Welcome to the Yamaha Star Bolt Motorcycle Forum

Why join our motorcycle community?

  • Membership is free and easy
  • Get technical support and information for your Yamaha Star Bolt motorcycle or search for information before buying
  • Use the member map to find riders near you
  • Participate in our monthly virtual bike show (or at least vote)
  • Get rid of these annoying boxes asking you to register  ;D

More importantly, make new friends!!

Author Topic: Crankcase Breather Reroute (Causing issues?)  (Read 270 times)

0 Members and 1 Guest are viewing this topic.

Offline dcdshadow1

  • Newbie
  • *
  • Posts: 15
Crankcase Breather Reroute (Causing issues?)
« on: December 03, 2020, 02:55:36 am »
I recently posted about my cam chain tensioner cap (this is what it is called. Itís the small cover on the other side of the cylinder from the cam chain tensioner). The gasket on this cap seemingly failed and oil began coming out of the bolt hole. Iíve got 3,000 miles on my bike, itís a 2019 with intake, exhaust, Ivanís flash.

The only thing I did differently before it leaked was rerouting the crankcase breather hose as shown on the threads here. After this the gasket blew, and it seems the cam chain tensioner gasket seeped a little bit. I checked everything and the hose wasnít kinked or bent wrong in any way, I simply rerouted it to the left side of the bike and faced it forward, using a hose end filter and zip tied it into place.

Iíve done some research and the only thing that could cause gaskets to fail like that with my engine being so clean and new is a pressure change, which most correlate to the crankcase breather being clogged or something similar. Was the reroute enough to bring up the pressure in my engine and cause the gaskets to fail? Maybe the end filter was not very high flow. Iíve seen some say that in its stock position the crankcase is under a slight ďvacuumĒ from the intake sucking in so pressure stays constant so I donít know if this plays a role.

Well since then I replaced the gasket on the cap and put the hose back to stock location. The new gasket has held up good and the cam chain tensioner does not show any sign of wear or weeping. The original reason I did this mod was for engine preservation and I didnít like that oil would build up in my air filter and sometimes even come out when riding hard. Iíd like to preserve my engine and not have any oil leaks or inconveniences. However I am now nervous to put the breather to its alternate location. I preferred this and had no oil leaks or anything before this, but now Iím worried that if the pressure change was enough that the increased pressure will find its way to another gasket like the cam tensioner or god forbid a head gasket. Any thoughts on this? Anyone have the reroute and seeing a similar or no issues? Or someone who has it stock and a lot of miles. Very curious.  ???



Offline lunkhead

  • Hero Member
  • *****
  • Posts: 1598
Re: Crankcase Breather Reroute (Causing issues?)
« Reply #1 on: December 03, 2020, 12:33:27 pm »
Vehicles used to use road draft to create a partial vacuum before manifold vacuum was used. The tube would hang down where air blowing past the end of the tube would create the partial vacuum. You could also run the tube to a catch can and another tube running from the top of the can to below the engine to get vacuum without polluting too much or just forget the can and do it way it was done in the past.

Gaskets shouldn't start leaking unless we're talking about a Harley or the mating surfaces weren't flat and clean. The most common place for leaks is at the rubber seals with shafts running thru them and the shift shaft seal is usually the first to go over time after many miles of using mineral oil. Synthetics do a better job at keeping seals supple and lubricated. Switching to a synthetic late in life can also cause an old seal to leak. The Bolt's motor isn't stressed enough to cause head or base gaskets to wear down and start leaking from parts moving in relation to each other as with race bikes.
C-SPƎC

Offline lunkhead

  • Hero Member
  • *****
  • Posts: 1598
Re: Crankcase Breather Reroute (Causing issues?)
« Reply #2 on: December 03, 2020, 07:34:48 pm »
Was the reroute enough to bring up the pressure in my engine and cause the gaskets to fail? Maybe the end filter was not very high flow.

The aftermarket breather filter doesn't flow much at all. Crankcase pressure is created from the small amount of blow-by of a healthy engine and isn't a problem as long as there are no "detectable" leaks. Blow-by creates very little pressure but anything above atmospheric will slowly force oil out to the lower pressure side wherever it can. An almost undetectable vacuum is all it takes to lower crankcase pressure enough to make the outside pressure higher than what the blow-by can possibly make inside so the pressure outside pushes back on anything that would otherwise escape thru a marginal leak. Only small leaks can go undetected and never cause a problem. You can run a motor with no crankcase vacuum until a seal wears and starts leaking then add vacuum and the leak will stop until the seal wears sufficiently enough to need replacing.
C-SPƎC

  • Advertisement

Offline dcdshadow1

  • Newbie
  • *
  • Posts: 15
Re: Crankcase Breather Reroute (Causing issues?)
« Reply #3 on: December 05, 2020, 10:40:38 pm »
I appreciate the information this is some stuff I wasnít fully knowledgeable in. Iím curious if there was not enough vacuum thus causing my seal to fail prematurely. The breather was routed to the left side of the bike as shown in the crankcase breather reroute thread, facing forward. Maybe it was in just the right spot or something that there wasnít any vacuum at all. Like I said, the breather is currently back to stock and everything has gone back to normal no leaks and my new gasket is holding well. I am just wondering if it is worth trying to find a better place for it or keep it in the stock position. Like I said, engine life, no more mess, etc. all sounds good but what went wrong with my previous setup I have no idea.

What do you reckon? Have you rerouted your breather?