Engine/Gearbox rebuild 84 3.2 Carrera

[bdonally]

Finally got underway on pulling apart the engine and gearbox from my 84 Carrera. Unfortunately it will tie up the car for most of the summer, so no DE in my plans for this season. I decided it had to come apart after finding metal in the oil filter - the subject of a post last fall. Its either bearings of the intermediate shaft gear - I am betting on the latter. The car had relatively low mileage - just over 160,000 km. However, it has had a lot of track time. I had the engine apart a few years ago to replace broken compression rings in cylinders 1,2 & 3, likely caused by an overly aggressive chip, 91 octane fuel, and a very hot weekend at Road America. I didn't split the case because there was no evidence that anything was in need of attention. The car has run well in the 35,000 km or so since the first rebuild. Well, actually, it was the second rebuiild. A previous owner was going to race the car and has a precautionary rebuild, installing ARP bolts and studs, longer valve springs with Ti retainers, new valve guides, etc. It was also converted to an Autothority MAF, and the intakes were cut open and enlarged and polished. After my broken ring rebuild, I installed a Steve Wong chips, and had it modified a couple of times to get rid of a bit of leaning out at mid speeds. During that testing, I did couple of dyno sessions to get the A/F ratio; saw about 215 HP at the rear wheels. Anyway, got the engine and gearbox out today. After looking at the various removal methods - the fixture on a jack method, the motorcycle lift method, etc. I decided to use the Kubota method. Worked great. I won't bother posting picture of the routine teardown, but once I figure out the source of the metal I'll be sure to share. I'm sure I will need some input once I get the case split. And when I open the gearbox.

[DRACO A5OG]

Break a Leg Brother!

[911 Rod]

Looks like fun!

[bdonally]

Hey Rod, where did you get the machine work done when you did your 3.4 build?
Looks like I need some head work - send me a PM if you want.

Bob

[bdonally]

Got the engine dismantled without too much drama.
From the looks of the intermediate shaft gear, I am pretty sure it is the source of the shiny bits in the oil filter.


The gear tooth edges are burred, and the contact surfaces are pitted.
I wonder if there is a root cause for this.
The IM bearings are worn but not a crazy amount:

The crank bearings are in good shape except for the thrust bearing. The crank has 0.008" of end play, which is the wear limit.
The mating gear on the crank looks good.
Possibly the crank end float is beating up on the IM gear?

Its easy enough to replace the gear and bearings. Fortunately the existing gear is a code 0, which appears to be the only one available.

Any feedback about anything else that might cause this failure is appreciated

[bdonally]

The crank looks great and measures at the center of the book tolerances.
The rod and main bearings are in nice condition.
Bearing clearances measured by micrometer and by plastigauge are as follows:
Mains: 0.05/0.06mm
Rods: 0.05mm
Standard practice would be to replace the bearings, but I hear quite a few issues with aftermarket bearings and I wonder about the chances of winding up with worse clearances.
Here are a couple of photos of the bearings.
Can anyone identify the symbol?

[Neil Harvey]

Originally Posted by bdonally

The crank looks great and measures at the center of the book tolerances.
The rod and main bearings are in nice condition.
Bearing clearances measured by micrometer and by plastigauge are as follows:
Mains: 0.05/0.06mm
Rods: 0.05mm
Standard practice would be to replace the bearings, but I hear quite a few issues with aftermarket bearings and I wonder about the chances of winding up with worse clearances.
Here are a couple of photos of the bearings.
Can anyone identify the symbol?

No sir , those main shells are no good. As long as the photo is not deceptive, the bearing has a lot of embedded junk. In one of the photos it shows a wear pattern. This should be mirrored on the other side of the shell if the main housing was straight.

[Tippy]

Looks like a detonation pattern on that main bearing, no?

[bdonally]

Originally Posted by Tippy

Looks like a detonation pattern on that main bearing, no?

What about the pattern leads you to that conclusion?
It is entirely possible - My first rebuild was to replace broken compression rings.
The breakage was attributed to a lean condition at middle engine speed that likely caused detonation, leading to the broken rings.
I didn't split the case at that time.

New bearings it is.
Question is whether the available Glyco are acceptable or to spend the serious money on the Porsche parts?

[KTL]

I'd go with the OEM Porsche boxed bearings. There's a definite quality control difference between Porsche boxed bearings and the aftermarket Glyco

This is a good thread that covered a lot of people's observations and comments on bearing quality. I think ultimately the bad batch of 3.2/3.3/3.6 rod bearings was identified as aftermarket Glyco made in South Africa? I could be mistaken about that, as i'm going by memory here.

Rod Bearing Controversy

Even though I mention the rod bearings being the problem, we have also encountered main bearings that don't measure up well. I myself had some aftermarket Glyco mains and wasn't pleased with how they measured up when placed in the case, bolted together and checked with a bore gauge. The quality has slipped a lot in the aftermarket bearings and it's a real roll of the dice. You're better off just sucking it up and spending the money to get the known good bearings.

[Tippy]

Originally Posted by bdonally

What about the pattern leads you to that conclusion?
It is entirely possible - My first rebuild was to replace broken compression rings.
The breakage was attributed to a lean condition at middle engine speed that likely caused detonation, leading to the broken rings.
I didn't split the case at that time.

New bearings it is.
Question is whether the available Glyco are acceptable or to spend the serious money on the Porsche parts?

Because crank journals are near round as you can get, so a pattern showing in the bearing tells me it was being hammered by detonation.

I could be wrong, but that pattern is very suspect

[bdonally]

Cleaned up the crank and measured everything 3 or 4 times.
Mains are consistently 59.985, and rods are consistently 54.975.
By consistent, I mean within +/- 0.002mm.
That puts the mains near the center of spec, and the rods near the low end.

There is nothing I can feel with a fingernail.
The few specs in the photos are some dust or lint.
To my eye, the surfaces look reusable, but I'd appreciate input.
I plan on getting coated bearings so perhaps that will keep the rod clearance in an acceptable range.

[bdonally]

I am bit confused with the wrist pin bushings.
As shown in the photos, the surface appears worn, partly bronze color and partly grey.
I have searched and haven't found any photos to compare.
The bushings measure within spec, 23.010 mm across the rod and 23.020 along it.
This results in 0.02mm clearance to the pins ( which are all 23.00), at the low end of the Porsche spec.
Seems to me if I have new bushing installed, the resulting clearance will be the same as I have now.
What should these bushings look like? Is the mottled appearance wear or a result of honing to size?
Any thoughts will be appreciated

[Neil Harvey]

The wear patter on the rod bearing is somewhat typical of a bearing shell that has little eccentricity. The bearings used in these engines have none or little form memory. However, it should be mirrored on the opposite shell, so check. Otherwise it can be indicative of several other issues.

Check the BE size as this type of pattern is often from excessive bearing crush. It usually shows further down towards the mid point, but it is worth checking. It would also be a good idea to check that the rod is not bent. Bearings show up the problems within the engine rotating assy, so don't leave anything to chance. Check everything.


The pin bushings look typical of pin bushings in these engines. If the clearance measured is 0.020mm (0.0008") this is on the low or tight side. Nothing wrong here, but expect to see some wear as you have less clearance for an oil film. It is only the oil film that keeps the pin off the bushing when running. Just make sure there is not flaking and the pin bushing is round. You could have them honed which will give a good finish and open up the clearance. By adding a few tenths, here will not hurt. Some engines that show hard wearing can have as much as 0.002" clearance.

[bdonally]

So the mottled appearance is normal? Is it the bronze coating being removed exposing the grey material or vice versa.?
Will honing expose more of the grey or more of the bronze?
I assume that the grey material is not the steel packing.
These small end bushings have been in the engine about 60000 miles.

Thanks for the comments about the mains and big end bearings.
I am going to replace them but it seems weird that the clearances check out with the 60000 mile bearings.

[Neil Harvey]

Bearings should last a long time if there is nothing wrong. The shells are tin coated and a very hard surface. They are made to last. As long s you have an oil film holding the crank off the bearing, there should be no wear. Its only on start up that the crank may touch the bearing. Hopefully if the clearances are no big, oil is retained when the engine stops and holds the crank off the bearing on start up.



Wear patterns on the pin bushings is typically from the pin being pounded against the bushing when the piston is trying to jerk itself out through the top of the cylinder. All very typical. Signs of wear on the cap side of the bushing is from the pin being pushed against the bushing under compression. 0.02mm clearance is tight, ok but it has to be expected that the oil film is thinner and some pin to bushing contact will happen. 60K miles and this is the only war, you are in good shape.