Leak down test, leaking through intake

[r0llinlacs]

So I have the top of my engine torn apart to replace the valve stem seals, with the heads still on. I'm using the air compressor method. The rocker arm assembly is removed so all of the valves are closed.

There is a big (30%) leak on cylinder 3, and it leaks through the intake. After doing some reading online, it looks like the only culprit is a bad valve or bad valve seat. I'm hoping for an easy fix like the intake gasket, but the intake gasket isn't a possibility, right? All other cylinders are 10% or less.

Also, is there any possible way to re-seat the valves with the head on the car?

[maxwedge]

Correct not the gasket, , try running the piston to tdc in that cylinder, make sure the piston would be held up by the piston, then try unseating the valve, reseat it and tap it back and forth to try and seat it firmly then retest the leakage.

[r0llinlacs]

Originally Posted by maxwedge

Correct not the gasket, , try running the piston to tdc in that cylinder, make sure the piston would be held up by the piston, then try unseating the valve, reseat it and tap it back and forth to try and seat it firmly then retest the leakage.

That's kind of what I was thinking.

The valve stem seal has been leaking oil into the valve which I'm sure is why it's not seating properly, and I have a feeling the gunk may not be completely hardened. So, what if I take the spring off, attach the valve to a drill and spin the valve against the seat to kind of smooth the valve to the seat? I realize I'd essentially just be smoothing out the build up, but it's a $600 car and it doesn't have to be perfect by any means. Anything it takes to keep the heads on.


Also, the harbor freight leakdown tester says up to 40% leakage is still in the "green zone" which means okay, but that seems kind of high to me. I've read 10% is normal, anything higher isn't good. What should I go by?

[maxwedge]

40% is close to a dead cylinder, I would dribble some seafoam into the intake port down around the valve, turn the engine over by hand just enough to crack the valve open. Let the stuff work for 24 hrs. Should soften up the carbon,worth a try.

[r0llinlacs]

Originally Posted by maxwedge

40% is close to a dead cylinder, I would dribble some seafoam into the intake port down around the valve, turn the engine over by hand just enough to crack the valve open. Let the stuff work for 24 hrs. Should soften up the carbon,worth a try.

Great idea! I'll definitely try that. I'll have to pull the valve spring since the rocker arm assembly isn't attached.

[Blue Bowtie]

If you can still find it, GM Top Engine Cleaner (P/N 1052626) might be a better choice for cleaning the intake valves and upper cylinders.

[maxwedge]

Originally Posted by Blue Bowtie

If you can still find it, GM Top Engine Cleaner (P/N 1052626) might be a better choice for cleaning the intake valves and upper cylinders.

Good advice, if you can find some.

[r0llinlacs]

Well I do have some carb cleaner laying around. I could spray that pretty liberally through the intake and it would work right away.

I'm now worried that the valve may be burnt and If I clean it, could make the leak worse?

[maxwedge]

What engine is this, carb cleaner is not as effective as top engine cleaner or Seafoam. Intake valves rarely burn, exhaust way more common.

[r0llinlacs]

It's a Mitsubishi 6G72 3.0l SOHC 24v V6

That's relieving that intake valves rarely burn.

Carb cleaner is all I have. Does seafoam come in a spray?

[maxwedge]

No, but you can pour into a spare spray bottle, no?

[r0llinlacs]

Originally Posted by maxwedge

No, but you can pour into a spare spray bottle, no?

Touche!