Seal removal on Dual Row IMSB

[JFP in PA]

Originally Posted by Boxstard

Does this poorly designed factory bolt take any part of the bearing failure?

Yes. Sometimes when the bolt fails, the IMS bearing can move off axis, timing chain(s) jump, and you get piston to valve contact related failure. The IMS bearing itself is still relatively OK except for the bolt failure. Other times, the bearing itself is tearing up, possibly causing the bolt failure; so it can go either way.

[Boxstard]

Originally Posted by JFP in PA

Yes. Sometimes when the bolt fails, the IMS bearing can move off axis, timing chain(s) jump, and you get piston to valve contact related failure. The IMS bearing itself is still relatively OK except for the bolt failure. Other times, the bearing itself is tearing up, possibly causing the bolt failure; so it can go either way.

Interesting... sorry one more question, this tapered bolt is common for factory dual- and single-row bearings? If so, obviously bearing design itself accounts for the failure more I guess.

[JFP in PA]

Originally Posted by Boxstard

Interesting... sorry one more question, this tapered bolt is common for factory dual- and single-row bearings? If so, obviously bearing design itself accounts for the failure more I guess.

Both the OEM single and dual rows use similar center bolts, but they are not exactly the same due to the bearing depth differences.

[Troutman]

Here's a photo of the stud.



You can see that the O-ring groove is the weak spot, the threaded part at the end is there to put that nut on which stops the stud coming loose from the bearing and falling into the IMS, causing all sorts of problems of which a match and a gallon of fuel word sort out nicely.

Been drilling out broken manifold studs today and re-tapping them. Dreadful job.

[Troutman]

With the O ring removed it's about 8mm in the groove, 10mm either side.

[Troutman]

Thought I would post an update on my wee project.
Everything is back in, I bought some new exhaust clamps as the old ones were bad.
Very straightforward apart from a persistent leak from the new thermostat, in the end i smeared some sealant on both sides of the new gasket and that fixed it.

The main difference I noticed was how light the new clutch is, I thought i hadn't bled it correctly but it's all good , just very light to press.
Engine goes really well, revs up so easily. Since changing the new front engine mount the whole car feels much more planted, one of the easiest things to do with the best gains is to change a worn out front mount.
Really pleased and now considering keeping it (i've had it 7yrs) as I wanted a 997 but after going for a quick blast in this yesterday I reckon I'll hold on to it, there is no way a 997 is £20k more fun than this.
Just started on the front brakes, I was getting some shudder at high speeds in Germany last year, so I'm going to replace discs and pads on the front. Then it should be good for a long road trip.