Head gasket sillicone sealant - bodge job?

There should never be any silicon sealant used near any head gasket on modern cars. However, on the astra diesel, sealer is used between the rocker box (bit below the rocker cover that is held down with the head bolts) and cylinder head. It could be this that he's seen.

It's a bodge. There should be no need to use anything like that on as unexotic an engine as an Astra.

I use headgasket compound when assembling them as it stops them from moving about and can save a shitload of aggro.

A *right* bodge. There is no real need at all to use any compound on a *new* head gasket. Any use of silicone in the quantity large enough to be seen from the outside probably means either no head skim or tthe old gasket reused or both. The excess silicone often blocks oilways in the head leading to failures of cam/followers etc just like your symptoms. I'll bet you've still got your old cambelt in there too! I'd be getting a complete refund from the so-called 'mechanic' if this proves to be the case. It's not as if it's a difficult or pricey job doing an Astra.

JB

Those guys are not always very clued up on cars. He was probably referring to the cambox which has no gasket, but does use a special sealant, many mechanics use silicone, it would probably be easily visible If it is above the injector level then it is the cambox and quite normal. Below, where the engine number is stamped is all wrong. mrcheerful

I always thoguh t silicone should *not* be used on cars with cataytic converters as somehow it can damage them.

No, it won't damage them.

It screws up the oxygen sensor not the cat.. but i guess if the ox sensor is screwed up, it may over fuel the engine, thus buggering up the cat,

not that this is at all relevent to the OP's engine, being a diesel.. and not a brand new one, it does not have cat's at all.

Only on the inlet/exhaust manifolds. The ethanoic acid released as RTV cures can stuff the oxygen sensors.

But the crankcase, timing chest (if chain driven cams) and cambox is purged though the breather system via the PCV valve into the inlet manifold. So using it on sump, cambox, rocker/cam cover etc. can all put acid fumes into the inlet. Only the water system is safe.

So you take the sensor out. Wait for the stuff to cure and then run the engine so the system is flushed with fresh air. Refit the sensor. The trade don't have time to wait while the stuff goes off so should be using a grade that doesn't give off the acid while curing.

I only got one comment to make

IT'S A DIESEL

So?

It doesn't have a catalytic converter.

Some diesels do!

"Tim" wrote in news:41f6e5b5$0$26014 $ snipped-for-privacy@news.zen.co.uk:

Why doesn't the government force a diesel 'air' filter on the exhaust, forget the cat, get rid of all that soot; I would rather have invisible poisons emitted from the exhaust! Would probably need to change it every day the crap given off my by neighbours diesel!

Will

The message from "Moray Cuthill" contains these words:

However, this kind of thread-drift is useful for those of us who don't already know everything and are willing to have a new thought shoved between our ears from time to time.

Most of the useful things I've learned over the years have come from incidental knowledge.

Silicone is well known to damage oxygen sensors and there is opinion that it damages catalytic converters too. Antifreeze does the same so a blown head gasket can end up being a very expensive repair on a modern car if it sucks all the coolant through the exhaust system.

Excessively rich fuel mixtures and excessive oil consumption also damage cats and oxygen sensors.

-- Dave Baker - Puma Race Engines

I can accept that for acetic acid cure silicone, but not for ethanol cure silicone.

What mechanism?

That I can believe - a large amount of any organic going through the cat isn't going to be good for it.

Mine does!