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Air leaking into LIM while doing a Valve job?

Pure2sin

Pure2sin

New member
I just installed some L92 springs with Viton seals and TI retainers. I used an air hold and it was working fine until I got to the last cylinder on the rear head. When I first pressurized the cylinder I could hear/feel air coming out of the LIM. I ended up getting the last two springs on because the compressor recycled fast enough for me to do it.

What would cause air to leak into the LIM like this while using a air hold in the spark plug hole? Could it be because of it not being at TDC?

These heads were re-manned about 8000 miles ago. They basically looked new when I installed them with my top swap.
 


maybe a valve was open, glad it didn't drop in on ya, that would have sucked a big one. if so was the intake rocker in the down position?
 
That's the weird thing. I had all the rockers off at the time. But when I did put the rockers on to check where the position was, one of the rockers was down.

Should it leak without the rockers on though?
 
ya know, probably not, i bet you got a bad valve seal, with the rocker off the valves should be shut. how did the plug from that cylinder look? and how does it run now?

id do a compression test when i got the chance to do so.
 
I still have a bunch of other stuff to add before I put it all back together. Mainly an intercooler. I wonder if I could have blown the valve seal when I first added pressure to the cylinder. I will have to recheck it tomorrow because now it has new valve seals and new springs and retainers and locks.
 
Pure2sin said:
I wonder if I could have blown the valve seal when I first added pressure to the cylinder. .
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When you say valve seal are you referring to the guide seal? More likely to be a burnt valve or seat. Or if your are lucky just carbon build up on the valve keeping it from fully closing. If it was leaking into the intake then its the intake valve and you should be able to see it on a vacuum gauge. How did the spark plug for that cylinder look?
 


This is normal. A valve leaking air from the cylinder into the intake or exhaust is common. When I do springs, I put air to the cylinder and any ones that are leaking a little, I tap with a rubber mallet. Usually helps them seal much better.

maybe a valve was open, glad it didn't drop in on ya,
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Not with the rockers off. All the springs hold the valves completely shut when the rockers are off. If a valve was open when the cylinder is pressurized with air, the air would run right out. He had a small air leak.

i bet you got a bad valve seal,
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The valve seal keeps oil from the rocker area getting down the valve guide and into the cylinder. It does nothing to seal the compression chamber.
 
BillBoost37 said:
This is normal. A valve leaking air from the cylinder into the intake or exhaust is common. When I do springs, I put air to the cylinder and any ones that are leaking a little, I tap with a rubber mallet. Usually helps them seal much better.


The valve seal keeps oil from the rocker area getting down the valve guide and into the cylinder. It does nothing to seal the compression chamber.
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your right bill. it was late and i was sleepy, i was referring to the valve not being seated to the head, the mallet trick works well.
 
Sometimes it takes more than a few taps with the mallet to get them seated properly, I'm surprised you only had trouble with the one. And obviously never do the tapping with the spring off.
 
So the valve could have just gotten stuck? Tap it with a mallet with the springs on? Wouldn't you be able to tell if I valve was stuck because wouldn't the spring look more compressed than the others even with the rocker off?

FoSHO99 said:
Sometimes it takes more than a few taps with the mallet to get them seated properly, I'm surprised you only had trouble with the one. And obviously never do the tapping with the spring off.
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Actually there was another valve on the front head that seemed to get stuck a little. I increased the pressure on the compressor and it seemed to help.

Other people are saying bent valve or possibly hole in the valve. I had no issues with the motor before I tore it down so I am thinking a valve is just stuck like you guys are saying. Plus the heads were done very recently so unless the valve job was done very badly I can't see it being a bad valve. If it was a bad valve wouldn't I have had issues before and leading up not now?

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im sure your ok, its a normal thing to wack the tops of the valves to make sure they seat all the way up in to the head to seal off the chamber, even a 100 psi ain't the same as normal combustion.
 
You won't really notice it from sight, if you did notice a difference in height it usually won't hold the valve up with that much air leaking by. Sometimes small particles or debris gets caught in there when you take the rocker bolt off and the valve closes, the valves will also spin a bit as it is. Tapping with a mallet will kind of reseat the valve or free up the particle causing a very small leak. If you have a big air leak after 5+ good taps then I would be worried. Don't get too wild if the piston is at TDC.
 
Thanks a ton FoSho. I took all the rockers back off and cut a piece of rubber hose and put it over the springs then hit it with a mini sledge a few times on each spring.

After I did that I re-checked the cylinders with the air hold and all of them held the air and didn't leak.

Problem solved. I put the rockers back on and the valve covers. Now I just have to get the FMHE mounted and the intercooler installed.
 
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