FT: Frame (Twin) Elephant trunk breather

Martyn Goodwin

Martyn Goodwin

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Marcus Bowden said:
Whats the Irving mod to pinion, please enlighten me Martyn.
bananaman
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Marcus,

My copy of "Tuning For Speed" 5th edition by P.E.I. in Chapter 15 "Twin-Cylinder Engines" at page 176 states the following in reference to the Vincent range

" Better crankcase ventilation is obtained by filing straight across the breather-valve sleeve until the slot is fully 3/8 in. wide, then rounding the outer edges of the flat so that the outgoing air has a clearer passage; the edges of the slot should be left sharp to act as oil scrapers. Replacing the external banjo and pipe with a union and a large-bore pipe running upwards and rearwards also helps ventilation. "

(By the way - I also have access to a First Edition of the same book and there is no mention of this matter in it.)

I have made this mod to my Comet and it works. I have widened the slot a wisker more than recommended by P.E.I. to the extent that the breather now opens to atmosphere at around 15 ATDC and closes around BDC. When the piston is decending the pressure otherwise created in the cases is released to atmosphere; when the piston is accending, then the 'breather' is closed thus creating a partial vacume. Result - no oil leaks! And NO oil exiting from the breather outlet.

Of course if your motors bore and or piston rings are toast allowing excessive blow-by the effectivness of any breather will be compromised.

Martyn
 
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youngjohn

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B9BAE993-344C-48DB-AD1C-0A6328660FA7.jpeg


Thanks for the mention Bill! Hope you’re well.

From time to time I produce a batch of PCV breathers built into a rocker inspection cap which is designed to go onto the front cylinder inlet.
All PCV valves are not equal and it took me about 30 attempts and lots of patience to find a valve with the right characteristics which would work well on my Rapide and Comet.

It’s not a magic cure for a worn out engine, but it works really well on my bikes and I’ve had good feedback from many of people who have bought them.
 
Dave61

Dave61

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youngjohn said:
View attachment 17502

Thanks for the mention Bill! Hope you’re well.

From time to time I produce a batch of PCV breathers built into a rocker inspection cap which is designed to go onto the front cylinder inlet.
All PCV valves are not equal and it took me about 30 attempts and lots of patience to find a valve with the right characteristics which would work well on my Rapide and Comet.
It’s not a magic cure for a worn out engine, but it works really well on my bikes and I’ve had good feedback from many of people who have bought them.
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Hi Youngjohn,
Will you be making a batch of these in the near future ?
If you are would you put me down for one.
Cheers
Dave
 
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youngjohn

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I’ll be making a batch in about a month. Just ordered the valves from the USA. I’ll let you know when they are ready.
 
Bill Thomas

Bill Thomas

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VOC Member
youngjohn said:
I’ll be making a batch in about a month. Just ordered the valves from the USA. I’ll let you know when they are ready.
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One for me Please John, It will look better than the ones I use, It will go on my new Comet.
Can't remember how much ?.
Can I send you a cheque, I don't have an account with ebay, Can't trust my computer.
I will P.M. you my new email, Orange has stopped doing them now, I am now on gmail, Many thanks Bill.
 
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