can't rotate engine after IMS bearing change

[JFP in PA]

Originally Posted by 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?

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.

[Joe Ricard]

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.

[bell]

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...

[Driver Ed]

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.

[aftCG]

Deleted, sorry

[Scnell Gelb]

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?

[JFP in PA]

Originally Posted by Scnell Gelb

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?

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................

[Driver Ed]

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?

[Scnell Gelb]

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?

[JFP in PA]

Originally Posted by Driver Ed

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?

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.

[PrimeMvr]

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!

[Driver Ed]

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.