this old xs
XS650 Addict
Probably pulling the motor this week, maybe. 4th time so should be getting good at it by now
. Will try one more fiddle with the breather because it's quick and easy to do and test, but not super optimistic.
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Can a head gasket leak into the crankcase?
- Thread starter this old xs
- Start date
. Will try one more fiddle with the breather because it's quick and easy to do and test, but not super optimistic.
pull the head, check the head gasket between cylinder and cam chain tunnel, that's the most common place for a leak.
AUTOMAN
XS650 Addict
and on the way up it does the opposite-so why should it have pressure?It's a 360° twin. That means both pistons rise and fall together. When both pistons go down, it tries to compress the air inside the crankcase. That gets forced out the breather. In other words, these engines are famous (infamous?) for high crankcase pressure.
Depends on what you consider excessive I guess...
AUTOMAN
XS650 Addict
360° twin or 10 cyl. V10 should not be building any pressure or vacuum due to pistons going up or down.
Only when blowby occurs via hole on piston/hole in head gasket/ or leaking rings does pressure occur.
Blocking hoses and adding check valves haphazardly is completely different than the original complaint.
When the pistons go from TDC to BDC, they go down together. That makes the internal crankcase volume about 650CC smaller. Since we have a breather, that 650cc excess is expelled out the breather..... along with any oil vapor in that slug of air. Since a bike is dynamic, the oil laden air is lost to the environment.
When we go from BDC to TDC, it's reversed... the expanding crankcase volume sucks in outside air through the breather and the cycle repeats.
Every time the pistons move down, we expel air. Call it what you want, vacuum, pressure.... fuckin' magic.... it's a 650cc slug of air that gets expelled every crankshaft rotation. If there's oil vapor in that slug, that the baffles failed to trap, it's expelled.
AUTOMAN
XS650 Addict
It's a 360° twin. That means both pistons rise and fall together. When both pistons go down, it tries to compress the air inside the crankcase. That gets forced out the breather. In other words, these engines are famous (infamous?) for high crankcase pressure.
Not the old xs's problem.
Net pressure is zero over 720° on a perfect engine.
Blow-by biases the pressure more positive. Excessive, and it blows out more with entrained oil than in.
We don't even know if it has a pressure problem. Might be a short dipstick and oil is overfilled.
Based on that logic, my air compressor is "net" zero.... and is not really relevant to what we're talking about.
On the power stroke and intake stroke, the pistons are forcing 650cc of air out the breather. The fact that it draws back in 650cc on each compression and exhaust stroke is completely irrelevant. Yes, it draws in exactly as much "air" as it forces out..... but every time it forces air out, there's oil vapor in that air....
I'd guess that at 60mph, that oil vapor is somewhere aft of the battery box before the next "in" cycle starts. . In other words, that oil vapor ain't gettin' sucked back in. It's fresh air in, oily air back out. Net 0 pressure, yes. Net zero oil loss? Nope. it's blown out... lost, never to return.
Agreed. I'm not convinced there's any problem with the rings or excessive blow by. I'd still like to see him add the stainless mesh inside the breather housing. I've seen that fix more than one engine using too much oil.
AUTOMAN
XS650 Addict
Guys, you can't put a one way crankcase vent valve on a 360 twin. You are creating a pump moving 40 cubes of air in or out, depending which way it checks.
I'm old, I could be missing something here. But I think our owner created the issue.
I'm old, I could be missing something here. But I think our owner created the issue.
Sure you can. You can buy 'em or roll your own. Either way, there's prolly thousands of 360° twins out there using a check valve.
I did and I'm completely happy with it. Was just cleaning that engine today after a thousand miles since last scrub job, and the difference pre one way valve to after is night and day better.
The catch can stays dry. Previously it was drenching the air filters with oil.
I was also setting valves and after spinning the crank from TDC to TDC to check the other cylinder, I could hear a very slight hiss, realized it was air slowly seeping back in to equalize the crankcase low pressure! ;^)
The catch can stays dry. Previously it was drenching the air filters with oil.
I was also setting valves and after spinning the crank from TDC to TDC to check the other cylinder, I could hear a very slight hiss, realized it was air slowly seeping back in to equalize the crankcase low pressure! ;^)
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It's not so much that the vacuum is the goal but it's a useful tool to help with a "clean" engine? Bonus? reduced crankcase pressure also reduces "pumping losses" a desirable goal in ICE design.Possible issues? A certain amount of oil needs to get to and lubricate seals both shaft and valve. To date we haven't seen/heard any evidence a slight vacuum affects seal life. Sucking air/dirt in towards seals also a possible negative. Many/most modern motorcycle engines use a similar system that sends that crankcase air into the exhaust during much of the operating range, burning off any oil mist and completing combustion of any fuel that escapes the combustion proccess in the cylinder. Like any system there's trade offs and less than perfect results. So far I think the installation of a one-way valve for crankcase ventilation is a simple and net positive for our engines. But the choice is yours.
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AUTOMAN
XS650 Addict
We used to run 70-80 inches of H2O vacuum in the case on the race cars. Dry sump, not like these. Good for 10hp at speed. Pumping, yes but mostly vacuum on bottom of rings. Stops the oil intrusion past the rings at decels, then sudden accel doesn't have a slug of oil knocking on the pistons.
Possible issues? A certain amount of oil needs to get to and lubricate seals both shaft and valve. To date we haven't seen/heard any evidence a slight vacuum affects seal life. Sucking air/dirt in towards seals also a possible negative. Many/most modern motorcycle engines use a similar system that sends that crankcase air into the exhaust during much of the operating range, burning off any oil mist and completing combustion of any fuel that escapes the combustion proccess in the cylinder. Like any system there's trade offs and less than perfect results. So far I think the installation of a one-way valve for crankcase ventilation is a simple and net positive for our engines. But the choice is yours.
My old Triumphs used dry sumps with zero problems(if you can believe a trump did not leak oil)
Normal is a negative 2-4 H2O" on any car.
Blending intake vacuum at p/t then intake velocity to take over at WOT.
Love to see what the old xs does this weekend.
You have to remember that these engines were designed in the 60's. The PCV valve wasn't standard on cars until sometime in the mid to late 60's. I had a '63 Falcon that didn't have a PCV valve. It was all new tech back then. None of the bike manufacturers used a PCV valve back in them days.
Road Draft Tube for the win!
The 75 XS650B dumped the CCV on the chain.
The 75 XS650B dumped the CCV on the chain.
AUTOMAN
XS650 Addict
I always wanted to redesign the ram horns so they did not split the crotch.
Newer Hemi's just rip the screws out. #8/6
Until I put long screws with spacers.
"factory fix" was a tie-bar that just cracked the manifolds in half the time.
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this old xs
XS650 Addict
Hello again everyone, good to see you've been amusing yourselves 
Anyway, I took Jim up on his suggestion (thanks Jim, BTW). My baffles are made up of 3 plates, I assume it's the same for everyone. Closest to the engine is a perforated plate, then a nearly full length plate with a hole in it, then the last plate is about 2/3 length with a hole in it and a plate welded above the hole on the back side.
I've fiddled with the position of that welded on plate in the past and it seems to have a big influence. I packed some stainless scourer in the box part (where the exit hole is), top and bottom. Next is the baffle, then a layer of stainless scourer is sandwiched in between it and the middle baffle, and finally the space between the perforated plate and the middle baffle is empty as per stock.
I've ditched the check valve and am just running the breather pipe to a filter above the right hand carburettor. Before I get too carried away, it's too early to say for certain, because the filter I used was absolutely full of oil from a previous iteration of the breather configuration that was a complete failure:
So last Sunday when I went for a cruise, once the air got hot enough it started to push the oil out of the filter. I will say I think it was only the oil that was soaked into the filter though. Quite promising!
I cleaned to filter out pretty thoroughly and today when I went for a ride the filter remained bone dry. Though it wasn't a long enough ride to properly test, I'm very hopeful.
I gave this a near zero chance of working (sorry Jim!) but it's faster than pulling the motor out. I get a weird chirping noise which I thought was the check valve, but it's definitely not. I have no idea what's going on with that, it sounds like a baby bird, or far off car alarm. Comes and goes, but if this works, I can just tee the breather pipe back into the airboxes as per the later models and I shouldn't be able to hear it.
Fingers crossed!
Anyway, I took Jim up on his suggestion (thanks Jim, BTW). My baffles are made up of 3 plates, I assume it's the same for everyone. Closest to the engine is a perforated plate, then a nearly full length plate with a hole in it, then the last plate is about 2/3 length with a hole in it and a plate welded above the hole on the back side.I've fiddled with the position of that welded on plate in the past and it seems to have a big influence. I packed some stainless scourer in the box part (where the exit hole is), top and bottom. Next is the baffle, then a layer of stainless scourer is sandwiched in between it and the middle baffle, and finally the space between the perforated plate and the middle baffle is empty as per stock.
I've ditched the check valve and am just running the breather pipe to a filter above the right hand carburettor. Before I get too carried away, it's too early to say for certain, because the filter I used was absolutely full of oil from a previous iteration of the breather configuration that was a complete failure:
So last Sunday when I went for a cruise, once the air got hot enough it started to push the oil out of the filter. I will say I think it was only the oil that was soaked into the filter though. Quite promising!
I cleaned to filter out pretty thoroughly and today when I went for a ride the filter remained bone dry. Though it wasn't a long enough ride to properly test, I'm very hopeful.
I gave this a near zero chance of working (sorry Jim!) but it's faster than pulling the motor out. I get a weird chirping noise which I thought was the check valve, but it's definitely not. I have no idea what's going on with that, it sounds like a baby bird, or far off car alarm. Comes and goes, but if this works, I can just tee the breather pipe back into the airboxes as per the later models and I shouldn't be able to hear it.
Fingers crossed!
If I recall correctly, it was beneficial to scavenging to cut the road end of the tube with a trailing 45degree slant.
Thing about those cars back then was the sills and outer panels could be hanging off with rust but the centre section would be rust free, thanks to the mighty power of Oil Mist.
