I have a t140 engine that i want to run with a dry belt primary. Where else to run the breather ? I have seen some run the breather through a hole in the front engine mount. Has anyone done that ? Whats involved and does anyone have any pictures of the modification ?
i've done breathers on a unit triumph, front and top:
some people run a front crankcase breather out from the side. other people put a fitting in the timing cover.
you'll need to put the old-pre OIF oil seal back into the left crankcase under the engine sprocket, and plug the little level holes in the primary chaincase, which is easy to do with patent-plate pins after drilling the holes a bit larger. mine works very well.
excellent, I just snagged the pictures from the web . we posted about the same time. .. as I wouldn't intentionally repost the same pics. in my haste, I didn't credit the source. .. i think I found your pics on triumph-rat. the t140 case half was from fleabay.
Last edited by quinten; 12/12/176:36 am.
Re: Unit 650/750 engine breather
#718506 12/12/1711:48 am12/12/1711:48 am
Without entering into a big debate on primary drives and so on, in my opinion the standard breathing system on any Triumph twin is adequate for it's intended use. The timed breather works fine, as does the later plenum chamber version. This is provided the engine is in good shape, too much blow by and both systems struggle.
Racing is different and I don't have the experience to comment on it. The same with belts.
I do however have experience with one-way valve breathers, from several Nortons, and lately from a pre-unit Triumph were the rotary breather was damaged beyond repair. I use Yamaha XS reed valves, they are available, affordable and compact. They work like Schmidt demonstrates, by reducing the under piston pressure by pumping gases out but not letting air back in. It takes a few seconds to reach this state but it will eventually create a lower than ambient pressure in there, in a reasonably healthy engine. This is exactly the same as the rotary breather valve is designed to do, but possibly more efficient. You don't want additional breathers in the rocker boxes or anywhere if you use a valve rotary or reed, that would in effect negate what you want to achieve with it. (Though Bunn advocated letting in a small amount of filtered air to flush out gases.)
The vent-to-chaincase principle is totally different. It works by reducing the effective under-pistons compression ratio by letting crankcase gasses escape through the main bearing and into the vented chaincase. There's quite a bit of resistance through the bearing though, so IMHO it can't be totally effective. That's why I drilled a good number of 1/4" holes in the cases of a tuned unit twin I owned, to see if it made a difference. Can't really say, but I used the bike for a decade afterwards and it stayed as dry as a biscuit on the outside and went well. Be that as it may, the standard set-up is good enough even for racing, so I don't mess with it anymore.
But thumbs up for one way valves, possibly PCV or brake assist valves, but definitely Yamaha XS650 valves They work.
Re: Unit 650/750 engine breather
#718619 12/13/1711:10 am12/13/1711:10 am
one way to see just how much air goes back and forth in a primary that breaths through the main bearing is to loosen the three screws that hold the rotor cover plate on. back em out halfway and start the engine. the plate on mine dances like gene kelley as the pulsing air hits the back of the little cover.
What about using the timing hole at the rear of the cylinders? I have seen several bikes using that with a hose running to the rear fender and I have been thinking of doing that on my current project bike.
Mostly Triumphs with a few BSA's a Norton, and two BMW's
Thanks for all the replies. I want to run the primary dry because it is one place less to leak oil, and besides the belt and clutch doesn't need oil. Even so i do not like the idea of running the primary in the same oil as the engine, its too thick for the chain.
Running the breather off the timing plug hole, i have heard can be problematic as oil is flung into this area by the crankshaft. Dave Degens uses the front engine mount as site for the breather tube.
650 race bike, one breather on the front similar to what Kevin shows. One breather on the timing cover
Pre unit dual engine race bike, one large breather hose on the timing covers...The rocker boxes are also vented with small tubing
T120/750 street bike with breather on the timing cover only
None of the above have one way valves All the breather setups function and don't blow oil out....It's easy to fit one to the timing cover..But you may not care for the look of external hoses on a stock bike..
650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Back in the mid 80s I owned a T140D. I bought a QPD? belt drive system for it. As it was dry running I had to block off the 3 drain holes on the cases and fit the seal on the crank. For breathing the kit included an adaptor that fitted into the Timing hole at the rear of the barrels. I ran a hose from there to the rear mudguard. The problem I (well not me, but anyone unlucky enough to be sitting behind me) had was the pressure forced a fine mist of oil out this hose. Not being very mechanically minded I tried a variety of methods to stop this without success.....If only I'd known about one way valves back then
Hi Jimmy, I doubt fitting a valve in that position would have made much difference. It would have pumped oil out of there anyway because the oil fling off the flywheel is at its greatest there. There is less oil fling at the front of the crankcase, and it's possible to device a labyrinth type of thing inside the snout to catch and re-direct the oil. I haven't tried it but that's where I would have placed the vent and possibly the valve too. On a Norton Combat engine I built I devised a one-way valve inside the breather housing, which is placed at the lower rear of the crankcase on this model. It would spit oil all the time, but as it vented into the oil tank it didn't matter. It also served as an additional oil return system when the cases were flooded, as can happen on those things, very useful!
Last edited by Stein Roger; 12/14/175:10 pm. Reason: Dufflexia
Unfortunately for me that was where the manufacturer stated it should go, even providing the coupling to fit in there. As I said I did not have much mechanical knowledge back then, I was only about 20/21yrs old and my apprenticeship was in shipbuilding. If only we had access to the knowledge base that the internet provides now. I really looked forward to buying and fitting my belt drive but the oil spray spoiled my enjoyment of it. I replaced it with the standard set up about 2yrs later when the belt failed