Breather Valve Problem ?

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I've used breather valves for many years but nothing as efficient as the SX650 valve. Since fitting the SX650 valve I've noticed my motor was not scavenging the sump oil as good as it should at low revs. I removed the valve yesterday and problem went.
The oil pump is in good nick, looks as good as new and gives great oil pressure, is crankcase vacuum causing the pump to struggle ? Has anyone else noticed this ?

As they say; "Yer don't get owt fer nowt"

Cash
 
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Sounds like your pump clearances are excessive, so the negative pressure of the crankcases the PCV gives is giving the pump more work than it can handle, a clogged oil filter can give the same problems. A refurb of the pump is in order plus an oil filter change if is not a recent fit.
 
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If you are speaking of your MKIII then Kommoando my have it somewhat diagnosed. If a 72, then I believe these valves should not be applied until the cases have been modded. There is just too much oil trying to push past this valve ( whether xs650 or motormite) to be functional. Blowing air through is easy but fill a hose with 50w and try blowing through is another story.

I resently applied a MKIII time cover to my 72, a nice addition, and upon removing the timing chain inspection plug while it was running, I was rather blown away, so to speak, with the amount of crank pressure coming out. I pulled the one way valve off immediatly.
I have a late set of 72 cases that I have machined and updated for this winters project.

In the season remaining I am thinking of appling a breather outlet to the timing cover and leaving the stock one at the lower left in place. Tie it in with a "Y" connection and see how she flies. This may turn out to be an option for people who cannot do the case mod. God know the 72's need to breath and redundancy may be the solution. How can it hurt?
 

rvich

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I put the XS650 valve on my '72. I mounted it high by strapping it to the backbone of the frame, just before the oil tank. This may not be the best location for pulling a vacuum with a lenght of rubber hose between it and the back of the case, but I have not noticed any problem with it or with oil flow. I get a good strong oil return to about 4500 RPM, above that it decreases, but up to about 6k before I see any coming through the breather. One of these days I will pull the cases apart and modify them, but until I do this seems to be working.

Russ
 
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I should have told you, My Commando is a Mk3 850 and the problem though not serious is worth discussion I would think.

The oil pump was overhauled out last year and is in bloody good condition. The return starts to flow immediately and looks strong and after a minute will show signs that the cases are near empty but they are not. On a run of over 45mph the tank will refill however anything under 45mph in top and the level settles on the minimum mark. The valve is working correctly and isn't swamped with oil, but when removed the oil tank level remains high.

Perhaps this usually goes un-noticed and to be honest hasn't caused any issues so far. However, my concern is it might and has anyone else notice this phenomenon. Is this why Norton have drawings of a valve but never fitted it ?

Any how, for the foreseeable future the valve will be left off.

Cash
 
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Cash, what you are seeing is common on reed valves connected to the timing chest. The oil that is missing from the tank is trapped in the timing chest. Return to the main cases is poor with no valve and gets worse with a valve. That is part of the reason for the location of the CNW reed valve and the modifications done to the cases. Jim
 
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Ludwig, It looks like you got a great idea there. You are exhausting from the crankcase instead of the chaincase so you should be in good shape.
In one of my earlier designs I had a single reed block bolted to a flat area milled and drilled near the main bearing and a hose from the block to the inside of the original fitting on the chest. It worked well but it was more work than the present design. I am still looking for that simple bolt on piece that eliminates all the problems. Jim
 
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There are two holes in TS crank case, [not counting unsealed ball-roller bearing] the lowest hole sets the resting level of oil for chains/cogs on start ups. The 2nd higher hole would act as a vent from crank case, if it was big enough to handle the flow volume-pressure pulse changes. Its been recommended to open these holes up SignificantlY and even add another, which I did in Peel Combat with moved oil drain to rear of cases. I was able to get three 1/2" holes to lower pumping friction and lower-dampen the pressure spikes by TS case volume added to sump volume.

In Combats with stock low breather the crank spin will pump oil out to tank way faster than the oil pump can, thru bigger passage. Maybe not as much pressure head as pump but plenty to about hit roof if oil cap off on mild rev ups. Peel oil level stayed normal and no leaks over redline use with a Krane PCV mounted horizontal along top of tank. Breather baffle was mounted on back of old magneto face. I used clear 1/2" ID tube with fiber weave, I never ever saw it stained by oil and it stayed dry and clean inside by white glove test at the low end near TS of tube. Amazing to me. I attribute this to the TS vent holes more than anything else.

Is possible that oil mist/layer on reed is adding mass to slow its response?
I will be putting PSI gauges on either side of valve to see what they say.
Maybe someone could beat me to it.
 

ML

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I'm not a sceptic of one way vacuum valves, but unless done properly i.e. Ludwig's and Jim's designs there is potential for adding on a device potentially undersize and located more for convenience that may not produce the expected benefit . My preferred method is not to rely on the crankcase breathing alone. I supplement with a 6mm bore from the inlet rocker cap. I originally used clear hose to see any gas / fluid movement, and it is noticeable. All this does is to take some of the pressure and volume off the timing side breather outlet. The motor is oil tight, no mist and no smoke and remains so after a long hard run, so that's one proven means that I'm happy with.

Mick
 

xbacksideslider

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My $3.57 -

Combustion gas blow-by adds volume to the gasses that the crankcase breather system has to evacuate. We have a 360* crankshaft and that means that the crankcases are seeing 750cc (or more) of volume increase or decrease every 180* but that back and forth so some extent cancels itself out, especially as engine speed rises and the time between highs and lows is reduced. What do the crankcases "cc" at?

We are not just trying to reduce crankcase pumping losses, we are also trying to (1) reduce windage losses to oil wrapped around the crank and timing chest what nots, (2) evacuate nasty combustion gasses from the crankcase, and (3) to help the oil pump scavenge oil back to the oil tank. We do not want too much vacuum in the crankcase because at some point that vacuum works against the oil pump.

Ideally the oil pump is scavenging ALL oil from the crankcase. It is a dry sump engine after all. But, at some engine speed(s), the high side outpaces the low side, resulting in too much oil in the timing chest and crankcase.

The '72 rear crankcase breather under such condition floods with oil and then cannot breath properly. It then is pushing oil up and against gravity through a small diameter hose, albeit with pulses of 750cc (and more) of swept area pushing air up and out that small diameter hose of far less volume than 750cc. It's like an elephant trying to inhale AND exhale through a soda straw.

The CNW reed valve helps that rear crankcase breather to evacuate gasses AND oil by converting it from a two way street to a one way street. Now it is exhaling only. Now the crank and timing chest whizbits can spin without ropes of oil hanging onto them.

So, I thiink that the '72 breather evacuates from exactly the right spot and all it needs is a reed valve.
 
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quote
"We are not just trying to reduce crankcase pumping losses, we are also trying to (1) reduce windage losses to oil wrapped around the crank and timing chest what nots, (2) evacuate nasty combustion gasses from the crankcase, and (3) to help the oil pump scavenge oil back to the oil tank. We do not want too much vacuum in the crankcase because at some point that vacuum works against the oil pump."

I have used a belt driven graphite vane pump to evacuate the cases on the last several racebikes that I raced. They would evacuate the cases to around 17 inches of vacuum and still the stock scavenge pump had no difficulty with keeping the cases clear of oil. I found that evacuating the cases to that degree was good for nearly five free horsepower over an open breather. If I were to build another racer I would try using a large two stage gear pump to evacuate the cases and scavenge the oil at the same time. Jim
 

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Breather Valve Problem ?


Breather Valve Problem ?



The first pic is of a Ford "gulp valve" on a turbo-mopar downpipe. This setup uses exhaust gas inertia to pull a crankcase vacuum. The valves are available in smaller sizes and consist of a disc type reed attached to a Bernoulli venturi welded into the exhaust.

Since the gulp valve, as with the engine driven or electric vacuum pumps, pull a vacuum into the teens, the second pic is of an adjustable vacuum relief valve, again of disc type, that is placed on a valve cover to limit total vacuum in the crankcase. A K & N type filter is placed over the vacuum relief valve to filter the air that it allows into the engine. Now you have a way to help the oil drain out of the head too - one of Mr. Axtell's pet peeves.
 
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I have used a belt driven graphite vane pump to evacuate the cases on the last several racebikes that I raced. They would evacuate the cases to around 17 inches of vacuum and still the stock scavenge pump had no difficulty with keeping the cases clear of oil. I found that evacuating the cases to that degree was good for nearly five free horsepower over an open breather. If I were to build another racer I would try using a large two stage gear pump to evacuate the cases and scavenge the oil at the same time. Jim

Music to me ears Jim, as solves my ponder if exhaust sucker would bother sump oil return. I'll stick to Plan A, hoping the check valve vent in frame tank will prevent low pressure to develop on the feed side of pump, yet not spill oil when stem is lower than rear of spine tube. 5 hp extra is like removing almost 20 lb mass in get go.

Ms Peel had over rev event with her vented TS case, Combat breather baffle ann Krank valve, yet no hint of oil in big clear hose. Oil came out every other seam and fastener location though.
 
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Cash, what you are seeing is common on reed valves connected to the timing chest. The oil that is missing from the tank is trapped in the timing chest. Return to the main cases is poor with no valve and gets worse with a valve. That is part of the reason for the location of the CNW reed valve and the modifications done to the cases. Jim

Thanks Jim,
That explains a lot. I've fitted breather valves since 68 not for any power gain or leak prevention but to stop crap migrating into the oil tank or cases. It's amazing how much grit you'll find in some breather hoses. I reckon I should fit a filter, or refit the valve and add a small breather to a rocker cover ?

Thinking cap time

Cash
 

maylar

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cash said:
The oil pump was overhauled out last year and is in bloody good condition. The return starts to flow immediately and looks strong and after a minute will show signs that the cases are near empty but they are not. On a run of over 45mph the tank will refill however anything under 45mph in top and the level settles on the minimum mark. The valve is working correctly and isn't swamped with oil, but when removed the oil tank level remains high.
Cash

My MKII does the same thing and the pump is brand new. I'm gonna remove my breather valve and see if it changes the oil level. Thanks for the report.
 
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Cash, I don't think a breather in the valve cover will help your problem. The oil gets trapped in the timing chest because with the reed valve connected more air is moving from the crankcase into the chest and there is less air moving from the chest back into the crankcase. The air movement carries oil with it.

If you install an open breather in the valve cover you will have air going into that breather, down the pushrod tubes into the crankcase, then through the holes between the crankcase and the timing chest and out the reed valve. This air movement will keep more oil in the chest. If you install the reed valve on the head the one way air movement up the pushrod tubes will tend to keep oil trapped in the head.

Another thing that helps prevent oil buildup in the MK3 850 timing chest is changing the oil pressure relief valve dump back to the pre MK3 design. You need to plug the dump hole into the timing chest and drill the hole that returns the overpressure oil into the feed side of the pump. It's a simple mod and I can post some pictures if you want them.

A good fitting oil pressure relieve valve will also leak less oil into the chest. Jim
 
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One question for Jim. My old Combat engine had the 850 timing side holes mod and breather with the old LH case breather capped. Now, prior to blocking the front pickup and opening up the rear return the engine would sump badly after 5-10 mins at 4000 rpm +. Tank would empty and oil would start peeing out the weakest barrel to case joint, usually LH and white exhaust smoke had to be seen to be believed. My question is why with all the oil in the cases and those 3 x 3/8" holes in the RH case could the oil not find it's way back to the tank via the 1/2" timing case breather? The pressures must have been enormous yet it chose to puke oil through a gasket rather than a relatively free passage to the tank. Or could it have been to do with oil tank pressure? At the time that was fed into the aircleaner so I don't understand why it did what it did. I'd like to try the LH case mod with reed valve as the 'Norvil' one way valve I have continuously fills with 'mayonnaise'. It doesn't seem to affect it's function though and keeps everything nicely oiltight (except when I reversed the connections recently)!!
 
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comnoz said:
.

Another thing that helps prevent oil buildup in the MK3 850 timing chest is changing the oil pressure relief valve dump back to the pre MK3 design. You need to plug the dump hole into the timing chest and drill the hole that returns the overpressure oil into the feed side of the pump. It's a simple mod and I can post some pictures if you want them.
Jim
Yes, Please.
 
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White smoke from the exhaust would mean that the crankcase is not being scavenged of its oil.

The 72 cases would do that if the oil pickup was not moved to the rear of the cases. It will not return through the breather in the timing chest or from the front scanenge hole because it tends to pile up in the rear of the crankcase because of the spinning crank and needs to be pulled out from there.

Once the oil gets deep enough in the crankcase to be whipped into a froth by the crank then all control is lost . The oil gets full of air bubbles and the volume of oil froth increases dramatically. At that point you have to shut it down and let the air bubbles escape or you end up with major smoke and leaks from every joint. It's like what happens when you put a cup of milk in a blender. When you push go the blender will suddenly be full of milk froth.

Oil tank pressure would not have anything to do with it. Jim
 
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Before I did the Combat oil drain mod, I'd whipped up pre-Peel into oil lather to find most of her 14 total leak sites. Never saw foamed oil to matter anywhere.

But I don't understand why Combat excess oil can pile up since the way the breather mouth is configured, oil should just shoot up through the baffle into big hose and out top of oil tank. I see this on wet sump start up pump downs, why not more so on the fly?

Peel standard Combat and TS breather mount plus the three 1/2" vents seemed and a tank top Dreer-Krank PCV solved all rpm wet sump and air free oil return to tank, and oil leaks/weeps, mists, even in breather hose, white glove dry as a bone inside up to tach pegging rpm. Only difference I've not seen others mention, is the extra big plus extra 3rd hole to connect biggest volumes. I made 3rd hole up by barrel.
Breather Valve Problem ?
 
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