TDC Mistake, set on Exhaust cycle
 

I was in the process of getting ready to change my water pump and got in a rush last week as I was pushed for time before leaving for work for a week and wanted to get the old pump off.

I set TDC and before locking the flywheel I forgot to check the cam timing marks to make sure it was on the firing stroke.

Even though I noticed the rotor was in the wrong position I continued to strip the belts off etc. before it hit me that it was not lined up on the firing stroke.

I went ahead and removed everything to get to the water pump and will be reinstalling it later this week when I get home.

Am I screwed or can I re-install the timing belt and then check by rotating the engine by hand to see if the timing marks line up.

Any advice is appreciated, trying to get my car ready for a DE later this month and don't want to screw up the engine.

Lesson learned, don't get in a rush!!!

Thanks,

Scott

I would go ahead and do as you said. Put it together then rotate by hand to recheck and adjust it needed. There is other ways but I'm sure some else here can explain better.

I would roll the crank back to get the pistons at half stroke, then rotate the cam to the correct position and then roll the crank to proper location.

Otherwise, yeah, put the belt on, and rotate by hand and make sure the lines match up.

Which evever way you want to go, should be a simple and safe fix as long as you watch what you are doing.

What did you use as your TDC guide?
The notch on the cam gear only has one TDC.

V2Rocket

I rolled the engine over by hand with a breaker bar until the mark on the flywheel lined up with the pointer on the bell housing and the #1 piston was at TDC.

I've done this before when changing the Timing belt but failed this time to check the mark on the timing gear and housing to ensure it was on the firing stroke instead of the exhaust.

Got in a rush and even though I noticed that the distributor rotor was not pointing
towards the number 1 sparkplug location pulled the belts off anyways.

Stupid mistake because I was agravated about having to replace the water pump.

Better to catch it now and correct than to bend the valves or worse.

Scott

Just put the cam tower back on at TDC. Line up your marks like always and you will be fine.

The crankshaft doesn't know what the camshaft is doing.

But the valves will know exact what the pistons are doing as they have in intimate meeting...

Some people....

+1

for the pistons/crank there is only one TDC position, it is not based on current stroke. its either up or down.

if the piston/crank is at TDC as marked, and the cam gear is at TDC as marked, then you're at TDC.

Okay, so help me understand.

You have a piston at TDC. You can rotate the cam 180 degrees without the valves moving on that cylinder?

Granted I only work on 16 valve engines, and I know I can't do that on them.

I was thinking that he took off the cam tower, not that he was only changing the belts. If the tower is off then it doesn't make any difference.

Since the cam tower is on the car then you are correct. However, all he needs to do is to turn the crankshaft 45 degrees, pulling #1 and #4 down for valve clearance. Then, set the cam gear to TDC, and return the crankshaft back to TDC.

I wouldn't try to "guess" on a tooth and spin the engine around to TDC, as even being 1 tooth off can still bend a valve.

That will teach me to try to answer questions when pressed for time...

Up and running
 

Luck was with me, installed the new water pump and re-installed the timing belt, removed the flywheel lock and rotated it by hand until it was back at TDC and found that it was only off by two teeth on the cam gear.

Locked the flywheel back down and released the tension on the belt to remove it and then rotated the cam to line up the mark on the gear with the housing.
Re tensioned the belt, removed the flywheel lock again and rotated the engine again to double check everything.

Installed the balance shaft belt and the other parts and it started right up.

Next time I will not get in a rush that's for sure

Thanks for the advice

Scott
78 911 SC Targa
87 944 NA Track Car