Noise from cylinder #8

[v8alex]

I've recently got my 3.5 RV8 running. Only had it idling so far as the rest of the car is not ready for driving yet.

Anyway, I noticed #8 cylinder to be a bit noisy - could hear a mechanical tapping from within that is not present on other cylinders. Also, noticed some soot sprayed up onto the head. So I guess the gasket is blowing slightly as can be seen from the pic below where you can see the crap from cyl #8 compared to cylinder #6:



I'm guessing, but a blowing gasket could also let more noise out and this tapping could be the spark, or valve noise - i.e. nothing to be worried about.

However.....So far, I have only been runninng with a mechanical advance. I have a Mallory Electronic distributor, and have not added the vacuum pipe. I did so today, and once the engine was started, the tapping noise had gone. The engine was running much more smoother and quieter. Is this a case of the vacuum advance moving the spark to a different point of the ignition curve ?

Also, I noticed the engine hot idle was about 1,750 rpm compared to about 850 - 900 rpm before. I played around with the idle screws and got this down to about 1,200 at which point, there was a return of the tapping noise, but not as severe as without the vacuum pipe fitted. I've not tried to get the idle lower than that for now.

So I'm a little confused:

1. I have a blowing gasket from cyl #8 - easy to fix
2. I have a noise from cyl #8 that seems to go away when connecting up the vacuum advance pipe
3. Engine idle is higher with vacuum advance than without

My biggest worry is the tapping noise, which could be perfectly normal and just a factor of having a slightly blown exhaust manifold gasket, but would appreciate comments on this and the behaviour with vacuum hose fitted and if there is anything I should be looking into.

Alex

[ian.stewart]

Exhaust gaskets blowing will make a tapping sound, as to why it stops when the vacuum is attached, I wonder if it is retarding the spark at low revs which may lessen the expansion on the exhaust port.

[Darkspeed]

The tapping noise is very likely to be the gasket blowing - I bought a car a short while ago with a reported blown engine sounded like a tin of nails blowing oil out of the valley gasket all down the bellhousing and onto the exhausts so a nice smoke show to go along with it all - car was very very cheap.

Turns out - 5 blown exhaust gaskets due to cheap block hugger headers with warped flanges and cracks in the manifold - a check on the dipstip showed up that the engine was over filled to the tune of about a gallon and a half - the extra half a gallon was due to the dipstick tube not being pushed fully home.

After draining out the oil and refilling with correct amount and welding up and facing the manifolds - the engine is a gem.

Anyway - in summary use a smidge of exhaust sealer on the leak and the noise go.

Andrew

[Darkspeed]

I would agree that the additional advance means that the mixture burn is being more complete before the exhaust opens so less pressure in the manifold.

Andrew

[v8alex]

Thanks folks - very helpful. I'll refit the exhausts with a little assembly paste and hopefully it'll be better.

Alex