Oddjob

Friend's Turbo motor grenaded at the track yesterday. 104k miles, DE car, but in good condition, was not abused.

Something on #1 let go. Oil pan shattered and the crank girdle. Assuming a rod bearing, but have not confirmed - bottom end of the rod is still intact so cant tell for sure until we get it on a lift.

I was in the passenger seat when it happened. No common symptoms of pending rod bearing failure: no low oil pressure or rod knock. Oil pressure actually was indicating high (above 5 bar, approx 6 bar at high rpm 5.5k plus).

I have never noticed a car running more than 5 bar, and this car did not do it prior to this wknd either - typically ran 4 - 4.5 bar at high rpm at operating temp (on track). First thought was that the gage or sender were wrong (if there was a prob. with the gage/sender, then it may acutally of had low pressure w/o us knowing). If it did have high oil pressure (bad PRV?), I would assume that would not lead to bearing failure; probably just push seals out/ cause leaks(?) - unless there was an obstruction in a line or galley.

Of the cars I know that have thrown rods through the block, they have had the rod knock and/or low oil pressure symptoms shortly before the explosion.

Anyone had a catastrophis failure like this with no common warning signs? Anyone had a high oil pressure symptom relating to a complete failure? Anyone know of a car that lost #1, not 2?

And anyone have a Turbo short block for sale?

V2Rocket

http://cgi.ebay.com/ebaymotors/Porsc...QQcmdZViewItem

Get it resleeved if necessary and crank up the booooooooooost

evil 944t

Over rev or detonation? Check the top of the piston for detonation marks.

Legoland951

I have never seen a motor grenade via breaking rod without warning first. There are always signs you can see after the fact.

If the rod broke and the piston stayed up (not damaged), you can use any late block (85.5+) with the metal/plastic balance shafts as they are the same. The turbo have forged rods and piston so thats all you have to change. Even the cranks have the same PN.

M758

I know of one 944 spec motor (83 vintage) where the rod broke. I think it was the number one rod. Bearings were fine it was just the rod. No warning at least noticeable to the driver.

Oddjob

We pulled the motor and head off last night.

Did not pull the bottom end yet. But looking up through the gaping holes in the pan, the #1 rod is broken about 1 ½” up from the crank journal. The rod does spin freely on the crank, so I am assuming the bearing is fine, but I have not pulled the cap off to check.

#1 piston is jacked/cocked in the bore close to BDC, the wrist pin is busted out of the piston skirt. Bottom of the piston and cylinder are really chewed up. Girdle is busted/shattered on both driver and passenger side of #1. Crank may be ok.

#4 exhaust valve is burned. That chamber and piston crown are sooted black. #1-3 look like they may have been running lean, chambers and pistons are clean (no soot, just tempered/darkened metal look). Im used to seeing a hard, crusty black soot on piston crowns. These are clean enough to read the orientation arrow and tolerance numbers. Exhaust headers for 1-3 are sooted white, #4 is black.

The #1 cylinder bore above the piston is fine (no damage/scoring), so doesn’t show any evidence of a cracked ring. The piston crown also shows no damage or marks (other than being too(?) clean/lean).

Spark plugs on 1-3 look pretty lean (crusty white), #4 has the tip burned/blown off.

Head gasket (wide-fire ring) fire rings are intact (except #1 has a torn, peeled edge that is likely damage from debris). No other signs of delamination, burning or blow-by on the rings. There is some peeling of the gasket fibers in the water jacket area, which look like heat spots, especially a large spot that is right up against the #2 fire ring.

Not sure what the cause/effect relationship is here. Lean on all 4? Not enough fuel or too much air. We don’t recall a boost spike or surging (car is running APE stage I chips only, so basically a DME ignition chip with stock boost). Fuel pump starting to fail, weak FPR? Not sure how any of that would break a rod. That would be some severe detonation/knock.

Any input appreciated.

87944turbo

What would happen if the FPR failed completely? Would it send constant full pressure to the injectors or the opposite?

JEC_31

Any signs of metallurical flaws in the rod at it's break point? Discoloration, change in grain structure, etc?

bjzorn

It sounds like to me it just my have been a weak rod, as JEC_31 said check for discoloration etc. good luck

brandon J

Matt Sheppard

I disassembled an '86 turbo motor (sinter-forged rods) last year that had a rather large occlusion in the #3 rod (circular, about the size of a dime, or a little smaller) that caused it to break in 3 pieces. The first and major break was about an inch above the big-end journal as you mentioned. Crank was fine as the big end was intact, piston collided w/ the valves and was toast and the middle section of the rod exited the oil pan/ crank girdle. The occlusion looked like it was caused by corrosion (?) or a void in the forging process at that 1" point above the big end. It was obviously darker than the freshly sheared/ shiney torn-surface of the rod.

another data point.

Were these forged rods - did they have the ...RAST on the end of the part #?

tyro

Close Matt..RARST

Oddjob

At this point, I do not know if we will be able to find enough of the rod to determine if there was a flaw. The broken end attached to the crank is basically shot peened from hitting the oil pan, so the fracture mode probably cannot be determined there. We have not pulled the bottom end yet, but Im not sure we will find much more evidence - I dont remember seeing the top rod section attached to the wrist pin, but it could be in there somewhere.... I will have to check the others for the RARST imprint - Im assuming that this engine will have the forged pistons.

tyro

Since you're just looking through the hole in the pan, I assume you cannot tell whether the wristpin moves freely on the rod?

Oddjob

Correct, and I cant remember offhand how much/if any of the con-rod was left attached to the wrist pin. I was so horrified at the appearance of the bottom of the piston and the cylinder that I didnt notice some important details...

Kind of like looking at road kill deer and trying to recall if you saw the spleen intact.

David Floyd

Did you get to enjoy the fireball ??? scared the crap out of me when my #1 let go at the end of the front straight at Road Atlanta, nasty damage.

Never found out the cause, I suspect a dropped valve ??