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

Engine has 34 hours since complete build. Power was down, so we did a leakdown: 40% on number 3.

So the engine goes into the shop for a look-see.
Gets worse the further we look - first is the burnt valve, no big deal. Then the shuffled heads and the gouges on the cylinder tops. Uh-oh. Then the scoring on the cylinder walls.

Can these cylinders be saved? They were brand new 34 track hours ago.
http://forums.pelicanparts.com/uploa...1148837443.jpg

http://forums.pelicanparts.com/uploa...1148837459.jpg

http://forums.pelicanparts.com/uploa...1148837499.jpg

http://forums.pelicanparts.com/uploa...1148837548.jpg

http://forums.pelicanparts.com/uploa...1148837568.jpg

Cylinder and heads:

http://forums.pelicanparts.com/uploa...1148837636.jpg

http://forums.pelicanparts.com/uploa...1148837682.jpg

http://forums.pelicanparts.com/uploa...1148837705.jpg

#3 and #5 had broken top rings, yet scoring is on nearly all the cylinders

heads can be flycut and cylinder tops can be cleaned up in a lathe, but the scoring suggests a new set of P+Cs is in order. and limit your boost in the future. it's been blowing past at least one head for a while too. no broken studs? maybe everything is not on the same plane. maybe swap the all-threads for something better.

you might want to go a bit deeper and check the rod bearings too, considering the detonation issue that broke the rings.

No broken studs. Has fully threaded studs that are non-magnetic (dilivar?). ARP will replace the threaded units. 'Fire ring' (slots cut in heads and cylinders) will help to locate the heads to the cylinders and help prevent blow by -

The boost has been a stock .8 bar since the initial build.
If the pistons were installed 'backwards', would it cause this scoring?

Those pistons look like they are higher compression than the stock ones. What compression ratio were you running?

Curious...did the pistions get fouled after the rebuild? Were all the carbon buildup cleaned before assembly? Nothing to do with the post, but just wondering if it can get that dirty only after 34 hours?

I would pull all the studs out and measure them- they all should be the same length, if not, they should be replaced. I also suggest against an all thread stud here- too rigid. As far as the cylinder faces, I would have them surface ground rather than decked in a lathe, but I would replate the cylinders and have them cryogenically treated if you plan on re-using them before having that done. I'd be willing to say that you've toasted them and you'll never get any kind of longevity out of them. Flame ringing also wouldn't be a horrible idea the second time around.

As far as the pistons being installed backwards, I don't think you can- the JE's don't have offset pins. The scuffing could have come from the piston heating up real fast and out expanding the cylinder. Coated skirts help that to some extent, but the coating is sacrificial so it won't last forever.

Almost looks like that one valve has a pre-burn slot in it? I'm wondering (especially with the broken rings) if you weren't detonating...

Are you sure you were running .8 bar boost? How about fuel? Was it quality? Ask Steve at Rennsport what he things about most fuels these days...

Bottom end.
--------

#6 cylinder -
Caps
http://forums.pelicanparts.com/uploa...1149892434.jpg

Bearing shell
http://forums.pelicanparts.com/uploa...1149892466.jpg

Other side of shells. THE ugliest thing you want to see on a 30 hour engine.
http://forums.pelicanparts.com/uploa...1149892518.jpg


Will be 'interesting' to see what the other bearings look like.

Craig,
You did a teardown a right right time. Anymore on that engine would have been catastrophic. The crank mains and journals will tell a lot too.

Other than the lost of power, what else did you notice that led you to believe that there was something seriously wrong with the rebuild? (i.e., strange noises?)

Noticed a loss of power late last year
Checked timing and mixture - both were fine.
Did a dyno run in December - down 56 hp.
Checked leakdown - 40% on #3 through the exhaust.

It will be interesting to see what the root cause is here... that thing looks like it has been through a war!!

All the best, Craig,


JA

Those are some ugly bearings , glad you caught it!

Ughh - I had a failure on a "pro" built engine years ago because the crank was not cleaned property. I should say spectacular failure since the rod went thru the case and it was in a race...

Have you noticed higher than usual oil temps?

I'm confused as to how this engine has 34 hours on a "complete rebuild". Those bearings look so ugly. I guess this is your track car? I don't race, but I wonder what 34 hours of race time traslates into street years...sort of the 7 dog year conversion. It looks worse than my engine that had never been a part in close to 20 years. I guess when things start to go bad in a turbo engine...they go bad real quick like!

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

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?

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

Yet the piston tops are in great shape.
http://forums.pelicanparts.com/uploa...1150061691.jpg

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
http://forums.pelicanparts.com/uploa...1150061978.jpg

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:
http://forums.pelicanparts.com/uploa...1150061797.jpg

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

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

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.

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.

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.;)

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.

Criag,

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

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)

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.

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

Craig,

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

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

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.

No chance of contamination.

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

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.

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!