my last broken engine....(probably not least)

[filh]

Here's my last victim . 1st cylinder Piston, with little damage.....
Block is of course out too . Piston are ...were .50
It's an used engine , I bought . it was rebuild and had 20.000km ( Seller's saying) Made 500km with it (one rally race) .
I have a strange feeling . I broke 5 engines , but found each time broken pistons (between rings).
I didn't rebuild the last one (bought used ) , but broken piston is the same diagnostic.
My machinist thinks about ignition timing problem , at high revs .
Timing is always well adjusted , following the Toyota tuning rules workshop manual .

As he once tested it before , at about 5500rpm , he found 44° timing advance . Much too much for him . Engine was not in charge .The machinist told me there's not much difference in charge ..

My question is : Have you ever heard about bad computer unit giving too much timing?????

My trust is fading away each time I break a 4age (always blue top )

Thanks for helping
Phil

[Rasteirinho]

If your engine was too advanced you probably would hear knocking. In my engine is easily perceptible.
If you had modified cams or compression ratio, forget the original timming.

Did you measured the piston rings gap in all the cylinders?

Only this piston was damaged?
Only on the side shown in the photo?

[filh]

Well , of course , you'll hear Knocking if engine is revving low , but I'm not sure that you can hear it at high revs. And it seems that knocking sensors are not very reliable (only expensive sensors 500€ like).

That engine was rebuild , but can't say the mileage it was used after rebuild .
No I didn't measure rings inside cylinder, and it's too late now . Block is out as 1st cylinder is scratched .

Yes , only the 1st piston is damaged .

What I find strange is that , even with new rebuilded engine , I got broken pistons (each time between rings). And I'm sure of the work done by the machinist . And it was always new pistons (brand MAHLE).
The last broken one is Toyota genuine .50

I know it would be better to have forged pistons , but I only have small cams ( +/- 252°) and adjustable cams gears .

Regards
Phil

[Uzelac]

Arent all Mahle forged?
They are soo expensive, i'm sure they must be forged

[gon]

that piston is melted on the rings ....
bad lubrification ? try installing oild squirters ... check your oil pressure ....
it could be due to detonation or lean condition ....
clean your injectors and make sure u do the chant in diagnostic plug when setting the time to 10º btdc. (too less advance also causes overheating )

there has to be a problem with that ... these engines are capable of much more abuse than 500km of abuse....

[tolisspi]

useful info.
good luck

[firehawk]

filh Wrote:As he once tested it before , at about 5500rpm , he found 44° timing advance . Much too much for him

Without the diagnostic plug connected, 44deg BTDC sounds about right so that shouldn't be a problem. See the included advance map from JMR's ECU article.

Edit: Also - detonation usually leaves visible dents on the crown of the piston and the combustion chamber. As if someone had hacked the top of the piston with a flat screwdriver. If the piston crown looks good, the problem may be pre-ignition - either caused by a too hot spark plug or glowing carbon deposits.

[filh]

Thanks Firehawk : No dent sign on piston and combustion chamber.

I'm using NippoDenso Q20R-U11 for years now.

Ignition was of course tuned with Diagnostic plug shunted.
I had a Ratio meter connected , and the mix was just a bit(just a bit), to rich at 6000rpm.
I paid ( so often) about 120€ for 1 piston with rings and pin.

But they're no more available with 82mm dia .
Gon , it's not melted , it's broken , but I didn't stop when I saw smoke . And I guess it was already in bad condition when I bought it . It was completly undepowered and I only drove 300km with it ! Wasn't just smoking much when I got it fixed .

I think the best way for me is to make another rebuild (already started) and to have a Dyno Bench tuning .

And I'll have the computer unit changed (to be sure about bad timing )


Hope Hope ....
Phil

[Rasteirinho]

I think if the problem was related with lubrification or fuel, the cylinder with less chance of being damaged was the 1st one.

My money goes to the pre-ignition or insufficient gap between 1st piston and cylinder.