Crankcase breather relocation, free power! - Triumph Forum: Triumph Rat Motorcycle Forums
Air Cooled Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, Bobber, T100, Speedmaster, America, Thruxton, and Scrambler. Sponsored by: triumphtwinpower.com

 12Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 246 (permalink) Old 02-12-2010, 04:21 AM Thread Starter
Site Supporter
Supernova
Main Motorcycle: 2009 Bonneville SE
Lifetime Premium
 
Forchetto's Avatar
 
Join Date: Jun 2009
Location: Asturias, Spain
Posts: 20,656
Other Motorcycle: Yamaha XV1100
Extra Motorcycle: Qingqi QM200GY-BA
Crankcase breather relocation, free power!

Jesus!...not another of Forchetto's long-winded and tedious write-ups...yes lads, get the popcorn out...

Removing the blowby gases from the crankcase is especially important on 360 degree engines as the simultaneous rise and fall of both pistons moves a huge amount of air within the crankcase. 180 degree engines on the other hand, tend to just move the air around the crankcase. Older bike engines had all sorts of weird and wonderful timed breather valves and oil traps, some so inefficient that makers directed the flow of oily gases to the drive chain and claimed it was "an automatic chain oiler".

Most would just let the gases spew towards the rear of the bike through a long hose pipe.

In the 70's emission laws came in banning open breathers so makers re-directed all the crap into the carburettors to be re-cycled and burned.

These blow-by gasses effectively lower the octane rating of the incoming mixture by diluting the charge, displacing oxygen and, being hot, also lower the charge density. Both efects tend to harm Torque/power output.

Oil mist carried in the gasses can also deteriorate the O2 sensors in the EFI bikes, and does no favours to things like the Air Intake Temperature and MAP sensors and other components in the throttle bodies.

Redirecting blow-by gasses away from the air box also helps keep carburettors or throttle bodies and other internals cleaner. Paper filter elements soon become contaminated with oil and moisture as a cursory examination inside the airbox will confirm. They're often found to be oily and/or damp inside.

Some systems are worse than others, ask the owner of an old Honda CB400F how often his air filter needs changing due to choking with oily damp gunge. On those the breather used to discharge straight onto the filter housing.

Most of today's airboxes incorporate a more or less effective coalescing filter arrangement to separate the bulk of oil mist and moisture from the gases, this muck collects in a blocked-off tube under the airbox. This has to be drained periodically by removing a bung. Have a look under your airbox to see it.

Doing away with this recycling of gases from the intake gives a consistent and measurable power gain, typically 1 to 1.5%. As an example on a 82-odd BHP Buell it has been found to give a nice and consistent 1 to 2 hp gain over a wide rpm range. The gain on a lower power Bonnie will be smaller but as a percentage it might be just over 0.5 bhp. On large-engined powerful cars as much as 5 hp has been seen.

Drag racers and other max power maniacs go all the way and even use a vacuum pump to evacuate the crankcase and reduce internal losses. Some people think that the suction inside the airbox does the same but the vacuum level at most speeds is far too low to have this effect.

Recycling the blow-by, the way the factory does, cost a little power over a wide range. A little bit of the power gains noted by our posters on removal of airbox are to be credited to the enforced elimination of the breather arrangements by removing the airbox.

I've done mine by replacing the pre-formed hose with a suitable 12 mm car hose formed into a "U" shape, some hose clips and a rubber-lined "P" clip to hold the filter on to one of the manifold bolts, have placed the small filter to stop muck getting in on full view, it's a nice chromed thing and adds a bit more bling as well as prompting questions from the general public: "What's that thing mister?". The hole that's left in the airbox can be blocked by a suitable rubber bung or screwing an old M8 bolt in there.

The easiest way would be to use the existing hose, disconnected from the airbox and fitted with a suitable filter on the end. This can be tucked in close to the airbox, on top of the crankcase.

AndrewI, PJB and mick 85 like this.

Last edited by Forchetto; 02-12-2010 at 04:28 AM.
Forchetto is offline  
Sponsored Links
Advertisement
 
post #2 of 246 (permalink) Old 02-12-2010, 06:58 AM
Site Supporter
Supernova
Main Motorcycle: 2012 Tiger 800XC
Motorcyclist
 
propforward's Avatar
 
Join Date: Mar 2008
Location: Bumbelch, Nebrahoma
Posts: 29,931
Other Motorcycle: 2007 Bonneville, ST1300
That reminds me, I really need to get a new crankcase breather.

Nice write up - of course if you pull the airbox off you get this benefit anyway (just sayin'. Sorry )

Well, everything seems to be in order then.
propforward is online now  
post #3 of 246 (permalink) Old 02-12-2010, 07:21 AM
World SuperBike
Main Motorcycle: 2010 R3 Roadster
Senior Member
 
fat frank's Avatar
 
Join Date: Oct 2008
Location: Houston, Texas
Posts: 2,355
Come to think of it, so do I. Just noticed the one on my bike is fouled up badly. A minor cost concidering what I've done.lol
Makes good sense to me. Nice write up, and another reason to hack that airbox.lol
fat frank is offline  
 
post #4 of 246 (permalink) Old 02-12-2010, 07:36 AM
Site Supporter
Team Owner
Main Motorcycle: 98 Thunderbird
Lifetime Premium
 
Slinky's Avatar
 
Join Date: Jun 2002
Location: Ciudad Quesada, Spain
Posts: 5,110
Other Motorcycle: Down to my last one
Garage
Interesting. Do you suppose that both pistons falling together meet a significant resistance, with the crankcase having to breathe thru a small tube? Same goes for the upward movement I guess, they would be be leaving a partial vacuum behind.

This would presumably rob power too.

'98 Thunderbird
Slinky is offline  
post #5 of 246 (permalink) Old 02-12-2010, 07:53 AM
Powerbike
Main Motorcycle: t100
Senior Member
 
Join Date: Jul 2008
Location: San Antonio Tx
Posts: 305
How long is a crankcase breather good for?
Sands is offline  
post #6 of 246 (permalink) Old 02-12-2010, 07:55 AM Thread Starter
Site Supporter
Supernova
Main Motorcycle: 2009 Bonneville SE
Lifetime Premium
 
Forchetto's Avatar
 
Join Date: Jun 2009
Location: Asturias, Spain
Posts: 20,656
Other Motorcycle: Yamaha XV1100
Extra Motorcycle: Qingqi QM200GY-BA
Quote:
Originally Posted by Slinky View Post
Interesting. Do you suppose that both pistons falling together meet a significant resistance, with the crankcase having to breathe thru a small tube? Same goes for the upward movement I guess, they would be be leaving a partial vacuum behind.

This would presumably rob power too.
The hose I've used is the same internal diameter as the original so it would fit on the existing pipe stub. I know some tuners increase the size of the breather outlet to ease the passage of gases as much as possible, and even fit additional breathers in the cylinder heads and even side cases.

One silly example is those Honda-clone engines used on lots of monkey-bikes, karts, pit-bikes,etc. The Chinese make these engines based on the original Honda Cub 50-70-90cc design, but increase the displacement to as much as 150 cc without increasing the crankcase breathing arrangements.

People fit extra breathers to get better throttle response and power.
Forchetto is offline  
post #7 of 246 (permalink) Old 02-12-2010, 08:49 AM
Site Supporter
Supernova
Main Motorcycle: 2012 Tiger 800XC
Motorcyclist
 
propforward's Avatar
 
Join Date: Mar 2008
Location: Bumbelch, Nebrahoma
Posts: 29,931
Other Motorcycle: 2007 Bonneville, ST1300
Quote:
Originally Posted by Sands View Post
How long is a crankcase breather good for?
No idea. They are cheap, so once a year is not excessive. They probably are still working fine even when they look grungy.

But I don't like them looking grungy.

Well, everything seems to be in order then.
propforward is online now  
post #8 of 246 (permalink) Old 02-12-2010, 04:03 PM
Formula Extreme
Main Motorcycle: Triumph Street Triple.
Senior Member
 
Join Date: Jul 2009
Location: Australia
Posts: 906
Other Motorcycle: Aprilia RS125
Thumbs up

Another good tip, Forchetto.

I've been using a foam style filter on the end of my crankcase breather tube, it's a well known mod in racing circles that the crankcase gasses are not good for motors...so we don't re-cycle them back into the carbs.

Just one thing...

Be careful that you don't get oil spewing out of the filter if you don't position it correctly.

Usually, it's wise to have the filter up higher, up near the carbs if you can.

Just keep an eye on it after a high speed run. If there is no sign of oil from the filter, fine.

If you see some oil ... get it up higher.


S.

2010 Street Triple. Black.

"Just because you're breathing, doesn't mean you're alive"
Sp00ky is offline  
post #9 of 246 (permalink) Old 02-12-2010, 04:40 PM Thread Starter
Site Supporter
Supernova
Main Motorcycle: 2009 Bonneville SE
Lifetime Premium
 
Forchetto's Avatar
 
Join Date: Jun 2009
Location: Asturias, Spain
Posts: 20,656
Other Motorcycle: Yamaha XV1100
Extra Motorcycle: Qingqi QM200GY-BA
Quote:
Originally Posted by Sp00ky View Post
Be careful that you don't get oil spewing out of the filter if you don't position it correctly.

Usually, it's wise to have the filter up higher, up near the carbs if you can.

Just keep an eye on it after a high speed run. If there is no sign of oil from the filter, fine.

If you see some oil ... get it up higher.
S.
Thanks for the tip. I'll keep an eye on it. All I get from it at the moment is a lot of hissing and puffing sounds.
Forchetto is offline  
post #10 of 246 (permalink) Old 02-12-2010, 07:02 PM
Formula Extreme
Main Motorcycle: 2006 Thruxton
Senior Member
 
ageofoctain's Avatar
 
Join Date: Apr 2009
Location: Austin, TX
Posts: 460
Garage
one way brake check valve

On Norton Commandos (and I believe older Triumphs, perhaps others) it's a common practice to install a one-way brake check valve (about $4 at your local auto parts store) in the breather pipe. It enables gasses to escape the crank case, but not enter, providing a vacuum effect. The reason people do this (and the reason I did it) is to reduce oil seepage caused by pressure and weak seals, and it definitely made a difference, but it also is thought to provide a small increase in power due to the lower crankcase pressure. I wonder if any benefit would be had by fitting a similar valve to a new bonnie, which doesn't have the oil seepage issues...
mick 85 likes this.
ageofoctain is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options
All posts must adhere to Forum Rules

Register Now



In order to be able to post messages on the Triumph Forum: Triumph Rat Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter your valid email address, that can receive an automated confirmation message. Otherwise, you won't be able to gain full access.

Email Address:
OR

Log-in













Similar Threads
Thread Thread Starter Forum Replies Last Post
Crankcase breather mod... Flaco Air Cooled Twins Technical Talk 9 04-21-2009 06:46 AM
Crankcase Breather 2ManyToys T3 Sport / Touring Forum 1 12-01-2007 09:35 PM
T140E Crankcase Breather Relocation Rockfish Classic, Vintage & Veteran 5 08-08-2007 09:48 PM
crankcase breather 6string Hinckley Classic Triples 4 06-22-2006 04:04 PM
Crankcase breather ??? danbike Air Cooled Twins Talk 5 04-15-2006 03:36 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome