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The 2 stroke Engine

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by Grant » Fri Oct 19, 2018 9:14 am

Martin R wrote:My old Yamaha 2-Stroke had a rotary valve (if I remember correctly) but when the garden equipment

Martin.. I think you'll find it was Suzuki that used the rotary disc inlet valve, Yamaha normally always had the reed valve as John Mentioned, we always used to use "Boyson Reeds", they were the racing upgrade and are still fitted my 400 36 years after I fitted them :P
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by Steve Payne » Fri Oct 19, 2018 12:56 pm

Yamaha FSIE had a disc valve, there was an easy way of getting a bit more power out your Fizzy, take the disc out and remove a little bit off the leading edge so it opened up a bit earlier. The down side was the fuel consumption was reduced but most of us didn't care much about that in those days.

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by Grant » Fri Oct 19, 2018 1:02 pm

Steve Payne wrote:Yamaha FSIE had a disc valve, there was an easy way of getting a bit more power out your Fizzy, take the disc out and remove a little bit off the leading edge so it opened up a bit earlier. The down side was the fuel consumption was reduced but most of us didn't care much about that in those days.

Steve

Yes you are correct SteveImage, I stand corrected, :oops:, yes anything with the carb on the side would run that disc method.
With regards to fuel consumption, my RD in the pics above has a production race tuned engine... It drinks more fuel than My Jensen!! :shock:
Last edited by Grant on Fri Oct 19, 2018 3:26 pm, edited 1 time in total.
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by Martin R » Fri Oct 19, 2018 3:07 pm

I stand corrected - I was thinking of my RD350B but, even that and also my Suzuki X7 had reed valves :oops:
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by Richie » Fri Oct 19, 2018 7:37 pm

If the piston pushes exhaust gasses out, How / why is the exhaust so "low" on the cylinder on the engine there?
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by Grant » Fri Oct 19, 2018 8:16 pm

Richie wrote:If the piston pushes exhaust gasses out, How / why is the exhaust so "low" on the cylinder on the engine there?

It pushes the burnt gasses out on the way up Richie whilst sucking more fuel in at the same time via the suction it creates from underneath the piston, the fuel gets sucked in by this method via transfer ports running beside the cylinder liner itself until it then enters the cylinder via the transfer ports,... hope that makes some sort of sense as I am not sure I have explained it that well Image
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by Richie » Fri Oct 19, 2018 9:35 pm

Which is why I was surprised not to see the exhaust at the top but then it dawned on me that if the exhaust port was positioned there, it would be open rather too long...
It's the intake charge, not the piston, pushing the exhaust gasses out.
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by Steve Payne » Sat Oct 20, 2018 7:21 am

Grant wrote:Yes you are correct SteveImage, I stand corrected, :oops:, yes anything with the carb on the side would run that disc method.
With regards to fuel consumption, my RD in the pics above has a production race tuned engine... It drinks more fuel than My Jensen!! :shock:


Fuel consumption was never that good on two strokes, seems ok on the smaller engines but the bigger stuff especially the higher performance engines could drink. I had a KH400 and that used to use crazy amounts of fuel considering its capacity, if you were lucky you could get 50 miles before you needed the reserve so high teens. I have a friend who used to have a Suzuki GT750 and that was low teens.

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by johnw » Sat Oct 20, 2018 8:38 am

Steve Payne wrote:
Grant wrote:Yes you are correct SteveImage, I stand corrected, :oops:, yes anything with the carb on the side would run that disc method.
With regards to fuel consumption, my RD in the pics above has a production race tuned engine... It drinks more fuel than My Jensen!! :shock:


Fuel consumption was never that good on two strokes, seems ok on the smaller engines but the bigger stuff especially the higher performance engines could drink. I had a KH400 and that used to use crazy amounts of fuel considering its capacity, if you were lucky you could get 50 miles before you needed the reserve so high teens. I have a friend who used to have a Suzuki GT750 and that was low teens.

Steve

2 strokes are amazingly light weight and simple engines in terms of moving parts (not port design!). I was always short of money as a kid, so went for a Ducati 250 Desmo for the better fuel consumption. I could keep up with a friend who was always 2 up on his 350LC, I would have to slip stream him on those long Lincolnshire straights to match top end, driving like that all night I would get 40mpg+.
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by johnw » Sat Oct 20, 2018 10:11 am

That us a really nice looking RD400 Grant. Are those stainless air cleaner clips? Did you rebuild it? Lovely piece of work. The fasteners are a nice touch. I remember as a kid drooling after a set of CDS stainless engine case screws. I remember many a happy night spent punching the stock screw heads back into shape as a kid, then having another go at them with an impact driver. :? Are those Micron expansion chambers?
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by Grant » Sat Oct 20, 2018 10:33 am

johnw wrote:That us a really nice looking RD400 Grant. Are those stainless air cleaner clips? Did you rebuild it? Lovely piece of work. The fasteners are a nice touch. I remember as a kid drooling after a set of CDS stainless engine case screws. I remember many a happy night spent punching the stock screw heads back into shape as a kid, then having another go at them with an impact driver. :? Are those Micron expansion chambers?

Hey JohnImage, Many thanks for your kind words John :wink:
Yes, I bought it when I was 18years old, I'm 54 now!! :shock: , I built it up in my bedroom at my parents house back then, it was all in pieces as the chap seized the crank as they used to in those days, well he did run it out of 2 stroke oil(idiot)Image, Anyway, I paid £100 for it and built it up much as you see it now really, I went over it again about 20 years ago. When I bought it came with a set of Allspeeds formula 3 pipes, I still have them in the loft wrapped up, those Pipes on it now are called Spec Pipes, I had them made in the last "20 year ago make over", the clips around the air cleaner pipes are the original ones but I had them chromed John, some of the bolts are stainless that I fitted and I just polished them along with the washers as you do in your bordem :lol: (its a sick fetish I have)Image,.. It really is a stunning Bike and I do still go out on it from time to time, very noisy,.. smells great as I drop a few capfulls of Castrol "R" in the tank too, it does the same as the Jensen, attracts people like ourselves from that era and is a good talking pointImage, you never really see or hear the old 2 strokes with the expansions anymore John do you.. Bloody Fantastic.. thank you for your kind words again John :wink:
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by Hilgert » Mon Oct 22, 2018 11:27 am

I would love to build an Interceptor with a 2 stroke Detroit V8 diesel in it :)
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by Rohan Christmas » Wed Oct 24, 2018 5:13 am

Here is a triple-rig ski race boat.
https://youtu.be/5_u6wOMMlgo?t=14
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by bigaadams » Sun Oct 28, 2018 2:52 pm

about the only device I can still buy in two stroke is a chain saw and weed eater and they trying their best to push very heavy 4 stroke models of weed eaters onto you now. They will wear you out quick due to the weight you lug around if you have the larger property to tend. But I remember well the two stoke bikes for both street and trail. I rode a number of these bike and used a lube oil in the fuel if I recall was called Blendzall or something along those lines. I could take a ride through the wood and return a bit later and still smell that exhaust mixture, unique odor to that stuff but it was the cats meow for lubing. I was getting to radical on my 250 Elsinore, Thumper, and figured I best sell it before a family member inherited it. Thanks for the walk down memory lane...
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