Timing belt broke while setting TDC

thekidd · 07-20-2014, 12:30 PM

I have taken the steps to start a timing belt change on my 1984 944 the other night. Got to the stage of setting the car to TDC, so I am turning the crank by hand and the belt just snapped, didn't hear it, and noticed when I looked to see where the cam gear mark was at. Snapped far left of the cam gear. And at that point I stopped, went in and cracked a beir. Now I think the cam gear was at about 1-1:30 before the belt broke, now it's at about 4oclock. Do I continue with this by only replacing the belts and doing a compression test, or should I take the head off and do a visual check of the valves? What's my odds here Docs.?

zedsn · 07-20-2014, 01:22 PM

I am pretty sure that by only turning it by hand your valves are fine. I would put the new timing belt on it where you think it should go and then turn the motor over by hand and see if you can get it to TDC. If not take the belt off and try again till you can get things to line up to TDC. I would think that you would only bend valves if the vehicle was running.

thekidd · 07-20-2014, 01:35 PM

Ty, I was thinking (hoping) that there wasn't enough force there to bend valves up. I rewind the cam, replace the belt and I should be OK? I'll do a compression test after that to verify that I'm OK. Thanks.

zedsn · 07-20-2014, 02:31 PM

Your cam still has some valves or valve that is in the down position so you are going to have to get everything back right in order to turn the motor correctly without hitting anything. Get everything lined up right and turn the motor over by hand for awhile with a socket and ratchet and if everything feels good with no interference detected then try to fire the car up and see if it runs. If it doesn't and sounds like it is spinning faster than it should then you have a bent valve or two and then do a compression test but it will be a mute point.

djnolan · djnolan's Garage

To get it back in time try the following:

If the belt is off, remove all of the plugs and put a dowel or pencil in the #1 sparkplug hole and using a wrench on the crank pulley, gently drop or raise the #1 piston to halfway down. If it hits something move the cam a little.

Once you get the #1 piston to the midpoint, all of the other pistons will be in the middle position and can't hit the valves. Then move the cam gear to the timing mark. Then slowly bring the crank to TDC per the timing mark in the bell housing.

At this point you should be close to in time and can put he belt on and do a fine adjustment.

Don't force anything and you should be fine.

Ga 951 · 06:41 PM

kidd
djnolan has it right. you get all the pistons at mid position with the crank 90 degrees off of TDC. You can check it with a dowel if you wish. Then set the cam to TDC and reset the crank to TDC. Install belt and you are back to where you started.

Doubt you damaged any valves. Remove the plugs so you aren't fighting the compression, you will feel some resistance when turning the cam due to the valve springs.

GL

MB968 · 07-20-2014, 09:18 PM

Once you get it back together, a compression test and or a leakdown test should tell you if the valves are OK.

Arizona_928 · 07-21-2014, 04:59 AM

that's really strange. I bet the belt was over tightened.

Some really good advice given. When you turn the cam/crank by hand you will feel the difference between compression and contact.

I think the only thing that can really go wrong is if you get the cam 1 pi out of rotation. that would tricky to set back to norm.

Slam · 07-21-2014, 05:27 AM

Do NOT put a pencil or a chopstick or anything else made of wood in the #1 spark-plug hole. It'll shatter and then you'll be in a world of hurt.

Use a plastic drinking straw if you must do this.

My guess is it's unnecessary. Move the crank a little, then move the cam, then the crank, then the cam, and so on, until you're timed on both. Then throw a belt on and, as the guys say, go round and round to make sure you're okay.

Rasta Monsta · Rasta Monsta's Garage

Is your cam box leaking, by chance? If so, might as well pull it, reseal it, and deal with your TDC issue that way. Not a big deal at all.

thekidd · 07-21-2014, 08:05 AM

No, my cam box is not leaking. I did a head gasket job about 20 months ago, so all the seals are pretty new. Except the front cam seal is leaking because I wasn't able to get the bolt for the cam gear off. That's why I didn't do a timing belt job then.

Capt Squid · 07-21-2014, 07:59 PM

You can bend a valve by turning the engine by hand. A buddy of mine did it.

Safe thing to do is remove the cam tower, find TDC and go from there.

thekidd · 07-21-2014, 08:19 PM

Took the cam gear off, got all straightened out. Thanks