Reed Valve for Grubee engines

Discussion in 'Performance Mods' started by jaguar, Apr 1, 2012.

  1. jaguar

    jaguar Well-Known Member

    Here is an inexpensive reed valve for the Grubee engine: But the problem is that it creates more compressible crank space between the piston and reed valve and so decreases the crankcase compression ratio (CCR). This makes the pressure of the intake charge less when the transfer ports are opened and so enters slowly and with less inertia to pull more charge after it. To offset that you would need to occupy unused empty space in the crankcase area with JBWeld. Below is a picture showing that space. Here is what I did: Measure the inner diameter of the hollow circular area of the side of the crank (the fat weighty part). Place the crankcase halves on the floor so that their interior side is facing up. Cut a strip of aluminum (from a cheap bread pan) and make a circle of it of a diameter slightly less than that of the inner crank circle that was measured. Oil it so JBWeld won't stick too well to it. Place it around the crankcase area that is needed to be filled in. Mix up some JBWeld and fill in that area and let it set and dry for a day. Pull off the aluminum. Check to see if the crank touches any of the JBWeld and file/cut/dremel those spots down. Put it back together. (Get a crankcase gasket before starting and maybe also crank bearings and seals from Get two of the skinny left seal since that seal wears out faster with increased crankcase pressure). Luckily it is easy to replace in the future by removing the magneto and just prying it out with a jewelers screwdriver. Grease everything and just push the new one into place with your fingers.

    Attached Files:

  2. jaguar

    jaguar Well-Known Member

    Possibly the new reed valve from Rock Solid Engines leaves less free space in front of the reeds. I have one on order now that I will bolt a 16mm Dellorto carb to.
  3. Fabian

    Fabian Well-Known Member

    The Rock Solid Engines Billet CNC Reed Valve leaves virtually no space inbetween the piston and reed valve cage; maximising crank case compression and boosting transfer port velocity and mixture motion.

    It is a very well designed product, though the carburettor will need a jetting change as there is no longer any reversion (blow back) with the reed valve installed.

    A side benefit of massively reduced reversion is a complete lack of oil and filth dripping from the air filter, not to mention a significantly quieter engine.
    Couple this benefit with a 3 inch silicon exhaust extension and engine noise is even further reduced.

    Music to my ears
  4. jaguar

    jaguar Well-Known Member

    Fabian, didn't you write somewhere else that the reed valve only boosted low and mid range power, and left top end power the same? That would be because of a lowered CCR. That intake area between the reeds and the piston is part of the equation when calculating the ratio. It isn't with a piston port intake. And with a small engine a small amount of space can make a considerable difference. The CCR needs to be increased on these engines, not lowered. In one hour I can have the engine off and cases split. Why don't you dig in and stuff the crank? Then you would have more top end power as well.
  5. Skyliner70cc

    Skyliner70cc Active Member

    I have the rocksolid reedvalve intake in mine. It is well designed, very compact, and I'll probably fire up the engine this Thursday using a NT speed carb. I have a high compression head from MM, mild porting, and a tuned pipe. not sure what carb to use initially. I want to use the Dax RT (Dellorto clone) but I used a similar one several years ago and it ran too rich on stock jetting (I'm at 6600 feet) and I see people at lower altitudes going down to 70 or 65 size jets and I'm thinking I would need equal or smaller at my elevation.

    If the rock solid reed valve instake works, I'll tear apart my other shifter bike's engine and install it along with other upgrades.

    yes, I'll probably order Jag's improved CDI this week. My new bike is geared for hill climbing and I want an engine that will pull all day long at midrange rpms up steep hills at fairly low bike speeds. My outersprocket on my shifter kit is 48 tooth, driven by a 10 tooth drive sprocket, and attached to the freewheel going to the rear cog is a 30. I don't care about top speed and will be happy if it tops out at 20mph.
  6. Fabian

    Fabian Well-Known Member

    As in my previous reply Jaguar, the crank case compression is effectively increased as there is reduced blow down through the intake port when piston movement reverses and starts to bring positive pressure to the crank case.

    Positive pressure can only be achieved when the intake port is closed but the reed valve setup allows positive pressure to build from the moment vacuum is no longer being generated, hence the time that is taken to fully close the intake port with the piston, is being used to build crank case pressure, rather than blowing it back out the intake port.

    Tests back in the early days of Honda 2-stroke development showed no real power gain with a reed valve but improved overall throttle progression and transition power before the engine passed into the tuned phase of the exhaust race pipe.
    Back in those early days, disk valves were popular because they presented no effective intake restriction and made the most amount of power. Problem was that such extreme timing made the engine very peaky and the power delivery very difficult for the rider to use and control.

    The Rock Solid Engines Billet CNC intake is very compact and beautifully fills the intake port minimising volume behind the reed valve cage.
    It has been well thought out and a much better design than the Arrow Cycles Reed Valve Intake which has greater volume behind the reed cage, reducing crank case compression.

    My experiences are that low end and especially mid range power is significantly improved, which is 'exactly' where i want the power improvement, as it is best suited to my application.
    I noticed very little if any top end power increase but i have no interest and no requirement on a stock standard engine to rev it past 5,000 rpm.
    The reed valve intake makes the greatest power difference between 2,500 and 4,500 rpm, or it should better be called "torque" increase.

    If anyone wants my opinion after having experience with Rock Solid Engine's Reed Valve Intake, the answer is simple - """Just Do It""" but the carburettor will need to be rejetted to work properly.
    I needed to go 6 jet sizes larger, from a Dellorto No68 to a Dellorto No74. It seems like a massive change, but that's what the engine needed, and yes, i did thoroughly check for air leaks, of which there were non.
    Last edited: Apr 29, 2012
  7. Fabian

    Fabian Well-Known Member

    Stuffing the bottom end may yield even more low and midrange torque and possibly top end power but the increase with only the reed valve intake has given what "feels" like around 25% more torque.

    As things stand, i don't need any more power for my application as i have a SickBikeParts shift kit (modified to enable a multi chain wheel sprocket set), and can simply change gears to (ultra low range ratios) to keep climbing seriously steep hills; outright power being of much less concern with such a system.
  8. jaguar

    jaguar Well-Known Member

    On my 55cc the CCR was increased from 1.1 to 1.2 by addition of my custom reed valve which rests inside the port and almost touches the piston. Then I increased it to 1.4 by stuffing the crank which I think now was a bit much. I think 1.3 is ideal for these engines slightly ported. But there seems to be a big difference between each size of engine, the bigger engines having a better CCR. Who knows what the CCR before and after is for a 66cc engine? I suspect I will have a 1.3:1 ratio on my 55cc after installing the Reeds from Rock Solid which should be perfect which is one reason I recommend stuffing the crank. If you don't believe me then do it yourself if you have a 48cc engine. Probably the 66cc don't need it.
    By the by, Rock Solid is going to let you choose what size mounting you want because of the difference in mounting bolt spacing between the 48cc and 66cc engines. Well, that's what they told me they were going to start offering. My mounting spacing is 42mm which is the same as for a 66cc engine. They said they would machine mine differently to fit.
    Neon likes this.
  9. Skyliner70cc

    Skyliner70cc Active Member

    I'm excited now...can't wait to fire up my ride after reading your experiences Fabian. More torque and more punch at low to mid rpms will help me climb those infamous Colorado hills.
  10. Fabian

    Fabian Well-Known Member

    @ Skyliner70cc

    That's exactly why i was so impressed with the reed valve intake: More torque and more punch at low to mid rpms will help me climb those infamous Colorado hills,

    or in my case, those Victorian high country hills.

    A side note: reduced vibration with reduced rpm and reduced noise that with reduced rpm; generally a nicer riding experience.