"The Timing belt" -read and learn- - Toyota Nation Forum : Toyota Car and Truck Forums

etxxz · 01-06-2005, 09:52 PM

If you dont know either we're car newbs. The point of this thread is for all those hardcore car know-it-all write exactly what the timing belt is, what it does, how it does it, how it moves, how it interacts with the cams, why does it wear, simptoms of wear and why is it so hard/technicly advanced to replace?

Thanks duds...there's nothing like free info...(maybe free food but watevah)
*btw people from other forums will be reading this too.

take a breather and get some popcorn

<---dont do this........too much

Kwanza · 01-06-2005, 10:03 PM

Here's a simplistic explanation... The timing belt times the camshafts/valvetrain to the crank. It's a belt/chain that runs from the crank to the camshafts. The crank turns the belt, and then the belt turns the camshafts. The thing with timing belts is, there are no wear symptoms. That's why manufactures reccomended changing the belt based on mileage/age. You can visually inspect for wear, cracks, splitting, etc. It wears because it's the normal thing for anything moving rubber-based belt to do. When the belt breaks, the cams no longer turn so the crank will just spin freely. Umm... they're hard to replace because the belt is usually covered by everything else. The crank pulley, accesories, drivebelts, fans, frame/body, covers, etc, all cover the belt, so it just takes time to get to it. Some cars literally require the engine to be partially hoisted to reach the accessories and in turn, the belt. Changing the actual belt is not hard... just takes time. Timing chains on the other hand (they work on the same principal as timing belts) can be a pain in the arse to change...

T800 · 01-07-2005, 12:33 AM

I do not get what your thread is all about. I maybe a newbe to this forum and yes I came hear to share my experience w/ my t belt alignment delemma in hopes someone has delt w/ the same issue in order to inlighten me on what maybe the problem. At the same time maybe I would be able to help someone else out. I don't work on cars for a living, but I have grown up working on cars and swing a pretty good wrench. T800

etxxz · 01-07-2005, 09:35 AM

kwanza covered a lot, but maybe there's a lot of technical info that there's missing. See, most people are good with wrenches, its really easy to take stuff apart and put em back together...the hard thing is doing it right. The point of the thread is to learn. Maybe someone will attempt to change this belt...and screw up

Pineapple · 01-07-2005, 09:48 AM

Taking it apart is not hard if the engine is out. The lack of space is the problem. In order to remove belt cover, you'll need to remove one engine mount.

T800 · 01-07-2005, 07:29 PM

I am just trying to trouble shoot the reason why my car stalled. I thought I explained the situation in my first thread. It really seems as if the belt skipped, but it did not. I am leaning towards the vacum advance unit on the distributor. I do have knowledge behind the wrench. I came here to exchange ideas on this problem.

Kwanza · 01-07-2005, 08:21 PM

I can literally give a step by step run down... but that will take too long. If you think you may have a broken timing belt... take off the top cover and check...

T800 · 01-07-2005, 10:03 PM

Belt is ok, alignment is on. I put a new belt in anyhow, It was due. Got it running again only buy turning the distibutor advanced. Took all the covers off again. Re checked alignment. Still good. Checked every thing in the distributor except the vacum advance unit. Going to bring it to some one with the vacum tester. Talked to the Mechanic down the road. Gave him the whole run down. He did mention that after the belt is replace and the tensioner is applied you should rotate the crank at least four revolutions and re check the marks. The tensioner may pull the cam gear out of alignment with the crank when its applied, but that is not what happened here.He did agree it could be the vacum advance. I have not come across a problem like this before. Thanks for your support Kwanza.

etxxz · 01-07-2005, 10:55 PM

toyotaspeed90 · 01-08-2005, 03:03 AM

timing belt:

crank turns the pistons (basically)..... cams need to turn as to open and close the valves to let air in to combustion chamber (area above pistons) and out of the chamber (exhaust)...... only way the cams can turn is by the timing belt. There are gears bolted to the end of each cam that the timing belt turn. There are marks on those gears and a similar marking on the head (any repair manual will show you these marks).

The crank generally has what is called a "key"... it's about 1/4" tall by 1/4" wide, runs for about 3/4" or so... when it is pointing up, the number one piston (the piston closest to the timing belt) is at what is called "top dead center" (which means the piston is at the highest peak it can be). This is generally where you want it all facing to make things easy

The timing belt on most non-toyota cars is considered difficult for one very good reason. Many cars don't have clearance between the valve (if open, pushing into the combustion chamber) and the piston (this happens a lot with honda's... and is called a "bent valve"). This type of engine is called an interference engine (meaning, if the timing belt breaks the pistons can and will hit the piston as it comes up). Most toyotas are non interference, which means there is a space when the valve is fully in and the piston is at top dead center. If the timing belt is wrong on an interference engine, then there runs the risk of smashing valves into the pistons.

this is not how a pushrod motor works, however.... only an overhead cam design

toyotaspeed90 · 01-08-2005, 03:06 AM

you can see the timing belt and the gears that are bolted to the cam in this picture:

smallport 4age.... as you can see, the timing belt runs down behind the cover... it wraps around the crank...

to swap the belt out on any 4a engine you also need to remove both the bottom covers, which requires removing the crank pulley as well

phil · 01-08-2005, 09:46 PM

So, is timing chain a better idea than a timing belt?
Would a chain last twice as long as a belt?(or even last the life time of the car)
I guess it would be a lot more work to change a timing chain?

etxxz · 01-08-2005, 10:12 PM

Quote:

Originally Posted by toyotaspeed90

timing belt:

crank turns the pistons (basically)..... cams need to turn as to open and close the valves to let air in to combustion chamber (area above pistons) and out of the chamber (exhaust)...... only way the cams can turn is by the timing belt. There are gears bolted to the end of each cam that the timing belt turn. There are marks on those gears and a similar marking on the head (any repair manual will show you these marks).

The crank generally has what is called a "key"... it's about 1/4" tall by 1/4" wide, runs for about 3/4" or so... when it is pointing up, the number one piston (the piston closest to the timing belt) is at what is called "top dead center" (which means the piston is at the highest peak it can be). This is generally where you want it all facing to make things easy

The timing belt on most non-toyota cars is considered difficult for one very good reason. Many cars don't have clearance between the valve (if open, pushing into the combustion chamber) and the piston (this happens a lot with honda's... and is called a "bent valve"). This type of engine is called an interference engine (meaning, if the timing belt breaks the pistons can and will hit the piston as it comes up). Most toyotas are non interference, which means there is a space when the valve is fully in and the piston is at top dead center. If the timing belt is wrong on an interference engine, then there runs the risk of smashing valves into the pistons.

this is not how a pushrod motor works, however.... only an overhead cam design

YES!! this, in combination with KAZANWA's response, is exactly what i was looking for. This is timming 1101 for you'll. But this confuses me a bit, now that we know what the belts, the cam, and the(ir) gear(s) does...HOW then, does the engine regulate the speed at which the belt will turn so that the camshafts can either keep up (or advance) the piston's movement while trying to synchronize everthing else

toyotaspeed90 · 01-09-2005, 03:58 AM

it's regulated by the amount of air that's let in through the throttle body (the "gas" pedal... even though it doesn't give any more or less gas.....)

if you were to start the car without the throttle body attached (which has a plate the size of the bore of the inlet called a "butterfly valve".... this valve rotates via a "pin" or "axle"... not sure what you would call it... that is connected to a rotating spring loaded device that the gas pedal is attached to via a cable) then the rpm's would just rise and rise and rise until it hits the rev limiter..... even a slight vacuum leak can cause this problem as well (higher idle when not in gear)

this is for a gasoline engine.... a deisel engine actually has no throttle body per say... it's just an open air inlet, and it's regulated by the amount of fuel that is given to the motor

another picture taken from google... this looks to possibly be a subaru....

the plate in the "hole" is the butterfly valve..... if you follow the center (black bar with 2 screws in it) upwards, you'll see the spring loaded device where the accelerator cable attaches... as the cable is pushed, the butterfly valve opens

now imagine me trying to describe how toyotas T-VIS works, lol

etxxz · 01-09-2005, 10:58 AM

i'm sure most people know what the Throttle body is, whwere it is and what it does. Connected to the throttle cable (gas pedal), it opens and lets more air in and it revs.

but it still doesnt answer the question about how it regulates the speed at which the T.belt moves (the cams, etc). I was refering to the part were, if the engine were to rev, the cams and the belt would have to turn faster right? but if the belt spins proportionally to the cams, in order to rev the T.belt would have to advance its pace to accelerate. I'm also thinking that the belt is stuck to this pulley and as the Throtle body lets more air thru, it causes a bigger explosion and then everything turning faster.

maybe i'm retarded and what i'm trying to say doesnt even make sense

*btw, that's one dirty TB!!