Reprinted from i Saluti, September 1996,
from the Alfa Digest via the Internet

Gasket Sealant Use in Alfa Engines


Q:

What kind of gasket sealant should I use when reassembling an engine? I recently stripped my V6 engine and found that almost half of the oil pump filter was covered in globs of RTV silicone sealant that had oozed out of joints and broken off over time. I definitely do not need to put the engine back in and find that some inaccessible gasket is leaking.
A:

The cylinder head(s) gaskets are never plastered with cement of any kind, they have a built-in adhesive that's activated by pressure. It is essential that the gaskets and prepared surfaces not be contaminated with oil or even your finger prints, do not handle head gaskets with bare fingers.

I find Permatex products best for other gaskets, paper type or cork or other material and then very sparingly. The cam cover gaskets are being put on with no adhesive but the older black semirigid type are generally cemented to the cam cover side only so that the cover may be removed and reinstalled without damage. People who use RTV in the rear main bearing caps instead of the "cigarette" seals are fooling no one, it's a very dangerous practice.

No leaks come from clean, smooth, scratch-free, non-pitted surfaces. A scratch is a valley and no gasket can fill that void and cements in those voids cannot withstand forces trying to push liquids past.

We are fortunate to have aluminum surfaces to work with where block sanders flatten out the uneven surfaces very easily. In some cases where the scratch or dent is too deep, an aluminum epoxy paste can be used to fill voids and then sanded smooth.

-Fred Di Matteo, AROC Tech Advisor


A:

RTV (room temperature vulcanizing) silicone comes in many different flavors for many types of sealing jobs. Used sparingly, it is an outstanding sealant. This is not the only type sealant that can cause problems. Permatex #2 gets hard and brittle and also breaks off ending up in your sump. No matter what type you use, the key is using it with discretion.

RTV, and most other sealants, have their places. They will not make up for grossly mismatched surfaces and they should not be used where there is high pressure.

-Jim Roth


A:

Excessive amounts of RTV can cause big problems, but any sealer used in excess can cause the same symptoms and assembling an engine without any sealer is a guarantee of leaks.

Here are a couple techniques I use to make sure there are no bits floating around inside my engines.

1. Apply the RTV sparingly. Use the applicator nozzle supplied with the tube. Cut it on a 45 degree angle at the 6 mm diameter step. On the 'point' of the nozzle, remove a 1.5 - 2.0 mm triangular notch. Hold the nozzle flat against the surface to be sealed as the tube is squeezed-this way only a narrow ribbon of sealer is applied. One of the 'gun' type tools designed to squeeze the tube makes this operation easier.

2. Let the sealer sit for 5-10 minutes before assembling. RTV cures after it absorbs moisture from the air. If you immediately assemble the parts, the center of the joint may never completely cure.

3. Assemble the parts and pull the bolts/nuts up with about 1/2 the normal torque. Let sit overnight and then finish tightening. This puts a compressive force on the cured gasket.

4. Carefully inspect the inside of the joint for any traces of oozing sealer. In the unlikely event you find any, scrape and remove it. The timing cover surfaces are fairly narrow, and some 'oozing' may be found. The oil pan rail is wide enough that 'oozing' is unlikely (and inspection is impossible).

Obviously, it takes a couple days to assemble an engine. I use RTV in only a couple places-in all cases without paper gaskets: timing cover, oil pan cigarette seals (squirt some into the hole before installing the seal), rear cover - oil drain on back of block cylinder liners to the block (without the factory O-rings), and water pump.

A couple other thoughts . . .

The surfaces must be absolutely oil free, use brake cleaner. If your car has an oxygen sensor use only 'sensor safe' RTV. Do not use RTV to seal paper gaskets. If you use RTV at the base of the liners, put all the liners in first (without crank or pistons/rods) and hold them in place overnight with the head (use your old head gasket) torqued to 30-35 ft-lbs.

Form-in-place gaskets (RTV, etc.) allow leak-free metal-to-metal joints in the engine. This produces a stronger structure, and precludes creep in the joints which shows up later as a leak. Most car manufacturers use RTV somewhere in their engines, any fluids collected during emissions testing are added to the tailpipe emissions when certifying a new car, so the OEMs are very picky about leaks.

-Jim Steck, AutoComponenti