Can a head gasket leak into the crankcase?

[this old xs]

Its been a long time, I have the oil level around 1/2 way between the 2 marks, tending to the lower side slightly. Being a 78 it has the revised oil capacity and dipstick, though for obvious reasons I'm nervous of running low on oil.

 

[Its been a long time]

Its been a long time, I have the oil level around 1/2 way between the 2 marks, tending to the lower side slightly. Being a 78 it has the revised oil capacity and dipstick, though for obvious reasons I'm nervous of running low on oil.

Understood, doesn't sound like that's your problem then.

 

[dave_a]

You said you put a check valve in the one breather tube? You mean like PCV valve?
If the CCase exhausts 650cc of air on the down stroke, pcv closes, how does it relieve the vacuum going up?
Or did I misunderstand its function?
(Its early)

 

[this old xs]

You said you put a check valve in the one breather tube?

I used a power brake booster valve I think it's called. You can search it on here. I've also tried one way check valves from China.

 

[dave_a]

My question remains: if it puffs out how can the CC get 650ccs of air when pistons rise? Except pull thru gaskets, seals and rings?

 

[Highpower]

My question remains: if it puffs out how can the CC get 650ccs of air when pistons rise? Except pull thru gaskets, seals and rings?

There are questions that haven't been answered by the OP:

1. What was the percentage of leak down for each cylinder?
2. What is the compression on each cylinder?

Any more than 10% difference for either the leak down or compression between cylinders is cause for concern.

In looking at the surface where the head and cylinder join, the most logical place where combustion can enter the crankcase besides past the rings is where the head gasket is close to the cam chain. I confess that I am not real familiar with these XS motors as my experience with vertical twins is with early Triumphs which don't have overhead cams. I had completely forgotten about the area between the cylinders being open to the crankcase.

If the rings were installed correctly and the bores were prepared correctly, leakage past the rings should be minimal. If there is leakage past the head gasket into the the center of the cylinder where the cam chain runs, it could certainly cause excessive crankcase pressure.

 

[this old xs]

I'm away with work so no compression test (even assuming my friend has a tester). Percent leak down would have to be 100%? I don't know for sure, I've never done a leak down test before but as soon as I removed the compressed air the needle went to 0 in about 3 seconds. While compressed air was applied it stayed in the green, don't remember where exactly without looking at the gauge.

 

[AUTOMAN]

I'm away with work so no compression test (even assuming my friend has a tester). Percent leak down would have to be 100%? I don't know for sure, I've never done a leak down test before but as soon as I removed the compressed air the needle went to 0 in about 3 seconds. While compressed air was applied it stayed in the green, don't remember where exactly without looking at the gauge.

forget compression
leak-down needed

 

[this old xs]

It should come as a surprise to no one that apparently I don't know how to interpret a leak down test. So I watched the first short video I found, it has a guy called Lake Speed JR in it and if you can't believe a man with a name like that when it comes to engines, who can you believe?

Anyway I thought you pressurised the cylinder and then removed the pressure with the idea being it should hold pressure. Apparently not. It's just the % difference between the feed pressure and the cylinder pressure.

This brings into question my friend's leak down tester and its Chinese gauges. As you can see in some of the photos, the cylinder gauge is reading slightly higher than the input gauge

Cold left hand cylinder



Cold right hand cylinder



My mate Lake Speed JR said you should do it hot

Hot left hand cylinder



Hot right hand cylinder



Even with a suspect gauge I don't think there's an issue with ring seal. You can really crank it up if you want



As I was waiting for the bike to warm up, I heard the brake check valve I've got on the breather start to "chirp" as it vented. Once it started, it didn't stop. Ran for quite a few minutes before it happened. I'm suspecting head gasket even more now.

 

[AUTOMAN]

Schrader valve in the end of the hose that screws into the cyl. head?
if so, take it out!
if not, that's the bestest sealing combustion chamber i have ever seen

fyi
2 stroke "leak-down" is for crankcase sealing

 

[this old xs]

I think there is a schrader valve in there.

 

[Jim]

It should come as a surprise to no one that apparently I don't know how to interpret a leak down test. So I watched the first short video I found, it has a guy called Lake Speed JR in it and if you can't believe a man with a name like that when it comes to engines, who can you believe?

Anyway I thought you pressurised the cylinder and then removed the pressure with the idea being it should hold pressure. Apparently not. It's just the % difference between the feed pressure and the cylinder pressure.

This brings into question my friend's leak down tester and its Chinese gauges. As you can see in some of the photos, the cylinder gauge is reading slightly higher than the input gauge

Cold left hand cylinder

View attachment 352462

Cold right hand cylinder

View attachment 352463

My mate Lake Speed JR said you should do it hot

Hot left hand cylinder

View attachment 352464

Hot right hand cylinder

View attachment 352465

Even with a suspect gauge I don't think there's an issue with ring seal. You can really crank it up if you want

View attachment 352466

As I was waiting for the bike to warm up, I heard the brake check valve I've got on the breather start to "chirp" as it vented. Once it started, it didn't stop. Ran for quite a few minutes before it happened. I'm suspecting head gasket even more now.

A leak down test, in this context, is actually a differential pressure test. It comes from the aviation world and then the hot rodder's adopted it. Been doing 'em all my life. You put the cylinder at TDC on the compression stroke (valves closed), apply a pressure to the cylinder and through a calibrated orifice, measure how much pressure is being lost in the cylinder. So one gauge measures the line (input) pressure and the other gauge measures the pressure inside the cylinder... the downstream side of the orifice.

In the airplane world, 80psi is the standard line pressure. Everything is compared to that. So when I say a cylinder's test is 80/75, it means we put 80lbs of pressure in and with the restricted orifice between the line and the cylinder, the cylinder holds 75psi of that 80psi we shot into the it.... continuously. That's a good reading btw.

It's a dynamic test, not a static one.... you don't put 80psi in and then shut the line valve off. You let the line pressure run continuously into the cylinder, then look at how much is lost across the orifice (the calibrated restriction). Were it a true "leak down" test, you'd only need one gauge... one to measure cylinder pressure. You'd shoot shop air into the cylinder, close the air valve, then measure the amount of time it takes for the cylinder to lose a specific amount of pressure... or "leak down" if you will.

If you're using a rig with 2 gauges, it's a differential pressure test, not a leak down test.

 

[AUTOMAN]

A leak down test, in this context, is actually a differential pressure test. It comes from the aviation world and then the hot rodder's adopted it. Been doing 'em all my life. You put the cylinder at TDC on the compression stroke (valves closed), apply a pressure to the cylinder and through a calibrated orifice, measure how much pressure is being lost in the cylinder. So one gauge measures the line (input) pressure and the other gauge measures the pressure inside the cylinder... the downstream side of the orifice.

In the airplane world, 80psi is the standard line pressure. Everything is compared to that. So when I say a cylinder's test is 80/75, it means we put 80lbs of pressure in and with the restricted orifice between the line and the cylinder, the cylinder holds 75psi of that 80psi we shot into the it.... continuously. That's a good reading btw.

It's a dynamic test, not a static one.... you don't put 80psi in and then shut the line valve off. You let the line pressure run continuously into the cylinder, then look at how much is lost across the orifice (the calibrated restriction). Were it a true "leak down" test, you'd only need one gauge... one to measure cylinder pressure. You'd shoot shop air into the cylinder, close the air valve, then measure the amount of time it takes for the cylinder to lose a specific amount of pressure... or "leak down" if you will.

If you're using a rig with 2 gauges, it's a differential pressure test, not a leak down test.

Actually, it is a mini airflow tester.

But..yes, diff. pressure test

 

[AUTOMAN]

 

[gggGary]

https://www.xs650.com/threads/crankcase-vent-using-a-reed-valve.61188/

 

[AUTOMAN]

All band-aides. This should not pump 200cc of oil out of the breather.

Yeah, its counter-intuitive as folks will run the engine with a higher oil level thinking that will prevent the level getting too low, whereas in reality it is probably causing more oil to be dumped through the breather.

s/a mopar 6.4l engines. they need to run 1qt. low

 

[AUTOMAN]

I think there is a schrader valve in there.

take out the valve at the hose end to the cylinder!
re-test

 

[AUTOMAN]

take out the valve at the hose end to the cylinder!
re-test

nice gage set psi and % and bar

 

[this old xs]

nice gage set psi and % and bar

 

[AUTOMAN]

Sounds stupid, but I'm wondering if it could leak to one of the oil galleries on the head studs maybe? Reason I ask is I've put new pistons and rings in, the bores were good, end gap is good, but I have terrible crankcase pressure which blows a lot of oil out the breathers. I've done most every breather mod on here and then some to no avail. Bike runs great, plenty of power, doesn't burn any oil that I can tell, starts easy.

I borrowed a mates leak down tester and just then used it. The air is coming out the oil filler hole (or breather if the dipstick is in), which says rings but I don't understand how. I squirted some wd40 in the bores and repeated the test with no change.

When riding, I've had some rides where it barely passed any oil, then sometimes it pukes heaps. I think this might be important - often it leaks oil from the cylinder head to cylinder joint (mostly left side) and base gasket. At the same time it will still blow oil out the breather.

I retorqued the main head stud crown nuts, they were loose but it didn't help.

I'm a bit stumped. I feel like this is a head gasket issue (head was lapped flat but I didn't check the cylinders) but leak down test says rings?

Answer-yes
Qualifier-head gasket must have a hole in it to leak that much into crankcase