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more on breathers

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
So i've had my Rapide for a few months now and its almost ready to be dependable. It sat for who knows how long and so far i've had to replace a lot. I've refurbished the mag, learned how to time the engine, replaced the kickstart shaft and crank, installed an Alton and podtronics due to a failing D6, replaced a slipping old clutch with a multi-plate, and had my shadow speedo rebuilt. I expected some of this, but there's one last thing that is driving me somewhat crazy.
 

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
Breathers.. i've read all the WhitakerPedia on breathers. My bike has the timed breather blocked off. i have a D breather cap on the front cylinder intake side and i just recently fitted a PCV to it. It still COVERS the back of the bike on rides longer than a few miles. Here's my thought. I want to find a motorcyle oil separator from some OEM source like Honda and vent one breather cap into that, drain the oil into another D series cap, and put a small filter on the outlet. This seems like a much better solution to me than a catch can. I just need to find one small enough that will fit near the top of the engine and not look like crap. Thoughts?
 

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
I have. From what i've read the D heads had more drainage and on a C the oil will spray right off the rocker and go out the cap. At first i thought maybe i had ring problems and i suppose it's possible that I do, but my plugs look pretty good and the bike has what i believe to be good power so i'm not sure.
 

vibrac

Well Known and Active Forum Website User
VOC Member
This is what I use on the racers I have written a bit on it in the old forum PM me and I will tell you where to find suppliers in UK
 

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b'knighted

Well Known and Active Forum Website User
VOC Member
Hi Useful',

You are nearly there, but if it were perfect, what would you have to talk about?

There has been so much talked and written about breathers since the bikes were in production that the solution is definitely out there, and is probably on this forum.
First I'd recommend searching past threads for a variety of opinions. You may find you need to answer some questions, like what size breather pipe do you use and a how long is it? - the idea being that perhaps it's volume has to be able to cope with the engine displacement without pumping out of the end. I think that was why Know Thy Beast suggests pipes to behind the pillion footrest.

My own thought is that the breather developed decades ago by Mac Read is the cure for all problems. It is disliked by some as it adds an external pipe, the so called elephants trunk, vertically from the ATD cover. This has a shuttle valve (PCV?) close to the cover and the blown gas goes to separator chamber which has a capilliary tube for oil to be sucked back into the D breather cap. The exhaust from this separator is a short oil free pipe. This is used with the timed breather outlet blanked.
There are other breathers also called elephant trunks which aimed to copy Mac Read's but not all were successful.
 

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
The bike actually came with a never installed Elephant trunk breather from Ron Kemp with a set of instructions. I hadnt considered it yet because i happen to think it looks terrible. I might just try it though while i'm figuring out this oil separator idea.
 

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
I would be interested in hearing more about the reed valve set up. I have seen references to it but not info on the complete set-up.
 

davidd

Well Known and Active Forum Website User
VOC Member
I have the timed breather on one racing engine and a Ducati reed valve on the other and neither pas any oil. However, I do leak down tests routinely (once a year on street bikes). The problem with the D breather is that you need D parts, the lines are small and there is no drain down because the lines are horizontal. On an engine with poor or unknown sealing I would use an elephants trunk breather as recommended. It has a lot of condensation area and an oversize tube for drain down. If or when you get the engine sealing under control I would use the timed breather.

The reed valve is rather big so it is difficult to hide on a street bike and it needs some mods to fit in-line.

David
 
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