bushmechanic

dunno Zaga

you'll have to buy one and let us know

zaga

ZAAGA

Dr_C

Way too small, only some 8mm...

Idle

Hmm, but after a few revolutions enough air has escaped to make the CC in a vacuum, would it not matter at that point that it's only 8mm id?

Dr_C

Certainly enough for the blow-by flow, but the pulse from the down moving piston needs to be vented too.

jon andersson

Yep. I installed a too small valve and blew the gasket in the top cover.

bushmechanic

it does look too small .. thanks Dr_C

the thread says they were using it up to 540cc

FWIW this is my breather filter on my 700, car fuel filter, quite restrictive and the ID of the fittings is 8mm



I don't have any problems with excess pressures but i have 2 reed valves between the main crank cavity and the gearbox. where there are 2x 8mm holes in total.

on my "new" engined 628 there is so little blowby it is hard to discern any outward flow at all even at 7 - 8000 rpm, it also has the 2 reed valves.

Goose916

Yep, I ordered one too . . . and immediately thought "there's no way this is gonna work". Ok, lesson learned, gonna find one Lineaweaver specified.

bushmechanic

you might be surprised Goose

internally there are only 2 small holes between the engine crank case proper and the gearbox, on the older bikes there is only 1 hole .. its smaller than the ID of that valve

the ktm dudes reckon it works

once a vacuum is created there isn't any air with which to transmit any pressure waves. on both my bikes (running the crankcase proper under a vacuum rather than the whole engine) I find the crankshaft seals actually get sucked inward with such great force that I have to make special retaining lips to stop them being chewed up by the bearings.

Idle

With my automotive check valve, on start-up I get a couple chuffs of air, then nothing. Even at high revs there is no air escaping asfaras I can tell.

There is no oil residue anywhere. Fwiw, I'm running 1100 ml of oil, (halfway up the sight glass cold)

A good way to test what's going on would be to put a ballon over the outlet, affix it with some tape then start it up.

If it's already warmed up, crack the oil filler to zero out the pressure first.