Originally Posted by v8hed
What should I use (if anything) on the mating surfaces/gasket of a new front timing cover? The mating surface on the block where the old timing cover was had traces of clear silicone sealer on it. Should I use some RTV on the new cover? I know I should use some blobs of RTV in the ends of the rubber pan seal, but what about on the main timing cover gasket?
I never use the stuff where it has a chance of getting into the oily side of the engine. I use non-hardening Permatex at the seal joints and a layer of wheel bearing grease on flat gaskets.
The Permatex is oil and fuel proof, silicone rubber is not. If Permatex happens to get into the oil it chops up into nearly microscopic particles that will flow with the oil without plugging anything and will drain with the oil change if the filter doesn't get. Given that it's approved for use on aircraft engines tells you it's harmless in the oil. Silicone rubber that gets into the oil circulates as particles, till something like a pickup screen or the filter get them. But anybody that's had an engine apart can see, lots of stuff circulates and splashes, often resulting in some level of damage. Further, Permatex will seal to an already oily surface, silicone rubber needs a very clean oil free surface to form a bond.
I apply a grease to gaskets for several reasons:
- holds them in place
- allows them to slide around as torque is pulled on the fasteners
- prevents them from sticking making removal so much simpler and cleaner.
If your covers are sheet metal they will deform a the fasteners are tightened, which is why you usually can't stop a gasket leak by pull more force on the fastener because it just furthers the deformation of the sheetmetal forcing the gasket away from the fastener and buckling the sheetmetal of the cover. Making some stiffeners from 1/8 thick steel that fits under the fastener and within the confines of the depressed edge of the cover, extending about 1/2 the distance to the next fastener hole, gets around the problem of distorting the cover.
If your cover is sheetmetal, then the lower lip is made from a separate piece spot welded to the cover. This forms a place where oil can get to the backside of the rubber gasket that seals this area, a layer of Permatex pressed into this gap will aid in closing this to engine oil which goes a long way toward reducing/eliminating leakage in the corners of this area.
Dry assemble this for a mock up, there are several sizes of gaskets used in the lipped area where the pan mates to the timing cover. You want to be sure of the fit or you'll likely develop leaks that can't be stopped without removing the engine to reseal the timing cover and pan interface.