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Location: wisconsin
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IMS shaft won't spin...case misaligned? Input appreciated...

So, rebuild is slowly moving along...

Rods resized, clearances measured, .002-.0024

Main bearings which looked like new recoated, clearances .0021 to .0026

Put the case together for a trial fit, nose bearing in, IMS shaft in (no oil pump). Figured those 2 thing help align the case. Did this to accurately measure clearances for the mains as I previously tried without the nose bearing and readings were way off...

After measuring the clearances (for the 3rd time), figured I would try to spin the intermediate shaft. It did spin but not as smoothly as I would like, but would go. This is with the old worn IMS bearing. Put the case back together and retorqued with the new bearing, absolutely wouldn't spin.

When you look at the case, with the bearings out, it looks like one side of the case protrudes about a couple thousands proud of the other side. So the thrust bearing isn't perfectly aligned longitudinally. Concentrically, its fine. It looks like the thrust bearing on the IMS shaft is whats keeping it from spinning.

Took a close look at the old IMS bearings, and the thrust faces are totally down to copper, the bearing surface only shows typical wear. They are the original bearings, date code 1987, so this is how porsche put this baby together...

Am I missing something obvious here? Is there something that aligns the case on the pulley side OTHER than this one thrust bearing? Clearly the nose bearing aligns it concentrically, but what about front to back? The flywheel side is pinned and aligns perfectly. I would think this would by design align the other side...

In the pic below (sorry, slightly fuzzy) I can catch my nail on the case going in one direction, but not the other. Again, looks like this side of the case is slightly proud?

Anyone else seen this? Scratching my head on how to correct? Clearly this wasn't an issue for 60k miles in the cars life, and this spun freely before disassembly. Also, aluminum case, not magnesium...


Last edited by bpu699; 11-05-2017 at 04:31 PM..
Old 11-05-2017, 04:19 PM
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What aligns the case when you bolt it together are the following:

- Case perimeter bolts
- #8 nose bearing
- Shuffle pin collars that are on the studs that protrude into the oil cooler interface

Absent these three things, the case halves will not bolt together correctly. Many people try bolting case halves together that don't have the M8 perimeter bolts or the collars on the studs by the oil cooler. It won't work.

There is no reason that your layshaft won't spin on a motor that was running before hand except for some weird warping or damage.

is this a mag case?
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Current: 1963 356B T6, 1970 914-6 conversion 2.7, 1973 T, 1975 930 Turbo Targa, 1978 928 Race car, 6.57L, 1983 911SC, 2002 911 Targa, 2007 997TT, 2009 997TT, 2004 40th Anniversary Carrera

Only reproduction 3.6 cases on the planet, coming soon www.taorminaracingdesigns.com
Old 11-05-2017, 04:59 PM
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Appreciate your help...

The two shuffle pins on the flywheel side are there. That side and the crank thrust bearing is perfectly flush...

I did not put in the perimeter bolts, not sure if that effects longitudinal alignment? Could it be that simple??? Never thought that would have an effect.

Nose bearing is in.... Crank was not in.

If I have time tomorrow plan to put the original bearings for the ims back in, and will measure new and old bearing thickness. The ims bearings are new Porsche/glyco...

I figure it's something silly I am not understanding here...

The thrust bearing is a very tight tolerance fit with the ims shaft face. It spins easily when the ims bearing sits in either case half.

Plan to play with it more this week, more pics to come...

It's a 1988 930, aluminum case as far as I know. I believe mag cases predate 1988...?

Last edited by bpu699; 11-05-2017 at 06:33 PM..
Old 11-05-2017, 06:28 PM
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Put the perimeter case bolts in.....they need to be there in order to align. They do not need to be torqued, or even have nuts on them. Try that and report back.
__________________
Current: 1963 356B T6, 1970 914-6 conversion 2.7, 1973 T, 1975 930 Turbo Targa, 1978 928 Race car, 6.57L, 1983 911SC, 2002 911 Targa, 2007 997TT, 2009 997TT, 2004 40th Anniversary Carrera

Only reproduction 3.6 cases on the planet, coming soon www.taorminaracingdesigns.com
Old 11-05-2017, 09:10 PM
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Just an update, in case it helps someone down the road...

Popped in the crank, tightened all the bolts, including the perimeter ones, new IMS didn't want to spin... Crank spun fine and freely with out IMS installed.

Dug out the old bearings, they look different than the new ones I got from Pelican. New ones have square shoulders, old had rounded shoulders.

The old original bearings clearly were slightly misaligned from the factory. When you look at the thrust faces, the opposing 1/2 of the thrust face on each is down to copper, and the other side un touched. So looking at the face of a clock, half of it is untouched and half down to copper. So, this is how it was aligned by the factory . Worked for 60k miles with no issues from new.

Searched tons of threads on here and apparently having one side of the case protrude a bit is common. Threads on here about difficulty sealing, aligning cam sprockets, etc ,etc. So, others have had the same... Porsche pins the case for perfect alignment on the crank thrust bearing, which is perfectly aligned.

Popped in the old bearings and crank, IMS shaft spun easily and had .002-.003 or so of play in either case half. Put both case halves together and it takes up the laxity and will spin, but almost no free play.

In comparison the new one had .001 or basically no clearance but the IMS spun easily in each case half. Put the case halves together, and it wont spin.

My case half is .005 proud on one side. Not much, but enough to keep the new bearing from allowing the IMS to spin. So the old bearings worked properly as they wore down the opposing thrust face slightly. The new bearings were too tight.

I am not having great luck with the Glyco bearings...

Options as I saw it, were to pop in the bearing and let it wear unevenly as it did from new (Didn't want to do that and have the bearing potentially spin). Machine .005 off the case where the thrust bearing attaches (Didn't want to do that and mess with a case that worked fine for 60k miles). Or machine the new bearing.

Did fix the issue by popping the bearing in a lathe and machining .005 off the inner thrust wall of one bearing, allowing it to slide forward .005 and aligning perfectly with the other bearing. Now, they align perfectly and the IMS spins easily and perfectly. So, all thrust faces should wear evenly...

Love my new lathe .

Lessons learned:

1) The glyco IMS thrust bearing is not the same design as the original Porsche item... The old design bearing may have more clearance? Did find another thread where the poster couldn't get the glyco IMS bearing to work and had to buy the Porsche item.
Wonder if it was a similar issue?

2) These cases are not always perfectly aligned on the IMS side... Go figure. The original style bearing would likely fit, but would wear unevenly as the thrust faces would be off. As it worked that way for 60k miles, probably a nonissue though not optimal.

Most folks probably don't torque the case with just the IMS bearings and IMS shaft in it to see if its smooth, so may not recognize this if it occurs or notice high friction from the IMS thrust bearing unless its severe.

Also returned my Glyco rod bearings which ended up increasing clearance too much, and got the new Porsche ones which fit perfectly with the proper clearance... The old coated bearings measured great with clearance, but felt new Porsche was a better safer long term proposition...

If I ever do this again, just buying the Porsche supplied parts...

Last edited by bpu699; Yesterday at 02:05 PM..
Old Yesterday, 01:56 PM
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