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Åke, that is an interesting thread-- Thank you for pointing it out. Is anyone doing that work for 928s?
I thought this comment (also from Michael Mount, the thread-starter) was very interesting and right on point for the detonation question:
Originally Posted by michaelmount123
Here's another important consideration in protecting your rod bearings: It's not only oiling system issues that can take out a bearing. Your tune is just as important as lubrication. Detonation, mild or worse, can easily cause a rod bearing failure. What happens is the uncontrolled combustion beats on the piston and squeezes the oil film out of the rod bearing. Many who lose a bearing will presume the root cause was the oiling system, when it was the tune that caused the damage. Those that experience constant bearing issues should look into their tune-up.
Further, you have to look past the tune at WOT. Those long sweepers where you're on the edge and modulating the throttle to save your life... Now you're in an often neglected area of tune: partial throttle, high RPM, high load. Is your tune correct in this situation? Your timing and fuel may be golden at WOT, and way off at partial throttle. Think about it.
Yup, spot on and why Todd's 1,000+hp turbo is still on the first build after all these years with stock rod bearings = zero detonation.
This also accounts for the success of other cars like Murf928 supercharger installs. They have a very mild tune done by the same person who helps Todd tune his car.
The WOT comment needs to be hammered into everyone's brain. The most dangerous point in the curve for detonation is at peak torque, not horsepower or RPM.
You see it all the time, someone with a big engine "lugging" it down low afraid to rev it up under load since that might "hurt" the engine.
Peak RPM has it's own issues to be aware of when tuning, but so many forget or are not aware of the lower torque curve and engines are blown.
This is why people playing with engine tuning should really find a local (or even a traveling) pro to help. Sure it may cost a bit up front, but is significantly cheaper than a failed engine. An experienced tuner like Luke who helps Todd with his engine can be the difference between a car that looks great on paper but doesn't last very long at the track.
Luke is why I've ditched any ideas of using MegaSquirt and going with AEM instead since that is his preferred ECU. Not that he wouldn't help me with MS, he knows AEM systems like the back of his hand, will make setup & tuning a lot easier (and cheaper in the long run).
...also why I'm encouraging Andrew to go with AEM & have Luke do the final tune.
So I got the oil pan off. It took some doing, but I got it off. I had to look at the least one bearing the one that was most accessible to me was cylinder number five. The bearings felt noticeably thinner than stock new bearings. And clearly this is the source of the copper in the oil.
The good news is, however, the crank appears to be in fine condition (at least for Barry number five). I'll look at the others tomorrow, But I think I dodged a bullet.
Inside. Bearing did its job. Glad I caught it. Outside of bearing. No evidence of hammering. Crank appears to be saved
Wow, that looks bad. I just did my rod bearings after seeing a lot of metallic swirl in the oil. I expected them to look like yours, but there was only a tiny hint of copper showing on one shell. But who knows, maybe my mains are all worn out.
The worrisome part of your post is the comment as to how the shell looks "noticeably thinner" than a stock shell. This is what I saw on my original GTS motor on the thrust bearing [I purchased the car knowing it had TBF]. Whereas that was a completely different failure mechanism the damage was horrendous. whereas I am sure you will not have that level of damage or anything close to it, given the shell has indeed suffered serious degradation of the wall thickness the question I would ask is "where does this leave your motor?" - put another way- where has all the metal gone assuming all shells are in the same sorry state. Losing the white metal is one thing but losing copper en-masse is quite possibly something else as things are then banging about somewhat [or so I would think].
If that were my motor the question I would now be asking would be "how deep is the rabbit hole and how far to do I need to dig into it to ensure I have reached the bottom of it"? My first reaction when I saw your photo of the shell was that the damage was "more than minor" [as supported by your observation]. If you are able to get away with no more than a big end shell changeout all well and good. For sure I am far from sure about what you should be doing next other than measure the crank pins and the conrods - the latter being impossible in-situ [I suspect] so presumably a plastigauge type approach?
It will be interesting to see what the consensus is on this matter.
Whereas the root cause of the failure seems likely to be the onset of knock from too much advance in the chip programming it may well be prudent to prove rather than assume that is the case. As to what can/should be done in that regard after the fact I do not know.
I noted with much interest Greg's comment about how destructive knock is on these motors because of the design specifics. I formed an opinion some time ago about 2/6 failure on the S4+ motors given I saw a tendency to knock on 2/6 before other cylinders at high rpm's with the stock tune. Fitting a faster exhaust exaggerated this and with ST2 I ended up pulling some high rpm timing rather than adding it. My conclusion being that those cylinders were flowing comparitively more air and thus leaning the mix a bit. Richening the mix did not seem to cure it but backing off the timing did. Not sure any of this is strictly relevant to your case but you may need to look deeper into what ignition advance/AFR combo you are using.
Either way my best wishes for a quick and hopefully not too $$$ painful recovery.
I will have to inspect each journal to make a full assessment, but if this one is representative of the others, I should be good with just replacing the rod bearings. Yes other will say I have to X and Y in order to achieve Z. And while I appreciate those thoughts, I'm pretty sure I'm just going to replace these rod bearings and see where things go from there. Of course, I will adjust the tune, and I will now likely follow each track event with a UOA from blackstone.
The issue is cost v. benefit. This is not an original car by any sense. It started life as an auto for example. If this engine is damaged beyond reasonable repair, I would likely just get a replacement engine or get an LS, or maybe ditch the platform altogether and go to a Cayman or a C5 Corvette.
Anyway, stay tuned. Have some late meetings tonight, so not sure if I'll get the other bearing out today or not. Just glad I know the source and likely know it salvagable with a couple hundred bucks.
AO, do you have a ball mic? Be interesting to see how much thinner those bearing shells are now.
Sometimes you don't even need a ruler:
I do have a set of mics (don't recall if they are ball or not) that I can at least measure the edges as I get them out. But DAYUM! I'm glad the ones I pulled last night don't look like that! Hopefully none of them will. Ouch!
Hmmm- reminds me of the chap who was driving a cart from London to Edinburgh pulled by an Ostrich. A few miles along the M1 just north of London the straps snapped and the Ostrich ran away leaving teh cart to coast to a halt on the hard shoulder of the motorway. Minutes later the cops pulled up and saw this chap sat in the cart respite with googles and a rain coat. The officer asked the chap what had happened to whit the driver explained "the big Hen's gone"!
So I got the oil pan off. It took some doing, but I got it off. I had to look at the least one bearing the one that was most accessible to me was cylinder number five. The bearings felt noticeably thinner than stock new bearings. And clearly this is the source of the copper in the oil.
The good news is, however, the crank appears to be in fine condition (at least for Barry number five). I'll look at the others tomorrow, But I think I dodged a bullet.
Inside. Bearing did its job. Glad I caught it. Outside of bearing. No evidence of hammering. Crank appears to be saved
The fact that the bearing tangs are both pounded in means that the bearing got pounded and then spun, simply by definition.
Really simple to check for pounding....either the bearing has a small amount of "spring" to it when you install it into the rod or cap or it does not. Since the cap is now loose, check the bearing fit into the cap. You should be able to put the bearings into the rod cap and then turn the cap upside down, without the bearings falling out.
Yours will not pass the "Dairy Queen" test and will actually be pounded a few millimeters smaller than the cap bore.
taylor drilled crank, havent heard that term in yrs....anybody use them anymore, I got one sitting around somewhere.....
Jay Steel (Taylor Engines) had the cranks "surface drilled" so that the oil did not have to travel to the center of the main bearing, before it reached the passage to get to the connecting rod journal. He hated this procedure and felt it "ruined" the crankshaft.....which most crankshaft designers would agree with.
This only helped the issue of the oil having to fight centrifugal force to get to the center of the crankshaft to feed the rod journals. (This is only an issue at very high rpms.)
Unfortunately, this also meant that the crankshaft had multiple holes drilled into each journal....completely eliminating any possibility of the oil passages to act like a tiny oil pump......which proper modern high speed oiling does.
It is very difficult to find a crankshaft specialist that will perform this operation...you've got a real collector's item.
it it appears only #5 spun. What are the odds that the I opened first was the one? (Don't answer that. It's 1 in 8!)
the rod cap seemed just as snug as the others and held the bearing in place without issue. Will be mic ing the bearings for wear. Don't have a ball mic, so I can only really measure the ends... still better than nothing.
I really think I got lucky. There were no audible rod knock noises and I just happened to see the copper. So I think I caught it before any appreciable damage occurred. I guess time will tell. I've already put in the new bearings. Will start reassembly tonight. Might even have it running this weekend.
07-26-2017, 12:16 PM
