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Thrown a piston?

Skylarking

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... Timing chain stretched, slipped and punched the passenger side pistons into the head, breaking most things they came into contact with. Pretty sure it lifted the head off slightly from memory because there was coolant in the valley under the intake manifold....
A broken timing chain will not push the piston into the head. The conrods and crankshaft control piston height not the cam shaft.
While the crank pushes and pulls the piston up and down via the connecting rod, the cam opens and closes the valve at the appropriate time (in relation to the piston move,ent). If a cam chain fails the piston will hit the valve in an interference designed engines. Such will push the valve up into the cam, trying to lift the head off in the process. But head bolts are stron so they will resist. What usually gives is the valves bend and punch a hole in the pistons... it makes a mess of the engine in any case... In a non interference engine, the pistons and valves can never collide so one simply looses power...

But. I’m no expert.....
 

shane_3800

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No. When a timing chain or timing belt breaks the valves will hit the piston. The piston does not hit the head. When the valves hit the piston the bend they do not lift the head off.
 

Skylarking

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No. When a timing chain or timing belt breaks the valves will hit the piston. The piston does not hit the head. When the valves hit the piston the bend they do not lift the head off.
What’s with the No?
If the cam chain breaks, the cam stops turning and the valve just sits their waiting to be slammed by the piston. When the piston hits the valve, the upward force of the piston is transferred through the valve to the cam (in OHC design) and that force tries to lift the head off.

As I said, head bolts are strong so the weakest part will breaks. It’s usually the valve that bends while the piston ends up with other damage (sometimes a hole)...

I never said the piston hits the head (that’s mechanically impossible unless the conrod lets go). But keep on playing semantics by now saying the valve hits the piston...
 

shane_3800

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What’s with the No?
If the cam chain breaks, the cam stops turning and the valve just sits their waiting to be slammed by the piston. When the piston hits the valve, the upward force of the piston is transferred through the valve to the cam (in OHC design) and that force tries to lift the head off.

As I said, head bolts are strong so the weakest part will breaks. It’s usually the valve that bends while the piston ends up with other damage (sometimes a hole)...

I never said the piston hits the head (that’s mechanically impossible unless the conrod lets go). But keep on playing semantics by now saying the valve hits the piston...

I just told you the valve will bend. The piston doesn't hit the head. I've repaird hundreds of engines with broken timing gear.
 

shane_3800

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If the forces were that great that the head bolts would snap how come the 6mm cam cap bolts dont snap?
Also only four valves per head will be open at one time so you have four valve stems vs 8 11mm head bolts.
Also the valves are on an angle to the piston so the stem is more likely to bend.

But I don't know what I'm talking about.
 

Skylarking

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I just told you the valve will bend. The piston doesn't hit the head. I've repaird hundreds of engines with broken timing gear.
Shane, below is what i posted... which was what you replied "No" to.
While the crank pushes and pulls the piston up and down via the connecting rod, the cam opens and closes the valve at the appropriate time (in relation to the piston move,ent). If a cam chain fails the piston will hit the valve in an interference designed engines. Such will push the valve up into the cam, trying to lift the head off in the process. But head bolts are stron so they will resist. What usually gives is the valves bend and punch a hole in the pistons... it makes a mess of the engine in any case... In a non interference engine, the pistons and valves can never collide so one simply looses power...

But. I’m no expert.....
My posy was in part to clarify what Sabbath may have meant by piston "lifted the head off slightly" as i doubt he or any high post count JC member actually things the valve cam controls piston lift... But you seem to be caught up in semantics now...

So just to clarify, I've highlighted what i said in my post as you saying "No" clearly means you think I've said something that is incorrect.

It can't be piston hitting the head cause i never said that.
It can't be head bolts snapping cause i didn't say that either.
What is said is that head bolts are strong and the valve bends and punches a hole in the piston.
Later I also said the weakest part breaks (either the valve and/or piston)...

So it's not an issue of whether you have repaired one or a thousand engines with damaged timing gear. The issue was you wrongfully claim statements from me that are not within my post. Reality is we are probably not far apart in what we are saying so to debate whether a piston hits a valve or a valve hits a piston or indeed how much force is needed to bend a valve verses how much force is needed to elongate a TTY head bolt a tho' isn't relevant in the grand scheme of this thread.

So I'm over the semantics and wrong attribution :rolleyes:

Just hope the OP doesn't continue to drive his car until he kills it ;)
 

Fu Manchu

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This is the best thread in ages.
*gets pop corn.
 

william77ize

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Yeah man, I'm taking it in tomorrow. Like I said earlier in this thread, the mechanic has a spare VE engine. Not sure if both vz and ve engines are alike one another though. I have had a look under the car and nothing is dripping so I don't think there are any leaks. It's shaking a little bit, just enough to notice it. It isn't shaking like a washing machine with cement in it thank god. So I'm just praying it isn't going to cost me an arm and a leg to repair it.
 

Sabbath'

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But I don't know what I'm talking about.
Probably the smartest thing you've said in this thread.

When i said it "Hit the head" did you not find it somewhere in your brain to attribute that i could have been referring to the head assembly as a whole? And the damage which it caused, which i alluded to included, but wasnt limited to hitting the valves and also snapping the camshaft retaining assemblies as the piston continued to repeatedly jackhammer itself into the valves?
 
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