Yamaha 2t before expansion chambers

I'm been hearing bikes of this type here and every time I look up, it looks like a smoking 4t bike with that chrome exhaust but sounds like a yamaha 2t... This kid was parked on one today so I took a few pics .. Not sure what it is really but I've seen maybe 4-5 of these machines around here ... The oil line is still hooked up from the oil tank so maybe the oil pump is still working ...

The engine and frame are probably original but any other part might have been changed ... That SA and shocks and chain tensioner ~might be all custom Gotta be a mountain rider by the looks of his tires ...





Oil tank

Here's the pipe that fooled me a couple times ...


Officially 'Made in Japan'

probably early 70s, that hadnt quite figured it out yet

Yep on the hose (I think) ... That side plate was loose and I wanted to remove it right there and have a look at what was inside ...

That oil tank is huge ... but so is that gas tank if it it stock..

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I saw this one also ... It had no fire and I told the guy he needed to set the contact points maybe ... This rider said he had disconnected his oil pump...

Might have started life as a Yamaha YG1. Don't know whether they ever marketed them in the U.S. A little concerned about the rider's safety gear.

That certainly looks like the same engine and frame with the air box and oil tanks in the same locations with slightly different design. No downtube in front of the frame and all the open space there, looks a little weird today .. But 196?, this was probably very cutting edge...

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As far as safety gear, I can understand no helmet in the mountains (now that I've been here ~5 yrs) with the slow speeds these guys ride at and even the old brakes .. But not the flip-flops... I can't ride without dabbing ... Yet, I don't see many blooody toes here on these guys ...

Here's a video of the old guy trying to roll that bike off to get it started ... No start and no fire at the plug ...

View: http://youtu.be/R4vta7I3miI

You can get a look at those ruts on that up hill and how slick and easy it is the wipe out with the front wheel ... That clay dirt is also giving very good traction also ... For every day riding, meaning specific dirt that I have to ride in each day, ~clay type dirt is OK with me ... That other model walking up the hill is just another distraction you gotta deal with.

they must think you are some kind of off road master compared to those bikes

Found this website, you might find it interesting.
http://www.pbase.com/jetdoctor/yamaha_yg1_80
A true gear head, watching a guy trying to start his Yamaha instead of offering the girl a ride up the hill.
How do you like living in the Philippines? Looks like an interesting place.

Just another big-bike rider here I'd guess but foreigners in general do get a free pass on lots of stuff... I do try to ride out of the beaten-out riding line as much as possible and pull a few wheelies ...Plus stand up more than most riders probably so my riding might look a little different.

Not sure where that gal came from but she might have been his fare and he needed to get running again before she topped the hill and rode on with another rider :0)

This place is certainly not for everyone and has plenty of short-comings but I'm pretty much ruined I think for living anywhere else now ... It's day after day of the same thing that I like .. It's like Goundhog Day and I'm Bill Murray riding a Husqvarna 250cc dirt bike. Of course the gals see us foreigners as Steve McQueen. I can't even imagine living else where now. Every ~16 months foreigners (depending on your visa type) have to leave this country for at least 1 day before they can return ... Leaving is traumatic.

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That was an interesting article ... YG1 80 was Yamaha's first commercially successful motorcycle ... And it would whip the hondas of that day ... So this bike was a big deal for Yamaha getting it's place in bike sales.

The engine is a 75cc rotary valve 2 stroke as compared to the piston port 2t engines today ... Not sure what that means really ...

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Found another one of these bikes while riding around in circles today ... I got video also this time..


What happened to the oil-pump in later yrs? This one is not connected.


Oilless?


Seat foam blends in so well with the dirt color ...


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I saw these kids on the bike and just wanted to get some of their suspension-work video ... They might have taken it a little more like a race ... The bike looked ok riding in the smoothest line up to ~15MPH but towards the end of the video right before he made that left turn so wide, the bike took a weird little bounce on that speedy downhill by the water-cans that the riders noticed

View: https://www.youtube.com/watch?v=7MS-xs8wXO8

on the rotary disc style theres a disc with hole attached to the crank. when the crank turns the hole is covered/uncovered and this gives you your port timing instead of having piston port timing. in can be a good setup but i think you have to mount the carb low by the crankas you can see.

Most of the early 1970's Kawasaki 2 stroke trail bikes were rotary valve from the small bore 100cc Trail Boss on up to the 350cc big Horns. Carb was on the side of the engine. Small Suzuki's back in the day were also like this Early Yamaha Ray.

The Can-Ams when introduced in the early 70s were all Rotary Valve right up to the early 80s. They had the carbs mounted behind the cylinder with an intake tract cast with the inner half of it into the inner case and the other half length wise in the left outer case. Airbox was behind the carb like a normal port induction 2 stroke. These Can-Ams had transfer ports surrounding the rear of the piston as well as the sides. They also made some pretty good horsepower for there day.

Maico 125cc 2 strokes MX dirtbikes were rotary valve as well. Carb was up to the rear position above the cases to narrow the engine and making carb adjustments easier.

ray ray, here is a few pics of the rotary valve itself. Port timing can be changed by simply changing or modifying the valves rotational degree of opening. Like the 1 pictured in the package marked 159 deg. "BRP" Bombardier Recreational Products/Sea-Doo/Can-AM/Ski-Doo, has used this setup for years on the snow machines and Ski-Doo's and the old Can-Am 2 stroke dirt bikes, swap out the rotary valve and it's like a port job. The induction inlet hole in the case can also be physically ported along with the transfer ports in the cylinder.

Nice description of rotary valve operation Big Timmy. We once bought a Kawasaki A7 Avenger 350 twin with rotary valves. Bought it cheap because it would only run on 1 cylinder. May dad discovered that on one of the rotary valves the fiber outer portion of the disk had come loose on the metal hub that attached to the crankshaft, threw the intake timing for that cylinder completely off.

ray ray, You're lucky you didn't get roosted by those kids!

Tim, that last diagram (ya6) give a pretty good view what is driving what in there ... But is that rotoValve on its own shaft or the crank?
Two-stroke is just gonna be a little funky apparently ... I'm really curious on that exhaust ... Did this rotoValve design not support expansion chambers that came along shortly along with the piston ports 2t engine?

And I can see the CARB is pointed odd in those CAN AM pics...But they do have expansion chambers .. Is the valve just being re-designed? Or did it need the piston ports also?

After seeing this roto design that apparently worked to some degree and got dropped \ modified, where did all the pollution get introduced from the engine or was it something that was absolutely necessary to push the engine HP ..

Yep and you gotta get really close with those helmet cams or it looks like you are a mile off ... I just wear safety glasses because its so hot here but might need to switch to goggles out there ...

Ray,
Yes the rotary valve ran directly off the end of the crankshaft through the cases side port opening. It just allows the incoming mixture to enter the lower half of the cases directly as the piston rises causing a suction. The rotary valve then closes that window while waiting for the piston to come down and pressurize the mixture up through the transfer ports. The Transfer ports are still opened and timed by the piston opening these ports as it goes down allowing the mixture to enter the combustion chamber.

An expansion chamber could still be used if one was available or was made. I had a Yamaha mini enduro with this same engine set up when I was about 13 or 14. It had an aftermarket cone expansion chamber and was very pipey. It was a stamped cone design, not rolled. I think it was made by Hooker. These expansion chamber pipes were also available for the rotary valve Kawasaki's and many other dirt bikes of there day.

From this I started building hand rolled cone chambers in High school metal shop back in about 1974 or 75 for my friends and my own Maico's. Also many for the DT Yamaha enduro's and RD and R5 350twins. Also quite a few matched cone pipes for the Kawasaki 350,400,500,750 H1 and H2 Triples. Usually matching the cone layout taken from the Denco Chambers on the market back then. I scratch built the silencers also but many of my buddies were arrested for leaving them off and running my pipes with open stingers. So was I, a few times. LOL!

The Can-Am's were a breed all there own. They had a 2 piece side case where the rear section of the left outer case, had the intake tract cast into it. It mated with the forward section of the left case where it fed into the rotary valve. This allowed the Carb to be mounted to the rear area behind the cylinder and it had a long smooth intake runner which was shaped in a way that helped to build velocity to the incoming charge. They were rated with the highest HP rating of there day back in I believe 1974 or 1975 for the 250s. This induction design was from the Ski-Doo Snowmobiles of the day.

The rotary valve as designed was simulating the exact same effect as the piston port engines. It positively closed the intake track off, similar to what a reed valve does now whether it is a direct case fed intake with a reed cage or reed valve with cylinder fed piston port design. The cylinder feed designs primarily took full advantage of the reed valve when they all started to have booster ports along side of the main intake port feeding the lower cases.

The expansion chamber would work equally as well on either design as intended as it has it's most effect when the piston opens and closes the exhaust port. Both of which are still a timing event controlled by the position of the piston on either 2 stroke induction design. That timing event today is now a variable timing event which is controlled by the exhaust power valves on modern 2 strokes. This has about the same effect when the exhaust power valve is open as it used to be to grind the exhaust port and raising the roof of the exhaust port up to increase flow and raise the power band. These power valved 2 stroke engines today allow for the best of both worlds and offer very wide adjustable power bands. Pipe design is critical and can only be made to produce the best effect at a specific RPM regardless of the power valve settings. Power valves being used now a days in my opinion on 2 strokes make any aftermarket brands trademark design on the pipe a slight compromise. As port timing changes to some degree with the power valve, thereby compromising the Expansion Chamber pipes maximum effect at a given RPM whether built for top end HP or max.torque at mid range.

I still love my old 2 strokes though and I just can't decide whether to buy a new 2 stroke or a new 4 stroke for my next off road bike or not.

yep it was a hooker my JT60 had one on it when dad brought it home but the stock pipe went back on pretty quick it was crazy loud dad ran one on his CZ too man you and i had to have been born under the same star or something

Sounds like the power valve is the big improvement of the 2t engine from its' earliest days ...

Both 2t and 4t are good bikes today but nothings screams to me like the 2t engine (and I know it will never drop a valve).

Only Hooker exhaust I ever owned was on a v8 engine ... And believe me, that 351 Cleveland engine was allowed to breath with those headers...maybe 2.5" tubes with Hush Thrust mufflers bolted straight to the header for an exhaust system ...

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Puch 250 Twin Carb. Everts replica. 1975 Puch Twin-Carb 250 worksbike. Only 97 pc made of. This model had both direct(?) and rotary intake systems..




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Those early expansion chambers, without any stinger on them, really robbed all power from my '74 DT 250 yamaha enduro bike at ~3K RPM and below... And I mean all power ... After that RPM, the bike got on the pipe! And you knew it was on the pipe after that low RPM robbery.

That Puch is a beautiful restoration and very rare. Its intake system was definitely a cool set up ray_ray. The direct inlets before the reed valve set ups were always neat to me but fouled plugs much more easily though back before synthetic 2 stroke oils became more popular. I used to buy Blenzall Green and Gold by the case. Those were the days when just about every non raced 2 stroke off road dirt bike had a compression release.

Ringa ding ding ding rap rap rap rap rap.

More modern 2 strokes of the last 35 years or more when coasting and off the throttle sound like the engine has shut off. You never here a pop from the engine at all unless you open the throttle a bit. Back in the old days you may coast a long ways and then open the throttle and you get nothing from the engine as the plug had just fouled. Reed valves and synthetics alone almost eliminated that.

Proper 2 stroke expansion chamber design would and should always have a stinger. It's total length is critical and if a silencer is used it should still be the same length with or without the silencer. Not something added on that increases that specified overall length. Silencer design is just as critical when used and it should then be packed as tight as possible to simulate not having it on the end of the pipe at all. Noise restrictions nowadays make that very difficult to get away with without pissing a bunch of people off. Yet most of the noise created by a modified 2 stroke passing by under power is actually coming from the intake side. Approximately 70% infact.

The first bunch of performance 2 stroke quads that were sold by Honda and were spark arrested and forestry legal started having airboxes designed with silencers built into the airboxs in 1988, like the 1988 TRX 250 Rs. 86 & 87 models did not. All 2 stroke Motocross bikes though of that era didn't have a spark arrestor and were intended for closed course racing so they didn't do this either.

You'll see that same thing under the hood of nearly every modern sport utility or 4 wheel drive vehicle now. Some have 4 and 5 different silencers molded into the inlet horn connecting the airfilter box to the throttle body, just to quite down intake noise. These things look like some kind of Tumor growing off the side of the stock molded plastic air intake passages. It's not a wonder the cold air filter system aftermarket is such a successful business to get into.

Sounds a little weird on that intake side noise but world is full of it ... I spent the last ~decade of my life in the states with my nose to the grindstone and missed alot I guess on engines and such ..

I know about zero on Puch bikes but looks like another bike company that fell off the grid ...

Here's another pic I found of a bike with a Yamaha YG engine I saw here ... Change that G to a Z, and you have a yamaha racer bike about a decade later? Ain't that cool? Looking back in time is almost ~always interesting to me ...ESP in the cases when it has ~direct ties to the current day.

This bike won't cost too much and I really need a small street bike of some sort to ride to the store and back ... I could ride one of these maybe... it has got an updated front brake.