UK952

There is lots of info here on number 2 failures but not much practical experience.

I would like this thread to compile the practical experience of failures and see what comes out.

If you have suffered a number 2 failure

under what cicurmstances? (road or track?)
cornering?
heavy load?

How many miles on the engine?

Oil pressure?

Oil level?

Oil type?

Slicks or road tyres?

and anything tried to prevent it happening again and did it stop it?


My sump is coming off in a while for a new gasket, looking for while Im in there options - but no point if they dont work are not required.

UK952

Anyone track regularly and not had a failure?
I have been on track a few times on slicks keeping the (15w50 synthetic) oil at the maximum and not had any issues yet, putting out over 300BHP
A friend of mine with a standard car on road tyres (but he is quick) let his oil level get low and he had a nasty number 2 failure.
I think it may be due to a combination of factors, low oil volume or pressure combined with a twist or flex in the block - I think if it was just an oil issue it would hit number 1 or 4 first.
Tony

M758

Me...
2 rod bearing failures in my 944 spec car. 2.5 NA motors

First one.
Engine 45k mile
Original rod bearings no mods
Oil pressure... this was the kicker, unbrakes 0.5 bar under accel 3.5 bar.
Oil used Mobil 1
45 + racing/track hrs
6000 RPM max shift point
Result - hole in block. Head survived
Tires = Victoracers (225/50 R15)
Reason - I believe had the balance shafts 180 out of phase for a while an cracked my oil-pickup tube. I only noticed the low oil pressure when reviewing my video after the incident. All looked good sicne I was doing a gauge check on the accels where things looked good and not watch the gauges in the brake zones.

Failure #2
100k+ motor
Newly installed rod & main bearings (2 weekend)
Oil cooler from 951
Amsoil 20w-50 Series 2000
Good oil pressure
baffled oil pan
RA1- 225/50 tires
6200 RPM shift point.
Oil level full, but never over
Oil pressure 4bar+

Result = spun bearing and bent crank. Rest of the motor good
Reason... Not really sure since I did alot of things right. My feeling is that I may have putt too much goop on the engine girddle when tring to seal the oil passages. This may have caused debris causing momentary oil stravation and rod bearing failure.

Note... my most sucessfull engine has 40+ races on it with 2 rod & main bearing change (new once racing and then replaced once after 30 races). This engine also has a cross drilled crank. The other two engines did not. All egines were driven in the same car to the same powerlevel and similar redline and the same driver & tracks.

Jeremy Himsel

Joe,

On your current motor, how did the bearings look when you changed them after 40+ races? Would have been interesting to see how much wear they had using plastigauge.

M758

I can't remember exactly, but they seemed to look realy nice.

I think wear just addes to the probelm, but is not root cause.

My thinking is that the oil flow to #2 and #3 are marginal. This means any hiccup to the flow can cause #2 to go followed by #3. So worn bearing mean more open clearances and the more open the clearances the more oil flow is needed to float the rods on the crank. So really old motors tend to be more at risk that motors with fresh bearings. However fresh bearings will not PREVENT a problem, they will only insulate you.

Example lets say under normall conditions you get 100 CC/min of flow to #2 100 cc/min to #3 and 150 CC/min to #1 and #4. This idea supported by some testing on cranks Greg Fordhal has done (numbers are pure fiction). Well with new bearing and tight may be you need only 60 cc/min to float the bearings. Maybe with worn bearing you need 80 cc/min. As you can see worn bearings mean greater risk. Also hot thin oil may actually require 10 more CC/min vs cooler oil so those 60 and 80 numbers become 70 and 90 cc/min. Then imagine a little oil froth and bit of air suck and bang your are at 85 cc/min real oil flow on #2 before you know and bang... rod spins in a matter of seconds.

It still can happen on fresh bearings, but it takes alot more to go wrong.

Seems like cross drilling my increase the oil flow bit and give you margin. Latest thing I hear is cross drill only #2 and #3 rod journals. Reason is this evens the flow between all 4 rods. So lets say drilling all the rods inrased the total flow by 10%. That 10% is great for #2 & #3, but wasted for #1 & #4. Drilling only #2 & #3 possibly incrases the overall flow by 10%, but now all of this goes to #2 and #3 thus increase these in effect my more than 10% and effectivly achieving balanced flow in all 4 journals. Seems like a smart idea and have spare motor with #2 & #3 only drilled. It has not run, but I hope it will work when I do run it one day.

badcoupe

when I pulled my original motor with 130k the number looked really bad, not spun but very close to it. I was fortunate to have taken it apart when I did. The PO was was a doctor and it usually sat parked indoors but he collected vintage ducati's and didn't want to put a clutch in it so I bought it that way and beat the crap out of it for approx 2.5 years doing a ton of streetracing and going bracket racing a few times. Thats when I tore it down for a rebuild and discovered the bearing issue. I checked the crank very closely for concentricity etc. After It won my scrutinous approval I perp drilled it myself. It's since been in 3 other motors and and has alway looked perfect and the same for the bearings.

ShApE

First time it was because i was really really low on oil and was taking a hard turn on the way to change my clutch at a buddy's house.

samluke

8 years DE and club racing. Freshened the motor at 130k as a precautionary measure and the bearings were like new. 4 years later and 170k miles and the motor still runs strong. Always Mobil1 and an additional auxiliary oil cooler.

UK952

thanks for the excellent feedback,
Tony

UK952

No one else got anything to add?
Tony

chilibluepepper

This is my story....
I toasted my #2 bearing about 3 years ago at Sebring while on track for DE. Car had ~93K miles, stock bottom end, freshly rebuilt stock head, running modified 26/8 turbo at 18 psi, a larger oil cooler, and Mobil 1 15-50 The engine had excessive leakdown in one of the cylinders. At the end of 7 "spirited" laps on a hot September day, the warning light came on, the oil pressure needle was bouncing of the bottom of the gauge, and a knocking sound became noticeable. I checked the oil level, and found about 2+ quarts of oil had disappeared during the session, and there were no signs it had leaked out the bottom. However, there was some light seepage out of one of the plugs on the cam tower. I believe the combination of hard driving at 18 psi with my "leaking down" cylinder, probably resulted in excessive pressure in the crankcase, which in turn promoted the oil migration/consumption. And finally, everybody knows what happens when you run hard on a track while 2 quarts low... bye bye #2!

Edited to correct turbo info and add type oil.

toddk911

#2 spun

100% street
about 150K at the time
oil pick up had small crack, but mech did not think that was the cause.

and IIRC it was driving fine and one day on start up I noticed the "clicking/knocking"

Drove very lightly for a day or so until I good get it looked at, then got louder and then started loosing oil pressure on the way to the mechanics.

mutzman951

My '83 N/A chucked a #2 when I lived in NJ. It spit the rod out of the block, and made a big mess on the road and the tow truck. 145k miles, 1 qt. low on oil, accelerating from an uphill stop, got to 3rd gear briefly, then BLAMMO! $5,000.00 plus towing.

I did a lower end on my '89 four years ago. It all looked shiny and new inside. The #2 was fine. Then, when I craked the block 2 years ago, the rod bearings were all in great condition. I beat the living hell out of that engine, with almost no wear.

I used Mobil 1 exclusively, except for the break-in period. I always kept the oil level up since that first incident. These cars do tend to "seep" some oil!


doug

dyson

Not my 951 but a friend's. 100K miles - happened during a track day. Oil (Mobil 1) started full but after lunch knocking started. No drop in oil pressure. Oil level checked and it was down 1l. Street tyres. Car had adj FPR and boost and was running about 18psi. Spun #2. Not a particularly agressive driver.

Also happened to a friend's NA during another track day. Very agressive driver bouncing off the limiter all day. Street tyres, no loss of oil p or oil level.

Thankfully hasn't happened to me yet. Always overfill the oil, check it between runs, and keep revs below 6K.

UK952

Interesting stuff thanks, any more?
Tony