can't rotate engine after IMS bearing change

[Driver Ed]

After a long holiday-related pause, I'm back under my car. I've replaced the IMS bearing, and the RMS seal and have replaced the tensioners and refilled the engine with oil. I then attempted to check to make sure that the cam chains hadn't skipped a tooth, but I find I can't rotate the engine all the way through to 360 degrees. The first half rotation was fine (spark plugs are still in place, so there was a point at which arm-power was providing compression) but I got it to about 340 degrees rotation and it just won't budge.

Eyeballing the marks I made on the camshafts before removing the IMS bearing, they both (exhaust cams on 1-3 and 4-6) look about the same distance away (so I'm guessing neither has skipped a tooth) but I would really like to definitively check and can't figure out what could be stopping the engine from further rotation.

My car is a 2000 Porsche 996 with a 5-chain engine.

Any advice? I would really like to get this job done!

[JFP in PA]

Obviously, this is not good. That said, without a "blow by blow" breakdown of how the IMS retrofit was conducted, it is nearly impossible to accurate determine what happened.

[Driver Ed]

I followed the steps laid out here Pelican Porsche Tech Article - IMS Bearing Replacement - Porsche 911 Carrera - Porsche 996 Carrera (1998-2005), Porsche 997 Carrera (2005-2008). I'm taking the plugs out now, but if that doesn't help, what next?

[JFP in PA]

Originally Posted by Driver Ed

I followed the steps laid out here Pelican Porsche Tech Article - IMS Bearing Replacement - Porsche 911 Carrera - Porsche 996 Carrera (1998-2005), Porsche 997 Carrera (2005-2008). I'm taking the plugs out now, but if that doesn't help, what next?

I hate to say this, but "another one".

I see nothing in that procedure about locking the engine at TDC before starting, I also do not see the use of cam locks before starting, and I see the use of set screws in an attempt to hold the shaft from moving. All of this is ill advised for an entire litany of reasons.

The only known method of doing one of these that cannot end up with jumped timing or other problems is the published LN method: http://lnengineering.com/files/IMSR-Instruction-Warranty.pdf

Over the years, we have had several cars flat bedded into the shop after blowing an IMS update because they used a method other than the one LN Engineering developed. Some of them we were able to save, others not so much.

If you followed this procedure, I think you are in trouble and the cam timing is off.

[Driver Ed]

Assuming that the timing is now wrong, which seems as though it is the only explanation, any advice as to a recommended procedure to follow? If i'm going to have to go through the pain of retiming the engine, I'd really rather do it only once.

[JFP in PA]

Originally Posted by Driver Ed

Assuming that the timing is now wrong, which seems as though it is the only explanation, any advice as to a recommended procedure to follow? If i'm going to have to go through the pain of retiming the engine, I'd really rather do it only once.

This gets very messy; you are going to need the special tools involved, which run $400-600. You are going to need to install cam holders, remove the cam covers, and then the cams on both sides so the engine can be rotated to TDC without anything hitting anything. This has been written up before, so do some searching.

Once the engine is at TDC, you need to lock down the crank, and then reinstall the cams, again using special tooling to re allocate them correctly.

This is what one of the aftermarket tool sets looks like:



Good luck.

[Driver Ed]

Thanks, I've ordered a tool set. But one more question: since I can't rotate the engine in the forward direction, will I damage anything if I rotate it in reverse? If I have read correctly, I won't be able to install the cam holder if the engine isn't at TDC, and I can't get the engine to TDC by rotating the engine in the forward direction.

[JFP in PA]

Originally Posted by Driver Ed

Thanks, I've ordered a tool set. But one more question: since I can't rotate the engine in the forward direction, will I damage anything if I rotate it in reverse? If I have read correctly, I won't be able to install the cam holder if the engine isn't at TDC, and I can't get the engine to TDC by rotating the engine in the forward direction.

NEVER ROTATE THE ENGINE COUNTER CLOCKWISE! That will break or bend things for sure.

You will not rotate the engine until the cams are removed, which will get the valves out of the way. Then it is rotated to TDC and locked to put it back together. The cam retainers will go in with the cams in any position.

[Driver Ed]

Originally Posted by JFP in PA

NEVER ROTATE THE ENGINE COUNTER CLOCKWISE! That will break or bend things for sure.

You will not rotate the engine until the cams are removed, which will get the valves out of the way. Then it is rotated to TDC and locked to put it back together. The cam retainers will go in with the cams in any position.

That's good to know. Thanks for the information. I'm not going to have time to work on it for a while but will post my progress when I do.

[occb2]

Not time properly. Common problem.

RObert

[ischmitz]

will this all be done with the engine in the car or does it have to come out? Just curious

[Driver Ed]

I'm actually pondering that question now. I have drained the oil again, and removed the chain tensioner and oil pump from the 1-3 side. My thought is that if I can loosen the four bolts holding the exhaust timing gears together



I may be able to advance the cam timing enough to get the valves out of the way so that I can get the engine to TDC. If I can do that, I can lock down the cams in the right place and retighten those bolts, and get the timing correct without removing the engine. I haven't had the chance to try it yet, but that's my current plan. I figure that if it fails, I'm no worse off.

[Joe Ricard]

If you have the cams in, at least one set of valves pushed open into the cylinders. One of the pistons is going to hit it and stop engine rotation again.

[JFP in PA]

Originally Posted by Driver Ed

I'm actually pondering that question now. I have drained the oil again, and removed the chain tensioner and oil pump from the 1-3 side. My thought is that if I can loosen the four bolts holding the exhaust timing gears together



I may be able to advance the cam timing enough to get the valves out of the way so that I can get the engine to TDC. If I can do that, I can lock down the cams in the right place and retighten those bolts, and get the timing correct without removing the engine. I haven't had the chance to try it yet, but that's my current plan. I figure that if it fails, I'm no worse off.

Will not work as you need to rotate the engine too far. The cams need to come out of the engine before it is rotated.

[Driver Ed]

It would be very useful to me for someone to explain in some detail their theory for what went wrong.

Here's my theory:
It seems to me that what happened is the because the IMS bearing on is on the transmission side of the engine (as is the 1-3 chain), and that because when I replaced the IMS bearing I needed to move that end of the IMS about 1/2 cm toward the 4-6 side, that the problem is likely to be on the 1-3 side and not the 4-6 side, which has its chain on the other end of the engine. When I moved the 1-3 end of the IMS back in position, I suspect that I inadvertently retarded the valves on the 1-3 side and that the exhaust valves on that side are what is now impeding the engine's movement. If there's a flaw in that theory, or a plausible alternative explanation, please enlighten me.

[bell]

Either side couldve moved since the crank wasnt locked....or both moved....it's the pressure from the valve springs which force the cams to turn along with tension from the chain tensioners.
also they could've moved backward.....you just don't know....
the tolerances are simply too tight and once the cams get out of time something hits.

Pull all the cams.....then do a leakdown test on each cylinder....
it's the only way you're going to know if you have bent valves, you may get lucky, but it'll depend on the force they hit.

[bell]

You made a major mistake which has already been stated, and it sounds like you're learning from it......don't make it worse.
you can easily pull the cams with the engine in the car, once the cams are out there is no chance of further interference damage since all valves will be closed ......

[Driver Ed]

I suppose one could characterize my "major mistake" as following a written procedure without fully understanding the ramifications of steps that were missing. OK, but moving forward, I want to understand in detail both what went wrong and to learn enough to evaluate further advice. Why would my proposed plan make things worse, exactly? Do you really think that I could have bent a valve by simply moving the crankshaft with a wrench? What exactly is the potential risk of rotating the engine backwards?

I do hope I don't seem belligerent -- it's just that I've recently been led astray by following "expert advice" and want to more fully understand what I'm being told so that perhaps I'll not only better understand the job ahead, but be able to avoid future potential pitfalls. I can only think that more specificity will help the next person who might come across this as well and maybe help them avoid the problems I've encountered. Thanks for any explanations.

[ischmitz]

Wow, I am following this thread very closely because I might at some point also go down this path. While I have timed 911 and 964 engines from scratch I never worked on the 996 yet.

Let me see if I have this straight:

The Pelican procedure suggests jamming the large IMS sprocket with three set screws through the case threads. I guess this is questionable as you either go too hard (stripping the threads in the case) or too light (not enough friction to stop the sprocket from moving laterally or rotationally given its surface where the set screws touch is slick with oil). The cams are loaded from some valves being pushed open. So the cam train acts on the chain (push or pull depending on degree to TDC1). The hope is that the IMS sprocket doesn't move and that the chains don't skip on any of the sprockets once the chain tensioners are removed. Hmmm...

The LM procedure has you move engine to TDC and lock the flywheel with a pin and then has you lock cam shafts in place with special cam holders. I can see where that eliminates any push or pull on the chains. I can see the downside is you need special tools (cam holders). Do you also need to remove valve covers?

Are these the only differences between the two procedures?

If so I guess the two variance in the Pelican procedure that "decide" about success or failure are:

- the torque on the three set screws; not enough and the shaft gets pulled off center, too much and there goes your case
- the degree from TDC1 you end up with when all three openings in the case show a solid metal surface of the IMS sprocket? lucky, no skip or else.....

Comments from the experts?

[JFP in PA]

Originally Posted by Driver Ed

What exactly is the potential risk of rotating the engine backwards?
.

Rotate the engine counter clockwise and you will run the risk of bending every valve; the engine was never designed to rotate in that direction and will not tolerate it.