IMS Install help! IMS bearing not centered

[Jake Raby]

There are a few things I don't understand here:

1) What is the nature of the load being put on the IMS? Is it bad for any engine component to apply a force opposite to this force?

Whats holding the IMS sideways in the bore is the timing chain for bank 1. That chain has load because at least one pair of cam lobes on that bank are opening valves. If you force the IMS sideways, you are stretching a chain thats already known to stretch and break. I have the only matter linked chains in the world, but they are far from cheap, if you ever need one. Also, never force anything within an engine, if it doesn't want to budge, you must find whats necessary and relieve the tension. If not, you'll be sorry.

2) Why is it important that the bearing is centered when rotating back to TDC?

Because rotating the engine ANY from the point you are at now will make the cam timing even worse, and you can crash valves into pistons. You can't get the flange back on to support the IMS, because its no longer centered in the bore, so rotating an unsupported IMS is a recipe for bigger disaster.

3) In my first post I proposed using the removal tool to center the bearing by overcoming the force from the cams. The large cylinder part of the removal tool could be used to keep the bearing centered while moving the engine back to TDC. What are the issues with this approach?

I invented and developed that tool, this was never its intended purpose. That said, you do not know how far out the cams are at the present, and you won't know if things will crash until you move the engine. Not saying this won't work, but I am saying that its not a smart approach.

Can you help me understand what exactly has gone wrong that requires retiming from scratch? Have I likely already let the chains slip (even with my 5-chain engine)?

The entire valve drive system has shifted when the flange was removed without the engine being at TDC and having the CAMS locked. Something had to move when the flange was removed, and its likely retarding bank 1. This means that the exhaust valves on that bank can crash into the pistons fairly easily, and you don't want to risk that.

Also, to "re-time from scratch," is it necessary to drop out the engine and take it apart?

No, it can be done in the chassis, engine assembled. Pull both cam covers, and have fun.

Now, do you guys see why we only sell our IMSR products through distributors supplying them to professionals? This sort of thing should be avoided at all costs, and this is not a job for the faint of heart. The learning curve is 90 degrees, and using a procedure that looks good on paper, is a lot different than one that was developed in the real world from trial and error.

I've made lots of errors, but thats what happens when you blaze the trail that leads to the super highway that everyone else decides to travel.

[gonzojive]

Originally Posted by Jake Raby

Whats holding the IMS sideways in the bore is the timing chain for bank 1. That chain has load because at least one pair of cam lobes on that bank are opening valves. If you force the IMS sideways, you are stretching a chain thats already known to stretch and break. I have the only matter linked chains in the world, but they are far from cheap, if you ever need one. Also, never force anything within an engine, if it doesn't want to budge, you must find whats necessary and relieve the tension. If not, you'll be sorry.


Because rotating the engine ANY from the point you are at now will make the cam timing even worse, and you can crash valves into pistons. You can't get the flange back on to support the IMS, because its no longer centered in the bore, so rotating an unsupported IMS is a recipe for bigger disaster.


I invented and developed that tool, this was never its intended purpose. That said, you do not know how far out the cams are at the present, and you won't know if things will crash until you move the engine. Not saying this won't work, but I am saying that its not a smart approach.


The entire valve drive system has shifted when the flange was removed without the engine being at TDC and having the CAMS locked. Something had to move when the flange was removed, and its likely retarding bank 1. This means that the exhaust valves on that bank can crash into the pistons fairly easily, and you don't want to risk that.

Thanks a lot for the explanations. I don't have a very mechanical background so I hope you'll excuse my perplexity.

In terms of forces acting on engine components, I'm not clear on why forcing the bearing back to center with the pull-out tool differs from the typical operation of the flange. Why would the forces from moving the bearing back to center stress the chain more than the usual?

I'm also pretty fuzzy on the shift you describe above when the flange was removed. How exactly would the timing get thrown off? During this shift, are you suggesting a sprocket has skipped a link in one of the camshaft-IMS chains? I'm not sure how the timing could be off otherwise.

Originally Posted by Jake Raby

No, it can be done in the chassis, engine assembled. Pull both cam covers, and have fun.

What steps are you recommending to re-time the camshafts, and where would replacing the IMS bearing fit into that procedure?

Before removing the cam covers, the Pelican Parts article on setting the camshaft timing says to put the engine at TDC and install the camshaft timing tool. This makes sense because the shaft is normally held in place by bearings built into the cover. I'm not currently at TDC, and you don't recommend rotating the crankshaft while the IMS isn't support. The timing tool only fits onto the camshaft heads at TDC, so I'm not sure how to proceed with safely removing either camshaft cover.

[Jake Raby]

Thanks a lot for the explanations. I don't have a very mechanical background so I hope you'll excuse my perplexity.

Ok.

In terms of forces acting on engine components, I'm not clear on why forcing the bearing back to center with the pull-out tool differs from the typical operation of the flange.

Because during disassembly, that occurred at the improper crankshaft position that have shifted the shaft within the engine, in a direction favoring bank 1. There's no way to reduce this load, or eliminate it without disassembling the exhaust cam sprocket on bank 1.

Why would the forces from moving the bearing back to center stress the chain more than the usual?

Because the chain is not normally in this position. With mechanical things, if you force them, you will break them, or fracture them and they will break later.

I'm also pretty fuzzy on the shift you describe above when the flange was removed. How exactly would the timing get thrown off? During this shift, are you suggesting a sprocket has skipped a link in one of the camshaft-IMS chains? I'm not sure how the timing could be off otherwise.

Any of the above could have happened, or whats more likely is one of the cams that was on the ramp of a lobe, being tensioned by at least one pair of valve springs twisted when the flange war removed. This is what changed the camshaft position, and then shifted the IMS assembly inside the engine.

Before removing the cam covers, the Pelican Parts article on setting the camshaft timing says to put the engine at TDC and install the camshaft timing tool. This makes sense because the shaft is normally held in place by bearings built into the cover.

Yes, but now you can't do that, since the cams have jumped from the relaxed position.

I'm not currently at TDC, and you don't recommend rotating the crankshaft while the IMS isn't support. The timing tool only fits onto the camshaft heads at TDC, so I'm not sure how to proceed with safely removing either camshaft cover.

You can't follow any procedure online or otherwise, because your scenario is not normal now that the cam timing has moved. No two of these scenarios are the same, so there's no accurate directive.

I'd highly recommend that you seek an M96 engine specialist, your questions and understanding prove to me that you'll be in over your head, or perhaps are already. Moving forward may only cost you more time and money if you decide to tackle this yourself. You could probably do it, but it won't be easy, and the learning curve is 90 degrees.

Someone thats proficient with these engines could re- time the engine in less then 4 hours, more than likely.

[gonzojive]

Originally Posted by gonzojive

What steps are you recommending to re-time the camshafts, and where would replacing the IMS bearing fit into that procedure?

Before removing the cam covers, the Pelican Parts article on setting the camshaft timing says to put the engine at TDC and install the camshaft timing tool. This makes sense because the shaft is normally held in place by bearings built into the cover. I'm not currently at TDC, and you don't recommend rotating the crankshaft while the IMS isn't support. The timing tool only fits onto the camshaft heads at TDC, so I'm not sure how to proceed with safely removing either camshaft cover.

Originally Posted by Jake Raby

Yes, but now you can't do that, since the cams have jumped from the relaxed position.

Right. What kind of risk is there in removing the camshaft cover while the camshafts are not secured with a timing tool + the engine is not at TDC? Presumably they'll pop out of their bore from the pressure of the valve springs. Will this damage the bearings on the ends of the camshaft (green arrow below)?


Here's my plan for getting out of dodge:
1) get the camshaft cover off without breaking anything
2) remove the camshafts, and in the process detach the end sprocket, relieving tension on the chain pulling on the IMS
3) uninstall the old IMS bearing, install the new one, and put the bearing cover on
4) rotate the crank to TDC while camshafts are still out. Install the camshafts once back at TDC
5) check the timing of both sides

It sounds like I might also want to check for bent valves?