can't rotate engine after IMS bearing change

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!

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.

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?

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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.

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.

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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.

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.

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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.

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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.

Not time properly. Common problem. RObert

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

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.

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.

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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.

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.

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.

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 ......

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.

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?

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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.

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The unfortunate answer to your question is to totally ignore the Pelican procedure and follow the LN directions to the letter (no short cuts or skipped steps). LN and Jake Raby developed this method and to my knowledge is the only one that will work first time, every time. We have used the LN procedure for years without any problems.

So glad I am picking up my new car that has Blake's Finger prints on it. Having done a Mini R56 and an E36 M3 cylinder head I can tell you the cam holder tools are ABSOLUTELY required.

The reason turning backwards is bad is the tensioners are on the "unloaded" side of the chain.....so when the crank turns backward it compresses the tensioner before the cam moves....making the cam out of time...basically.... Any time you remove anything related to the timing chains/tensioners you must lock the crank and the respected bank of cams. I personally have installed roughly 40+ LN bearings on boxsters and 996s......you must follow the procedure.... Pulling the cams isn't a big deal, as long as you have the tools to retime... and it's easier to do in a 996 than a boxster with the engine installed...

Thanks, that's pretty much what I figured. It makes sense to me that turning the engine backwards runs a risk because of the timing chain (or timing belt on other engines), but since I already know my timing is already wrong, it seems less of a risk! As for following the procedure, I faithfully followed the one I had.. however.... Since this is my first one, rather than my 40th, I figured I'd learn something. I would rather it had not been the hard way! I'll do a couple of measurements this weekend, but I think I'm going to remove the engine to finish the job. It's just too tight to do much in there with the engine in place.

Deleted, sorry

I have read this sorry IMS tale several times by different authors/cars/different Forums. The cause cited is always that the Pelican Parts Instructions are both incorrect and damaging . These experts all agree these instructions are wrong and may cause expensive damage to your engine.That seems like an issue that the hosts of this Forum could easily correct. I have read many kind helpful posts by JFP who is clearly exasperated by the Pelican Parts Instruction problem. He is one of the top M96 engine guys around. Yet Pelican ignores his advice. Why? It makes no sense at all. I am not knocking Pelican , I have lots of their parts on my car,have Wayne's book but I am always leery of following any of their Instructions - not because they made one mistake(I make plenty more!) - but that this error has been up there for a very long time uncorrected. Worse, Pelican also sell the LN IMS with the correct Instructions- so they must know? What are we missing?

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Believe it or not, I think I can answer your question: Back when there was only an IMS problem and no solution, just about everyone was looking for a fix. After considerable experimentation, Jake and Charles developed the now familiar procedure that uses special tools to hold everything while replacing a bearing that even Porsche said cannot be changed with the engine assembled, now a very successful and widely accepted product market by LN and used all over the world without issue. Pelican attempted to develop and introduce a low cost alternative, using a less expensive OEM style sealed single row bearing and a procedure that did not use the special tooling, but based upon holding the IMS shaft with set screws. While this methodology can actually work under certain circumstances, it completely lacks the "bullet proof" nature of the LN system, and can lead to all sorts of unintended outcomes. People drop the set screws inside the engines, they over tighten them and end up moving the chain gear on the IMS shaft, we have even seen engine cases stripped or cracked from the set screws. Unfortunately, the most common failure is for the cam allocation to jump on three chain engines. This is not to say that there have not been "human engineering" issues with the LN procedure's; it is not for lack of a good reasons that both LN and Jake have totally moved away from technical support for this procedure. As with any complicated process, there is one way to do it right, and many ways to totally screw it up, and lots of people have done exactly that, usually by trying short cuts or trying to cheap out on the process. I recently responded to a post on another site where an individual with a OEM IMS had the center bolt on the IMS snap off and fall to the bottom of the bell housing. He was annoyed because he could not get the IMS cover flange off after removing the bolts and could not understand why. After he posted photos of the problem, I noticed that one of the chain tensioners was still in place, and ask if he had locked the engine at TDC, locked down the cams, and removed the tensioners prior to trying to remove the flange cover; his answer was no, he was going to do that when he got around to ordering the tools. While he still had a broken center bolt to deal with, he never once realized he was one move away from a complete disaster, the chain tensioners were exerting enough load to prevent removal of the flange cover, which if he had gotten it off would have resulted in the IMS shaft jumping to one side and the cam timing jumping as the chain loads released. He would then have had a bad IMS in an engine that was not at TDC with cam timing problems and could not be rotated without doing even more damage. Yes, I am a vocal critic of the Pelican procedures because of the number of otherwise good engines that were either endangered or worse by using it, and the people who attempted to use it. The procedure is a really bad idea, which unfortunately can actually work, but at very high risk. But by far, the biggest problem in IMS refits that go bad is the actions of the people that try to do them. To be completely fair, I have seen these go bad even at the hands of professionals, including dealer techs using the LN tooling and procedure's. There are many ways to do this wrong, and only one way to do it correctly. To anyone that asks, I suggest getting the latest version of the LN procedure's online (a PDF file), read it, re read it, and then read it again; so that you understand what is involved. If you do not understand these instructions, or do not want to purchase the tooling, don't do the retrofit yourself; take it to someone that does understand it and has the tools. Jake once commented that he has greater confidence with someone doing a retrofit for the first time than someone who has done several. and has become more casual about it. That is a very wise observation, as the first timer is going to basically be scared ****less and take his (or her) time to check and double check each step, making sure that they understand the method and have everything they need before starting. That combination of fear and caution typically leads to a successful refit. You cannot be careless with a $15K engine that your next move can reduce to being a boat anchor. As for the set screw procedure, the world would be a better place without it; but unfortunately that boat has already sailed. If asked, I would tell people to ignore it and follow the LN procedures, but then this becomes the moment that the "human engineering" factors step in................

As it happens, I'm midway through removing the engine, having decided to bite the bullet and get it done with confidence. At the moment, I'm stuck on the step of removing the rear bolt for the air conditioning compressor. I've tried to see it with a mirror but have had no luck so far. Any hints or good photos of that?

JFP in PA I think you are very generous to keep bailing Pelican out by advising people who get in trouble with the IMS replacement. Perhaps your last post could be a "Sticky" here so you don't have to keep re-writing the same saga. Or, Pelican should pay you each time you help them out !:-). Thank you for your generosity in sharing your knowledge and experience.Pity nobody at Pelican reads it?

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Yes, undo the compressor and lift it up or move it to the side, which is easily said but not so easy to actually do. Pelican had a pretty good write up on this: Removing the air conditioning compressor is one of the more difficult tasks. Like on earlier Porsches, you leave the compressor in the car when removing the engine. This allows you to avoid emptying the system of A/C fluid, a task that requires specialized equipment. A- The compressor is held on by two bolts in the front, and one hidden in the rear (underneath the manifold). The orange arrow shows the right side compressor bolt. You can access and remove this bolt from the passenger compartment. B- The other bolt can be accessed by using a swivel socket (green arrow) through a gap in-between the intake manifold (inset photo C). D- Take some plastic wrap and lay it down in the back of your passenger compartment, and pull the compressor out of its mounting place on top of the engine. As the engine is lowered, you need to then route the hoses out of their channels and tuck them into the passenger compartment.

Kudos for the DIY spirit. There's no substitute for the right tools, especially when doing a job that requires precision. When I rebuilt my first 911, I invested almost as much money in tools as parts. I've kicked myself every time I tried a "workaround" that turned into a "hack job" that took five times as long as it should have. Cam timing is simple, but critical. Take your time, check, double-check, triple-check and before you button it up, check again. Good luck!

I finally had some time in the garage yesterday, and got the engine *almost* removed. One thing that puzzled me for a while is that my car is equipped with a fuel cooler, so I had to disconnect two fuel lines that run through a "can" attached to the top of the A/C compressor. Neither my manuals nor online photos mentioned those, and I didn't want to crack open the refrigerant lines by mistake. The second tricky part (that I have not yet done) is disconnecting the power steering lines. Since they appear to be brass fittings, I want to be careful not to mangle them, so I'm going to purchase a second set of crowfoot line wrenches today and try to get those disconnected this evening.