Breather check valve

[dxhall]

My ‘96 Carb Sport is cursed with a front crankshaft seal leak.  I’ve taken it apart several times and replaced the seal, to no avail.

It occurs to me that the leak is caused by excess crankcase pressure.  All of the breather lines, however, seem to be clear.

MG Cycle lists a breather check valve, part no. 28150560.  I can’t find that valve in any of the exploded diagrams.  Does anyone know where this check valve is in the breather system?  I haven’t seen any such thing on my bike.  I’m wondering if I should have one, but don’t.

[John A]

It is in the large hose at the top of the block. It just sets in the metal tube the hose attaches to.

[dxhall]

Thanks for the quick reply.  I don’t recall there being any such valve on this bike.  Any idea what would happen if it’s missing?

[John A]

I don't know, and I'm thinking the Sport may be different than a Cal series.  On my new Cal2, way back, it had a check ball valve that could close itself off, resulting in blowing out a quart of oil in an instant at road speed. It blew the oil back up the tube that was below the oil level until the end of the tube was out of the oil. I had that engine apart a couple times before I figured that one out.  The valve was redesigned so that on the outlet the hole was made square so the ball couldn't close it off.

[antmanbee]

I think the Sport is like a Centauro or V11 Sport. The spine is the breather chamber and there is the big S hose from the top rear of the engine to the underside of the spine with no valve.
On the top of the spine there is a smaller hose that goes to the airbox to vent any pressure either negative or positive.
On the lower left side of the spine there is a smaller hose that drains condensed oil back to the sump.

[Old Jock]

Intrigued by both John A's answer and antmanbee

Now I've got Magnis so they may well be different.

On my spineys I have 2 hoses not just one, left and right feeding down to the sump from the back of the spine

I'm guessing JohnA's Cali was a similar set up to the Spineys as described by antmanbee and the valve he is referring to is the main engine breather at the back of the engine on top feeding up to the frame and the oil pipes that jetisoned his oil overboard the pipes that are at the base of the sump. I never knew any of the Tonits had that set up, but I don't know the Cali Tontis. Would like to know a little more about that.

Anyway back on topic, I had/have seal leaks from a now (hopefully fixed) blowby problem. I think it's damaged the seals and they will need replaced next winter. This lead me to do some research on the whole system and from everything I've read (there is some info on This Old Tractor) there is no valve on the spineys.

The consensus is that if a valve were installed on the main breather it would cause oil fluctuation in the sump as it is always open to atmosphere through the oil return lines coming from the back of the back of the frame. If the pressure went negative/positve due to the check valve on the main breather line opening and closing, this could then cause the oil level to fluctuate in the sump and possibly lead to aeriation of the oil resulting in foaming, therefore it was omitted.

Just my understanding of the system

 

[antmanbee]

I was going by memory from my recent work on my V11 sport. The V11 only has one hose from the lower left side of the spine to the sump. The Centauro has two. One from each side to the sump as you stated. That seems unnecessarily redundant to me to have two.
The Cali Tontis are not the same as the spine frames. Cali Tontis have the check valve and the spines do not.
Excessive blowby will overwhelm either breather system I would suspect.
Both systems vent to the airbox.
I'm not sure why they used the valve on the Calis and not the spines, most likely due to my not having a complete understanding of the two systems.

[dxhall]

The Sport 1100 has the (1) the S-shaped formed hose that goes from the top back of the engine case to the bottom of the spine just below the steering head; (2) a banjo bolt on top of the spine just behind the steering head, which once held a hose that went to the air box; and (3) two hoses at the middle of the sides of the spine which go to a banjo fitting at the sump drain plug.

I’ve replaced the front crankshaft oil seal on the d—- thing three times.  It still leaks.  Can’t figure out what’s wrong.  Got a new crankshaft sleeve (it’s what the seal turns on) from Curtis Harper last week.  I’ll take it apart again and try that with another new seal.

[Old Jock]

I've got the problem as dxhall and his description of the system matches what I have.

I still cannot understand why the check valves are installed/omitted on bikes with a similar system, it just makes no sense (Calli Vs Spiney), unless it's possibly connected to he difference in frame volume (Tonti Vs Spine)

I think Pete said that the breathing on the 1100 is marginal, it was on that thread about the grey cafe machine where the owner had taken his engine out out to 1200

I did try to measure the sump pressure when I had the blowby problem it was quite small, under an inch of water as I remember, but I'm pretty sure I still have blown back and front seals too. I'll check the journal and bearing dimensions when I'm replacing them in the winter, just to be sure.

I've installed an additional breather on the dizzie blanking plate that just goes overoard to atmosphere with a -8 hose, the bike has only had one short run out since this was completed (for an inspection). When I looked it appeared that there was oil coming out of the hose. I would have expected vapour and perhaps a little drip or two, but cursory inspection indicated more oil coming from it than I expected.

I've now got a small catch tank that I'm going to install on the line, to see if it helps. The seal leaks appear reduced, after cylinder relining and new rings (got 20psi increase on one side and 40 on the other when I did a before and after compression test).

I'll report back on success or failure of the breather mod

Like dxhall it's driving me crazy!!! 

[Idontwantapickle]

I've got the problem as dxhall and his description of the system matches what I have.

I still cannot understand why the check valves are installed/omitted on bikes with a similar system, it just makes no sense (Calli Vs Spiney), unless it's possibly connected to he difference in frame volume (Tonti Vs Spine)

I have wondered about this and I also see the difference in volume of the frame tube the only obvious answer. What I don't understand is how leaving the valve out is any sort of improvement. The valve would keep crankcase pressure lower, how is that bad? Or was the profit margin on a sport so low that a $2 part would break the bank?
Puzzling.

Hunter

[antmanbee]

I would think having a valve would be more pressure in the crankcase as it restricts air flow in either direction.
On the V10 Centauro the vent hoses from the heads go into a plate where the distributor used to be on the old Tontis.
On the EV the head hoses go to the frame on either side of where the main down tube ends.
The V11 sport has no hoses from the head.
I don't know what a carbed Sport has.

[Old Jock]

I explained earler the thinking on why the valve was omitted see post #6, perhaps you're sceptical, I wouldn't blame you. When you enter the realm of high speed gas flow all sorts of wierd shit goes on and it's way above my limited intellect.

As Antmanbee states the valve is opening and closing really fast, probably too fast for a ball valve to handle due it's inertia and the spring force it has to overcome. I'm guessing here, but common sense tells me that the valve would want to open and close every revolution as the pistons are pressurizing the crankcase on the downstroke and reducing crankcase pressure on the upstroke. If your engine is reving at 4K that's aboout 133 times per second it's opening and closing. You'd need some sort of light reed valve to be effective, there are faster acting valves out there but 133 openings and closing/sec is a big ask and double that at the red line.

The Bunn system that's oft talked about for British bikes, is a pricey breather system. I read that the reason for the high cost is the development and cost of manufacture of the reed valves, devloped by Bunn himself and unique to that system

The Centauro and Daytona have head breathers on the dizzie blanking plate, again supposition but it may be because there is no direct link between the pushrod tubes and the heads, therefore the heads require to be vented via a hose to the crankcase. The Sports have none as they can vent directly via the pushrod tubes, which form a direct contact between head and crankcase

I'm as big an ameteur as anybody with this, I just happened to look into it a little to try and solve my problem

[acogoff]

May not be your problem, but to quote you "a banjo bolt on top of the spine just behind the steering head, which once held a hose that went to the air box". I would be thinking that if this hose were missing, you would not be getting the negative pressure required for the breather setup to function. I ran into this on Triumph that was seething oil - hooked up the airbox suction hose like the stock setup had been and it was all better.

[Tom H]

There is an O ring that is on the crank between the alternator and the spacer. Did you replace it?

http://www.harpermoto.com/parts-lookup/1990-1999-moto-guzzis/sport-carburated-1100-1994-1996/generator-en-2-3-4-5-6.html

On the loops, there is one under the crank timing gear that can cause a leak like the front seal. Not sure if your bike will act the same?

Good luck!
Tom

[antmanbee]

There are two drain back holes in the head and cylinder sleeve on both sides just inside the two lower stud holes, back to the crankcase.
 
Regardless of which breather system, spine or Tonti frame, there is only a 5/16" hose that is vented to the airbox.
The rest is completely closed with hoses running from breather box to heads and crankcase.
That is a small diameter for pressure to be released. Especially if you have blowby.
I think the idea of adding the vented dizzy plate to another breather box with some mesh stuffed inside to help condense any oil mist and then exiting to a small filter on top might solve the pressure problem. 

[antmanbee]

May not be your problem, but to quote you "a banjo bolt on top of the spine just behind the steering head, which once held a hose that went to the air box". I would be thinking that if this hose were missing, you would not be getting the negative pressure required for the breather setup to function. I ran into this on Triumph that was seething oil - hooked up the airbox suction hose like the stock setup had been and it was all better.

Yes this hose needs to go to the airbox. That is the only outlet of the closed breather system. That is the small 5/16" hose I was referring to.

[dxhall]

Hmm.  A prior owner scrapped the stock airbox and fitted K&Ns.  He then scrapped the hose that connected the spine to the airbox, and left the banjo at the top of the spine open to the air. 

If the system requires negative pressure  (drawn from intake vacuum) to operate, then this mod could be the cause of my problem.  I’ll put a hose fitting into the end of one of the K&Ns, run a hose to the top banjo, and see what happens.

[antmanbee]

It wont change anything. Vented to the filter or vented to the atmosphere is the same pressure wise.
It would be a good idea to run it to the filter though, as grit could get sucked into the breather box without a filter.

[dxhall]

Wouldn’t the inside of the filter be a low pressure area when the motor is running?

[acogoff]

    Yes, run it into the filter, there is some vacuum there. Only half the suck of the original, but may work out. A stock filter setup would be the best bet if you can find one.

[antmanbee]

I don't think there would be much difference unless the airbox was quite restrictive. The small amount of vacuum there is not enough to affect either positive or negative pressure to the breather box.
I usually remove my airboxes and run a foam sock filter to the velocity stacks. I use a small KN just connected to the 5/16 hose that goes to the breather box.

[John A]

It wont change anything. Vented to the filter or vented to the atmosphere is the same pressure wise.
It would be a good idea to run it to the filter though, as grit could get sucked into the breather box without a filter.

True in my experience. there is not enough low pressure in the airbox to make a difference.   Oil fumes in the intake can lower the effective octane of the mixture. In our application its just a theoretical, I don't think it makes any difference there either 

[Old Jock]

I don't think running the hose to the airbox will do much either, but willing to be proved wrong.

I'm running pods too, coincedence that both bikes running the pods have breathing problems?

The thing is how many Sportis run pods, loads as far as I've seen. I've certainly not heard of so many having pressurisation problems and leakage

However, playing devil's advocate, although the (negative) pressure in the box is small, so to is the crankcase pressure we are talking 2" water max (probably less). Could it be that although absolute pressure in the box is almost nothing, relative to crankcase pressure it may be significant?

This is a difficult one for me to swallow if it is, my battery is where the airbox used to live and the bike came with pods and did not leak. The leaks started after I stripped it all to refurbish, perhaps I'm a clutz or I disturbed the bedded in parts I just have no clue.

Once I get the catch pot in and run some miles, even with the shot seals I should (hopefully) be able to see if leakage from the mains seals is at least reduced, I'll repoort back on it

Oh on mine that O ring on the spacer before the alternator definately got replaced

John

[acogoff]

     If your intakes have the little screw for attaching the vacuum gauges, an experiment may be to just temporarily plumb one of those with a pipe to your top nipple on the frame tube and see what happens? There is for sure some suction at that point if you do not want to modify your pod filters just for testing.