Navigator Engine breather resiting

Does anyone know the volume of air displaced through the breather

Its the capacity of the bike, the volume displaced by the pistons moving up and down.

If you want a small bore breather then fit a reed valve in the pipe run and this increases the effective diameter of the pipe.

To get a cheap reed valve search for an EGR valve in motorcycle parts on ebay, there is a Yamaha one that fits in a straight run.

The reed valve reacts at all engine revs a Norton is capable of and allows the air under the piston to escape on the downstroke but closes on the upstroke creating a small vacuum.

Correct, used very successfully on the 750 and 850 twins to eliminate oil leaks. Get the EGR valve first and then match the outlet stub to the pipe that fits the EGR valve.

I expect it will escape though the oil tank breather ð

Yes back to the tank so the oil mist can condense out and the air alone continue out the tanks own breather (as per Dans comment), well that's the theory

Once the air pressure has stabilised the movement out of the engine breather will be the ring blowby and any air sucked in from any weak joints, without the reed valve its the same net result but the air is continually moving in and out, and not very efficiently.

Previously Andrew Wibmer wrote:

Previously john_holmes wrote:

Yes back to the tank so the oil mist can condense out and the air alone continue out the tanks own breather (as per Dans comment), well that's the theory

Once the air pressure has stabilised the movement out of the engine breather will be the ring blowby and any air sucked in from any weak joints, without the reed valve its the same net result but the air is continually moving in and out, and not very efficiently.

Thanks John,

there are quite a few little gems of information like this I have come across. One of the pleasures of this lark are trying to make small improvements to the original without moving too far from standard. Rather hoping after my little rebuild there wont be any / much blowback or weak joints, but then again...

I did the crankcase breather mod many years ago to fit a 20 tooth final drive sprocket. I used a disc brake caliper nipple to make the connection. Never had a problem, if there was I could see it without removing the primary chaincase ! As to crankcase breathing, 5.85 mm breather has to cope with + and - 175mm3 of air every revolution of the engine (yes??) so imagine a lightweight at say 4000rpm... oooh. If the crankcase breather is fed up to the oil tank I suspect the oil mist will tend to condense in that tube building up until it dribbles into the oil tank (as it should do). The oil tank tube is about 400mm above the crankcase outlet which could create a constant back pressure head of say 0.4 bar ?. It is a good thing air is compressible!! I feed my crankcase breather down the back of the frame channel into a plastic receptor to avoid this back pressure to some small extent. As for a reed valve connection operating as a one way valve, this might halve the load to cope with + and - 87.5mm3 of air, if it works,which would help. There was never much development of these lightweights. Perhaps some thought should be put in to improve crankcase breathing ? Any thoughts?

GRAHAM

Presumably you can only drill the crank case when it's split and apart, or is there a secret way of keeping the dwarf out of the cases?!

what you could do is drill the hole and tap. and flush out the swarf by sucking it out through the original crankcase breather. When you remove the original breather to blank it off you can pass a pipe cleaner through your new connection and out the old one as belt and braces you got it sorted.(if the pipe cleaner sticks you can remove the blanking stud under the original outlet and flush out there and put the blanking back ). There is a picture in the forum reference highlighted by Andrew that shows where the blanking plug is.

what you could do is drill the hole and tap. and flush out the swarf by sucking it out through the original crankcase breather. When you remove the original breather to blank it off you can pass a pipe cleaner through your new connection and out the old one as belt and braces you got it sorted.(if the pipe cleaner sticks you can remove the blanking stud under the original outlet and flush out there and put the blanking back ). There is a picture in the forum reference highlighted by Andrew that shows where the blanking plug is.

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The reed valve only has to cope with the out flow of the engine capacity until the air within the cases have stabilised, it creates a partial vacuum as the air is not allowed back in so then less will come out. All you have to do is compare the mayhem of the outlet of an open breather to one with a reed valve, difference is night and day.

Hi Andrew.

I passed the alternator cable through a rubber oil tube (replacing the tapered bung for the exit of the primary chaincase to solve possible oil leaks there first . The new crankcase breather fits tightly over. When I did this originally I was experimenting and so kept to original crankcase channels to be safe. I obtained a spare engine that had a breather connection in one of the rocker covers, and I fitted and fed this to the oil tank breather with a clear hose to monitor crankcase breathing at the top of the engine. If there was pressure it would manifest as oil bubbling in the clear tube, but I never found that to be the case and so was confident that the breather modification I had done was doing what it says on the can. The reason for the modification was not to tackle crankcase breathing but to fit a larger sprocket.

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Video showing difference between a breather with and a breather without a reed valve.

https://youtu.be/LBqUDIYxgAA

The big question is what difference does it make to the operation of the engine? Mike P recommends taking the ball bearing out of the breather in the ES2 so it breaths more freely? ... I can understand moving it to stop it being hit by the chain, but does it have any other advantages?

dan

Nope, you've lost me, if the crank case is open to the atmosphere air will pump in an out but the only increase in pressure will be if the breather is too small to let all the pressure out. With a reed valve you'll have neg pressure (as you say) as well?

I dont think the lightweights have a rep for eating crank seals, it's the gearbox and chain case that usually leak!

I should add that I might sound authorative but it's all bravado!