75 850 MKIII Reed Valve?

Romi3 · Aug 14, 2014

Hello everyone!

Have searched and read up the xs650 valve to help eliminate crank case pressure, which in turn helps with minor leaks. I looked and looked but I have not found any clear step by step instructions with images included. For the first few short distance rides, I had zero leaks but last weekend when I took it out for about 40 miles on some twisties (had a blast!!) and was able to get on it bit more, I noticed when I got home that there was a fair amount of oil drips on my rear tire. YIKES!!! I looked and found a slight leak around the tach drive, so I educated myself there and ordered the updated unit from oldbriitts, but I also noticed a leak coming from behind the primary (well that's where it seems to be coming from). It's nothing big, but still, I'd like to get this thing leak free and I hear the valve is AN answer. Any help on detailed info regarding how to install the xs650 valve would be appreciated.

Thank you.

Fast Eddie · Aug 14, 2014

The reed valves go in the breather line from the engine, so long as you don't fit it the wrong way around (test it by blowing through it) I'm not sure what you can do that's very 'wrong'.

I fitted a Jim Comstock sump plug / reed valve and am amazed at how little gas movement there is when I check the breather outlet in the oil tank. The fact it prevents sucking air back in, and is therefore only ever ejecting excess gas, is clearly the right way to go.

It obviously won't help if you leak turns out to be from the gearbox though!

JimC · Aug 14, 2014

Romi3 said:
Hello everyone!

Have searched and read up the xs650 valve to help eliminate crank case pressure, which in turn helps with minor leaks. I looked and looked but I have not found any clear step by step instructions with images included. For the first few short distance rides, I had zero leaks but last weekend when I took it out for about 40 miles on some twisties (had a blast!!) and was able to get on it bit more, I noticed when I got home that there was a fair amount of oil drips on my rear tire. YIKES!!! I looked and found a slight leak around the tach drive, so I educated myself there and ordered the updated unit from oldbriitts, but I also noticed a leak coming from behind the primary (well that's where it seems to be coming from). It's nothing big, but still, I'd like to get this thing leak free and I hear the valve is AN answer. Any help on detailed info regarding how to install the xs650 valve would be appreciated.

Thank you.

It's pretty common for a well assembled Commando to run dry until you start thrashing it. This leads me to believe crankcase pressure is the cause of a lot of those pesky leaks. It only makes sense that a pressurized vessel is more likely to leak fluids than an unpressurized one. Going a step farther, I doubt a vessel under vacuum will leak outwardly even if not sealed properly.

Romi3 · Aug 14, 2014

Fast Eddie, thanks for the info.

So, the valve is just an inline valve and is to be intalled in the hose between the case exit and the oil tank return?

Torontonian · Aug 14, 2014

It's one of the best things you can fit to the Commando and real affordable too. It only works fitted to expell gases / stop re-entrys , so yes just blow on it to test . This is for gases so it's the line that spits into tank not any return or supply. Mine sits on top of the oil tank under the front of seat but closer to the crankcase another good option. Doesn't help much with primary or tranny leakages ,that's another kettle 0' fish.

Fast Eddie · Aug 14, 2014

Romi3 said:
Fast Eddie, thanks for the info.

So, the valve is just an inline valve and is to be intalled in the hose between the case exit and the oil tank return?

Yes, and at the risk of insulting you, but just to be clear, we are talking about the breather pipe from the engine... and not the oil return pipe...

Romi3 · Aug 14, 2014

Ok, I get now. Pretty simple, I guess. Thought it was more of an extensive procedure, but I'm glad it's not.

Also, I'm married so I'm immune to insults, whether intentional or unintentional. Ha!

comnoz · Aug 14, 2014

Romi3 said:
Ok, I get now. Pretty simple, I guess. Thought it was more of an extensive procedure, but I'm glad it's not.

Also, I'm married so I'm immune to insults, whether intentional or unintentional. Ha!

I have a sump plug breather available with a reed valve that simply screws into the sump plug hole. Since it runs at engine temperature it does not have the condensation and plugging problems that the XS breather has. Jim

Torontonian · Aug 14, 2014

Sounds like a plug ? :lol:

Fast Eddie · Aug 14, 2014

Torontonian said:
Sounds like a plug ? :lol:

Plug maybe... Or advice...?

It would be a bit daft if we weren't allowed to mention bits that make our bikes better.

I've gone one of these, it sits under the engine (obviously!) totally out of the way, provides for neat routing of pipes etc, and works really well.

The idea of an open breather seems prehistoric to me now !!

Romi3 · Aug 14, 2014

Cmnoz,

So the sump plug breather eliminates the need for the reed valve? If so, where can I find one?

I'm all about keeping things clean and simple.

Thank you,

comnoz · Aug 14, 2014

Romi3 said:
Cmnoz,

So the sump plug breather eliminates the need for the reed valve? If so, where can I find one?

I'm all about keeping things clean and simple.

Thank you,

I have them in stock. I will send a PM.

SteveA · Aug 14, 2014

Romi3 said:
Cmnoz,

So the sump plug breather eliminates the need for the reed valve? If so, where can I find one?

I'm all about keeping things clean and simple.

Thank you,

The sump plug is a refined reed valve solution. You are still fitting a reed valve, but the reed valve is in a plug unit that replaces your large sump plug/filter.

I have Jim's crankcase fitting reed valve. No more work for me since my cases already had the fitting boss for it. From what I can see the sump plug replacement makes fitting a reed valve easy enough. The was a long running thread on here about it probably a couple of years ago....

Dkt26 · Aug 14, 2014

Romi3 said:
Cmnoz,

So the sump plug breather eliminates the need for the reed valve? If so, where can I find one?

I'm all about keeping things clean and simple.

Thank you,

Buy it. Excellent upgrade.
Screw it in. Cut and plug your old breather hose. Fit it to the new breather or replace the whole line. Takes 10mins.

Romi3 · Aug 14, 2014

Sounds like the solution I was looking for. Thanks again everyone! Looks well built.. like a nice piece of artwork.

NorComCycles · Aug 14, 2014

Here's some quick pics to show a mk 3 fit-up. I use a chrome elbow to guide the hose where I want it, and also to match the breather outlet to the larger mk 3 hose size.
New herringbone (extremely expensive), and it is good to go.

The hoses as they meet the oil tank.

The view that is seen when looking at the bike under normal circumstances (side stand, etc).

The elbow attached to the breather, with the outlet hose zip tied in place (loosely, of course, the hose must not suffer any reduction in internal diameter).

Hope that helps,
Lyell

Romi3 · Aug 14, 2014

Lyell,

Apprecite the images. So, your oil tank breather hose just runs to the bottom and stays open? Do you run an inline filter on it?

JimC · Aug 14, 2014

Don't quite understand this open venting. Everything that's being vented comes from the crankcase, so why not dump it back into the oil tank, which in essence is a large catch can? Any fumes escape the oil tank by way of the tank breather spigot. You'll have a new dimension of excitement if that sump plug breather decides to gulp a slug of oil while you're cruising. Maybe it's a back to the fifties thing.

comnoz · Aug 14, 2014

JimC said:
Don't quite understand this open venting. Everything that's being vented comes from the crankcase, so why not dump it back into the oil tank, which in essence is a large catch can? Any fumes escape the oil tank by way of the tank breather spigot. You'll have a new dimension of excitement if that sump plug breather decides to gulp a slug of oil while you're cruising. Maybe it's a back to the fifties thing.

The open vent is his oil tank vent, not directly from the breather. Oil does pass out of my breather hose so it must go into the tank. Jim

NorComCycles · Aug 15, 2014

Romi3 said:
Lyell,

Apprecite the images. So, your oil tank breather hose just runs to the bottom and stays open? Do you run an inline filter on it?

The oil tank breather on the bike pictured runs open. Certainly with the reed valve, a filter would not be necessary, as there is no "draw" from the engine, and air only ever exits. A filter that breathes freely enough would really do no harm, but not actually achieve anything in a practical sense, although if an issue of oil discharge existed, it may offer a temporary "absorption" area.

The tank breather could of course run to a catch can if desired, and that certainly would pretty much completely eliminate any possible oil emission, if that proved to be a problem.

In respect of filtering air that might be drawn back into the motor, a catch can essentially only elongates the breather hose.

And of course, even without a reed valve, the length of a breather pipe can make a filter meaningless, as even an engine can only draw air so far, and any "contaminants" remain in the hose, never making it to the oil tank. I have seen numerous breathers run down the length of the rear fenders, and that does make for a long breather hose.

75 850 MKIII Reed Valve?

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