manifold gasket failure

[ardiesse]

I've got a recurring manifold gasket problem which has got me well and truly beat:  manifold gaskets only last me maybe a couple of thousand miles before they split, usually at the centre inlet manifold face.

When I put my FX back on the road, it had this problem.  The machine shop at work milled the manifold faces true, and so far the problem hasn't come back.

My FC, though, now that's a different story.  When I got it back on the road, it was only a year or so before the idle went bad and the exhaust sounded raspy.  The manifold gaskets had split at the inlets, and had their guts blown out at the exhaust.  So I took the manifolds off and got the machine shop to machine the faces true, and I thought that would cure the trouble.  I checked the fit of the manifolds to the cylinder head with feeler gauges before fitting the gaskets, and the faces were true to within 0.002".

Maybe the exhaust system is putting too much load on the manifolds, I thought.  I made certain the exhaust pipe was correctly located in the exhaust manifold, then adjusted the clamp on the LHR engine mount bracket to hold the exhaust pipe in the correct position.

New manifold gasket before driving to Tassie for the Nats.  I got to about Albury on the way back, and the idle went bad.
New manifold gasket before driving to SA for the Monaro Nats.  I got to about Narrandera on the way back, and the idle went bad.
New manifold gasket again, and on the way back from Berrima yesterday, the idle went bad.  Confirmed the problem by squirting spray-degreaser at the centre inlet manifold face with the engine idling, and the engine just cut.
I'm taking the car down to Melbourne next weekend, and I have to replace the manifold gasket before I go.

Now, comparing aftermarket manifold gaskets with a NOS set I have, I notice that the NOS ones are about 1/16" thick, and the aftermarket gaskets would be lucky to be half as thick.  The gaskets that come with an ACL VRS gasket set are the three-piece style, like the originals.  The Pro-Torque manifold gasket (HA138) is a single-piece gasket.

In my father's day, manifold gaskets never gave trouble.  Are aftermarket manifold gaskets crap?
Has anyone else had recurring manifold gasket problems with a standard grey-engined Holden?
Would an extractor gasket work any better?
Where can I get manifold gaskets that work?
Is there anything obvious I've overlooked?

I need the wisdom of the collective on this one.

Rob

[Trevor_B]

Hi Rob,
Only advice I can offer is to use "Permatex Ultra Copper RTV Silicone Gasket Maker - Maximum Temperature" or similar on both sides of the gasket when assembling. That way you are assured of a complete seal. Being silicone it is also flexible so allows for heat expansion. Only downside is that you see some of the silicone around the gasket edges.

I usually use the single piece Pro-Torque manifold gasket.

Cheers,
Trevor_B

[Harv]

G'day Rob,

One thing it may be is the rear exhaust hanger(s). Even with the front hanger done up well, if the rear is not right (too loose, rubber with low tension etc) the exhaust can bounce around (up and down) when you go over bumps. It acts like a huge lever, and puts a good torque on the manifold bolts/gasket.

Cheers,
Harv

[ardiesse]

Harv,

I was wondering something like that.  The rubberised canvas strap at the rear gave way a little while back (I made a replacement out of some old conveyor belt), but I noticed that the tailpipe wanted to sit at least four inches below the rear bumper, and so there was a lot of tension on the old strap.  I shoved a couple of pieces of wood between the rear floor pan and the tailpipe, and then jacked up the end of the tailpipe so that the "natural" place for the exhaust to sit was at the right height for the strap.

That said, the rubber insulator in the hanger under the LHR floor is not in very happy condition.  I know Rare Spares sells the HK-T-G equivalent insulator, but it's a different size from the FE-EK ones.  Are the FE-EK insulators available as a repro part?

Rob

[ardiesse]

Question answered.

Rare Spares lists "FE-HR rear exhaust hanger kit" EB1001.

[hsv-001]

I have o couple of ideas on this . Yes even when I put a V6 into an old Holden I make a front bracket to carry the passenger side manifold as the flex and weight combine to crack the manifold . But if you are running an original sideplate and manifold then check that the locating rings [sleeves] are not holding the manifold off the head face . This is common when shops simply machine the manifold to head face and then the rings are too long and hold the manifold away , so you need to grind down the locating rings to allow the manifold to get close enough for the gasket to seal . Worth a look . Cheers Haydn

[ardiesse]

Haydn,

Thanks for that suggestion.  When I checked the fit of the manifold faces to the cylinder head I can't remember whether I had the locating rings in place - I think probably yes.  But worth checking nonetheless.

It seems to be the case with grey manifolds that the exhaust manifold faces slowly "retreat" with time, so that the gasket doesn't seal properly at the exhaust faces, and is compressed too hard at the inlet faces, leading to splitting.

Rob

[fcwrangler]

Rob, there is a set of NOS gaskets on eBay (fc holden) for $20 buy now.
Jim

[ardiesse]

Jim,

Thanks.  But as of yesterday evening, job done.  New intermediate exhaust hanger kit installed, and the exhaust is much better damped mechanically than before.  New (actually 10-year-old Rare Spares single-piece) manifold gasket in place.  Idle good.

Let's just see how long this one lasts.

Rob