cam belt cause problems?

[Jezz]

good so am i.

 

right what point are we acctualy disagreing over?

 

The point that the crank can act on its own and spin faster than it was spinning at failure, causing oil pressure issues.

[Jake]

no im not saying there are all uncompressed.

 

Oh, I thought when you said ....

if the belt snapps then the cam lobes do not spin on the lifters or push on the valves, therefore the valve spring is uncompressed so the valve will remain closed against the head. not allowing fuel or oxygen in so no compression combustion or anything.

...you meant that when the belt snaps the valve springs were uncompressed.

 

 

^^^question asked^^

Which question?

 

you guys mechanics?

We're both software engineers, does that mean we don't know how the Supra engine works?

[madmarf]

The point that the crank can act on its own and spin faster than it was spinning at failure, causing oil pressure issues.

 

 

 

right i think i may have layed that on wrong, my bad if i did, i didnt exactly re read my post. however are you saying that when a cam belt snapps that the oil pressure isnt higher than it should be and cant cause any problems?

[madmarf]

We're both software engineers, does that mean we don't know how the Supra engine works?

 

 

 

 

 

 

 

 

no thats not what i said. i was asking that so i can talk in mechanical terms not in laymens terms. just a comunication question.!

[Jezz]

right i think i may have layed that on wrong, my bad if i did, i didnt exactly re read my post. however are you saying that when a cam belt snapps that the oil pressure isnt higher than it should be and cant cause any problems?

 

Yes.

At failure the pump is still being driven from the crank. The engine cuts reducing engine speed resulting in a drop in oil pressure. I cant see of any way that oil pressure would raise to an unacceptable level just because a cam belts failed.

[madmarf]

Yes.

At failure the pump is still being driven from the crank. The engine cuts reducing engine speed resulting in a drop in oil pressure. I cant see of any way that oil pressure would raise to an unacceptable level just because a cam belts failed.

 

 

 

that is so on a supra i agree. however on some other engines, this isnt the case. ones where the pump runs off the cam belt, ie. some fords, some bmw's etc etc. now days its all off the crank agreed.

[SimonB]

Ok, I'm bored so here's some info to correct some of the statements in this thread.

 

The valves wouldn't close, the cam shafts would stop rotating -not necessarily immediately if they were really whizzing round but pretty quick because there's a lot of resistance there due to the valve springs. The position they stopped in would determine which valves were open, closed or somewhere in between. The valve spring would indeed press the bucket and shim upwards, but that pressure won't rotate the cam even if it was pushing at just the right bit of the lobe because one of the other lobes on the cam would have to compress another spring if the cam rotated.

 

The reason you need higher oil pressure if the engine speed is higher is to make sure the main and con rod bearings have a strong enough oil film to stop the crank from touching the bearing and damaging it. Since the oil pump is driven by the crank, the oil pressure will always be correct for the speed the bottom end is rotating. The engine sensors would in fact continue working fine as the ignition would be on. But if they didn't it wouldn't make any difference - the only sensors for general engine operation are oil pressure (which just lights a warning light), cam and crank position (obviously the cam sensors would stop signalling and the crank would continue which would cause the ECU to flag an error), oil level, coolant temp, intake temp and manifold pressure (or MAF). None of those have any bearing on oil flow.

[madmarf]

Ok, I'm bored so here's some info to correct some of the statements in this thread.

 

The valves wouldn't close, the cam shafts would stop rotating -not necessarily immediately if they were really whizzing round but pretty quick because there's a lot of resistance there due to the valve springs. The position they stopped in would determine which valves were open, closed or somewhere in between. The valve spring would indeed press the bucket and shim upwards, but that pressure won't rotate the cam even if it was pushing at just the right bit of the lobe because one of the other lobes on the cam would have to compress another spring if the cam rotated.

 

The reason you need higher oil pressure if the engine speed is higher is to make sure the main and con rod bearings have a strong enough oil film to stop the crank from touching the bearing and damaging it. Since the oil pump is driven by the crank, the oil pressure will always be correct for the speed the bottom end is rotating. The engine sensors would in fact continue working fine as the ignition would be on. But if they didn't it wouldn't make any difference - the only sensors for general engine operation are oil pressure (which just lights a warning light), cam and crank position (obviously the cam sensors would stop signalling and the crank would continue which would cause the ECU to flag an error), oil level, coolant temp, intake temp and manifold pressure (or MAF). None of those have any bearing on oil flow.

 

 

i agree with nearly all that, well said. but same, i give up too. i may be a newbee guys and i know im not always right, but i also dont bull about things, not everyone knows everything including me and there would be no parlimant without debate . agree to disagree and move on yer

[j_jza80]

How might it cause damage then?

 

Belt related damage, loss of power making the car suddenly more difficult to control.