Possible Causes of Leaking Exhaust Valve in rebuilt 4AGE

[GeeEss]

Hi there,

Lifted the Covers this afternoon and I couldn't see any obvious damage on either IN/EX Lobes or Shim surfaces on No.3.

Didn't have a chance to check clearances (AWOL Feeler Gauges) but will do so tomorrow.

I guess it could also be a sticking valve but how do you check for / diagnose that issue? assume Head would have to come off & the guide inspected.

If clearances are within spec I will wait until the Head comes off and/or a Borescopy has been done; too much speculation otherwise.

One thing I wanted to bounce off people is this. . .

I told the Dyno guy the day before that the engine had only done 600km since the rebuild and he said to change oil again (specced Penrite 15W-40 Run-In Oil) B4 the Dyno run. He seemed pretty genuine / reasonable but a couple of things still had me going "hmmm";

1. He had it on Dyno for 4hrs before suggesting there might be an engine issue; whereas another guy diagnosed a valve leak after listening to it for 1-2 mins.

2. Wasn't the engine a bit green at 600km old for him to be running it to 7000rpm?

[allencr]

Didn't have a chance to check clearances (AWOL Feeler Gauges) but will do so tomorrow.
Just see if the shim/lifter will rotate with your finger, it won't if it's tight.

If the valve & seat were OK & just needed to be adjusted right to seal OK, that amount of running will have chewed them up pretty good. If they do seal, I wouldn't expect them to last too long.
Also, there will be some carbon built up, so don't set'em tight, expect them to close up and check the adjustment again in 1-5 minutes of running.

[GeeEss]

I've never done a head, so wouldn't know how to do that; but did read an article that suggested popping the valve(s) out & checking that the stems weren't bent by rolling them along a known flat surface.

I think I'll get a borescope done so I know what's happening.

[oldeskewltoy]

bent valve will be somewhat obvious... the valve and bucket will be low, causing excess clearences. This is because if bent the margin(valves edge) will be rest on just one point, this will keep the valve from returning fully.... and so excess clearence is a likely sign of a bent valve

[SHEPPO3930]

as i said on ae86dc, you need to check the valve clearances as this is the quickest indicator of a stuck open valve. then follow that up by checking if the ports are fluid tight - pour some petrol down the suspect port. a well sealed valve won't leak. if the fluid level drops, it's leaking into the chamber and that means it's time to lift the head off.

also, IMHO, there's no need for a bore scope, it's just a waste of money. you wont be able to see a valve stuck open half a mill'.