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Discuss all things tuning in this section. News, products, problems and results.
So the story is I built my own engine, thanks to the HPAcademy engine building course!
It's in my race car with a very loud exhaust. I was tuning it on the dyno, and when I got to the full power tuning I was advancing the spark and making more and more power, and I thought it wasn't knocking. But it turned out I just couldn't hear the knock from inside the car. It's so noisy, and it's a tin can inside that car, nothing obvious was audible. But the guy standing outside the car in front of the engine could hear it very clearly.
This is before I knew what 'normal' values were for that knock sensor reading on that engine. And it wasn't obvious on my diy knock ears either. It just sounded like a lot of engine noise. It wasn't until I was told it was knocking that I listened more closely and had to do some steady state tuning around 4000rpm, and playing with the ignition timing, then I was finally able to "tune" my own ears to be able to hear it.
Anyway, my question is do you think I've done any damage to the engine that would warranty a teardown and inspection? Or is it probably fine?
In total it did about 3-5 full power runs with audible knock happening, the max advance it hit was around 4degrees higher than where knock is detectable. It is now tuned with good safe timing and seems to be running great so far.
If I do tear it down for an inspection, what things in general should I check for?
Pull the spark plugs (look for tell-tale aluminum piston splatter on the electrode), and use a borescope in each cylinder for a visual inspection. Assuming nothing horrible shows up, follow up with a compression or leak-down test of each cylinder. Further non-invasive testing you can do includes cutting the oil filter apart to look for bearing material, and/or sending an oil sample out for analysis.
If the compression / leakdown is not very close for each cylinder, or I saw bearing material in the oil filter, then I would then tear into it for a full inspection.
Usually when knocking occurres at not maximum level it can cause two things:
1) Piston receives more heat and if piston-to-wall clearance is not big enough it can get stuck in the bore because of excessive expenditure.
2) If the pressure becomes too high piston can get a crack in the area between the compression rings.
I would use micro camera to inspect the condition of cylinder wall to make sure the piston did not get too big in the bore. And compression test would definitely show if there is anything wrong with piston itself in terms of cracking...
That's the camera I'm using for boroscoping cylinders- i bought it on ebay for USD 28 and it's very handy.
You don't say what the engine is, or the components used.
In some cases you should expect to be OK, but in others you may expect some damage.
As the others have pointed out, a compression and/or cylinder leakage test may help identify if there is a collapsing land issue which will often show up initially as a pinched ring, if there's bearing damage* that can show as an oil pressure drop or material in the oil and/or filter, a cheap boroscope can help identify if there's damage to the piston top.
While you're at it, while checking it for aluminium flecks, have a good look at the spark plug insulation around the tip as sometimes detonation can cause cracks or complete failure there.
*If you have access to the sump, might be an idea to drop it anyway and check the rod side b/e shells for any deformation or damage.