Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)

Dan1950

Dan1950

1974 MK II Roadster
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This looks like it grew there. Just cut, trimmed the hose and it tucks right in ahead and above the battery. All I need to do is cable tie it to the top tube and add some hose clamps.

Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)


Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)


Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)


Less than $50.
 
Dan1950 said:
Your rational?
Click to expand...
The reed should be as close to the source of pressure (undersides of descending pistons) and as fast acting (carbon fibre reeds) as possible to have best effect on dropping peak crankcase pressure.
The hose beteween the lower crankcase (I assume - not shown in photo) and the reed valve will cause a delay in response.
If the lower hose is from the inside of the timing cover then it is worse again - takes even more time for the pressure wave to get into the timing case.
I believe that in this application speed of valve response to the initial pressure pulse is everything.
Yours is an improvement over stock but could be much better.
 
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That's a fair concern, but I find it's working fine in that location. What I did read a few weeks ago on here, is the further the valve is from the crankcase the more likely it will become blocked by mayonnaise from oil/water vapour. I'll check mine post winter riding, to see if there's evidence of this. If not, I'll leave it up top, like Dan's.
 
I don't disagree with the the logic that closer is bettter. But I put mine up top like that two years ago and it works fine as far as reducing the oil leaks. Might be interesting to see some data on this. Where could one attach a line for crank case pressure?
 
During warm up any breather will get a little bit of off-white goop in it no matter where it is located. Should also clear easily enough to function as designed particularly once the motor is fully warmed up.

Looks good to go Dan. I think the orientation of the breather is about as good as it gets for that style breather. I don't use that type of breather, cuz I had no place to hide that ugly thing. Mine is all pretty and bolted to the timing chest where the magneto would normally bolt in. Cases are modified to get more air out of the crankcase, and into the timing chest. Not ideal but it all works.
 
slimslowslider said:
EGR and PCV mixed up in the thread title, I guess.
Click to expand...
Not really, the XS650 valve that is being used as a PCV on Yamaha's and Commando's is really an EGR valve when used in its original engine (some Chinese engine so its cheap). Mike at XS650 repurposed it as a PCV and then once word got around it then got tipped off for Commando use again as a PCV. When I need one I go onto ebay and search for a Motorcycle EGR valve and get lots of choice.
 
kommando said:
Not really, the XS650 valve that is being used as a PCV on Yamaha's and Commando's is really an EGR valve when used in its original engine (some Chinese engine so its cheap). Mike at XS650 repurposed it as a PCV and then once word got around it then got tipped off for Commando use again as a PCV. When I need one I go onto ebay and search for a Motorcycle EGR valve and get lots of choice.
Click to expand...
Used to introduce fresh air into exhaust.
 
As far as mounting closer to the engine to prevent condensation sludge? My thinking is that mounting it high will allow vapors to condense before they reach the reed valve. If there is any condensation at the valve, the orientation and the fact that the hose is vertical at the junction with the valve might tend to mitigate the problem.

I also realize that the distance will reduce effectiveness somewhat but I still think it will prevent positive pressure build up in the crank case by preventing air being drawn into the crankcase. The only increase in pressure would be from blow-by and if there is that much blow-by we have more serious problems to consider.
 
maylar said:
But that's not Exhaust Gas Recirculation. It's more like Air Injection.
Click to expand...
Dave, you beat me to it. EGR stands for Exhaust Gas Recirculation [exhaust gas introduced into the intake manifold to reduce NOX emissions]. Yamaha uses that valve to introduce additional oxygen [atmospheric air] into the exhaust system to finish burning any unburned fuel in the exhaust. This was common in automobiles in the late 1960s to 1980s. The reed valve(s) acted to prevent the pressurized exhaust gas from backing up into the system. Here in the USA, these valves were referred to as "gulp" valves in the automotive trade. This system was commonly referred to as A.I.R. [Air Injection Reaction] system. See

A.I.R. explained

The Yamaha system is more rudimentary, as there is no pump to inject the air. The difference between atmospheric pressure and the lower pressure in the middle of the exhaust system [between power pulses] draws air into the system. The valve prevents flow reversal during the engine's power pulses.
 
This is my set up the reed valve sit between the engine mounts just by the hoses as close to the crank case where the breather hose comes out, I don't run it back to the oil tank and goes into a catch bottle that sit behind my GB in between the engine mounts all well hidden, but my 850 motor is mounted in the Featherbed frame so have the room for the catch bottle behind the gearbox.
Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)
Yamaha EGR Reed Valve Breather Hack '74 MK II Completed (almost)
 
It may be the camera angle but in the first pic it looks like the breather hose from the timing chest is siting on the engine cradle (causing it the arch slightly downwards) & the PCV is below the level of the outlet hole in the timing chest ... this surely cant be right as the valve will fill with oil & not work correctly????
As i said it say be the camera angle of my eyeso_O;)
 

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