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Hi Guys, I recently had my engine rebuilt in my MY06 STI by a reputable builder following a head gasket leak. The engine now has 9:0 compression, forged pistons, rods, sleeves, oversized valves, 272 cams, new crank etc. I previously installed a Haltech elite 1500 well before the head gasket issues (previously 7.5:1 compression) and road tuned it myself intially before getting the tune verified by a workshop with a AWD dyno, never had any issues with it. Fast forward, so I installed the new rebuilt motor, and got specific instructions from the builder out bedding the engine in. So I dry hired a dyno and followed the procedure the builder recommended, hold engine at 2000rpm and 0kpa load for about 10min, cycling off if coolant temps rise, which they did quite rapidly, so much so that I could only hold it there for about a minute before backing off to idle to let the temps come back down to keep it under 105c. After 10 or so minutes I moved to the 3000rpm 0kpa that he recommended, it wasn't getting hot as bad by this time, and could get a bit longer before cycling off load to cool down. after 10 min I attempted to mover to the recommended 4000rpm 0kpa, but could not achieve this (kept going into boost), so I rolled on and off the 4000rpm point tuning the fuel at as low as load as I could. This signalled the end of the engine break in, so I started tuning all the load cells at 2000, 2500, 3000, and was about to move to 3500rpm when the engine stalled and seized. Upon stripping the engine, the builder found the intake valves on pistons 1 & 3 (share a common cam) had contacted the piston, and one intake valve on #1 had snapped off can caused the engine to seize). While we're not quite sure why, everything points to the intake cam on this side skipping a few teeth. This is disturbing enough, but he also found that the upper bearing half on all conrod bearings had excessively worn, to the point that copper was starting to become visible. Now at the moment, we don't think the 2x events are related, but the conrod bearings suggest that detonation or abnormal combustion pressures were "hammering" the piston, as the bearing also looks to have copped a flogging.
I can't understand it. I didn't hear any detonation while I was tuning, but I also wasn't using audible detection gear. In preparation for the new engine, I did take a fair bit of timing out of the map to account for the increase in compression from 7.5 to 9.0, and in retrospect, this resulted in a quite low 10-12 deg of timing between 2000-3000rpm at 0kpa. This may have resulted in elevated EGT's, but I wouldn't have thought it would have bought on pinging.
Further info, I had turned off short term and long term fuel trim, and was tuning each cell's VE to achieve the target AFR's on the attached table. I included a pic of the head from the side of the engine that didn't lose a valve so you can see the condition of the valves and combustion chamber. Both old and new tunes were on 98 octane pump fuel and utilising the Haltech canbus wideband for tuning purposes.
Has anyone experienced pinging or detonation in this manner before at low RPM and loads? Could there be anything else to explain the abnormal bearing wear?
what were the rod oil clearances and big end diameter measurements?
I don’t know that, however the fact that only one half of the bearing is worn says to me clearances weren’t the issue. I’m not ruling it out totally, but I’m mainly trying to establish if something I did during tuning could have contributed at the moment. The builder has been building these engines for over 20yrs, and is very well regarded, so I’m not keen to ask those questions until I’m sure nothing I did caused it. When I do find them out, I’ll get back to you.
The first thing that really needed to be checked is whether in fact the cam timing had shifted. This would be a pretty rare event unless the engine was turned over backwards and if it has jumped teeth you'd really want to find out why before rebuilding it. I'd be checking that the cams aren't showing any sign of seizing in their journals.
The bearing wear could be indicative of knock although generally I seldom see knock show up on the bearings without it also being evident on the piston cron and/or top ring land. I'd check all the rings are free in the ring grooves to ensure the ring grooves haven't nipped up due to knock. The timing you're quoting for 0 psi 'should' be more than fine for pump gas even at 9:1 but I always recommend using audio knock gear anyway. by the time you can hear knock from the drivers seat with just your ears, it's way too late and has been happening for a while.
Were you monitoring oil pressure by any chance? What oil were you using for the run in period?
Hi Andre, the builder has established that the intake cam timing on that particular head had indeed moved in relation to the crank, as there was witness marked on piston #3 from the intake valves, and the destroyed intake valve on Piston #1. No such evidence or marking on the other intake cam or either exhaust cam. He established by mocking it back together that the AVCS alone through a faulty solenoid can't cause contact to occur. Being unable to turn the engine over due to the valve damage, it would had been hard to check the timing position prior to disassembly.
The engine has been completely stripped now and he has not mentioned anything about cam journals, and he is definitely looking at everything in great detail now that there's no obvious cause, however I will ask him. Unfortunately I can't drop in and view everything disassembled myself as he's ~1500km away, although I have no reason to doubt him.
On the knock front, my fear was exactly that, it may have been knocking without really being audible however I thought I would have been firmly in safe territory with the figures I had. I couldn't beg, borrow or steal an audible device and the dyno didn't own one, I will be buying one before going back to the dyno cell, that's for sure. The car was sitting for over 12 months while the build was happening, however I drained the fuel tank and put new fuel in it. I've attached a photo of the piston 1 & 3 (don't have one of 2 & 4 at the moment), obviously #1 is damage by the valve, but I don't see anything on either that look like detonation damage. Note: #3 has debris on it as well that was blown into all cylinders once the intake valves on #1 was broken off.
I did have oil pressure & temp monitoring, as well as fuel pressure hooked up, and was logging the first half of the break in session, however in an absolute astoundingly stupid amateur move, I stopped the logging at one stage when I left the dyno cell, and forgot to re-enable it when I returned and continued. I then did not save the log file when I shutdown to tow the car off the dyno. I will never make those mistakes again... The times I was checking it, the pressure seemed fine, however I know that's only useful while the engine was running fine and data trumps beliefs.... As an engineer, I live off data, so this in particular hurts a lot.
The Oil I used was https://www.penriteoil.com.au/applications/baseoils/mineral/10-tenths-running-in-oil-15w-40-mineral which was discussed and approved by the builder.
If oil pressure was an issue though, I would have thought both halves of the conrod bearing would show at least some damage, as well as other bearings.
Found out Rod clearances range from 0.0017" to 0.0020"
Have added a close up pic of the bottom half of #2 conrod bearing for comparison to top half in image 2940 in my first post above.
Have also added close up pics of #2 & #4 pistons. I can't see any detonation damage or scorching on them. Note there does appear to be slight marks from debris sucked into these cylinders on them at one of the edges.
Builder also reports that cam journals look good and cams rotate freely.
This sounds like the old "I didn't screw up the build, you screwed up the tune and I'm not paying" story.
I'm highly skeptical based on the info you supplied that some magic unaudible knock blew the motor. Either the parts were bad (bad judgment from the builder or he advised you to buy something but you wouldn't spend the money) or the assembly was bad.
It's not like that at the moment, no fingers are being pointed, and I'm quite happy with how our correspondence has gone so far. Both of us are trying to establish the facts and determine a cause. He has stated that he does not believe detonation or excessive combustion temps cause the valve to piston contact, which will be the biggest cost. My concern is that eventually it will get to a point that if no cause can be found, then awkward conversations will have to be had.
During the build I took all of his advice and it was quite an expensive and thorough build. So far, if I was in his position, I would be asking the same questions he has. If I were the builder and wasn't involved in the install and tune, I'd want to be sure that the end user hasn't just screwed up and is trying to make me rebuild it for free too.
The main thing from my point of view is that it is suggestive that I may not have had things right during my tune, and if there hadn't been valve to piston contact for what ever reason, then I may have thrown a rod bearing not long afterwards anyway.
More important still, when the engine is rebuilt, how do I ensure the same condition isn't repeated and I lunch another set of rod bearings, and potentially more.