dwallace

I know this would be a bad situation no matter what, but what would happen if the no1 piston was set at TDC on the exaust side? I know the valves would hit the pistons, but would it be driveable? What would happen to the head? The pistons? Etc.?

I've swapped the head gasket a couple of times and always did the timing by eye. I have aftermarket pulleys (including drive pulley) so there would be no notches indicating the position. So I've always done it by the no1 piston position (TDC) and then set the cams to the horizontal notches and "TOP" markings. Oddly enought the first time I did it the car idled better than it ever had (or at least since I began putting aftermarket stuff on). Stock idle--it's great. Anyways I'm assuming I have done the timing fine each time, but I was just wondering what kind of issues would result if rotation was off 180 degrees?

Mad-Machine

honestly, that is a good question. As all the combustion processes start in the head (ignition, valve position, cam sensor) I do not think it would be an issue. As long as the piston was in the same position, it should work just fine.

I also hope that you turn the engine over by hand a couple of times before you start her up, just to make sure that the pistons are not hitting the valves and the like.

MAXXTIB

Most aftermarket pulleys show the timing marks, The timing belt gear on the cranshaft must be a stocker since they don't make an aftermarket part, the gear on the head should have a little hole in it and it should be a 12:00 at TDC, but if there is no small hole in the gear just go by the the pin on the timing gear since it should also be at 12:00 at TDC.

On our cars if your 180 out it should not run very well due to the crank sensor and cam sensor being off and out of sync, you will def get a cel, but on older carburated cars it is also a problem since you will be 180 out with the distributor and firing the ignition on the exhaust stroke.

Mad-Machine

I forgot about the crank sensor... but honestly, I do not think it will make a difference. The crank would still be in the exact same position if it was at top dead centre.

MAXXTIB

Your right the crank sensor will be in the same location regardless at tdc but since the crank works on a 720 degree cycle and the cams are on a 360 degree cycle and if your 180 out your plug will be sparking when the piston is down and not at tdc, you thinking of 180 degrees on 360 degree cycle but thats not how it works, when your 180 out that meens your 180 out of a 720 degree cycle, if you 360 degrees out on a 720 degree cycle the car would run fine as lonng as the ignition fires at the right time and since our cars fire in batch it would run.

Mad-Machine

that may be true.. but physically, the crank cannot do more than 360 degrees in one revolution. Irregardless of how many degrees it takes to bring the piston back to firing position. In that respect, it does not matter where the crank is in relation to the ignition sequence.. the piston will still be in the "up" position (tdc) and the sensors for the crank will still be telling the computer what it needs to know.

You are however, correct in mentioning carbed, non-computer controlled cars, provided that the distributer is run off of the crank. If it is run off of the cam(s) then the crank is again irrevelant as long as it has the piston in TDC

dwallace

I did turn it by hand and everything checked out okay. And like i said its runnin better than ever--I was just curious to see what would have happened if i had done it wrong...thanx for the info.