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Engine breathing #737031
05/30/18 3:51 am
05/30/18 3:51 am
Joined: May 2009
Posts: 291
Omaha, NE, USA
Paul Sammut Offline OP
BritBike Forum member
Paul Sammut  Offline OP
BritBike Forum member
Joined: May 2009
Posts: 291
Omaha, NE, USA
Hi, I carried out a search of the forum and couldn't find any previous threads on this, but forgive me if I just missed it. My Series C Rapide leaks like a sieve after a run and there is a massive, embarrassing puddle under the bike soon after stopping. My reading tells me that the most effective solution appears to be the elephant trunk set up, but it is an eyesore that disfigures that beautiful engine. Are there any effective alternatives that you have tried, please?
Kind regards,
Paul


Paul

'74 Commando
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four
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Re: Engine breathing [Re: Paul Sammut] #737061
05/30/18 2:14 pm
05/30/18 2:14 pm
Joined: Aug 2010
Posts: 323
New Hampshire, USA
David Dunfey Offline
BritBike Forum member
David Dunfey  Offline
BritBike Forum member
Joined: Aug 2010
Posts: 323
New Hampshire, USA
Paul,

Breathers are highly addictive, so I normally stay away them. The stock timed breather is fine, but it may be: one, mistimed, or two, overwhelmed by the poor condition of the engine. If you had the results of a leak down test and they were good I would say it is mistimed. A leak down tester can be bought from Harbor Freight for about $50. It can be used to tell you if the rings or valves are leaking more than they should. I can describe its use if you wish.

The timed breather can be checked by attaching a length of clean plastic hose to the breather pipe. With you degree wheel set at TDC on the rear cylinder. You can blow through the hose as you turn the rear wheel forward. You will not be able to blow through the tube at TDC, but keep easing the wheel around and at one point the valve opens and you can blow through the hose. The degree wheel should read somewhere around 70 degrees ATDC. Continue on and somewhere around 30 degrees ABDC the valve will close and you will not be able to blow through the breather. If the timing is way off you would have to remove the timing cover and shift the breather gear a tooth or two as necessary. This is a bit of work, but checking it is pretty easy and it may be fine.

There are basically three types of breathers, timed, atmospheric and PVC. We covered the timed breather. The atmospheric is just an open hole that has no timing valve or ball valve. It lets air in and out. The PVC styles would have a check valve, like a ball or reed that allowed air out, but not back in. I mention this because there are many Elephant Trunk breathers out there and some are atmospheric and some have check valves. Generally, it is not a good thing to mix breathers. It is best to have one style and stick with it, otherwise, they may work at cross purposes. If you want an atmospheric breather, block the timed breather off, and vice versa.

There is nothing wrong with using an big breather to stave off a necessary rebuild as long as you know that it is a matter of time before you need a cure for the problem.

David

Re: Engine breathing [Re: Paul Sammut] #737814
06/06/18 1:35 am
06/06/18 1:35 am
Joined: May 2009
Posts: 291
Omaha, NE, USA
Paul Sammut Offline OP
BritBike Forum member
Paul Sammut  Offline OP
BritBike Forum member
Joined: May 2009
Posts: 291
Omaha, NE, USA
Hi David,
My apologies for a delayed response - I'd actually responded a week ago in some detail and hit "Post Reply" but the message did not appear to go!

The claim at the time of my purchasing the bike was that it'd had a top end rebuild. I've doubted that for some time as it has smoked fairly prominently from the exhausts. I think most of that is that oil exiting from the exhaust is coming from the rockers. I changed out the rocker feed bolt metering wire but saw no change. I did a leak-down test a few months ago and don't remember the exact numbers, but somewhere around 20% loss in the front and 25% in the rear cylinder. I also do not recall the compression data but I do remember thinking it was reasonable. I shall repeat both measurements.

I think your suggestion of checking the breather timing is excellent and I will do so the moment I get some time. If there appears to be nothing wrong with the timing, I fear I might well have to dismantle a lot more than removing the timing cover!

Thank you, again, for your kind advice.

Paul.


Paul

'74 Commando
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four
Re: Engine breathing [Re: Paul Sammut] #737815
06/06/18 1:36 am
06/06/18 1:36 am
Joined: May 2009
Posts: 291
Omaha, NE, USA
Paul Sammut Offline OP
BritBike Forum member
Paul Sammut  Offline OP
BritBike Forum member
Joined: May 2009
Posts: 291
Omaha, NE, USA
Hi David,
My apologies for a delayed response - I'd actually responded a week ago in some detail and hit "Post Reply" but the message did not appear to go!

The claim at the time of my purchasing the bike was that it'd had a top end rebuild. I've doubted that for some time as it has smoked fairly prominently from the exhausts. I think most of that is that oil exiting from the exhaust is coming from the rockers. I changed out the rocker feed bolt metering wire but saw no change. I did a leak-down test a few months ago and don't remember the exact numbers, but somewhere around 20% loss in the front and 25% in the rear cylinder. I also do not recall the compression data but I do remember thinking it was reasonable. I shall repeat both measurements.

I think your suggestion of checking the breather timing is excellent and I will do so the moment I get some time. If there appears to be nothing wrong with the timing, I fear I might well have to dismantle a lot more than removing the timing cover!

Thank you, again, for your kind advice.

Paul.


Paul

'74 Commando
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four
Re: Engine breathing [Re: Paul Sammut] #738094
06/08/18 11:06 pm
06/08/18 11:06 pm
Joined: Aug 2010
Posts: 323
New Hampshire, USA
David Dunfey Offline
BritBike Forum member
David Dunfey  Offline
BritBike Forum member
Joined: Aug 2010
Posts: 323
New Hampshire, USA
Paul,

I am glad that you did a leak down test and unfortunately 25% is too high. With that kind of blow-by you will need an elephant breather on your elephant breather. On the racer the blow-by usually starts at about .5% after break in. When it hit 7% after a few years the new owner did the top end. I broke a top ring at a race in Cresson, Tx years ago and the reading was 60%. Also, if you do a leak down test, you can listen through the carb and the exhaust to check the seat condition. Listening through the breather will tell you the ring condition.

I suspect that you want to do some riding this summer. It may be worthwhile to install an elephant breather simply to lower the crankcase pressure so you can get some miles on it. Then, the top end could be done over the winter.

All the best,

David


Moderated by  John Healy 


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