5 replies to this topic

[NED1108]

My 998 was overhauled about 7000 miles ago. Due to detonation issues and an oil lekkage I had to remove my engine. Today I discovered damage on all cylinder (see pictures). Does anyone know what could cause this type of damage. The engine is original with a first oversized piston. Is this caused by piston slab? No damage found on de pistons.

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Edited by NED1108, 18 May 2012 - 05:13 PM.

[Cooperman]

Hard to be absolutely definate here, but it looks as though the engine has run with too much ignition advance which has caused the piston rings to bear excessively on that face. What is the condition of the pistons? You might get away with a hone and new rings, but without close inspection and measuring it's not possible to say for sure.

[NED1108]

That would be possible because of the detonation issues, although the ignition timing was correct.

[Cooperman]

If the compression ratio is higher than standard, or the distributor advance curve is wrong, or the fuel was too low a RON figure for the engine spec it could detonate causing that damage.
Whilst the distributor could have been set correctly for static or, say, 1500 rpm, the timing could have advanced too quickly and caused detonation. Maybe a fault in the vac. advance control or a bob-weights issue (if points-type ignition).

[bmcecosse]

If the engine was 'detonating' the ignition timing was very obviously NOT correct..... But surely such detonation would be obvious? Why did you let it go on?? Exactly what damge are you seeing in the engine? Hard to see much in those pics....

Edited by bmcecosse, 18 May 2012 - 07:03 PM.

[NED1108]

Distributor was also swapped without results.