Engine Damage from Failed Distributor

[Mahler9th]

Modified 3.2L crank from a 3.6L racing engine. We think this was caused by ignition issues from a failed factory 3.6L distributor. Not from belt failure, but by bearing failure.

The distributor in question was bought used and had a new belt and a mag pickup installed about 5 hours ago. No sign of bearing issues at that time.

Not sure when the issues started, but the end result was a broken crank at Sears Point about a month ago. No fun.

I have since purchased a JB Racing distributor. Impressive part and company.

Keep an eye on those 964/993 distributors-- they are getting older and older. Not just the belts.

[Antonov]

Good friend of mine just suffered significant engine damage to his varioram 993 due to failed distributor belt. Sorry to see this.

[winders]

I ordered a JB Racing twin plug distributor a couple of weeks ago after Mike experienced this failure.

I do not want to experience this!

[gtc]

Which bearing failed, and how?
Seems odd to me that it would manifest itself at the opposite end of the crankshaft.

[Mahler9th]

Not sure which of the bearings failed. After some general symptoms showed (unexpected and subtle lack of power) troubleshooting started. As part of this rotors and belts were inspected and found to be okay and properly timed.

Symptoms continued.

We surmised that failure was progressive. So who knows when plugs were firing in or out of order.

Finally the thing completely let go and the belt broke. The cap and rotor were all broken up. This step occurred during a simple test start in my shop.

Once the engine was returned to firing all plugs, the crank broke. Saturday quali between turns 2 and 3 when I was warming up my tires. Engine went off song... clankity clank. Back in the paddock we noticed that the crank pulley was moving in and out by 1/8+ plus. Shut her down. Started packing up.

['76 911S 3.0]

Originally Posted by gtc

Which bearing failed, and how?
Seems odd to me that it would manifest itself at the opposite end of the crankshaft.

I'm guessing that somehow the distributor locked the crank near the #8 bearing and the reciprocating mass from the flywheel caused the crank to break at the other end?

[Trakrat]

WOW!!!! definitely looks like it was a sudden SMACK

[juanbenae]

sorry to hear this Mike. is the case still good?

[Steve@Rennsport]

We rebuild a LOT of 3.6 distributors and replace all four bearings (along with the belt) at this time.

I've been seeing more & more bad bearings now as the 'fleet' grows older.

[Mahler9th]

The distributor probably did not lock the crank. Not mecahnical damage. I think the damage was perhaps caused by mis-timed firing of the plugs. The upper and lower plug sets may have fired at inappropriate times.

If a stress crack is created from this, I'd guess the crank can then later fail.

Thanks Toby. So far, it looks like the case is okay. But there was other damage.

I think JWE may repair/refurb these things, but I am not sure. I do know that they replace them from time to time.

There may be an increasing failure rate, but only PAG would know based on ww sales of replacements.

Part of the point here is that a failed belt is not the only failure mechanism. In my experience, when I checked the belt and the rotor timing, it was okay. But that does not mean it was okay all the time-- just when I checked.

I would not say these things are ticking time bombs, but.... folks should likely consider being proactive beyond just belt replacement.

[Matt Monson]

Damn