Crank Shaft Damage

[xr6twin]

Hey Guys,

Not sure if anyone has every heard or experienced this problem but Iv just discovered a huge amount of damage to my crankshaft after doing a total engine rebuild, reinstalling the engine back into the car and noticing a servere oil leak coming from the rear main seal.

Ill set the scene first:

Tightening up the 6 bolts that hold the flywheel to the crank.

Using a Loctite thread locker, as per the workshop manual.

The bolts started getting tight before they had contacted the surface of the flywheel.

At this point I knew there was an issue so I removed the bolts and checked the threads for damage.

Failing to find any damage I put the flywheel back on, squirted a bit of thread locker in the holes and screwed the bolts back in.

This time the bolts did begin to contact the flywheel before they got tight.

I continued to torque the bolts up as per the OEM spec.

All seemed sweet untill it came time to kick the engine over for the first time after the rebuild.

It started and purred like a kitten till it started to heat up.

There was a bit of a knock starting to form in the bottom end so I ran over to kill the engine, but before I got to the key there was a loud crunch.

After killing the engine, I noticed a lot of oil dripping down from between the gearbox and the engine.

I pulled the gearbox back off much to my discust and found what can only be described as a brand new rear main seal that had never gotten the oportunity to see a better day.

I check all around the seal housing and the crank for some sort of evidence of damage that could have caused the seal to be ripped appart.

Again failing to find any imediate damage, I purchased another rear main seal and made extra sure it was installed correctly.

The car went back togther ok, and managed to find its way down to the dyno at Autotech to get run in and tuned.

It was once it got home and was sitting in the driveway, I noticed a rather large puddle of oil sitting directly below the bellhousing.

I stuck my head under and sure enough, there was an impressive amount of oil dripping from the plate that sits between the gearbox and the engine.

A few choice words were exhanged between myself and the car, much to my neighbours amusement.

So once again the car is back up on ramps with the gearbox on the floor.

Amazingly the rear main seal was still perfectly in tact.

This ment one thing, having to take the engine back out in order to rip the sump off and find out what is going on.

What I found when the sump came off nearly bought me to tears.

Large pieces of shrapnal had been floating around in the sump during the dyno run and had put large gouge marks in the bottom of my brand new Mahle Pistons and had momentarily been hit by the crank shaft balancers damaging them as well.

How the engine didnt lock up on the dyno is beyond me but it managed to survive, and until lifing the sump off, it had give no sign of the extent of the damage inside.

More investigation into where the fragments of metal had come from revieled something very odd.

Like I said earlier, the flywheel bolts had gotten tight before locking the flywheel down, and once I had taken the number 7 Main cap off found why.

The use of loctite on the bolts had created a hydraulic lock type effect while tightening them up, and me being a heavy handed Elec Fitter, had caused the back of the crank where the flywheel bolts to, to fracture in order to release the pressure that the hydraulic lock was creating.

This explains the crunch when the engine was first fired over.

One of the bolt holes had fractured that badly, it had pushed a piece of fractured metal off and this had caused the first rear main seal to get torn to bits.

Due to the difficulty to see into that area by only removing the gearbox, I was unable to see the damage that had been caused.

The piece of metal that had broken away from the crank shaft left a small gap just big enough for unpressurised sump oil to leak out past the new seal and still cause a major oil patch without giving any other signs of damage.

The only way of fixing this problem is to replace the entire crank shaft and in the future be more careful when tightening up the flywheel bolts.

If anyone has ever heard of this same stuff up please let me know.

[Adam]

I've seen the same thing happen to thermostat housing. Water got down in the holes and when the top section was put back on and the bolts were tightened the pressure cracked the housing.

You only need 2 drops of Loctite on the thread of each bolt, but pretty much every one of my guys at work would coat the entire bolt with the stuff. High strength too! :banghead:

[xr6twin]

yeh its just one of those things, you give em a good cover and screw it in not thinking that it could cause big damage.

[turbotrana]

Mumma Mia, the power of hydraulics. I bet you wont be doing that again. For some reason I have only ever coated the bolt.

[Ralph Wiggum]

Bolts go in dry, torque to initial torque, removed 1 at a time apply a SMALL amount of loctite (normally no more than 3 threads worth and wipe off excess) and refit and retorque bolt to initial then final spec. Repeat in sequence.

This stops the problem you have encountered and will also stop loctite seeping between the flywheel/flexplate and crank and resulting in a loose flywheel/flexplate.

Hard luck tho mate shame you hand to find out the hard way!

[Trough Lolly]

f*ck me that's crazy, my heart would sink finding that too..

Glad it didnt lunch your motor though mate, I gather the pistons were ok?? just a few battle scars on the bottoms?