930 rebuild in progress.......I need your help and opinions on the mess inside

[briankeithsmith]

I think CBRacerX is on the right track. Either high oil temps, or possibly oil not changed often enough (not saying you don't change your oil enough, especially with only 34 hours on it).

I recently rebuilt a 3.6 that had run hot, and it looked exactly like yours. In the case of this particular engine, it looked like they truly stayed with a 7500 mile oil change interval...

For me, depending on time of year, I change my oil after every other event, or after each event (summer). If I've had an event where I got a good amount of track time, like I did in May with First Settlers (approx 8 hours), I change the oil after that event, regardless of season.

Craig : Don't read my post wrong, I'm not implying that you haven't changed the oil or anything like that. I'm just stating what I've seen in other instances, so please don't take it the wrong way.

I'd be curious to know oil temps though??? And what kind of additional oil cooling do you have? Extra coolers?

thanks,

Brian

[Craig 930 RS]

Oil temps were nice and low. I have 3 oil coolers.

At this point, we have "only speculation as to why it happened" or what the root cause of the multiple failures were.

I'd hate to guess.....

Piston scuffing...anyne see it so bad before? Ideas? Extreme heat?

[WERK I]

My guess pre-ignition and/or detonation was the culprit for most of what you see.

[Craig 930 RS]

Yet the piston tops are in great shape.


The initial prognosis is this (not my analysis):
Extreme heat. P&Cs got very, very hot. Lean? Possibly. Oil temps? Probably not.

At this point, it is water under the bridge - I just don't want anything like this to happen again. I mean, we are talking possibly over $15,000 to fix a 30+ hour engine...

So what are we doing about it?
1)'Imagine Auto fuel head mod' Truly helps with lean running.

2) Nice valve job. A 5 way with no wavyness at the seating area


3)Checking and balancing the injectors

4)Ni-resist ringing the heads and cylinders to locate and retain head-to-cylinder relationship. I never want to see these walk around and cause this again. Thos are NOT dirt and oil marks - those are gouges...as if a box of tools were dropped on the cylinders. Hammered from head movement:

[CBRacerX]

Go get 'em - good luck! The Flame Rings are a great thing.

[Steve@Rennsport]

Originally posted by WERK-I
My guess pre-ignition and/or detonation was the culprit for most of what you see.

Now, THAT is a piece of true wisdom,...

[Mr Beau]

As it doesn't look like things look too hot, it appears that too much ignition timing was used for the fuel octane. More fuel may help but the damage here may not have been caused by lack of fuel.

[CBRacerX]

I asked about the elevated oil temps not because I thought heat alone caused the damage, but because when the oil flow is reduced or blocked to one or more rods, you get a lot of heat generated that transfers to the oil. If Craig had seen this as a sudden symptom, it might help the diagnosis. Full teardown will surely show such an issue as bad crankshaft oil passages.

[WERK I]

Originally posted by Craig911
Yet the piston tops are in great shape.


The initial prognosis is this (not my analysis):
Extreme heat. P&Cs got very, very hot. Lean? Possibly. Oil temps? Probably not.
4)Ni-resist ringing the heads and cylinders to locate and retain head-to-cylinder relationship. I never want to see these walk around and cause this again. Thos are NOT dirt and oil marks - those are gouges...as if a box of tools were dropped on the cylinders. Hammered from head movement:

Craig,
Oil contamination on the piston tops could have occurred after the damage was already done. If the piston bores were heavily scored, the rings would no longer be able to scrape the bores of oil excess. Oil contamination of the incoming mixture effectively raises the likelyhood of detonation. The gouges you see appear to be from extreme temperature gas trying to escape from the head/bore surface area.
I've been looking at the number one cylinder at TDC in the photo provided. The deck height looks very low(numerically). Maybe its the angle of the photo. It would be interesting what the deck height is with the same thickness base shims that were in the previous build. My $0.02, I wouldn't run 8.0:1 compression on a CIS track engine. I think you are running on the hairy edge of pushing the thermal limits for a CIS engine. Maybe others will disagree, let the debate begin.

[sand_man]

I'm running 7.3:1 in mine. IA fuel head, SC cams, 3.4L, twin plug ignition, B&B headers, B&B I/C, Zork tube, K27-7200, Tial wastegate with .8 BAR spring, ARP head studs, ARP rod bolts. My engine is still in the break-in period so I'm trying to avoid over 5,000 RPMs for first 500 miles or so. After that, I'll hook up my Innovate LM-1 and take some AFR readings at higher RPMs. I can tell you that the engine is hella fast based on what I can tell. Very smooth and very responsive. We get 93 octane here.

[Mr Beau]

Criag,

How much timing were you running, and does your car have boost retard on the distributor? If so, was it functioning?

[Craig 930 RS]

24 degrees. It is all functioning - is the retard the connection to the forward portion of the IC? (Car is not here, been in pieces for weeks)

[beepbeep]

I also believe pre-ignition broke the piston rings (hapends a lot on 1-bar otherwise stock 930's). After rings broke, you suffered lot's of blow-by which contaminated the oil.

Contaminated oil together with high-rev beating your crank and rods took made crank bearings wear much quicker.

8:1 on single plug (first pic show twin plug, second single plug?) engine (with CIS?) is pushing the luck. It might be timing retard that froze or batch of bad fuel or whatever.

I recomend twin-plugging the heads and going EFI, if economically possible.

[Craig 930 RS]

Man, do people read the background on this engine?

It isn't 1 bar - .8
It has twin plug
It didn't have blow by
Hi revs didn't beat the crank

Sorry, some of the guesses are getting ridiculous

[Mr Beau]

Craig,

You said you were running 24 degrees. What would a single plug version of your engine normally run?

[Jeff Alton]

Craig, I don't know which oil coolers you have, but seeing as you have 3, any chance one or more was contaminated before you got it?

Cheers

[Mr Beau]

Twin plug needs less ignition timing than single plug. If you ran 'single plug' ignition timing I'm leaning towards cylinder pressures that were too high which broke your rings.

[Craig 930 RS]

No chance of contamination.

I've just learned that the previous build used short skirt 98mm pistons...

[sand_man]

Originally posted by Mr Beau
Twin plug needs less ignition timing than single plug. If you ran 'single plug' ignition timing I'm leaning towards cylinder pressures that were too high which broke your rings.

Interesting! I'm running Electromotive XDi twin plug and I have the timing set at
10 degrees for initial
21 degrees for 3000 RPM
-3 degrees for 8000 RPM
RPM limit set to 6,500
I also have a MAP sensor. I'm still in the break-in period, so I'm not driving the car hard. I wonder if I should readjust the timing curve? It was set this way just to get going.

[sand_man]

Not to hi-jack (sorry craig), but I just wen't out to the car and turned the 3000 RPM timing knob back to 15 degrees! We'll see what happens on the drive home!