Ran into problems replacing camshafts after pad replacement

[maytag]

Originally Posted by JFP in PA

First of all NEVER rotate one of these engines backwards, you will do a lot of damage if you do.

It sounds like you have missed on the cam timing, so you will need to very carefully remove the bank 2 cams. Then recheck bank one, reset the engine and start bank 2 over again.

I've heard y'all say this before, but I'll tell ya what: if there is so much slack in the timing chain arrangement that you can't turn these motors backwards (as y'all explained last time was the reason) then why don't we experience issues when you let off the throttle abruptly after a red-line pull?
I guess I don't understand the reasoning.

Explain for me?

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[JFP in PA]

Originally Posted by maytag

I've heard y'all say this before, but I'll tell ya what: if there is so much slack in the timing chain arrangement that you can't turn these motors backwards (as y'all explained last time was the reason) then why don't we experience issues when you let off the throttle abruptly after a red-line pull?
I guess I don't understand the reasoning.

Explain for me?

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Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.

[jaykay]

It may be valuable to state how is the clockwise direction is indicated on the accessory drive end of the engine. I don't remember seeing an arrow on the stock crank pulley way back when I pulled it off.

This direction will be opposite for 996s when using clockwise as referenced to the pilots view looking forward.

Any danger for those installing under drive pulleys or turning the engine over by hand?

[maytag]

Originally Posted by JFP in PA

Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.

So..... without arguing, I'm still gonna ask HOW?
I don't see any way that valve to piston contact can occur in one direction but not another. Those bits are, for all intents and purposes, fixed in relation to each other. I just don't see how the backwards rotation changes that?

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[Anker]

Originally Posted by JFP in PA

Because when the engine truly rotates backwards, the valve timing will result in instant piston to valve contact; even rotating by hand, the mechanical advantage is sufficient to bend valves. When you back off of WOT, the engine is still rotating clockwise; the only way to get it to rotate counter clockwise is by someone turning the crank backwards.

Or spinning 180 degrees without both feet in! Can happen on track and in autocross. Important to do full brake and full clutch immediately when you spin, otherwise the car will pull the engine backwards when you roll backwards after the 180.

[maytag]

Originally Posted by Anker

Or spinning 180 degrees without both feet in! Can happen on track and in autocross. Important to do full brake and full clutch immediately when you spin, otherwise the car will pull the engine backwards when you roll backwards after the 180.

No, see, now you're off in lala land again, Haha. If it spins backwards under those conditions, then your tensioners are still pumped up, and no contact can occur. I've tested the theory, inadvertently.
I can tell you what WILL happen though. ;-)

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