Author Topic: 77 Reed Block  (Read 6540 times)

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Offline PCMAX

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77 Reed Block
« on: July 25, 2016, 08:28:59 PM »


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?
« Last Edit: July 25, 2016, 08:37:37 PM by PCMAX »
74 MX250A, 75 CR250, 82 CR125, 82 YZ250J, 84 XR250,

Offline Mick D

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Re: 77 Reed Block
« Reply #1 on: July 26, 2016, 12:41:40 PM »
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.
"light weight, and it works great"  :)

Offline tony27

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Re: 77 Reed Block
« Reply #2 on: July 26, 2016, 06:07:06 PM »
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

Offline Mick D

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Re: 77 Reed Block
« Reply #3 on: July 26, 2016, 06:40:25 PM »
Great work Tony, thanks :)

Peter is thinking of trying it without the reed arrangement.
Looking forward to hearing his comparison opinion if he does :) :)
"light weight, and it works great"  :)

Offline PCMAX

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Re: 77 Reed Block
« Reply #4 on: July 26, 2016, 07:03:21 PM »
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
74 MX250A, 75 CR250, 82 CR125, 82 YZ250J, 84 XR250,

Offline tony27

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Re: 77 Reed Block
« Reply #5 on: July 26, 2016, 07:20:56 PM »
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

Offline jimg1au

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Re: 77 Reed Block
« Reply #6 on: July 26, 2016, 07:25:13 PM »
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

Offline Mick D

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Re: 77 Reed Block
« Reply #7 on: July 26, 2016, 10:55:25 PM »
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?
"light weight, and it works great"  :)

Offline jimg1au

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Re: 77 Reed Block
« Reply #8 on: July 27, 2016, 03:30:07 PM »
at least he knows thats the main thing
jim

Offline PCMAX

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Re: 77 Reed Block
« Reply #9 on: July 27, 2016, 07:44:04 PM »
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.


« Last Edit: July 27, 2016, 07:46:45 PM by PCMAX »
74 MX250A, 75 CR250, 82 CR125, 82 YZ250J, 84 XR250,

Offline tony27

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Re: 77 Reed Block
« Reply #10 on: July 28, 2016, 06:41:17 AM »
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
« Last Edit: July 28, 2016, 12:52:26 PM by tony27 »

Offline Lozza

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Re: 77 Reed Block
« Reply #11 on: July 28, 2016, 05:34:31 PM »
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
Jesus only loves two strokes

Offline tony27

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Re: 77 Reed Block
« Reply #12 on: July 28, 2016, 06:13:11 PM »
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

Offline Lozza

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Re: 77 Reed Block
« Reply #13 on: July 29, 2016, 12:06:10 AM »
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
Jesus only loves two strokes

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #14 on: January 03, 2017, 06:05:22 AM »
Hi, I tried the GEM reeds on my 69'er squarebarrel GS250. It runs greath ;D
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!

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #15 on: January 03, 2017, 06:40:13 AM »
An I've also made a model 76 reed cylinder.
But this time I used a selfmade case with Yamaha reed.
It goes like hell and need also the big exhaust pipe of the 400ccm!!


















Offline shelpi

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Re: 77 Reed Block
« Reply #16 on: January 03, 2017, 11:05:06 AM »
no like button So LIKE!

Offline tony27

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Re: 77 Reed Block
« Reply #17 on: January 03, 2017, 01:40:40 PM »
Did you make a sub plate for mounting the GEM reed block to the earlier cylinder rather than build up with weld? Looks like a very elegant way of doing it that would be able to be reversed
Your homemade reed block looks good, do you remember what the yamaha reed you used was out of?
Very impressive work

Offline Lozza

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Re: 77 Reed Block
« Reply #18 on: January 03, 2017, 04:42:05 PM »








I still don't know why people think reeds are open at BDC  there is no intake charge ready to flow through the piston port when they are exposed .   :o
Jesus only loves two strokes

Offline Tomas

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Re: 77 Reed Block
« Reply #19 on: January 03, 2017, 07:47:07 PM »
That makes sense. Windowed  piston allows more flow, more continuous flow therefore 250 pipe is restrictive and 400 pipe allow for more/fresher charge in cylinder. Also larger pipe should allow expanding gasses to escape faster when exshaust port is open which on the other side creates  vacum in crankcase and sucks new charge above the piston and windowed piston helps to extend this. Bit like when atomic bomb creates mushroom cloud but much much faster  :) Like your creation and how you apply physics in two stroke modifications. Good work

Offline Tomas

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Re: 77 Reed Block
« Reply #20 on: January 03, 2017, 07:55:30 PM »
Also. If you dont mind me to ask. Does your cylinder have any kind of boost port added/drilled? Thank you ;)

HeavenVMX

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Re: 77 Reed Block
« Reply #21 on: January 03, 2017, 11:30:31 PM »

 You can draw more air through a drinking straw than a 100mm conduit.

This is one of the most ridiculous statement I have ever seen posted on this site. It is not only plainly wrong on so many levels it requires us to ignore every principle relating air flow that it is not even funny. The real clincher in this statement is the reference to 'draw more' air through a straw which is far far harder to do than to push and the 'more' indicates a higher quantity. Just think about the proposition that more air can flow through a 5mm tube compared to a 100mm tube. The flow rate is directly related to pressure difference, cross sectional area and air density.

Try putting a straw in your mouth and only breath through it and then start running. See how long before you either open your mouth or pass out FFS. Then after you have recovered try the same thing with a 100mm tube.

I think or hope you are confusing flow velocity with flow rate ::) At a given flow rate the air velocity through a straw would be many many times higher than a 100mm tube.

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #22 on: January 04, 2017, 03:08:19 AM »
Did you make a sub plate for mounting the GEM reed block to the earlier cylinder rather than build up with weld? Looks like a very elegant way of doing it that would be able to be reversed
Your homemade reed block looks good, do you remember what the yamaha reed you used was out of?
Very impressive work

Yes, there is a sub plate between cylinder and case in both cases.
For the square barrel the GEM Kit includes this plate and you just have to customize it for the round intake hole.

The yamaha reed is out of a RD350YPVS or Banshee 350 Engine.
« Last Edit: January 04, 2017, 03:10:21 AM by Maico-Mac »

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #23 on: January 04, 2017, 03:31:31 AM »
I still don't know why people think reeds are open at BDC........

I don't think so too!
But after BDC when the Piston wents up the flow goes trough the holes until the piston skirt takes the lead, therefore they are so high  ;)
In the picture of the radial barrel the piston is not on BDC, it has ~30mm to go.

I think it's not good to open the 3.overflow to the intake, as shown in PCMAX cylinder,
because this spoils the flow.

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #24 on: January 04, 2017, 03:37:59 AM »
Also. If you dont mind me to ask. Does your cylinder have any kind of boost port added/drilled? Thank you ;)

There are no extra ports added..

Offline tony27

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Re: 77 Reed Block
« Reply #25 on: January 04, 2017, 09:52:14 PM »
That means a YZ85 reed block will also fit, from what I've read there is a v-force unit that fits into the RD350YPVS & Banshee cylinders
Always surprises me just how small old reed blocks are compared to newer bikes, often the smallest modern bikes have the same size as something older 3-4 times larger

Offline Maico-Mac

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Re: 77 Reed Block
« Reply #26 on: January 05, 2017, 04:11:09 AM »
That means a YZ85 reed block will also fit, from what I've read there is a v-force unit that fits into the RD350YPVS & Banshee cylinders
Always surprises me just how small old reed blocks are compared to newer bikes, often the smallest modern bikes have the same size as something older 3-4 times larger

Yes you are right, v-force is possible. But I don't think it's necessary.
I'm always surprised how good the small reed blocks work on higher revs. My expectation was that they will restrict the revs on a lower level than without reeds. But this is not the case  :D

Offline shelpi

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Re: 77 Reed Block
« Reply #27 on: January 08, 2017, 12:01:56 PM »

 You can draw more air through a drinking straw than a 100mm conduit.

This is one of the most ridiculous statement I have ever seen posted on this site. It is not only plainly wrong on so many levels it requires us to ignore every principle relating air flow that it is not even funny. The real clincher in this statement is the reference to 'draw more' air through a straw which is far far harder to do than to push and the 'more' indicates a higher quantity. Just think about the proposition that more air can flow through a 5mm tube compared to a 100mm tube. The flow rate is directly related to pressure difference, cross sectional area and air density.

Try putting a straw in your mouth and only breath through it and then start running. See how long before you either open your mouth or pass out FFS. Then after you have recovered try the same thing with a 100mm tube.

I think or hope you are confusing flow velocity with flow rate ::) At a given flow rate the air velocity through a straw would be many many times higher than a 100mm tube.
what Lozza is saying is correct when certain conditions arise ie, 1 of them being in carburation there is no way you will get the correct metering (flow of fuel) threw a large carby have you sucked fliud threw a straw and the a bigger piece of pipe it gets expedentsially  harder as the diameter increases and that is opposite in the way you have applied it ( you see its in the application that changes the the rules in play) cause and affect

HeavenVMX

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Re: 77 Reed Block
« Reply #28 on: January 08, 2017, 02:28:01 PM »

 You can draw more air through a drinking straw than a 100mm conduit.

This is one of the most ridiculous statement I have ever seen posted on this site. It is not only plainly wrong on so many levels it requires us to ignore every principle relating air flow that it is not even funny. The real clincher in this statement is the reference to 'draw more' air through a straw which is far far harder to do than to push and the 'more' indicates a higher quantity. Just think about the proposition that more air can flow through a 5mm tube compared to a 100mm tube. The flow rate is directly related to pressure difference, cross sectional area and air density.

Try putting a straw in your mouth and only breath through it and then start running. See how long before you either open your mouth or pass out FFS. Then after you have recovered try the same thing with a 100mm tube.

I think or hope you are confusing flow velocity with flow rate ::) At a given flow rate the air velocity through a straw would be many many times higher than a 100mm tube.
what Lozza is saying is correct when certain conditions arise ie, 1 of them being in carburation there is no way you will get the correct metering (flow of fuel) threw a large carby have you sucked fliud threw a straw and the a bigger piece of pipe it gets expedentsially  harder as the diameter increases and that is opposite in the way you have applied it ( you see its in the application that changes the the rules in play) cause and affect

He was referring to air flow not metered fuel flow. You are referring to the venturi effect through a carburettor causing a negative pressure immediately after the slide which is related to air speed through the venturi not quantity. As I pointed out for a given air flow, air speed is higher in a smaller tube. The fuel area ratio (metering) in a carburettor is a correlation of the negative pressure created by air speed through a venturi and the jet sizes.

Fuel is a non-compressible medium unlike air. The idea you are referring to about sucking through a straw is related to the fact your lung capacity is unable to draw a vacuum on a large diameter pipe but is able to draw a vacuum on a straw and there is also the fact you are lifting the water (heavy stuff compared to air) up a pipe/straw. If you tilt the pipe/straw point where the weight of the medium is cancelled out and apply your 'suck' I think you will find the larger diameter will make you choke very quickly as it delivers a much larger volume of water.

If you apply your 'suck' principle to just air it is far easier (less effort) and faster (no flow restriction) to fill your lung through a 100mm pipe than a 5mm straw. Think about it.

Think about fuel injection, the fuel delivery and air delivery systems are separate and independent. Therefore if the air flow situation was as originally posted all formula 1 and Moto GP engines would have straws as air intake stacks to maximise air flow  ::) :o they would certainly be easy to package.

Anyway if you believe the initial proposition then I have got some lovely pig that you may be interested in, they come in several colours and all fly perfectly ;) ;D joking OK joking

Offline shelpi

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Re: 77 Reed Block
« Reply #29 on: January 08, 2017, 02:54:24 PM »
Like I said depends on application
orifice size depics flow rate, all pretty simple really as long as it is not mixed up in its application and mediums
once confusion regns no amount of explanation will sevice
cheers
oh look a squirrel

HeavenVMX

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Re: 77 Reed Block
« Reply #30 on: January 08, 2017, 03:44:24 PM »
Like I said depends on application
orifice size depics flow rate, all pretty simple really as long as it is not mixed up in its application and mediums
once confusion regns no amount of explanation will sevice
cheers
oh look a squirrel
You are trying to relate venturi effect as setting flow rate.

A venturi is a measuring device which allows you to measure flow (we are discussing air flow which is a compressible medium) by generating a representative signal (in the case of a carburettor this is the vacuum applied to the jetting system to draw fuel in) which is proportional to air speed through the venturi this 'signal' is then compensated for air density and cross sectional area. This is achieved via the jetting in a carburettor. There are many ways to measure airflow besides a venturi as seen in fuel injection systems.

in industrial instrumentation situations every venturi design has it's own characteristic table which is a relationship between the differential pressure across the venturi to medium speed for a specific medium, medium density and cross sectional area. This is converted into a flow constant graph which is used to convert the differential pressure across the venturi to a calculated flow in KG/sec or some other unit of quantity.

Anyway I am busy herding my pigs that keep flying away so over and out.

Offline GMC

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Re: 77 Reed Block
« Reply #31 on: January 08, 2017, 05:15:23 PM »
The confusion with the straw statement comes from the misunderstanding between volume and velocity.
Volume being the amount of air that travels through the straw / tube and velocity being the speed at which it travels through the straw / tube.

A larger carby will allow more air to travel through it but it will travel at a slower speed thus not having the same venturi effect so may not draw in enough fuel, especially at lower RPM

Ultimately volume and velocity must be in harmony with each other
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HeavenVMX

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Re: 77 Reed Block
« Reply #32 on: January 08, 2017, 05:20:58 PM »
Thank Christ!!! The voice of reason.

The volume/velocity harmony is relevant, as you say, for the operation of a carburettor not when considering flow in isolation.

Offline shelpi

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Re: 77 Reed Block
« Reply #33 on: January 14, 2017, 09:55:50 AM »
The confusion with the straw statement comes from the misunderstanding between volume and velocity.
Volume being the amount of air that travels through the straw / tube and velocity being the speed at which it travels through the straw / tube.

A larger carby will allow more air to travel through it but it will travel at a slower speed thus not having the same venturi effect so may not draw in enough fuel, especially at lower RPM

Ultimately volume and velocity must be in harmony with each other
thank you