about ready to start the IMS project

[JFP in PA]

Originally Posted by Jamesp

Locking the cams with the cam locking tool is not necessary for an IMSB replacement.

You have got to be kidding...............

[Jamesp]

Originally Posted by JFP in PA

You have got to be kidding...............

And you work on these cars? Not mine if you don't even know that at TDC the lifters are sitting on the Cam circles and it is physically impossible for the valve springs to move the cams. I suppose you use two cam locking tools and the crankshaft zero lock along with bolting the flywheel end of the crankshaft to the block before changing an IMS?

[JFP in PA]

Originally Posted by Jamesp

And you work on these cars? Not mine if you don't even know that at TDC the lifters are sitting on the Cam circles and it is physically impossible for the valve springs to move the cams. I suppose you use two cam locking tools and the crankshaft zero lock along with bolting the flywheel end of the crankshaft to the block before changing an IMS?

Yes, I do work on these cars, and have been called upon to reset the cam timing on more than one three chain motor that jumped time when the owner removed the tensioners without locking the cams while the engine was at TDC. You should never pull the tensioners on the three chain motors unless the engine is locked at TDC, and the cam lock is in place. To do so is inviting a disaster.

[Jamesp]

Originally Posted by JFP in PA

Yes, I do work on these cars, and have been called upon to reset the cam timing on more than one three chain motor that jumped time when the owner removed the tensioners without locking the cams while the engine was at TDC. You should never pull the tensioners on the three chain motors unless the engine is locked at TDC, and the cam lock is in place. To do so is inviting a disaster.

Well then you should be using 2 cam locks, not a cam lock. It would be interesting to understand what would you think could drive the cams to move independent of the chains as there is no driving force to rotate them at TDC to lose timing. I've had my 3 chain apart and set the timing without the cams locked, all that was needed was TDC as there is nothing to cause the cams to rotate independent of the chains. Tearing the engine down for the first time after an IMSB failure, I made the choice not to be at TDC because I thought I might have valve to piston interference if I rotated it. A poor choice as I can confirm through personal experience the valve springs will rotate the cam independent of the chain if not at TDC, and they will not, and indeed can not if the engine is at TDC. I prefer to complete jobs without unnecessary parts (cam plugs) and time (messing with the cam locking tool).

[JFP in PA]

Originally Posted by Jamesp

Well then you should be using 2 cam locks, not a cam lock. It would be interesting to understand what would you think could drive the cams to move independent of the chains as there is no driving force to rotate them at TDC to lose timing. I've had my 3 chain apart and set the timing without the cams locked, all that was needed was TDC as there is nothing to cause the cams to rotate independent of the chains. Tearing the engine down for the first time after an IMSB failure, I made the choice not to be at TDC because I thought I might have valve to piston interference if I rotated it. A poor choice as I can confirm through personal experience the valve springs will rotate the cam independent of the chain if not at TDC, and they will not, and indeed can not if the engine is at TDC. I prefer to complete jobs without unnecessary parts (cam plugs) and time (messing with the cam locking tool).

As I have always been brought into the issue after it has already happened, I can only surmise what is causing it. That said, I would put my money on the removal of the tensioners, and perhaps the order in which that is done. Removing the tensioners has a similar effect as valve spring tension would, only to a lesser degree. When one tensioner is removed, the load on the chains is asymmetric due to the released tension. I have discussed this problem with other shop owners that have encountered it, and that seems to be the general consensus of what happens.

You also have to ask yourself why Jake even developed and LN produced three chain cam locks at all if they are not required during an IMS retrofit.

[Jamesp]

Originally Posted by JFP in PA

As I have always been brought into the issue after it has already happened, I can only surmise what is causing it. That said, I would put my money on the removal of the tensioners, and perhaps the order in which that is done. Removing the tensioners has a similar effect as valve spring tension would, only to a lesser degree. When one tensioner is removed, the load on the chains is asymmetric due to the released tension. I have discussed this problem with other shop owners that have encountered it, and that seems to be the general consensus of what happens.

You also have to ask yourself why Jake even developed and LN produced three chain cam locks at all if they are not required during an IMS retrofit.

My experience has been that tensioners in or out, or going in or out, won't make the chains jump timing on the cam sprockets. I messed with the tensioners with the engine out on a stand, they do tend to rotate the cams a little but don't cause the chain to jump teeth on the cam sprocket. Not sure what the folks did who brought you their cars, but it would not surprise me if they fibbed a little to save face.

The Cam locks are used in disassembly, assembly and final adjustment. The factory tools are pretty basic. Why Jake developed his is a good question, they may be superior in some manner to the factory tools.

[JFP in PA]

Originally Posted by Jamesp

My experience has been that tensioners in or out, or going in or out, won't make the chains jump timing on the cam sprockets. I messed with the tensioners with the engine out on a stand, they do tend to rotate the cams a little but don't cause the chain to jump teeth on the cam sprocket. Not sure what the folks did who brought you their cars, but it would not surprise me if they fibbed a little to save face.

The Cam locks are used in disassembly, assembly and final adjustment. The factory tools are pretty basic. Why Jake developed his is a good question, they may be superior in some manner to the factory tools.

Well, I can tell you the others, including some shops that have gotten themselves into trouble not using them, would not agree with your assessment. After you hear the same scenario for the third or fourth time, particularly from someone you know fairly well, you have to consider it as a potential fact. We have never encountered this issue in my shop, but my guys always use the cam locks, regardless of how many chains the engine carries.

[flaps10]

My amateur observation is that you can only be at zero valve spring load on one cylinder head at a time. If you've assembled the M96 you may recall two TDC locations. You install one bank, rotate the engine 360 degrees then install the chain for the other bank.

While you're on that second bank the valves for that head are unloaded, but at that moment there IS spring pressure on the first bank. In short, there is no position of zero valve spring pressure. A five chain motor, set correctly, will lock the head with valve spring pressure, allowing removal of all three chain tensioners