Are my pistons knackerd?!? * pic inside *

[YoSono]

well i took the head off my GTD block (RA engine code) to discover this:



now, i'm not a big engine expert, but to me it looks like the engine has had a timing belt snapped in the past, and the exhaust valves have been stuck open and bashed into each piston face. I've checked all the cam followers / guides / valves / and piston bores for any damage, and there isn't anything to report, so obviously the problem was sorted, and driven around with the pistons looking like this?!?!  

what kinda difference does this damage make to the engine performance, and is it repairable? wanna know, so as i know if i need new ones, or whether i can just repair n clean the old ones.

cheers for any advice  

lee.

[tylernt]

It sounds like the head or at least valves and valve guides were replaced after the head banging incident. Those are the biggest valve impressions I've ever seen on pistons!

That said, there are several guys driving around on pistons with valve impressions, with no ill effects so far. You have probably lost a bit of compression due to the impressions but if it still starts in the cold, well, no problem.

If you're on a budget and it ran well before disassembly, keep the pistons. If you have the money to do it right, I'd replace them.

[crazybushman]

I rebuilt my 1.6TD a few months ago, and it had the same impressions (maybe not quite as deep), the car ran fine before I did the engine, and it still runs fine and makes good power.

Cheers!
Tyler

[YoSono]

well, to be honest, i bought the engine complete from a scrapyard, cheap! the car turned up, and i jumped on the chance at getting the engine out before it had even gone into the yard to be dismantled. So, before i took the engine out, i had the chance to test drive it around the yard. This was back in december, so it was pretty cold at the time, and it had trouble starting (had to bump start it in the end) no glow light plug came on, so i thought that was the answer, but hey, it could be due to these pistons?

When i started taking the engine to bits, i noticed that someone had put 2 new glow plugs in, which were the ones for the non-turbo engine... at this stage i thought that this could have been why it wouldn't start from cold you see.

So, lets say i replace the pistons, is this gonna be mega expensive? and what do you mean by "cam caps" is that another term for "cam followers"?

cheers guys
lee.

[YoSono]

...Also, will the pistons out of any of the other (non-intercooled) TD's fit? such as the JX? or CS?

thanks
lee.

[SMOKEYDUB]

when a valve hits that hard there is a good chance of the piston mushrooming out and making the piston ring stick which would make it hard to start because of low compression.

[hillfolk'r]

my old jetta engine looked like that,,but it ran,,i popped the first head gasket,and found that and i know i didnt do it,,,,,,it ran ok though,,,,,worst hole had 440psi,,,,best 480,,,,,also some yoyo totally sprayed the old head gasket with spraytack permatex copper,,that was nice :roll:

[steve]

My crank bolt broke a year ago (same effect as loosing the timing belt) and my pistons had hardly a trace of valve in the soot on the piston top.  The cam and head were severely thrashed though.  So I suspect it's not from a t-belt breakage... unless I have super strong pistons in my 1.6 TD for some reason.  But that looks like maybe a problem that accumulated over time from a cam timing problem.

[YoSono]

interesting... i was checking the VW part number on the head gasket, and it is the thinest one out of the three they have for the RA engine code. Could this also be somethign to do with it? When i took the head off to i did notice tiny fragments of aluminum, on the exhaust valve heads (not sure if thats the technical term, but i'm taking about the flat face of the valve, the thing that has hit the piston) i didn't think much of it when i was cleaning them, as there was no damage... but now i know where that aluminum came from.

It seems like the general consensus is that the engine will still run fine, if i did stick with the pistons, should i go and get them professionally reground or something, so that the tops of the pistons don't look as nasty as they do atm. When i say reground, i mean taking off the lip caused by the hitting valve.

Other than that, i'll hope n pray for a set of secondhand RA pistons in good condition

cheers
lee.

[steve]

I would defnintely smooth and blend out the sharp corners in the problem area.  Aluminum is not a good metal for fatigue resistance so any reduction of stress risers seems like a good thing.  I wonder how much this will affect the compression ratio?

[gldgti]

check the piston projection over the top of the block... the compression ratio might still have been fine anyway, given it had the thinnest head gasket on it... i agree, get the high parts around the damaged area machined off at least

[YoSono]

so what are the side-effects of low compression? would it smoke a lot? and give less power? I'm wondering if this could be the reason why it wouldn't start on ignition (had to be bump started) and that it put out quite a bit of white smoke.

is it because there is a new indentation of the top of the piston, that creates more space in the chamber as it compresses, and therefore lower compression rate? sorry if this sounds like dumb ass speak, but i'm new to all this diesel milarky, and am interested to know

lee.

[steve]

the temperature achieved during compression has to be high enough for combustion.  the lower the combustion ratio, the lower the temperature and harder to getter going on cold mornings.  Once it's warmed up it's not so big a deal.

Yea, a big dent effectively makes the combustion chamber bigger.  thus less compression pressure and temperature.

also a consideration is that idealy all the combustion chambers should be the same volume and shape for a smooth running engine.

I think if it were me I'd say it's time for a rebuild and do it all up right.  check everything, replace whatever isn't up to snuff, and you're good for good long time.  Then you don't have to worry about it and be fixing a melted pistion that left you stranded on some hill in the snow.  I've been known to do less than ideal too.  but I haven't regreted doing a complete rebuild a few years ago.  she runs like a champ.

[fspGTD]

Moved to troubleshooting.  Not IDI engine / power enhancement related.