Timing stuff

toyota
timing-belts

#1

I drive a 1971 Toyota DEATHTRAP. High center of gravity, short wheelbase, armstrong steering, thighmaster brakes, gas tank under the passenger seat, etc.



It has timing GEARS. Your recent show talked of timing chains and belts.



Why has a reliable gear system given way to a breakable chain and further to a strechable, breakable belt???


#2

The Toyota DEATHTRAP has a push rod engine that is quite dated in design. There would be a great deal of hardware($$$$) needed to accomplish gear driven camshafts on a dual overhead cam engine.


#3

manufacturing costs. A flathead or overhead valve engine both have the camshaft and crankshaft quite close together. Very few productions engines had the gears driving each other, most had a short stout chain between the gears which usually lasted the life of the car. Overhead cams moved the cam and crank further apart. Dual overhead cams on v type engines increased the distance and number of turns necessary so most manufactures have gone to belts which are cheaper and quieter.
I always drove Chrysler products which for years had a 60, ooo change interval except in California whick required the Manufacturer to pay for belt changes for the first 100,000 miles. There the recommended change was at 105,000.


#4

Using a belt permits a different engine design–space used by the timing gearset can be used for other engine components, and the valve gear need not be so close to the crankshaft. It also may save fuel due to less frictional losses than with gears. Plus it’s likely quieter. Timing chains will usually last the life of the engine as long as oil is changed when it should be. Gears can also suffer failure if oil is neglected.

On the downside, you have a belt that must be changed every xx miles to prevent possible engine damage should the belt fail, if you have an interference engine. Usually this is 2 or 3 changes in the lifespan of the engine, along with the water pump, which would likely need to be changed about as often, even without a timing belt. It’s a trade off, like everything else in life.


#5

gear drive = noisy engine. Car manufacturers like quiet.