bend a valve by being one tooth off on the chain?
 

OK, you engineers out there, can you bend a valve by being one tooth off on the cam chain?

This would be cranking the engine over by hand not running.

Tom W

That would depend on the engine type.....

BUT on most MB's they will still be OK in the chain jumps 2 teeth.

How much overlap is there on such a typical benz motor?

Tom W

Talked to a friend that works on those cars & he said MOST likely no bent valves.
He suggested you get it back in time & put some atf in the spark plug holes & see if the compressoin comes back up.

Wouldn't two teeth be partially engaged anyway? I would think the two teeth on either side of the missing tooth would keep it from slipping, at least with hand turning.

Well, we are suffering from a lack of communication here. No teeth are broken off the chain is just one tooth off from where it should be.

Tom W

Thands Doc,

Now, the atf will help with rings but it seems to be leaking out around the valves, manifested by air coming out the intake and exhaust ports when applied in the spark plug holes.

Is there any chance that there is stuff from 8 years of sitting that is keeping the valves from sealing?

Tom W

Oh, I'm a visual person. Words sometimes confuse me and I have to resort to looking at pictures. That makes more sense now.

Actually the teeth would have to break off the sprocket not the chain, and I have never heard of teeth breaking off sprockets only gears.

Tom W

I think there is a great chance that "stuff" is holding a valve or 2 open.
Can you get the engine started?

It is sitting right now with no intake system or exhaust. I was wanting to verify whether the valves are bent or not because of wishing to avoid installing all that and turning around and removing it again.

Yes, one thought is to assemble everything and pull it if necessary to start it and run it for a while (if it will start) so that all extranious "stuff" will blow out and get a good seal.

Thanks for your comments.

Tom W

When I changed my timing chain the chain slipped and I could tell I did not get it back in the right place at first while turning over by hand. The amount of torque needed to turn my 560 was not much until the slip. After I had the chain fed all the way through I had one extra link.:eek:

As long as you did not over do it your valves should be. How do you know you are only off one tooth??? If you have the intake off you could turn it over with the starter and feel by hand if you have any pressure at the intake side. For the exaust side I would think a compression check would show it unless you think both sides are bad.

As M.B.Doc said if you really want to know if one tooth would do it you should post what motor you are asking about.

I believe for my 560 it takes 16deg to bend a valve. one tooth is 13 degrees. My timing chain had stretched 11deg at 100k miles.

It would be very unlikely to bend both intake and exhaust valves. Do you have the cam held in place at TDC when applying the air? Or have you removed the rocker arms?

It is also real posible that carbon of rust has fouled the valves enough to pass compressed air.

I would have to agree with the post that mentions stuck valves. If a valve is stuck, then sure it'll collide unexpectedly.

I had this experience in rebuilding my m110 in my w123 280e. In the end I just took it to a shop with all the new guides, valves, and grease of choice, and let them have at it. Came out real nice.

But with regard to timing, I'd say your best bet is to get the no 1 piston at TDC before setting the valve train over it. In that case, I'd take a depth gauge and get the true TDC position. You'd be miraculously suprised at how the TDC on the damper is even ~0.3 degrees off due to deformation in the disc material or in the mounting hub. I was quite surprised that a slight hot burning issue was caused by none other than a 0.3 degree offset from the true TDC. That was after getting the whole thing put together!

Anyways, yes, you can get valve piston collisions due to a misplaced chain. Check the specs on your engine so as to when the intake and exhaust both open and close. Take your cam gear and measure the radius. Get the circumference. Take the link to link distance, and then divide the gear circ. by the link to link distance. This is how many links can sit on the gear. Then divide 360 degrees by that number and this is how many degrees offset you will have as a result of misplacing the chain by one link. CHeck this against your "valve opens at" measurement and there you have your answer.

If the calculation gives you a number that is greater than your book's number, then you very well could have bent valves this way. I bent 4 intake and exhaust that way before saying "f' it, i'm buying all new valves and sending it to a pro".

-Troy