964 Re Rebuild

[Alan Goettel]

An old time PCA Racer once commented that he knew he could probably rebuild his own engine, but he payed the big bucks because too many freinds had rebuilt their own motors, two or three times. It stuck in my mind.

I rebuilt my 3.6 two years ago, and the only problem that I had was a nasty oil leak from a backwards breather gasket. That backwards gasket thing left me wondering what else did I do wrong? My confidence got better as I roled up 7,000 miles. I even commited the mortal sin of declaring the job a success with some out of region DE friends. The track was just starting to dry up so I was out running 4 tenths looking for grip.

As I was coming off the track I noticed the idiot light was on and the pressure gauge was flatlined. It had been raining a couple of days, and there was the possibility that it was electrical. I had the car towed home to play it safe.

I drained the oil and found what appeared to be a rounded piece with internal splines. I pulled it apart earlier this week, and found that the IM Shaft / Pump coupler had failed on the pump end. I found another chunk on the bottom of the case. It looks like it broke pretty cleanly, and all peices are accounted for.

The pistons, rings, cylinders, and rods all look good. I haven't split the rods yet, but the main bearings are scuffed a little, but the crank mains looks no worse for the wear. The IM shaft bearings look good. The little bearings got nicked up but all bearings were sitting nice and snugly.

My original rebuild was at 93,500 miles. I replaced all of the bearings with OEM parts, and upgraded the rods bolts to ARP. All of the original components were up to spec, so I just added new OEM Rings, chains and chain rails. New wrist pin bushings were pressed in, and the rods bottoms were resized.

The oil pump spins freely by hand, and the IM shaft looks good. Unless there was some kind of imbalance/vibration it is hard to immagine what else could cause the failure. I'm happy with what I found. My work held up well. The worst wear that I saw was on a couple of 4-6 cam lobes, and scratches on some of the same cam tower journals.

What would you do next?

[BoxxerSix]

Clean and inspect/mic everything for wear. One cannot visually see wear on the terms of thousandths of an inch. New bearings, int shaft coupler, inspect/rebuild oil pump, etc would all be minimums on my list of things to replace regardless.


Would be nothing worse than to put it back together under the assumption all is ok by a visual standpoint only to have a rod or main be worn out of spec and cause a failure of larger proportions soon down the road, all for the sake of saving pennies on the dollar at this point since it's already apart.

[Alan Goettel]

That was my minimal plan also. This is way too time consuming to attempt any shortcuts. Second teardown was definately much quicker than my first. I'de prefer to avoid any thoughts of a three-peat.

Originally Posted by BoxxerSix

Clean and inspect/mic everything for wear. One cannot visually see wear on the terms of thousandths of an inch. New bearings, int shaft coupler, inspect/rebuild oil pump, etc would all be minimums on my list of things to replace regardless.


Would be nothing worse than to put it back together under the assumption all is ok by a visual standpoint only to have a rod or main be worn out of spec and cause a failure of larger proportions soon down the road, all for the sake of saving pennies on the dollar at this point since it's already apart.

[Flat6pac]

Most of the times I ve seen failure of the intermediate shaft it has been caused by the cams locking in the cam carrier.
Bruce

[Alan Goettel]

Originally Posted by Flat6pac

Most of the times I ve seen failure of the intermediate shaft it has been caused by the cams locking in the cam carrier.
Bruce

That would explain the wear on the 4-6 cam lobe, and cam carrier. I was guessing that is was just because they were higher and farther away, so they got starved first. Thanks for the suggestion, I was having a hard time seeing how they would be related.

I could understand how that would stress the gears and damage the shaft, but
The I/M Shaft didn't fail. The coupler with the oil pump shaft did.

Thanks,
Alan

[Flat6pac]

Maybe the pump had already failed. The other times I had seen the breakage was from the pump getting an 8mm nut out of the oil tank, directly into the gears and bang, massive damage.
Bruce

[BoxxerSix]

Originally Posted by Flat6pac

Maybe the pump had already failed. The other times I had seen the breakage was from the pump getting an 8mm nut out of the oil tank, directly into the gears and bang, massive damage.
Bruce

This ^

I would suspect pump damage/failure. Pull it apart and take a peek at the gears.

[Alan Goettel]

I'll pull the pump apart to see what that tells me. The IM bearings looked good, and the pumps spins freely by hand. It seems like it would almost have to be some kind of pump jam to blow out the coupler. Thanks for the help, it's been pretty quiet around here this weekend.

I am going to split the rods today. I am also going to take some pictures, and attaempt to post them

Originally Posted by BoxxerSix

This ^

I would suspect pump damage/failure. Pull it apart and take a peek at the gears.

[Flat6pac]

I have another one of these to do soon once I have the drip fixed in the Carrera that marks it s spot when its parked...
Bruce

[911 tweaks]

Alan & Bruce...keep posting please...great info here...

Bruce...when you repair this engine pictured here, please start a new thread & put a link to it on your red 85' carrera thread...

Thx for sharing your experiences guys ...

Bob

[lucittm]

Alan,
You have had time to think about this and time to examine the internals. What do you think caused the failure of the coupler?

This would be my short list:
1. The coupler failed catastrophically due to stress or it was damaged during mfg. Picture?
2. There was a hydraulic lock placed upon the oil pump possibly by a failed pressure bypass.
3. A small piece of aluminum went completely through the pump enough to temporarily slow it down but not enough to lock it and it went out and is now in the oil tank or the thermostat housing.

Mark

[Alan Goettel]

I didn't take the pump apart, but I took the screened intake extension off, and as far as I can see there is not a mark on any of the pump internals. Its possible that something jammed up the pump and got spit out, but I would suspect that it would have left some kind of a signature.

Maybe it was a bad coupler, but maybe doesn't inspire confidence.

I

[lucittm]

Alan, if it is any consolation, I had a similar (mechanically) episode recently. I was driving to work and BANG, a loud noise, lots of lights, and the engine kept running. I pulled over, shut it off, and remembered to exhale. I did not know the mode of failure but both of my belts had broken, the broken belt switch was in pieces, and the tension roller (and a hunk of aluminum bracket) for the AC/alternator serpentine belt was laying down by the crankshaft pulley. I pulled the pieces out, threw them in the back seat, and drove the short distance to the house. Boy, the engine was hot when I had finished the 2 mile drive back to the house!!!

When I inspected the serpentine belt, I found the perfect imprint of the broken belt sensor roller pressed into the back of the belt. I deduced that the sensor roller had broken off because the ball bearing in the roller had frozen. The roller fell onto the belt and it was trapped between the belt and the serpentine belt tension roller. This instantaneous tightening force on the belt broke off a large chunk of the tension roller mount and broke the serpentine belt. The broken belt flew into the cooling fan v-belt and broke it as it went over one of the pulleys.

One of my good friends over at IMA Motorsports in Chantilly, VA expertly welded the tension roller and mount back onto the AC compressor bracket and with two new belts, I was back in business. Oh, and I replaced the broken belt sensor roller ball bearing with another bearing. I hope this one lasts a bit longer.

Mark