Name this bolt! Multi-part, bazaar mode of failure! - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Jake Raby · 11-01-2010, 12:35 PM

Ok...
Who wants to guess what happened first?? I have more pics to share, but they'll give away the mode of failure completely..

See that bolt? what is it? where is it from? It was in perfect condition before it's ride up the "conveyor belt" (timing chain) where it met the exhaust cam and thats finished the engine off.

This happened at 60 MPH, the car wasn't on the track.. Bazaar!

Stroked & Blown · 11-01-2010, 01:44 PM

OUCH! Looks like a rod bolt.
My guess is that the bolt somehow worked its way loose, gnashed the timing, and the material in the cylinder is from valve contact.

Jake Raby · 11-01-2010, 01:50 PM

The material in the cylinder, is the cylinder... After the rod bolt stretched, worked its way loose and fell into the sump where it was picked up by the timing chain..

The remaining single rod bolt wasn't enough to tie the mass together, so it broke and shot the cap through the top of the block. When the rod became disconnected it acted much like an axe and chopped through the bottom of the cylinder.

.......and some people are REUSING the stock rod bolts!

extanker · 11-01-2010, 02:08 PM

are you saying this motor ran for a time [it would take some time for the bolt to back out] with one con rod bolt

Frank M · 11-01-2010, 02:29 PM

I have seen rod bolts break (not on a Porsche) mostly on Toyota 4 cylinders and once a 2.3 Pontiac quad 4. Toyota had a run on them at one time.

they tend to break on the shank midway between the head and threads.

once the bolt breaks the bearing usually come out of position, slips under its mate then breaks the opposite rod bolt.

usually catastrophic damage ensues.

Jake Raby · 11-01-2010, 02:35 PM

Quote:

Originally Posted by extanker

are you saying this motor ran for a time [it would take some time for the bolt to back out] with one con rod bolt

Yes... And its not the first time we have seen this.. I have seen an engine run fine with one rod bolt shot through the top of the case! It was taken to a dealership and they didn't know what the bolt was or where it was from!

The engine ran like this for a good while, until the remaining bolt snapped from seeing double the normal load as it was trying to retain the rod cap all by it's self.

Look closely, the bolt in the picture never broke. Its also not stripped.. It literally fell out during engine operation.

.....and people wonder why the only engines I'll warranty are ours with full upgrades!

mikefocke · 11-01-2010, 04:14 PM

for the entertainment value they provide ... so many puzzles and weird failure modes for him to marvel over.

cnavarro · 11-01-2010, 04:20 PM

Quote:

Originally Posted by Jake Raby

Yes... And its not the first time we have seen this.. I have seen an engine run fine with one rod bolt shot through the top of the case! It was taken to a dealership and they didn't know what the bolt was or where it was from!

The engine ran like this for a good while, until the remaining bolt snapped from seeing double the normal load as it was trying to retain the rod cap all by it's self.

Look closely, the bolt in the picture never broke. Its also not stripped.. It literally fell out during engine operation.

.....and people wonder why the only engines I'll warranty are ours with full upgrades!

Just like the '06 Cayman the local dealership dived into. The rod bolts were finger tight! Probably would have suffered the same fate if driven any longer.

Jake Raby · 11-01-2010, 04:55 PM

Quote:

Originally Posted by mikefocke

for the entertainment value they provide ... so many puzzles and weird failure modes for him to marvel over.

My trophy shelf of blown up parts sure does grow quick! What took me 20 years to accumulate with aircooled failures I'll have far exceeded with the M96 in less than half that time!

I've never seen so much carnage from driving the speed limit!

Jake Raby · 11-02-2010, 07:14 AM

We finished the autopsy.. The entire bottom end of the engine was garbage..
AWESOME! Now to induct these onto the trophy shelf as offerings to the Gods of speed!

litteng · 11-02-2010, 08:03 AM

from an engineering POV it is awesome to see these things scattered about, but as a customer driving the same thing I cringe...

what a condemnation of Porsche business management over quality

Frank M · 11-02-2010, 08:12 AM

With that blackening on the big end, it looks like the rod bearing had been spinning prior to snapping the other bolt.

yelojkt · 11-02-2010, 08:30 AM

Any idea if this engine been opened up before or was it a factory built motor?

BYprodriver · 11-02-2010, 08:44 AM

Quote:

Originally Posted by litteng

from an engineering POV it is awesome to see these things scattered about, but as a customer driving the same thing I cringe...

what a condemnation of Porsche business management over quality

Maybe Porsche is outsourceing engine assembly or remanufacturing.

Excellent example of why critical bolts don't get installed without final torqueing.

Jake Raby · 11-02-2010, 09:19 AM

Quote:

Originally Posted by Frank M

With that blackening on the big end, it looks like the rod bearing had been spinning prior to snapping the other bolt.

That happened when just one bolt remained to fasten the rod cap..

The engine still had the factory case half sealant, it had never been torn down.

The bolt wasn't installed loose, the material it is made of and the torque to yield nature of it allowed the bolt to loosen over time and operation.

seningen · 11-02-2010, 10:22 AM

Quote:

Originally Posted by Jake Raby

Ok...
Who wants to guess what happened first?? I have more pics to share, but they'll give away the mode of failure completely..

See that bolt? what is it? where is it from? It was in perfect condition before it's ride up the "conveyor belt" (timing chain) where it met the exhaust cam and thats finished the engine off.

This happened at 60 MPH, the car wasn't on the track.. Bazaar!

Nice rod bolt where did you find the nut?

as hard as those damn things are to break loose (I must be a whuss, I need a breaker bar to move them), hard to believe they will come loose on their own and back out.

Bummer.

We've switched to ARP rod bolts on our builds, hope they fair a little better.

M

Cloudsurfer · 11-02-2010, 09:36 PM

Quote:

Originally Posted by seningen

Nice rod bolt where did you find the nut?

as hard as those damn things are to break loose (I must be a whuss, I need a breaker bar to move them), hard to believe they will come loose on their own and back out.

Bummer.

We've switched to ARP rod bolts on our builds, hope they fair a little better.

M

The stock rods are cracked cap design and do not use a rod nut- the bolt threads into the rod itself.

Jake Raby · 11-03-2010, 08:45 AM

The ARP rod bolts are still in development here.. I approach these things that will be included on our engines with extreme care. We'll be running a set in our ITR car next season, I plan on a tear down at 20 hours to measure stretch and etc compared to the stock units.

The main reason for this is to find the optimum torque values and procedures, things that the MFR normally can't dictate absolutely and only practical application will quantify.

Until then the billet rods are the only proven solution as they use an ARP custom aged bolt that I have 13 years of experience with at outputs over 650HP.

Paul · 11-03-2010, 03:05 PM

Nice description of yet another failure mode. You're having way too much fun at work, makes my day seem boring!

Jake Raby · 11-03-2010, 03:43 PM

Quote:

Originally Posted by Paul

Nice description of yet another failure mode. You're having way too much fun at work, makes my day seem boring!

Thats just it...
This isn't work When it becomes work I'll sell the whole place and go find a job. I promise.