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Crankcase breather check? #796556 01/25/20 4:13 pm
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splittie65 Offline OP
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I have just put back together the crankcase halves of my '67 TR6C.

Is there a way to check that the cranckcase breather at the end of the camshaft has connected correctly before going any further?

I turned the cam as the halves went together and it went together cleanly. Is that sufficient?

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Re: Crankcase breather check? [Re: splittie65] #796561 01/25/20 5:11 pm
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Nick H Online Content
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If you have a hose on the breather, you can blow in it while turning crank. You will notice that it will vary from free to blocked as you blow.


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
Re: Crankcase breather check? [Re: splittie65] #796576 01/25/20 7:11 pm
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koan58 Offline
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I've never made a note of the precise timing of the breather, but as NickH says it should open/close with crank rotation.

It should certainly be open when the crank is at 90 deg ATDC and closed at 90 deg BTDC.

If you messed it up (doesn't sound like it) the tongues of the breather disc will be squashed into the bush, and the cam won't freely spin. You will feel a pulsing resistance to spinning of the camshaft. For this to have happened, you would have had to ignore the fact that the cases would not easily come close together, and then carried on clamping them with the bolts. I doubt and hope that is not the case!

I have made that mistake and another one which comes from simply tightening bolts to close cases which don't naturally close.
The other one concerns the placement of the thrust washers on the ends of the layshaft. Due to having to remove and re-install the cluster (having not got it right first time) I didn't notice/check that the washer at the drive end was still on its peg. I ignorantly just clamped it all up, guess what, the peg was pressed flush into the housing. That wasted a week to resolve. I think the moral of the story is self-evident. Don't follow my example!

Re: Crankcase breather check? [Re: splittie65] #796654 01/26/20 5:13 pm
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splittie65 Offline OP
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Thanks guys....feel a bit more reassured now.

The crankcases pushed together within a millimeter, before even putting the bolts on.....and both camshaft pinions move freely.

Re: Crankcase breather check? [Re: splittie65] #796700 01/27/20 1:41 am
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TR7RVMan Online Content
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Hi splittie65, Sorry for the delay. Had to dig into the archives...

Disc lets air out as pistons fall, blocks air coming back in as pistons rise. Intake cam is hollow. Has 1/4" hole drilled just to right of the right cam lobe to allow free passage of air to disc. The rotating cam may also act as a centrifuge to help separate oil from blow by. A very clever arrangement.

I did a diagram & testing method for disc type breather. Since breather plate & cam disc have to holes (more like triangles) the cam lines up breathing every 1/2 turn cam.

The holes in motor case are vertical. The drive slots in cam are offset at about 1:30 o'clock (between 1&2). The holes in cam disc are offset from drive tangs. So... when holes in cam disc align with holes in motor case exactly, cam lobes point to 10:30 & 4:30 looking from left side of motor. No matter the way cam disc installed as long as tangs enter cam.

This is real life test. Hook long 3/8" hose to breather pipe under motor. Remove adjuster access cap for left intake rocker. Blow into hose with mouth. Rotate engine normal direction with wrench or rear wheel.
Breather disc will pass air just before left intake valve fully open.
Then disc is fully lined up to holes just as intake valve is closing & you feel air passing freely.
Air passage stops just before intake valve is closed.

However.... It passes air again when valve is fully closed.... Don't let this confuse you. Remember it's fully open every half turn of cam. Keep blowing as you turn & that tests the 2nd have turn. I didn't record rocker positions for that.

The passage & blockage of air is very obvious when you do this test. When it's off, it's obviously off & it stops the air. If it's not obviously off, that is a fault. If it feels restricted, that's a fault.

The idea is this. Air exits crank case when pistons fall. Blocks air coming back in as pistons rise. So the crank case runs in negative pressure as pistons rise. (A vacuum).This is why crank sprocket seal has spring towards sprocket. To prevent primary oil from being sucked into crankcase while pistons rise.

This test is easy to do with motor in frame or on bench. Ok... not that easy to hook hose to breather motor in frame, but really no big deal. I've not done it, but I think hook hose to breather pipe at rear fender if all hoses are sound.

On later primary breather bikes, you can feel the negative pressure as pistons rise when you put finger over end of fender breather pipe. Fun stuff!
Don


1973 Tiger 750
Re: Crankcase breather check? [Re: splittie65] #796984 01/30/20 8:07 am
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Stein Roger Offline
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It's a simple system and it works. It is however a bit limited by the rather torturous route through the cam and rotary valve, and it can be prone to collecting oil which it spits out.
By putting a hose on the outlet and routing it back on the bike you may think you have taken care of these spits, but oil and emulsion will collect in the hose and plug it. This renders the whole system ineffective, as no breathing out occurs. BSA A65 didn't even have a outlet stub, and is all the better for it.
I usually leave the outlet bare and try to find other ways to mitigate the problem. Triumph inserted a short piece of pipe into the inlet hole in the cam on some cams. They idea must have been to let the pipe stick through the layer of oil that wraps itself around the cam as it spins. This phenomenon is well known and is why many engines have scrapers close to the crankshaft.
The extra pipe is another obstruction in the system though, and I don't like them.
I'm thinking that trying to evacuate the oil more efficiently is a good thing, making sure the oil pump works at its best and that the return system is open and to correct dimensions.
On the Triton I'm working on, oil spitting is an issue, and I suspect the restriction in the custom return system is too small. This effs up the system in two ways, residual oil level becomes higher, and the increased back pressure forces more oil through the rockers, and more drain back over the cams.
I like the timed breathers, but the later engines that breathes through the primary are less troublesome in this respect.
One last word on timed breathers; don't ever try to "help" it by adding breather hoses everywhere, unless there's a reed valve or other PCV valve connected to it, or you just sabotage the system.

SR

Re: Crankcase breather check? [Re: splittie65] #797001 01/30/20 1:45 pm
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kommando Online Content
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On a set of Norton cases which uses the same type timed breather I have removed the timed breather innards and on the pipe exit have added a reed valve breather used as an add on to the later crankcases with an untimed breather, the route's tightest spot in is the exit of the reed breather so it should breath as well as the upgraded later cases. Looking at the Triumph cam you just need to add an extra hole to the cam shaft and the reed breather outlet becomes the tightest spot too once the timing mechanism is deleted. The reed breather becomes a timed breather but it adjusts for the engine revs and is good for 10000 rpm.


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