Crank pressure relief PCV reed and crank oil seal

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T Batnes
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Crank pressure relief PCV reed and crank oil seal

Postby T Batnes » Thu Sep 19, 2019 1:31 pm

I will install a XS PCV reed valve https://www.mikesxs.net/yamaha-xs650-reed-type-engine-breather-valve-pcv.html on the mag side crank pressure relief outlet on my W/NG engine, that is undergoing some modifications (7,5:1 piston, Franklin P2 cam).
I understand I should then install an oil seal on the crank towards the primary side.
Which seal, how and where to install I wonder. Would be greatful for a tip or two, maybe a picture as well?
Ariel W/NG '41/'43 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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T Batnes
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Re: Crank pressure relief PCV reed and crank oil seal

Postby T Batnes » Sun Oct 06, 2019 11:48 pm

Got the seal from Draganfly, it fits over the distance piece between the engine sprocket and crank case. Not a real seal, but more like a rubber grommet that will be sucked against the case when an underpressure is present within the crank case, and then prevent air from entering the crank case. Lets see how this goes...
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Ariel W/NG '41/'43 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby pappleton » Mon Oct 07, 2019 5:22 pm

I could be being a bit 'dim' here, but is there a steel shim between the seal and the crankcase? If the seal spins with the spacer, wouldn't the seal then wear the alloy case away?
BR,Paul
Paul Appleton '53 VH plunger, '53 VHA rigid - in many boxes, '58 H.D. pan/shovel rigid

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Re: Crank pressure relief PCV reed and crank oil seal

Postby GuyWalton » Mon Oct 07, 2019 6:05 pm

surely the air will go down the splines .
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T Batnes
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Re: Crank pressure relief PCV reed and crank oil seal

Postby T Batnes » Mon Oct 07, 2019 7:43 pm

No shim, just the rubber. Rubber isn't under any pressure, it just sits loose against the alu surface. I reckon that putting some grease on the surface will help initially with keeping a sort of seal, and to lubricate things, and later an oil film wil form doing the same thing. The steel distance piece will sit tight against the bearing inner, and thus make sort of a seal towards the splined part of the shaft. It might help in keeping much air from entering the crank case from the primary chain case, but some will pass I believe. But probably less than what is expelled the easy way out through the reed valve on the breather, thus maintaining a slight underpressure in the crank case. At least the Ariel guys thought so back then...
Ariel W/NG '41/'43 "Bitzer", Triumph Thruxton '04, IZH-49 '56, Tempo Standard 150 '54.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby will_curry » Mon Oct 07, 2019 7:52 pm

That seal was used on the competitions bikes to stop the crankcase oil flooding the primary
chaincase when revving the engine hard rather than keep the gases in. My solo has the seal
and I have to top the chaincase up. The sidecar outfit however doesn't and that I periodically
drain, despite the best efforts of the chain oiler. The roadgoing bikes which no-one in their
right mind would thrash as hard don't need it.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby david.anderson » Tue Oct 08, 2019 9:41 am

One of the main causes of oil leaks in a single is excess crankcase pressure. Every time the piston rises 500cc of air is sucked into the crankcase and the crankcase is then pressurised as the piston goes down because the breather is unable to expel all the air. By fitting a reed valve to the breather pipe, air can only be expelled but not sucked in. However air can still be sucked in around the drive side bearings (and the magneto shaft unless that is well sealed.) The fitting of the crankshaft oil seal helps to seal the engine and enables the reed pcv to operate more effectively and reduces the oil mist that otherwise appears around every gasket joint, so it is worthwhile.
The sprocket spacer abuts the bearing and prevents any air from escaping down the splines.
The original oil seal is more of a Vee shape and has a garter spring around the outside. Many modern seals eliminate the garter springs that were previously used, just as the Draganfly oil seal has done.
David

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Re: Crank pressure relief PCV reed and crank oil seal

Postby Keith.owen » Tue Oct 08, 2019 11:48 am

Hi,
Just a comment.

I fitted a Yamaha reed valve to my VH which has a crank case breather ( I fitted it in line with this) and the reduction in oil leakage is radical.

Before I could never get the rockers to stop leaking around the head gaskets, now the engine is pretty much oil tight (I do get a bit of mist from somewhere, I think the de-compressor, but nothing to fret about).

Needless to say the oil pressure in a single isn't that high in the first place - the problem was down to crank case pressure due to poor breathing.

The PCV is a boon!

Keith :mrgreen:
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Re: Crank pressure relief PCV reed and crank oil seal

Postby will_curry » Tue Oct 08, 2019 1:15 pm

BSA used mechanically timed breathers on their twins and thus the Huntmaster has a timed breather.
Triumph also used a timed breather on their twins. This was to overcome the inadequacies of what was
essentially a series of holes which couldn't cope with a large volume of gas rapidly pulsating.

I tried connecting the crankcase and timing case breathers on the sidecar outfit - a 500 single - into the
pancake air cleaner so that the inlet depression sucked the gases. It wasn't the most successful idea I've
ever had. The first real test was the Land's End in 1976 - I think. On the approach to Blue Hills - the last pair
of sections and about 400 miles from where we started - the outfit was noticeably off-song with all the oil
which usually leaked out elsewhere now dripping out of the air cleaner. I removed the element and all was
well again and we cleaned both sections. I tried adding an oil separator but that just got in the way so
in the end i went back to bits of pipe pointing at the back chain. Oh well.

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Re: Crank pressure relief PCV reed and crank oil seal

Postby nevhunter » Wed Oct 09, 2019 12:20 am

The way the PC valve works probably doesn't suit the situation as well as a one way valve especially with a single which has anything but a smooth action, Note how the carb slide rattles back and forth in a single. Lots of engines have had timed mechanical breathers and some have flappers. The largest ones are on the older speedway motors and just vent straight out of the bottom of the crankcase. If the motor is breathing a lot you would need a rather generous set up, compared to the average original.. A PCV is set up for a "flow through "crankcase system with filtered air entering somewhere and the vapour going into the manifold (inlet) WHEN the vacuum in the intake is LOW. Ie on load. It must close at idle or it runs roughly. Too lean. Nev


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