Ran into problems replacing camshafts after pad replacement

[Fchotika]

Hi folks,

I have the engine out in my 2001 3.2S. Have replaced the cam pads on both sides. I started with bank 1 at TDC and removed the cam assembly, replaced pads and retime with a new chain and ensure the links lined up to the marks. Replaced the valve cover and checked rotation. Rotated the engine 720 degrees and looked fine. Next I moved on to bank 2 and removed the cam assembly. Realizing I didnt rotate the engine another 360, I went back to set bank 1, with bank 2 already out. Checked the alignment and all looked good. And held the cams down. Now when I try to rotate 720 degrees clockwise, at about 540, I feel resistance and no longer can turn the crank, spark plugs are all out. Bank 2 is out som must be something with my timing in bank 1. Am I hitting the valve and piston from the resistance I feel? Cyl 1 looks like the exhaust valve is open, cyl3 has the intake valve open. Cyl 2 is neutral.

What do I do now? Should I release the exhaust sprocket bolts, with he cam held down, allow the cam assembly to rotate back to a neutral position( no valves opened), set the engine back to TDC and retime bank 1 cams again?

Any advice appreciated. Better finding out if I did something wrong now with engine Out vs in the car and having a blow up on start.

[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.

[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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[maytag]

Ok, I've been racking my brain, trying to imagine a scenario where this whole "turning it backwards breaks stuff" can be true.
Is there something about the cam chain tensioners that they "unwind" when the motor turns backwards? So the chains get slack and the timing changes that far?



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[JFP in PA]

Originally Posted by maytag

Ok, I've been racking my brain, trying to imagine a scenario where this whole "turning it backwards breaks stuff" can be true.
Is there something about the cam chain tensioners that they "unwind" when the motor turns backwards? So the chains get slack and the timing changes that far?



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Yes, rotating the engine backwards, even by hand, leads to instant interference. Several people have discovered this the hard way.

[Fchotika]

Ok. Thank you for the advice. I definitely did not turn the crank backwards. So I found that my cam hold down was too tight. Backed it off slightly and added oil to it allowed the crank to turn. Looks good so far with 3x 720 Deg rotations. Working in the ims and rms next.

[maytag]

Originally Posted by JFP in PA

Yes, rotating the engine backwards, even by hand, leads to instant interference. Several people have discovered this the hard way.

You didn't answer the why, or how. Do you not know?
While doing leakdown tests, I had zero problem turning the crank either direction to get each piston where I wanted it.

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[JFP in PA]

Originally Posted by maytag

You didn't answer the why, or how. Do you not know?
While doing leakdown tests, I had zero problem turning the crank either direction to get each piston where I wanted it.

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With no oil pressure, all the hydraulic tensioners go dead, the chains go slack and there is enough slop to make the cam drive the equivalent of a couple of teeth out, which leads to contact. Some people seem to get away with it, probably because their hydraulic tensioners did not completely bleed down, or they were doing it on a five chain engine. It is worse on three chain engines than on five chain, probably because of the short chain between the cams holding everything more in time.

[maytag]

Originally Posted by JFP in PA

With no oil pressure, all the hydraulic tensioners go dead, the chains go slack and there is enough slop to make the cam drive the equivalent of a couple of teeth out, which leads to contact. Some people seem to get away with it, probably because their hydraulic tensioners did not completely bleed down, or they were doing it on a five chain engine. It is worse on three chain engines than on five chain, probably because of the short chain between the cams holding everything more in time.

Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.

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[Starter986]

Originally Posted by maytag

Aaaaaahhhhhh.......
Ok..... I can buy that. All of it.
Thanks, JFP.

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Yeah... JFP explains things in a manner that leaves me thinking, "Gotcha". I like knowing "why"... "how".

Cheers, MT.

[Fchotika]

Great know how here. Thanks again.

Before I put back the transmission, can I test start the motor to see if it’s all running well? Flywheel on of course. That way if any running issues I don’t have to remove the trans again. I am doing this on a lift with an engine bar attached.

[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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[maytag]

So for the record;
3.2 motor from an '03 S, has been sitting on the floor in my garage for months. Hasn't run since June. No oil in the sump, been draining for months. So we can all assume no oil pressure in the hydraulic tensioners, right?

Motor turns either direction just fine. No contact, no noises, no resistance. Two full revolutions of the crank, each direction.

Now it's also fair to assume the hydraulic tappets are also "soft", so valves not going full lift. But I would assume if one is true, so is the other.

This is pretty definitive, to me.

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[piper6909]

I have no experience with timing on Porsche motors, but I do have some experience with Subarus. I've found that if a motor is out of time when you try to turn the crank by hand, if you do it slowly enough, the piston will hit the open valve and stop. Forwards or backwards. If you're careful and don't force it, no damage happens. Are Porsche valves THAT fragile? You'd think that if you turn backwards slowly and carefully enough, if you hit, you could hit the valves without damage.

Also, if you ARE off time in a Subaru, you can ALWAYS rotate the motor backwards enough to put all pistons back in the middle position. Subaru's timing marks are, in fact, set at the point where all pistons at the middle position, not TDC. I guess Porsches are not the same?

[Fchotika]

Hi folks, got all my timing sorted and the cars runs well. Next problem to tackle is the engine to transmission mating. Tired for 4-5 days but still cannot get it to seat properly. Best I got it in was 1/4” gap. Just bought the 800lb HF jack with better adjusting head to try again. I took out the clutch plate and tried and it mated up no problem. But with the clutch plate it is been very difficult. Thus my alignment is likely off. My question: I have also read that you have to “draw” them in by two case bolts on each side greadully. Is this true? Or if I have them should just mate up flush right?

[elgyqc]

Originally Posted by Fchotika

Hi folks, got all my timing sorted and the cars runs well. Next problem to tackle is the engine to transmission mating. Tired for 4-5 days but still cannot get it to seat properly. Best I got it in was 1/4” gap. Just bought the 800lb HF jack with better adjusting head to try again. I took out the clutch plate and tried and it mated up no problem. But with the clutch plate it is been very difficult. Thus my alignment is likely off. My question: I have also read that you have to “draw” them in by two case bolts on each side greadully. Is this true? Or if I have them should just mate up flush right?

So you were able to start the engine without the transmission? How did you support it?
On installing the transmission, I had similar problems (5-speed) and spent a lot of time fiddling around. My first problem was that my tranny jack was not quite high enough so I added a 2x6 between the jack and the transmission. Still it wouldn't slide all the way on, I think the gap was about a half inch. I measured everything and decided that at that distance the input shaft was already part way into the pilot bearing and the splines were in the clutch disk so I put a couple of bolts in and very gingerly tightened them, keeping the gap even, and got it all pulled together.
Good luck