steveg
Posted a lot
Posts: 1,586
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Jul 17, 2015 18:35:49 GMT
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I'm trying to work out whats been going on with engine in my latest project. It was oiling up the plugs and lacking compression on one cylinder. One of the bores has deepish vertical score in it and the others have a few minor ones. The pistons have some scrapes as well. There are some marks on the top of all of the pistons that look like something has been in there but they are only at the back. The back of the valves don't look all that gunged up so I was expecting a broken ring and damaged oil control rings. This pistons look like this. I'm hoping that a hone and new rings will be enough but wonder what it was that got in and caused the damage, if that whats happened. I wonder if the engine has been overheated at some point as it's had a water leak (evidence of coolant stains and a new water pump), could the damage be detonation ? I have been looking for pictures of overehated pistons and all the ones I have found look like drink cans that have been dug out of a fire ! It isn't anything interesting unfortunately only a Mk4 Astra, if I can make it work it will be a cheap daily so I can get on with my other projects.
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Jul 17, 2015 18:48:41 GMT
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Have you cleaned it up ? If not i would tend to think someone has had that apart before fixing something before ?
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steveg
Posted a lot
Posts: 1,586
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Jul 17, 2015 20:01:50 GMT
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I have cleaned the top of the piston up a bit to get a better idea of what the marks are. I don't think it's been apart, I can't see any evidence of anything being taken apart apart from the new water pump. I will have a good look at the head tomorrow. It might be that the damage is just where the head is closest. It just seems odd that all of the pistons have similar marks. You might think if a plug had broken it would just be one.
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Jul 17, 2015 20:07:37 GMT
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Hi, I've seen and used worse, so yes hone the bore and new rings. The marks in the middle could be pinking evidence, so makes sure the timings correct to stop further damage.
Colin
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Fungus
Part of things
Posts: 960
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Jul 17, 2015 21:16:50 GMT
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I had a polo that broke a spark plug electrode off and did the same thing, could be the cause?
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steveg
Posted a lot
Posts: 1,586
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Jul 17, 2015 23:17:49 GMT
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Thanks for the replies. It should be OK timing wise as it's all ECU controlled, it's probably swallowed something. I might have a look round to see if anything is missing.
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Jul 18, 2015 10:19:45 GMT
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Does look like it's had solids through it. Possibly the marks are there because that's where the squish zone is on the head?
The bore scratches are likely the same cause where something has found it's way down the side of the piston.
Maybe run without an air filter at some point?
What engine?
Nick
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1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Jul 18, 2015 15:29:53 GMT
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^ I'm thinking same as vitesseefi If all pistons are same, it's not a failing sparkplug etc (as they would only affect 1 cyc) Possible pinking but bore damage says not. I'm thinking lots of small foreign bodies (missing airfiler / grit ?) due to piston dents and scratches on bores. Does engine run at an angle with damage on the "low" side of the block? or is damage on the intake side / squish area? * me not an engine expert, my guesses may or may not help
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dyno
Part of things
Posts: 14
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Jul 19, 2015 16:12:12 GMT
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Check the ends of the valve guides. Have had this problem on our X14XE engine.
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Jul 19, 2015 19:45:03 GMT
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That is evidence of something solid popping in for a look.....
If all the pistons are the same it's come via the intake i would suggest. Pre-ignition would leave localised damage if it any at all.
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Needs a bigger hammer mate.......
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steveg
Posted a lot
Posts: 1,586
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Jul 19, 2015 21:18:00 GMT
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Thanks for the replies, been busy doing non car stuff all weekend. It a late 1.6 8 valve with the fly by wire throttle. It doesn't seem the sort of car that would have been run without a filter but there is always a chance something might have got into the casing during a filter chance and wasn't spotted. I haven't stripped the head yet so will check the guides etc, that wasn't something I had though of thanks. What I don't want to be doing is rebuilding it all only for whatever it is thats been floating about in there to do more damage. I'm at the stage now where I might load the important bits in the car and take it to be looked at. It will need a hone and rings at least, might have to have new pistons though. Normally you can spot what gone on fairly easily this just seems a bit odd, it's not like there are huge steps in the bores or anything.
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