Dangers of Silicon Gasket Goo with Triumphs, Ariels and other makes

This stuff can be very helpful when gasket surfaces are less than satisfactory. On a engine covers perhaps, when the cover or engine case surface have been the victim of over enthusiastic owners with less than a reasonable set of tools, (hammer, chisel, stilson and bigger hammer). When surfaces are good there should be no need for gasket goo at all except to hold the gasket in a couple of places whilst offering up the cover.  A light draw file or similar, or lap the cover on emery and flat surface, should be all that is needed to get a seal.

The reason for this little story is, I was just cleaning up an oil pump for a unit twin triumph, and as part of that process I like to check the vacuum of the filled /lower chamber. There was no vacuum pull back on the piston as I operated up and down with my thumb covering the inlet holes to the upper chamber. After blowing with compressed air to see if that would dislodge any swarf it was obvious a more thorough investigation was required. To remove the spring nuts from the bottom of the plunger pump I like to hold the square nut in the vise, then with a neat fitting bar through one of the fixing holes it is usually easy to undo. Holding the body in the vise, soft jaws or not may see the pump body distort and render the pump useless.

The reason I found, was red silicon gasket goop, commonly used by many for years. This stuff has the reputation for causing engine damage and I can only assume the reason this particular pump was available is because the rest of the motor was made unserviceable by the goops over enthusiastic use. With the return side of the pump out of action the feed side keeps on pumping to the crank but will eventually run out of oil to do so. This is a plain big end bearing motor and requires pressure to live as the pressure gives a thin film of oil between the crank journal and the slipper bearing material. 10lbs per 1000rpm (hot) is not an unreasonable ask for long life. Metal to metal is not good with plain bearings but in a roller bearing big end a crank case full of non returned oil  would be ok until the rider noticed a a slippery feeling from oil blown out the breather. The rider of the machine from where this pump in question came from, may not have had time to notice a slippery feeling but instead he may have  been busy controlling a momentary lockup moments before his engine internals carpeted the highway. This may have also happened after he had just rebuilt his top end and was pleased with his efforts. In my years in the classic brit industry I have seen lots of blown engines for many reasons, undergeared, prolonged highway use in hot climates ,comes to mind but lack of oil, “ not bothering to check” , oil pump failure or lack of running in are a couple of others.

What I’m trying to say is if you own a Triumph twin, a quick look in the tank may indeed confirm the presence of returning oil from the crankcase but will not guarantee that the engine has oil pressure 5-10 or 100 miles down the road. The pressure pumping side of this device ( the smaller piston)can and will also fall foul of the same “ball off the seat “problem, caused by foreign matter in your oil. A decent inline filter will help but a light or gauge is desirable to keep an eye on things. If you have looked at any of my bikes (stock or weird) you will see a gauge and sometimes a light as well. I have had blokes say that they don’t want a WORRY gauge, I prefer to see what’s happening and not worry.  Triumph had gauges on pre war and post war panel tank models and indicators on the pre 62 bikes. That same pressure relief valve with indicator was on the first unit models as well, tucked away in front where it was impossible to see when riding. They then had nothing (go figure) until the later 60’s when all models had a pressure switch and light fitted, all the way to the end.

Using some sort of gasket goo/cement between the case halves is unavoidable but use sparingly, I don’t use goo on the timing covers, barrel base , rocker box to head joint  or gearbox gaskets but may use some on one side only with the primary. Lots of older bikes have no gaskets so some goo would of course be needed. If joint faces are in good condition and a decent modern gasket material is available then none should be required. Contrary to popular myth, Triumphs don’t leak between the case halves, at least in 35+ yrs I have not seen any. It’s usually elsewhere and ends up dripping  at the bottom of the cases and that is what people see. Only once have I seen an actual case joint leak and I did it. I used a red loctite cement which I think must have had alcohol?? in it, as it dried quickly and by the time I bolted the motor into the frame and tightened up the bottom frame/case bolt a few days later, it was too late. A lot of work for nothing to rectify it. I use Permatex grey between the case halves as the grey blends in nicely with the aluminium colour unlike red or black goop. There are lots of great gasket cements out there now, choose wisely