported flange face that I reckon was from a reed conversion.
It looks like any bolt up reed is going to have a small area and obviously be a long way back...

How helpful is a reed on the CR250?

[JohnnyO]

The reed on the 250 was really good, I have a GEM one here for a 125 but never used it because it looks too restrictive..

[FourstrokeForever]

There is no machine work required to fit a GEM reed to a CR250M,  I had 2 bikes set up with them and they are bolt on. The only machining required is to the intake side of the piston

No offense intended.....but you are dreaming. The inlet tract MUST be machined for the GEM reeds to work effectively. Otherwise, you are increasing the length of the inlet tract thereby negating any possible advantage of having the reeds. Secondly, the physical size of the reed block WILL NOT FIT ONTO THE STANDARD INLET MOUNTS. Yes, the intake side of the piston requires work as well, as does the transfer ports.

[tony27]

An old thread talking about the same thing, welding on dt Yamaha reed housings was a period thing

http://forum.ozvmx.com/index.php?topic=13174.0

No offense intended.....but you are dreaming. The inlet tract MUST be machined for the GEM reeds to work effectively. Otherwise, you are increasing the length of the inlet tract thereby negating any possible advantage of having the reeds. Secondly, the physical size of the reed block WILL NOT FIT ONTO THE STANDARD INLET MOUNTS. Yes, the intake side of the piston requires work as well, as does the transfer ports.

If the GEM reed is the correct 1 for the motor it has the correct bolt spacing & is the same overall length as the standard manifold. I can show you a GEM reed block & piston port manifold together to show that.
There are holes needed in the piston & ideally the reed block & barrel should be blended as should the standard manifold

[JohnnyO]

There is no machine work required to fit a GEM reed to a CR250M,  I had 2 bikes set up with them and they are bolt on. The only machining required is to the intake side of the piston

No offense intended.....but you are dreaming. The inlet tract MUST be machined for the GEM reeds to work effectively. Otherwise, you are increasing the length of the inlet tract thereby negating any possible advantage of having the reeds. Secondly, the physical size of the reed block WILL NOT FIT ONTO THE STANDARD INLET MOUNTS. Yes, the intake side of the piston requires work as well, as does the transfer ports.

Another forkn vmx know all..
My CR250M was fast with good power.
I won 2 Australian vmx titles and several Qld vintage dirt track titles so I'm pretty sure it worked. And like I said it bolted straight on!

[Rossvickicampbell]

GEM addition to the CR250M was an absolutely pearler - made a big difference as JO says.

[Momus]

An old thread talking about the same thing, welding on dt Yamaha reed housings was a period thing

http://forum.ozvmx.com/index.php?topic=13174.0
 

Thanks for that Tony; couldn't find that thread  earlier.
With regard to weld fitting Yamaha reeds old sage Firko reckons:



« Reply #14 on: May 18, 2010, 04:24:42 PM »

You can run a reed cage as long as it's a period piece of equipment. GEM, Mossberger and even a DT/MX Yamaha reed block welded to the Honda barrel is acceptable. I'm certain you won't get away with later setups unless you're a master of disguising your work  .

[FourstrokeForever]

There is no machine work required to fit a GEM reed to a CR250M,  I had 2 bikes set up with them and they are bolt on. The only machining required is to the intake side of the piston

No offense intended.....but you are dreaming. The inlet tract MUST be machined for the GEM reeds to work effectively. Otherwise, you are increasing the length of the inlet tract thereby negating any possible advantage of having the reeds. Secondly, the physical size of the reed block WILL NOT FIT ONTO THE STANDARD INLET MOUNTS. Yes, the intake side of the piston requires work as well, as does the transfer ports.

Another forkn vmx know all..
My CR250M was fast with good power.
I won 2 Australian vmx titles and several Qld vintage dirt track titles so I'm pretty sure it worked. And like I said it bolted straight on!

I am far from a know it all. Unlike some that have won many titles and so there word is gospel.... I am not here to argue or lead others astray. Nor do I intend on making anything personal. I am simply going by my own experience. Perhaps my wording was a bit strong 
The GEM reed valves on MY CR250M did necessitate machining to the inlet port so they could be fitted. I had the reed valves with 3 petals either side so in effect, a 6 petal reed block. What was yours? There was absolutely no way the GEM was going to bolt up to the standard inlet port. The inlet port needed to be opened up both vertically and horizontally. I forget the height measurement but width was 75mm just so the reed cage could fit into the port. The mounts were 6 bolt. Not 4 like the stock set up so the inlet tract need to be machined to the base metal of the barrel and the original holes welded. Then machined again for a flat mounting surface. Only then could the 6 mounting holes for the GEM be drilled and tapped. Was your GEM reed set a vertically split set?
Anyway, long story short....The effort was well worth it. The Elsinore became a bike that was rideable everywhere. Not just in a straight line! It had bottom end response, a useable mid range and a top end that went on forever. It took a lot of time to get the jetting right, but with some valuable input from Gary Jones, the father of the Elsinore, It became a whole world better than the stock "light switch" Elsinore.