Why does timing a car engine have to be so complicated?

Question

Im a trainee mechanic and I when doing timing belts there is usually 2 or 3 pages of instructions. Why do you have to time everything to their timing marks and make sure cylinder 1 is at tdc etc?

As long as you lock the camshaft, crankshaft and anything else that needs timing, why does it matter what position the engine is in? In other words why cant you just lock everything up, remove and replace the belt, that would be like you havent touched anything right?

Answer 1

I agree that it could be changed with the engine parts locked in any position. But all the engines I have ever worked on the parts can only be locked in a certain position and that is with number one at TDC.

Answer 2

Im guessing you know almost nothing about how an engine works, or you would see the ignorance of your own question. you have a thousand or more parts spinning at any one given time, thousands of rpm a minute. The only thing, that keeps all those parts from self destructing, is that timing chain or belt. The one thing in common all those spinning parts have that hods them together now. is that belt. If you have to take off the belt and pulleys there is no way to lock everything together, you just took it off??

due to the precision, and that most engines arei interference engins (meaning one thing is off, it self destructs) you need someone a little competent who can put it back together right.

And wait until you find a twin cam engine, you are really giong to drop your load. If you think timing a car is complicated, you may want to consider another line of work.

Answer 3

Timing marks are there to make sure the job is done right every time. And what happens if the belt jumped a tooth. When you install the new belt it will still be out of time. Custumers pay good money to have their cars worked on and they expect it to be done right. Even if most of them have little idea what is involved in the process. What it boils down to is.... What kind of mechanic you want to be. And if TDC is that hard to find for you maybe should look for another line of work.

Answer 4

It tries to end up one tooth off almost every time. Camshafts hate to sit at the TDC position for any cylinder and I've never worked on one that could be locked closely enough to prevent one tooth of movement. Maybe I wasn't using a precision pin but the cams always seem to fall off to one side or another. Add to that the effect of the tensioner - unless you can manage to keep the slack out of the non-tensioned side as you put the belt on it will try to go on wrong, which will show up when you release or adjust the tensioner.

Answer 5

The instructions are actually telling you how to do it. It is not always the case that you are "belt swapping" I recall timing up a Vauxhall Corsa after I changed a head gasket. I had to start afresh and set the cam with a dial test indicator as there were no marks and settings on this engine once the cam and head had been removed. As you continue with your profession you will encounter much more difficult situations then the one I have just described.

Answer 6

the answer to ur question is u can just lock the cam and crank to change the belt but y risk some thing moving while ur doing it then u put it back together and bang knacked engine . for the extra time it takes to line every thing up b4 u take the belt off so u can check to c if its all lined up b4 u put the belt back on is not Worth the risk of totalling a customers engine and have to fork out the bill . after all it only takes 10/15 Min's max to line it up b4 u start

Answer 7

If the belt or chain is still in place a smart mechanic ALWAYS lines up the timing marks to check the static timing of the engine.Not doing so is asking for problems.Remember the old saying...there's not time to do it right, but there's time to do it over?Now consider this from a customers standpoint.You "fix"his car and the timing is off and you have to tear it apart again.Do you think you'll ever get any more business from him or anyone that asks him if he knows a good mechanic?

Answer 8

Have to agree with Roger on this one. Tell me this you wannabe mechanic. What would you do if the belt was broke or already off on its timing? I do`nt need to read the instructions to set the cam timing , that is common sense after a while. maybe you should find another line of work. Mickey D`s only has one page on how to cook fries. Just remember when the buzzer goes off to take the fries out

Answer 9

If the timing belt is still on just cyl 1 at tdc and check that everything else is aligned. What if the belt broke? What if the belt stretched and skipped? Hell of an embarrassment if you screw it up. Once you learn it , it only takes an extra few minutes.

Answer 10

If the timing is not perfect, the car will not run as efficiently or smoothly as one in time. If the timing is far enough off, a piston will come up in the cylinder at the same time a valve comes down in the cylinder and the engine will be destroyed.



If you were not taught the reason timing is critical, I sure hope you never work on one of my engines.

Answer 11

you have to put number 1 piston up because that,s the 1 if fires on first. if the belt happens to break then the timing is in a different spot. that,s why before putting on a new belt the crank has to be on top dead center and the cam lined up first.

Answer 12

you can do it your way IF nothing moves. i always line the marks up before i take the belt off, but what if something DOES move. now you have no reference points. what if it was out of time before you started working on it? what if you need to take the head off? bend a few valves in a dohc v6 and you will see the light.

Answer 13

a question we would probably expect from a trainee first year mechanic. not to be dismissed out of hand but explained at length.

I feel many have already tried to assert reason why it is critically important to align timing up such as Precision of moving parts etc.

many engines do have timing 'pegs' to align parts up such as crank.cam(s) and fuel pump etc.

so in answer to your question why so many pages ?

it is to spell out in exact step by step ladder type of way so as to avoid any possibility of getting it wrong.

it is very easy for example to say put crank at this point..cam here. belt over this..over that.. t h en..we often find the belt wil not quite 'fit' the segmented teeth it is supposed to fit straight over as per book.

this is where understanding the engine , its parts and how it all works becomes so important.

later on you will learn about valve overlap etc. all very important stuff but necessarily long winded.

example here maybe old single overheard Ford engine as in Cortina.. belt goes over crank at TDC (notch on front cover) over aux pully (oil pump etc) and cam ( dot on cyl head and arrow on plate mark)

we follow the set up as per manual and find.. the belt will NOT fit over the teeth, seems far to not reach far enough but easily goes to next tooth back!

putting it back to the easy tooth will put cam crank timing well out! we need to move cam pulley BACK a little to allow belt to slip over the teeth. THEN repostion to mark(s). release tensioner. turn over twice to alow belt to set its own tension then lock up. by turning over we find if any valve impact occurs as well as being able to see that at TDC after two rotations we have cam .crank etc at correct postion. hopefuly not too long winded for you. good luck with your choice of vocation.

Answer 14

It isn't complicated, the instructions are clearly written for a bird of no brain. Why not ask whoever is training you?