Ever wondered about trade "secrets" in garages? Well, some are true, some are made up, so this section may be of use to many of you. Also covered are general points to watch when working on cars - there are some nasty hazards!

MOT Centers may be looking to increase sales - instead go to your local council MOT depot where they don't do any repairs. Therefore the test will be more fair (i.e. without technician bonuses affecting the outcome of the Test). The only downside to this is that the MOT will be the full fee, but that is a minimal extra expense when considering the cost of un-needed repairs. Most larger garages (main dealers especially) have a parts related bonus for the technicians. For instance any sales of brake pads/discs, tyres, exhausts etc recommended after the technician checks a vehicle can mean extra income for that technician. This has a negative impact on customers as they are often told a repair is necessary when in fact the part may have some life left in it. I have personally seen examples where owners have had new parts un-necessarily.

Hydrofluoric Acid & Flouroelastomer, and used engine oils

Rubbers used for seals and gaskets in cars very often are made of fluoroelastomers - a very versatile and tough material for any situation where a gas/oil/fluid/air tight seal is required. However, under certain conditions, this can become hazardous as it changes into hydrofluoric acid. This occurs in temperatures of 316ºC or higher, but especially over 400ºC. Water or water vapour has to also be present for the heated seal to change into this dangerous acid, but if it occurs amputation is the only answer to prevent it spreading in the event of skin contamination.

So, those latex gloves you see worn in garages aren't just to keep the technicians' hands nice & soft, they are also to protect against this type of hazard. Wear them at all times when working on your car's mechanicals, and these will also prevent oil/grease soaking into your skin. Used engine oil is a carcinogen, and therefore another very good reason to wear gloves.

Additionally, Renault have now superceded their old flourine grease with a silicone type grease when applying to 'pencil' type ignition coils that are fitted to each spark plug (as opposed to a common coil for all plugs). This may be related to the above safety warning and could be to prevent the fluorine becoming dangerous after an engine fire.

Contact lenses and MIG/TIG/ARC welding may cause blindness

It has been reported that wearing contact lenses while welding or even being near a welder, may carry the risk of blindness if the person is wearing contact lenses. Apparently the lenses can fuse to the front of the eyeball under certain conditions, when in close proximity to an electric field such as a welder. Removal of the lenses after this has occurred has been reported to also remove the front of the cornea. Whether this is true or not, it's adviseable to wear glasses instead.

Soft metal can wear out harder metal

Believe it or not, but when a soft metal (eg an alloy) is in contact with a harder metal (eg steel), in many circumstances the hard metal will actually wear out more than the soft metal. I found this out when I overused a small compressor once, and heard the big ends starting to knock. Upon stripping down the pump I found that the alloy connecting rod was in an almost serviceable condition, but the crankshaft had 2x 3mm deep grooves worn into the bearing journal. I'll never forget that time as the cheap compressors nowadays have no changeable bearing, but instead rely on the alloy con. rod material and also the oil to provide a low friction surface against the crankshaft. Metal particles also would have played their part - especially after the wear process had begun, but I could not believe the good condition of the con. rod. I showed an engineer friend and he confirmed this strange wear by saying "of course - don't you know soft wears hard?"!!!

This may explain also why steel hinge pins wear out, yet the alloy hinges are fine - a simple pin renewal makes them work fine again.

Strange Tyre Wear Patterns

Not usual with TVRs but a small possibilty....but the rear tyres sometimes can wear in a diagonal pattern to such an extent that the tyre can have perhaps 5-6mm of tread in some places, whilst wearing down to the banding in other places. I have seen this occur on some Renaults & Peugeots, and have yet to work out exactly why this occurs. Tyres wore like this from new, wheels were perfectly balanced, shock absorbers in good condition, wheel geometry checked & correct. So far the most likely cause is tyre construction - as the problem seemed to happen on certain types of tyre. However, if anyone out there has experienced this problem it would be good to hear from you so maybe a link could be found to pinpoint the problem. Clues also lead me towards torsion bar rear suspension, as that is the type I have found it to occur on so far. Perhaps it's the way the rear axle acts with each side - they are joined by solid frame and it's possible there is a resonance over bumps which cause this "phenomenon"! Thanks in advance for any input.

Mark