Timing Belt went today... TURNS OUT MY HEAD IS OK!!!!!

[Chad Giffen]

Well I guess some bad came out of today...    but it could have been way worse.

My car has 174,XXXkm on it. It had the timing beltdone at 92,XXXkm. I knew it had to be replaced soon and had planned on doing it early next month as I am proabably moving to vancouver.

I was driving to the college a cbout a block away from my house and suddenly the car died. I mean it died fast. I gave 1 one crank to see if it would start. Nope. Then I knew there was a good chance it was the belt. Didnt try and start the car again, and luckily I was able to coast it home.

I pulled of the upper timing cover and the belt was completely off the sprockets. I actually thought this was a good thing. It would have gave the valves a chance to slam shut RIGHT AFTER the belt let go. So I am hoping there was no piston/valve contact. I only cranked the engine ONCE after it let go.

Anyways im ordering the parts today even though I am close to fucking broke. Luckily I had saved some money for the moe to vancouver so I will have to dip into that.

Guys think I damaged my head???

[Kristopher]

There'll always be valves open.

[Jason Harwood]

Who knows!

Possibly

Im sure you nailed a valve or 2, people always do.

[Chad Giffen]

Im betting on the fact the cams were no longer attached to the crank when the belt went. The valve springs should have slammed those valves shut as soon as the belt let go. When I inspected the car.....   all the valves were in the closed position.

In addition I was going real slow speed when it happened. No more than 2500rpm. Im pretty confident those valves springs would have slammed shut the valves before the pistons had a chance to make contact.

Again the cams and crank were in no way connected through the timingbelt when it went. (THANK GOD) 

[Marke Bailey]

doesn't matter. the only time the crank and valves will not contact is when the engine is at top dead center. if it was in any other position it probably hit them.

[Chad Giffen]

the only time the crank and valves will not contact is when the engine is at top dead center.

ughhhh   may want to rethink that one marke. That IS when the valves and pistons will make contact; when the piston is at top dead center.

[Kristopher]

There is never a case when all 16 valves are shut at the same time...physically impossible since their position is determined by the camshaft lobe pushing on the rocker which opens the valve. Has nothing to do with the timing belt. And since your tbelt and cams became disconnected they subsequently get 'out of time'. That's when there's carnage. Sorry.

[Marke Bailey]

the only time the crank and valves will not contact is when the engine is at top dead center.

ughhhh   may want to rethink that one marke. That IS when the valves and pistons will make contact; when the piston is at top dead center.

I'm not talking about piston position, I am talking valve position. I have done my own timing belt twice and helped John do it on 2 of his cars too. when the entire engine is at top dead center you can disconnect the timing belt and rotate the crank without making contact with any valves. that is the only time it will happen. as you know, there is a set of exhaust valves slightly open at TDC. when tension is released they slam shut. that is why we must move the exhaust cam 2 teeth when reinstalling the belt.

[Chad Giffen]

Holy cow......     how am I the only one seeing this.....    Im sure john will be able to explain things better when he reads this.


Ok Marke...     believe it or not....   having the timing marks lined up on the camshaft sprockets is actually not the only position they can be in for all the valves to be closed and to be able to turn the crank feeely without fear of hitting valves WHEN THERE IS NO TIMING BELT INSTALLED.

Remeber theses are four stroke engines....    so ther are not one but two instances when all the valves will be closed during engine operation: the compression stroke and a part of the power stroke. Thats almost a full rotation of the crank.



This is taking into account that there is always a timing belt attached.

When there is no timing belt attached, the valves springs possess enough force to move the camshafts lobes so that all the valves on that camshaft are closed (or closed enough no piston interference is possible).

Of course when you are doing your timing belt, you want the calshaft sprockets in the particular position so they line up so you can time your engine properly, but it is not the only time all your valves are safeguarded from piston contact.

Look at it this way....    say you are looking at your timing belt and you know from looking at it that some of the valves are fully open because the valve springs on those valves are fully compressed. Now if you cut your timing belt between the camshaft sprockets....   BANG!!!!  the valves springs will automatically close the valves regardless of where the pistons are. You would see the camshaft sprockets automatically move forward or back proabably 20-40 degrees.

The reason most people bend valves is because the belt usually only jumps a couple teeth and continues to turn both the crank and the camshaft sprockets. In my case, the failure was so instantaeuously severe....   the belt released from the camshaft sprockets and crank so that the camshaft sprockets immediately stop turning and would not continue to turn even with the crank still spining.

[Marke Bailey]

Look at it this way....    say you are looking at your timing belt and you know from looking at it that some of the valves are fully open because the valve springs on those valves are fully compressed. Now if you cut your timing belt between the camshaft sprockets....   BANG!!!!  the valves springs will automatically close the valves regardless of where the pistons are. You would see the camshaft sprockets automatically move forward or back proabably 20-40 degrees.

they will move to a position of least resistance. not necessarily the closed position.

edit:
also by your diagram you have to remember that when cyl. #1 is on the compression stroke, #4 is on the exhaust stroke. #1 & #4 move up at the same time and #2 & #3 move down. with a firing order of 1-3-4-2.

[Kristopher]

By your diagram just look at cylinders 2 & 3 and the valve positions. There isn't a time when all 16 valves are fully closed. There is also no way on earth that your cams are going to stop dead at the 'safest' position instantaneously to avoid being nicked by the pistons. Even at idle when tbelts break on an interference engine there is some damage. We're talking about 42 revolutions per second on the crank, so 21 revolutions per second on the cams. I know guys who have swore they got off lucky only to find bent stems once the head was in a machine shop.

[Chad Giffen]

There is also no way on earth that your cams are going to stop dead at the 'safest' position instantaneously to avoid being nicked by the pistons.

I disagree. I say there is no way in hell the cams and cam sprockets have enough momentum after being released from the timing belt to continue on and compress several valve springs (along the whole cam) enough to put the valve in harms way.

I see what you guys are saying about 16 valves never being all closed at once, but that is when the timing belt is installed. We are referring to when the timing belt is not installed.

Hasnt anyone ever had there head off the car and rotated the camshaft sprockets....   whenever the camshaft sprocket is in a resting position, the valves dont protrude enough for piston contact.

[Kristopher]

Ah yes, with the belt popped then each cam is separated. If the cam rests in the right position it is possible to turn the pistons w/o contacting the valve, so x2 cams then it's possible. What I disagree on is the probability of both cams coming to rest instantly in that position.

I do wish you luck though, I hate seeing engine damage from things like this.

[Chad Giffen]

fingers crossed.

[John Hartman]

I have had several twin cam heads off in my days of wrenching. Most of them DSM heads. Even with the cams disconnected via a broken belt, you cannot set it up somewhere so that NO valves are open at least part way.

remember we are not talking about one cylinder here but all 4.  Each cam works 8 valves so at least 2 will be open.

Now, even if by some fluke when the belt broke, the engine stopped in such a way as to have one piston down and only 2 of that cylinders valves open, you cranked it to try to restart it.  Just like any one of us would have.  Now, there there is no way all the valves are still good.  If those valves were closed, and the piston was down, when you cranked it, the valves did not move because the cam cannot turn due to no belt on it.  The piston however did move, assuming the crank and rod are still good.

Assuming all is stock or stock replacement inside that engine(no aftermarket pistons with larger valve reliefs cut in them, no really strong stainless alloy valves, no real thick spacer head gasket), some valves are bent.  Probably 4 or 8.  Some won't be badly bent, but won't seal to the seat.

Even if it looks good, I strongly suggest you send the head to a competant machine shop so that they can test it to see if the valves seal.  They seal each chamber and pull a vacuum on it.  If they don't seal, its obvious, but not visible some times.  I'd hate to see you go to all that trouble and then have to do it again, plus another head gasket, set of bolts, oil, coolant etc.

Hey, I wish you luck, it would be really great for you if we were all wrong, but the chances are VERY minute.