Timed breather with in line breather valve?

Anyone ever replaced/augmented the pre 1972 timed breather either deleting it for an in line breather valve or augmenting it with same? I run a single Mikuni on this 1971 (in build curently) and usually run a hose to the rear fender such as Triumph 650s......Does this offer anything positive?, or am I over engineering this? (I have been accused of that in the past)

A reed valve is likely to work better than the timed breather. In principle they might be used together but the reed valve has the potential of letting the case pressure reach less than atmospheric pressure while the timed breather will reset this to atmospheric each time it opens if configured in parallel to the timed breather. If in series, I would think the reed valve would not have much effect but maybe some. Has anyone any experience on this? My 68 commando has a pcv valve between the breather and oil tank and seems to work quite well but can't actually state it is better than just the stock breather. On the other hand my 72 was noticeably improved by the reed valve in the breather line.

ilikevelos said:

A reed valve is likely to work better than the timed breather. In principle they might be used together but the reed valve has the potential of letting the case pressure reach less than atmospheric pressure while the timed breather will reset this to atmospheric each time it opens if configured in parallel to the timed breather. If in series, I would think the reed valve would not have much effect but maybe some. Has anyone any experience on this? My 68 commando has a pcv valve between the breather and oil tank and seems to work quite well but can't actually state it is better than just the stock breather. On the other hand my 72 was noticeably improved by the reed valve in the breather line.

Click to expand...

I run a RGM breather valve on my 850....I was thinking of adding one to the 1971 timed breather, as I think you have done.....might stop the occasional slobber at the end of the vent hose needed by the Mikuni application. "Belt and Suspenders?"

Instead of the timed breather works but with the timed breather gets you the same issue as the timed on its own. The timing is best at one set of revs and the further away from those revs the less well it works, like the inlet and exhaust valves. Improved today with variable valve timing which is what the reed valve achieves..

kommando said:

Instead of the timed breather works but with the timed breather gets you the same issue as the timed on its own. The timing is best at one set of revs and the further away from those revs the less well it works, like the inlet and exhaust valves. Improved today with variable valve timing which is what the reed valve achieves..

Click to expand...

Thnx for the explanation.

kommando said:

Instead of the timed breather works but with the timed breather gets you the same issue as the timed on its own. The timing is best at one set of revs and the further away from those revs the less well it works, like the inlet and exhaust valves. Improved today with variable valve timing which is what the reed valve achieves..

Click to expand...

Can you please tell me what the timed breather working rpm range is?

On my 71 I have a Comstock reed valve and blocked the time breather off. Never any issues.

Adam Lynam said:

Can you please tell me what the timed breather working rpm range is?

Click to expand...

I have no idea, you would have to run an experiment which is pointless when the reed valve is available.

I have a 70 model and have run more permutations of breathers than probably anyone here...

I had the original timed breather - The bike was prone to leaks. It's design is cool, but it's not up to the job

Next, I added the timing chest blanking plate reed breather modification to the original timed camshaft breather so I had 2 breathers going. One reed valve and one timed rotating disc - The bike didn't leak as much, but places like the tachometer cable port showed oil drippage occasionally.

Eventually, I added the Jim Schmidt camshaft port reed valve breather inline with the original camshaft port breather - This cured all my leaks except the odd drip after long hot rides. I think the second reed valve helped the timed breather seal better so it drew a better vacuum than just the rotating disc, so no leaks to speak of after the double reed valves.

Finally, I drilled 1/4" hole through the breather port disc centers, so the timed breather is disabled on the upstroke and has a bigger opening on the exhaust stroke. The reed valve alone provides the resistance to the bike's exhale and it seals well on the piston upstroke.

So, I have dual reed breathers. One on the end of the camshaft and one on the back of the timing side blanking plate. Both of my reed breathers are above the crankcase floor level so they can't be underwater if my crankcase sumps. This means when I kick the bike over when it's sumped with oil, the air exits both ports without having to push the mass of the sumped oil up a breather return line. I don't have to worry about blowing my crankcase oil seal out the primary side due to sumped oil blocking the breather... In my case, sumped oil just gives a little more resistance to the spinning crankshaft and just splashes the oil around everywhere, which is not a bad thing...