Minor piston damage, will I get away with it?

Minor piston damage, will I get away with it?

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VAGslag

Original Poster:

90 posts

114 months

Tuesday 28th July 2015
quotequote all
I've just built an engine up to swap into my audi A3... The donor engine was a 1.8t that had been rebuilt with +0.5mm mahle forged pistons in 2009, it had since suffered a rather major turbo failure (snapped spindle) and I got it on the cheap.

Before I bought the engine we did a leak down test which was all good. I've put new rods + bearings in it as well as a different crank (and a few other ods and sods). The bores were 100% and head pressure tested fine.

Upon assembly I noticed a very small notch on one of the pistons, I guessed this was probably from where it ingested a bit of the turbo, thought nothing else of it and put the rest of the engine together.

I'm now having second thoughts! . . To give you a better idea this damage was right on the rim of the piston. Imagine if you got a junior hack saw and took a notch out the very rim/edge of the piston, must have been about 0.5mm deep, if that.

What's people thoughts, will I get away with it? . . I know every proper engineer will tell me I'm doomed, but what's peoples real life experience with these things?

For the record I'll be running abut 320hp when done, and if it's of any relevance I have an EGT gauge with alarm installed.

Appreciate your thoughts on this guys, thanks in advance

stevieturbo

17,229 posts

246 months

Tuesday 28th July 2015
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Pictures

VAGslag

Original Poster:

90 posts

114 months

Tuesday 28th July 2015
quotequote all
Thats the thing Steve, the engine is already together and in the car! . .

I'm not sure how to better describe the damage than as above. But as said, it really is very minimal...

stevieturbo

17,229 posts

246 months

Tuesday 28th July 2015
quotequote all
Never worry about it then lol


PeterBurgess

775 posts

145 months

Wednesday 29th July 2015
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I presume the pistons had to come out of the block to change the rods? if so did you check all the rings were free to rotate? Quite often an impact at the edge of the piston can trap the top ring. If one is lucky the rings make their own gap again with the reciprocating piston action and gas pressure behind the ring when the engine is used. We have been told of two occasions when using the engine has restored compression from what must be trapped ring both times it took around 50 miles.
The damage you describe should not be a problem in itself.

Peter

Evolved

3,553 posts

186 months

Wednesday 29th July 2015
quotequote all
Would the damage not be a cause for hot spot which could then lead to det? Without pics it's hard to say but as it's all back togther I guess the proof is in the pudding. For the cost of a new piston, or even a full set if have prob just swapped when it was apart.

Get it fitted and run it, if it fails you have your answer.

PeterBurgess

775 posts

145 months

Wednesday 29th July 2015
quotequote all
Piston and head alloys do not usually lend themselves to being the cause of preignition when sharp edged as they do not glow. Carbon build up can cause preignition but it sounds like the damage described is not deep and is over a small area.

Peter

VAGslag

Original Poster:

90 posts

114 months

Wednesday 29th July 2015
quotequote all
Thanks gents...

Yea, I had it stripped down completely to a bare block and had all the ring out to check ring gap so I know rings are all good.

It's obviously a bit late now anyway!? lol but had everyone been saying "you're fked, it's going to fail and take everything else out with it" then I might have done something about it. . . But the above is pretty much exactly what I wanted to hear!

It's due on the dyno for final mapping in a few weeks, if I suffer any catastrophic failures you lot will probably be the first to hear about it! lol

Thanks again