marks on top of piston ok to carry on fitting head

[peterg60]

hi all got some marks onto of the piston and would like to know if they ok to re-use. i noticed them when i was swapping over the conrods to some forged ones. the engine was brought from a running 80,000 mk4 1.8t 20v agu engine code. i fitted the engine into my mk1 project got it all up and running and sounded and was running ok. only drove the car in and out of the garage as its not ready yet. havent cleaned the pistons just let them soak in clean petrol. rings looked fine no damage but bore no 2 and 3 have a mark on them it feels smooth. so here some pitures i took today


piston 1



piston 2



piston 3




piston 4





also cylinder bore 2 and 3 have a mark on them it smooth





cylinder bore 3



here is the valves none are bent







so what u think? are they doomed? or can i just go ahead and fit the head
edit. just been out and checked bore 2 and 3 . number 2 has no deep mark at all tryed scraping gently with my finger nail bore 3 has a mark bout 10mm long . i can get my fingernail in

 

[<tuffty/>]

I wouldn't be using them mate... that mark on cyl1 looks like its fractured the crown and that will weaken the piston... I wouldn't risk those... I have used pistons with very light marks before as they can be wet sanded out...

As for the bores... have you run a honing tool down them? I normally lightly hone bores to deglaze them when fitting rods to engines... if a very light hone doesn't get rid of the marks you may have to go in a little harder but you obviously can't take too much out... the pictures aren't the best so can't say much more than that about them..

Have you turned the head over by hand to check the valves? whats the history of the engine? looks to me like the cambelt has gone... there are marks on the opposite side of the pistons too where the exhausts have hit too...

They should look like this cleaned up...

<tuffty/>

 

[peterg60]

I wouldn't be using them mate... that mark on cyl1 looks like its fractured the crown and that will weaken the piston... I wouldn't risk those... I have used pistons with very light marks before as they can be wet sanded out...

As for the bores... have you run a honing tool down them? I normally lightly hone bores to deglaze them when fitting rods to engines... if a very light hone doesn't get rid of the marks you may have to go in a little harder but you obviously can't take too much out... the pictures aren't the best so can't say much more than that about them..

Have you turned the head over by hand to check the valves? whats the history of the engine? looks to me like the cambelt has gone... there are marks on the opposite side of the pistons too where the exhausts have hit too...

They should look like this cleaned up...

<tuffty/>

i havent used a honing tool but i think i will take the pistons out and hone the bores. i will also turn the head over by hand and check the valves. i go and do that now and get bk. when i brought the engine it was running i drove it and it was fine.. i changed the cambelt as used a different tensionor.

 

[peterg60]

just been out and turned the head is it supposed to be hard to turn by hand? the valves open by say an 15mm not really sure what im looking at . but they all seem straight when looking via the exhaust outake and intake

 

[murran]

the cambelts gone on it at some point in the past and its been repaired thats all.

the heads of the valves have put those marks in the piston crowns when theyve hit.

should be fine to reuse. ive repaired quite a few of these after a cambelt failures. never replaced any pistons with these marks.
only thing i do is make sure theres no slight lips or high bits around the little dints. these cause hot spots on the piston crown and can be a cause of pre-ignition.

id be more concerned about the marks on the bores. can you feel them with your nail? as said...the bores need honing see if they are just surface or might be a small crack in the bore, bores also look quite glased and shiny to me too.
unusual marks tbh not seen ones like that before. wierd.

 

[peterg60]

cylinder bore 2 is fine cant feel nothing when i use my finger nail looks like a stain. cylinder bore 3 i can feel a scratch with my finger nail bout 10mm long

i didnt hone the bores but i think i have to know.

whats the best way to remove the slight lips?

 

[murran]

the ally of the pistons is very soft a bit of sand paper will suffice but try to only sand the high spots where the dint are. not the surrounding area.
if your stripping the pistons out then do it on the bench.

but look at the bores first get them honed and look closely at where the marks are. i think you'll find little cracks into the water jacket.

 

[peterg60]

ii hone the bores at the weekend and post back

 

[aragorn]

No way would i reuse those pistons.

In some crappy 1.2 corsa or something maybe, but in a turbo motor thats undoubtedly going to end up tuned etc not a chance.

If you can feel marks on the bore walls with your fingernail, the bores are probably shot. A 1 size overbore takes 0.25mm of metal off the bore wall, and if you can pick it up with your nail, chances are its at least 0.25mm.

Personally, i'd go buy another engine unless your prepared to build that one properly with a big rebore and new pistons.

 

[<tuffty/>]

If it was just the little marks around the outside edge of the piston crowns then I would agree with a little gentle sanding they could be reused... but... the mark/dent in the middle is what makes these unusable IMO...

I would not want these pistons in a turbo engine at all... I don't know what turbo you plan to use but even a K03s will produce some pretty high cylinder pressures and with a compromised crown I would not be using them personally

<tuffty/>

 

[peterg60]

Well some good news machine mans been and said the marks on cylinder wall are from water stilling on pistons 2 and 3. Like the engine has been sitting for a long time on its side. He said engine has had a cambelt failure and the head valves look fine its either had a new head or been recondition. he took the head for a check over. His coming to hone the bores Friday and bring me new piston rings. now for the piston im still deciding what to do. i can get hold of some apu passat piston in great condition for not much. or get some news ones and live on bread and water for the rest of the month lol

 

[peterg60]

also could i run apu pistons into my agu block ? im sure both have 20mm wrist pins but are the piston ok to fit in

 

[murran]

if your unsure about the marks in the pistons and the bores......... just go buy another short motor. after all youve got a head in good order......

personally i think those pistons would be ok running around normally on a standard set up. but if your going to be tuning it and running more boost and such like. going on trackdays etc.... i wouldnt want the thought of those slightly damaged piston crowns on my mind.

i'll be interested if those marks are just from the engine being sat on its side out of a car. i dont think so, i think there will be a hair line crack into the water jacket behind the rust mark.

 

[PAULF]

Get new pistons. They have been hit by valves and compromised.

You've gone to the trouble of stripping it this far, don't take shortcuts.
You may get away with honing the bores, and fitting oversize rings (if you can still do such a thing now - it's been a while since I last did that - Astra 1.6D Van ). If not, get the rebore and oversize pistons.

If the valves hit and made those marks, they are bent. It may only be fractions of a thou', but they are almost certainly out of true.
What are you wanting the car for?
If it's to keep you going for a year or so. then fine, everything probably will last as is. If you want to mod things, or keep it a while -
you really should remove the valves and DTI the stems
It will cost, but you're already halfway there time-wise now, so unless cash is REALLY tight, do it right, not twice :icon_thumright:

(Having said all that, I got away with it on my L200 after snapping the cam belt and actually breaking rockers when they hit)

 

[peterg60]

things cant get any worse. i was cleaning the sump out this after noon and guess what i found at the bottom. the oil squirter from clyinder 1 that sits at the boottom of the bore. im done with this block. got a few questions im going to pick up a passat apu block trm complete no marks in bores no marks on pistons. i know i have to remove everythink of my agu block onto apu block . i need to know i got some forge rods 20mm wrist pins and some racing bearings will the bearings be ok to use on the passat apu block? i think the apu has 20mm wrist pins
. also will i need to use the orignal mk1 mount or will the 20v mk1 mount work
thanks

 

[Broken Byzan]

different engines entirely.

APU is 058 and AGU is 06b, accessories wont swap

 

[peterg60]

thanks every one whom replied i just sourced a engine collect next weekend. ayp engine going to get my agu head fully recondition and fit new rings and hone apy block and fit my forged rods lol well thats the plan

 

[murran]

wierd. has the oil squirter snapped off? is the little banjo bolt that holds it on also in the sump?

think youve made the right desicion sacking this block off. is it a short engine your getting?

your head should be ok as its obviously been repaired previously. just a strip and check/clean and lap the valves in.

 

[<tuffty/>]

Its easy to ping squirters off when dropping in rod/piston assemblies... the rod catches it on the way down if not careful... also need to watch the little buggers when honing..

<tuffty/>

 

[peterg60]

well machine guy came today gave my block a hone and he said its all ok no cracks. so i decided to use the block. picked up a apu passat block today took piston out and oil squirters all match.and in good condition. got some new rings aswell and the head is being stripped cleaned new valve guides and skimmed so all looks good hopefully lol

 

[bumere46]

not bad
I will take a pic and show you my pistons on my 4.2L V8 A6