Possible Causes of Leaking Exhaust Valve in rebuilt 4AGE

[GeeEss]

Car: JDM AE92
Engine: Bigport 4AGE
Block: Standard Pistons, new OEM spec rings
Head: Ported to suit Quads / Headers; with standard Valves
Cams: Tomei 264 PonCams / T3 Adjustable Cam wheels.
Gasket: 1.0mm Cometic MLS
Ignition: GZE CAS / Yaris? COPs
Induction: AE101 Quads
Exhaust: AE111 FGK Headers / 2.25” FGK Exhaust
Idle: AE101 / 111 ISCV

Issue: Probable Exhaust Valve (Dry=Wet Comp. reading) damage due to? (Cylinder 3 Compression 30% down on others).

Symptoms: Car idles OK but stumbles badly off the line (i.e. opening throttle off idle). Has very poor power throughout rev range. (10% lower than stock Big-port on Dyno).

When I originally assembled the engine I mistimed the Camshafts. I downloaded what I thought was a timing diagram for the T3 Cam-wheels and over advanced the Exhaust Camshaft 2 teeth. The car wouldn’t even start until I revised the timing. I thought the Valve damage might be due to this but if so why is only No 3 down on compression?

NOTE: Tomei advertise units as P&P so I just bolted them in @ OEM Cams / official 4AGE Manual procedure. (i.e. didn’t dial them in).

I would really appreciate any pointers / ideas (i.e. an idiot’s guide U-Tube video) WRT timing / dialling in 4AGE Cams. . as I’d really like to know what I did wrong so I don’t repeat it. . .

Cheers; GS

[fixeruperer]

before you dial anything in, id find out why that cylinder is down. set the gears at zero.
have you done a cylinder leak down test on it ? to pin point, what in the cylinder/chamber is leaking compression.

when i dialed my cams in, i moved them so very little.

[GeeEss]

After the initial mis-time; the cam gears were set to zero. I personally have never done a leak down test but the the Dyno guy did do (I think - he ran a compressed air line to CYL#3) a leak down test and he said the rings were sealing fine, and as mentioned I did a wet comp test when I got home & CYL3 reading was unchanged at 125. .

I'll lift the Cam Covers to check valve clearances / stuck valve on no. 3

[fixeruperer]

if he did a leakage, youd know if it were rings or valves.

[GeeEss]

Q1: (Assuming Block's just been faced) How much material needs to be removed from Head before a 4AGE (w/ standard pistons) becomes an interference engine?

Q2: How would this (being an interference engine) affect installation / timing of Cams?

[andrew_mx83]

did you check the valve clearances? if you had the valves ground or mixed up the lifters then a valve could be getting held partially open all the time. is the head noisy (as in tappet noise)?

[Willofan]

Hi GeeEss,
Thinking about what you have described and listening to it the other day, could you have turned the cams over seperately opening both valves on No3 so they touched possibly bending the stem or damaging the valve face.
I did this on one of my 18RG heads recently just turning over one cam without turning the other in sequence.
If you lift the cam covers, you will see if a valve is bent with lots of lash between follower and cam.
Good luck
Rgds, Chris

[pandaah]

Check valve clearance of that cylinder, that will tell you, might even be too tight, did you bleed the lifters maybe they pumped up and got jammed?

[MR22ZZ]

Was the crank at TDC when the cams were installed as cyl 3 is the one which opens the valves when you bolt down the cams dialed to TDC on Cyl #1

[trdee]

Check valve clearance of that cylinder, that will tell you, might even be too tight, did you bleed the lifters maybe they pumped up and got jammed?

4As dont use hydraulic lifters. they use shims.

[pandaah]

Ahh I see, well id still check the clearences and compare good to bad cylinders and you'll more than likely get too tight or too loose, lease too right is an easy fix

[pandaah]

Tight* 10char

[oldeskewltoy]

you might have more than one problem....


You mentioned you are using ITBs... did you get them syncronized? Multi throttle type application require syncronization to properly perform... ESPECIALLY in off idle, part throttle situations.


Concerning the exhaust valve. How was the head rebuilt? Were the valves match machined as in a multi angle valve job? Were they hand lapped?

[andrew_mx83]

my money is still on one being held open by too much shim....

[GeeEss]

Thanks everyone; off to pop the lids off now. . . < with bated breath >