Leak down test results.

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JPanyon
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Re: Leak down test results.

Post by JPanyon » Mon Sep 12, 2016 10:20 am

That cylinder bore looks perfect from what i can see here? So next, divide the problem in half, and test just the head for cracks and leaks.

Bolt the head down to a flat surface using some ingenuity and parts locally available. Put pressure into the spark plug hole and verify that the head Does or Does Not leak. If it leaks and you can't see a source of the leak, remove the valves and look under the valve springs and at the valve seat area.

One rider here had a crack under the intake spring through to the intake runner. Oil and air were being sucked back and forth through the crack. This oil/air mist bypassed the breather check valve and used the head's oil return passage instead. The excess mist made it into the intake runner, got sucked into the combustion chamber and produced smoke under the "right" engine temperature/load conditions. Your problem may be similar, but not identical...?

Once the head is verified good, then chase after the piston/bore area. Others might prefer doing the cylinder region first, but the head is "sneakier". Piston and bore problems seem to show more easily spotted (visible) damage than heads.
Last edited by JPanyon on Mon Sep 12, 2016 10:35 am, edited 2 times in total.
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1948 Indian Chief, 1954 Harley Police Special, 1965 BSA Rocket Lightning, 1972 BMW R75 /5, 1975 Norton Commando, 1977 BMW R100 /7 with "Unobtanium" accessories

2002 Ural BC 1st year 750, my unofficial pickup truck for delivering groceries to the disabled.
My Hack Monkey, (rescued from an Animal Shelter).... https://youtu.be/p7pC38IvvoM

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 10:24 am

JPanyon wrote:That cylinder bore looks perfect from what i can see here? So next, divide the problem in half, and test just the head for cracks and leaks.

Bolt the head down to a flat surface using some ingenuity and parts locally available. Put pressure into the spark plug hole and verify that the head Does or Does Not leak. If it leaks and you can't see a source of the leak, remove the valves and look under the valve springs and at the valve seat area.

One rider here had a crack under the intake spring through to the intake runner. Oil and air were being sucked back and forth through the crack. This oil/air mist bypassed the breather check valve and used the head's oil return passage instead. The excess mist made it into the intake runner, got sucked into the combustion chamber and produced smoke under the "right" engine temperature/load conditions. Your problem may be similar, but not identical.
Hey long time no talk.
He might need to adjust piston pressure relief valve ?? No :lol:
Look at piston

rivers
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Re: Leak down test results.

Post by rivers » Mon Sep 12, 2016 10:46 am

Sorry for the thread tweak. But I gotta ask, What the hell is that hole in the center of the piston?
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Re: Leak down test results.

Post by JPanyon » Mon Sep 12, 2016 10:48 am

Yes Van, I see that ""hole"", but does it go through the piston? I'd expect a whole bunch of troubles if it did penetrate. Pistons are cheap, so replace it. But, he's had an unusual amount of prior troubles from what I remember and now is a good time to check each piece of the puzzle, while they're laying on the bench. I know you'd do this, if it were one of your machines... :wink:
John Panyon,,,Biking since 1961 on wheels left behind but never forgotten
1948 Indian Chief, 1954 Harley Police Special, 1965 BSA Rocket Lightning, 1972 BMW R75 /5, 1975 Norton Commando, 1977 BMW R100 /7 with "Unobtanium" accessories

2002 Ural BC 1st year 750, my unofficial pickup truck for delivering groceries to the disabled.
My Hack Monkey, (rescued from an Animal Shelter).... https://youtu.be/p7pC38IvvoM

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 10:48 am

rivers wrote:Sorry for the thread tweak. But I gotta ask, What the hell is that hole in the center of the piston?
Well.
This would made number 3 questions.

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 11:09 am

Ok folks.
BOB figured it out.
Hole in one

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Re: Leak down test results.

Post by rougaroo » Mon Sep 12, 2016 11:23 am

Van & I figured it out. This is one for the record books. Ryan, you are one lucky, lucky owner. Go buy a lottery ticket today!

That "hole in the center" isn't a hole. It is a washer from the air filter hold-down bolts that was sucked through the carb and past the intake valve and has gotten welded to the piston top. Normally something like this holes the piston and destroys the engine.

The blow-by isn't coming from the pistons or the rings, it is coming past the intake valve that isn't seating right because it has gotten buggered where the washer came through. Gasses are passing around the valve and into the valve cover, then through the push rod tubes. Look at the picture of the valves in the head. The intake valve is the larger valve on the right. Now look closely at the edges of the intake valve - see how they look beat up and not a perfect circle?

Since the piston is intact and the cylinder walls aren't scored, you will probably be able to get by reworking the head and replacing that valve and valve seat.

And note to everyone: Washers go on the OUTSIDE of the air filter.

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Re: Leak down test results.

Post by ryrypizza » Mon Sep 12, 2016 11:28 am

rougaroo wrote:Van & I figured it out. This is one for the record books. Ryan, you are one lucky, lucky owner. Go buy a lottery ticket today!

That "hole in the center" isn't a hole. It is a washer from the air filter hold-down bolts that was sucked through the carb and past the intake valve and has gotten welded to the piston top. Normally something like this holes the piston and destroys the engine.

The blow-by isn't coming from the pistons, it is coming past the intake valve that isn't seating right because it has gotten buggered where the washer came through. Gasses are passing around the valve and into the valve cover, then through the push rod tubes. Look at the picture of the valves in the head. The intake valve is the larger valve on the right. Now look closely at the edges of the intake valve - see how they look beat up and not a perfect circle?

Since the piston is intact and the cylinder walls aren't scored, you will probably be able to get by reworking the head and replacing that valve and valve seat.

And note to everyone: Washers go on the OUTSIDE of the air filter.

Rougaroo
That's kind of what I was thinking. But wouldn't the center of the ring be convex, it it was stamped in there, and wouldn't there be a corresponding mark near the valves. I can't check at the moment because I am not hom but I think the hole in the middle is concave

EDIT: ok I see what you're saying. Welded to it and that's the ring. Hmmmm. Ill have to check when I get home.
Last edited by ryrypizza on Mon Sep 12, 2016 11:32 am, edited 2 times in total.
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2002 patrol w/ mod tops and power arc

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 11:32 am

Ryan.
Even though it 750 2002.
It used 650 valve train. Confirm with Terry or Gene

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 11:34 am

:bow: Bob
Why it is always the left cylinder not right?.
Lean out alignment set up :lol:

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Re: Leak down test results.

Post by rougaroo » Mon Sep 12, 2016 11:36 am

Easy check: take another of the air filter bolt washers and put it next to the washer-on-piston. It is just pure coincidence that the washer is in dead center of the piston. Riding in the center the washer is thin enough that it doesn't hit either of the valves or the top of the head. There has to be some head space between the top of the piston and the head or else the gas/air mixture would have no place to compress. That washer just found the perfect place to ride. Again, no joke, go buy that lottery ticket. You were about a minute and a half from a blown engine if that washer came loose.

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Re: Leak down test results.

Post by rougaroo » Mon Sep 12, 2016 11:40 am

Van asked:
Why it is always the left cylinder not right?.
Lean out alignment set up :lol:
Old musician's joke: How can you tell if the drum riser is level? The drool falls from both sides of the drummer's mouth.

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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 11:44 am

Ask Darrell
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Re: Leak down test results.

Post by gobium » Mon Sep 12, 2016 11:46 am

Never happened on efi
They all not do that! :sarcasm:
Last edited by gobium on Mon Sep 12, 2016 11:46 am, edited 1 time in total.

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Re: Leak down test results.

Post by ryrypizza » Mon Sep 12, 2016 11:46 am

gobium wrote::bow: Bob
Why it is always the left cylinder not right?.
Lean out alignment set up :lol:
Well this is the right cylinder, the nut from the air cleaner was sucked in to left cylinder and I replaced that piston.
-Ryan
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