Crank pressure relief PCV reed and crank oil seal

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allan.walker
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Re: Crank pressure relief PCV reed and crank oil seal

Postby allan.walker » Wed Oct 09, 2019 8:50 am

On-topic (although arguably off-marque!) I have an Indian Enfield Bullet, bored and stroked to 625 cc. The standard breathing arrangement could not cope with the additional air volume variations beneath the piston, so I fitted an EGR valve from a 125 Yamaha (the same one as sold for use with Yamaha 650 twins and has been co-opted into use on many other bikes.)
Although it is used as an EGR valve in its original application, the point is that it is a one-way valve and ideal for use in crankcase breather applications.

It is a reed valve so it can cope with high-speed operation (although in the Bullet this is not essential.....) but the point is that it works. After the engine has been running, removing the pipe from the engine to the inlet of the reed valve results in a hiss as air is sucked back in to the crankcases.

The leaks, weeps, misted gasket joints etc. that the engine suffered from are a thing of the past.

btw, I've never heard of a vehicle engine breather system needing to inhale air from the outside before expelling it back through a pcv and then into the combustion chambers. it seems counter-intuitive to me....an air cooled crankcase? Of course, my experience is limited! :?

My old Rover P5B (3.5 litre V8) 'exhaled' from various points into the inlet manifold. The inlet depression helped 'suck' air from the crankcase to maintain a slightly negative internal air pressure inside the engine and prevent oil leaks.

There were filters in the breather hoses to the manifold (which also act to prevent a flashback) and if they became blocked the crank oil seals would leak like the Torrey Canyon (reference for our older members....)

Sorry for the off-marque diversions. :oops:

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Re: Crank pressure relief PCV reed and crank oil seal

Postby admin » Wed Oct 09, 2019 10:50 am

allan.walker wrote:On-topic (although arguably off-marque!) I have an Indian Enfield Bullet, bored and stroked to 625 cc. The standard breathing arrangement could not cope with the additional air volume variations beneath the piston, so I fitted an EGR valve from a 125 Yamaha (the same one as sold for use with Yamaha 650 twins and has been co-opted into use on many other bikes.):



Where did you plumb the line to, which operates the Yamaha valve ?
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Re: Crank pressure relief PCV reed and crank oil seal

Postby allan.walker » Wed Oct 09, 2019 1:40 pm

On the Bullet, I have a Hitchcock's extended oil filler/wet-sumping alleviation pot. The breather on the drive side of the crankcase below the barrel connects to that, and the outlet from the oil filler (which normally breathes to atmosphere via a hose) is connected to the reed valve.

Without the extended filler, the breather pipe from the crankcase breather can be connected directly to the pcv (replacing the 'duck bill' breather.)

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Re: Crank pressure relief PCV reed and crank oil seal

Postby admin » Thu Oct 10, 2019 12:38 pm

The EGR valves i looked at had an input/output and a third take off to the carburettor (or induction ?) which operates the valve ?
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Re: Crank pressure relief PCV reed and crank oil seal

Postby allan.walker » Thu Oct 10, 2019 3:02 pm

Grrrr!
I just typed a reply and it disappeared before I posted it.....

Trying again....

I think that mentioning an EGR valve has confused things. I only used the phrase because that's how they are described on Ebay.

The item I used is from a Yamaha 125 in which it functions as an EGR; I have no idea how it is plumbed-in on the Yam.

It has one inlet and one outlet, just what is needed for our purposes as a one-way breather valve. Therefore the breather outlet on the engine is connected to the input of the reed valve and then the outlet from the reed valve vents to atmosphere, usually via a hose.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby alan.moore » Thu Oct 10, 2019 6:10 pm

admin wrote:The EGR valves i looked at had an input/output and a third take off to the carburettor (or induction ?) which operates the valve ?


Looking on Ebay there are two different types of these valves for Yamaha's.

One type, as Allan describes/uses, looks like the Yamaha XS650 valve (which appears to be only available from the USA https://www.mikesxs.net/yamaha-xs650-re ... e-pcv.html ) and has a large bore inlet and an outlet port. I've just bought two from Ebay for £16...hopefully I will find a reed valve inside ( https://www.ebay.co.uk/itm/YAMAHA-CYGNU ... SwRF1b4ccv)

The second type appears to have an inlet and outlet pipe plus a smaller pipe operating a diaphragm type valve, this is not suitable.

It appears that neither valve is an EGR valve as it does not transmit any exhaust gases (the pipes are rubber so would melt if this were the case), what the valve does is introduce air from the airbox into the exhaust port to cut down emissions by allowing excess fuel in the exhaust flow to be burnt in the exhaust pipe. The reed valve type allow extra air to be drawn into the exhaust all the time the engine is running. The valve with the diaphragm (small pipe feed) is operated by air depression (high suction) on the inlet valve side of the carb when the throttle is closed (idle or overrun) and only allows air to be drawn into the exhaust port under these conditions.

If the valves, similar to the ones i have bought from Ebay, work this source is cheaper and an easier route then sourcing them from the states. I will report back when they arrive.

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Alan
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Re: Crank pressure relief PCV reed and crank oil seal

Postby M.Bagshaw » Thu Oct 10, 2019 9:07 pm

That part from Drags, what is the part number please i can't find it & was wondering if it might fit my 1928 Model C?

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Re: Crank pressure relief PCV reed and crank oil seal

Postby Knud.Degnbol » Thu Oct 10, 2019 9:19 pm

You don't need it. If your 28 is like mine, you have 2 breathers from the engine. One of them blows air with oil in it onto the rear chain. The other on the primary chain. In 10 years I have hardly had to adjust the chain.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby alan.moore » Thu Oct 10, 2019 10:40 pm

The only crankshaft seal I could find on Drags was 1249/49, the photo shows the version with the garter spring. Drags also list a shim to go with this seal, 1297-49. A shim was mentioned in an earlier post.

There are also details in the website knowledge base
http://www.arielownersmcc.co.uk/members ... p?show=484

This lists the seal as RS 365-3 and also gives details of the shim
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alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

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Re: Crank pressure relief PCV reed and crank oil seal

Postby M.Bagshaw » Fri Oct 11, 2019 7:39 pm

Knud.Degnbol wrote:You don't need it. If your 28 is like mine, you have 2 breathers from the engine. One of them blows air with oil in it onto the rear chain. The other on the primary chain. In 10 years I have hardly had to adjust the chain.


I was thinking it might stop oil seepage rather than breather?


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