bukh pistons - advice needed

[Birdseye]

friend taking his bukh to pieces (oil consumption) showed me the piston. this has what looked to me like machined lines down the side of the piston at 90 degrees to the gudgeon pin. the lines were very even, of identical width and number on both sides, and ran only from below the oil control ring to the skirt. they corresponded in location to a deeper than normal part of the skirt ie th lined part of the piston was about one inch wide on both sides

the advice he has received from several sources is that this shows overheating and the marks are scoring. I dont think so since there is no evidence of any seizure / smearing - the lines are just as if they had been machined, there is also no corresponding marking in the bores, though the engine had at one time overheated with a blown head gasket.

has anyone ever seen a piston with lines machined vertically in the sides? if so, what are they for?

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[Joe_Cole]

It's donkey's years since I worked in the industry but at one time I worked at a factory which manufactured pistons. FWIW I can't remember any which had vertical lines machined into them.

It's quite possible for a piston to be scored, but not the cylinder bore (aluminium piston, iron or steel bore....the softer metal will be the one which gets damaged first)

Why not talk to Bukh though? They should know the answer.

Joe

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[philip_stevens]

"Why not talk to Bukh though? They should know the answer."

phone 01202 668840, fax 01202 660713, but catch them quick or they will be at the boat show.

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Philip

 

[sjohn_gibson]

Without seeing the actual piston(s) it is hard to be sure but it is unlikely to be machine marks.

Is the scoring in line witb the gudgeon pin or is it on the thrust side of the piston?

Scoring in line with the gudgeon pin is associated with overheating.

Examination of the piston rings, including the scraper ring for corresponding damage is worthwhile. Although the bore shows no signs of damage close examination with the Mk1 eyeball (+ magnifying glass if required) usually shows something.

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