1.8t Piston damage (failed cambelt)

[coyleben]

Hi, i have taken the head off my 1.8t today and piston no 2 is heavily scored with valve damage, will it still work when reassembled??

I have a pic http://tinypic.com/view.php?pic=2q32b9i&s=7

Thanks

[phil miller]

hi mate from the pic it doesnt look that bad, whenever a valve and piston have a coming together it will leave marks like this, if in any doubt get a local engine builder or mechanic to take a look

[Crasher]

Not ideal and at the least you should polish off any sharp edges to avoid detonation hot spots. I have taken pistons out that looked like this and you can sometimes see cracking on the other side but I have also known engines run like this with no problems. As the head is off (the most difficult step in removing the pistons), if it was my engine I would be fitting a set of new pistons after running the honing stones round the bores a couple of revolutions.

New 1.8 T pistons such as the typical AUM piston 06B 107 065 N aren’t daft money from Mahle (033 16 00), NÜRAL (87-502900-10) or KS (40 434 600) and all you would need to add is a set of rod bearings and rod bolts at about £3 each and a tube of sump silicone seal.

[coyleben]

Hi, Thanks For the reply, Is it a big job to change the pistons?

How do they get removed? Can you remove them with the engine in the car from the sump ??

Any help would be great, Thanks Ben

[Crasher]

With the head off, very easy. Take the sump off (which on a 1.8T is a good idea anyway) and then using a 12 sided 14-mm socket (from memory) remove the con rod bolts and the pistons just push out BUT getting them back in requires a ring compressor. I suggest you practice using the old pistons first. It would be a good idea to get hold of a cylinder hone (Goggle it) and pass this around each bore a few turns on a drill.

If you decide to do this, keep me posted and I will advise you as you need it.

With the sump off, get a new oil pump pick up (about £15) and clean the inside of the sump with paint stripper to get all the sludge off so the surface is spotless and shiny. Polish the gasket face up with a wire brush in a drill before putting the sump back on, I will post a picture of the way to apply the VW sealant when you get there.

[coyleben]

Thanks very much, ill keep you posted

[a8 tech]

Personally I would re work the crowns and repair the head, I would avoid replacing the pistons and defiantly avoid having to hone the bores.

What you find if the bores have circular black marks then this is a sign of blow past all be it a small amount but its the cause for oil consumption and honing will worsen it.

If you wish to rework the short motor then replace it don't repair it.

I faced a similar issue 4 years ago with an S3 which had contact on every cylinder from the inlet valves, now the engine had covered 90k with no prior excess oil consumption so we rebuilt the short motor but found the oil consumption increases after the repair.

Stripping the engine again after leak test found no issue I found small black marks on the bores halfway down so replaced the short motor and fault sorted.

Recently I bought a none starter s3 and found the same piston contact but no bore damage so just re worked the head and cleaned the crowns and all is fine as my mate bought it.

Just check the piston protrusion to ensure there is no damage below

[Crasher]

Rod bending is a good point, I doubt he has a dial gauge but I have to strongly disagree with your dislike of honing and top ridge wear worries, I have rebuilt hundreds of engines this way over the last 25 years and have always had excellent results. I would not do this if the top of the bore exhibited a significant wear ridge though. I doubt he has the finances or lifting equipment to change the block as I did on my 1.8T.

[coyleben]

Hi, Is it possible to replace just the 1 damaged piston? or do you have to replace them all? Thanks Ben

[a8 tech]

Rod bending is a good point, I doubt he has a dial gauge but I have to strongly disagree with your dislike of honing and top ridge wear worries, I have rebuilt hundreds of engines this way over the last 25 years and have always had excellent results. I would not do this if the top of the bore exhibited a significant wear ridge though. I doubt he has the finances or lifting equipment to change the block as I did on my 1.8T.


I do agree with the repair you suggest but only if you do it lol

Not spoke to you for a while anyway crasher, hope your in good health :D:D

[Crasher]

Yes but it is not ideal as the new one may weigh significantly more/less than the original as I found once.

Yes old man, I am alive-just...

[coyleben]

Hello, the other 3 pistons are fine but i have cleaned up the worst piston today and i think i may get away with not replacing it?

What do you guys think?

Heres a better pic of it

http://tinypic.com/r/25zs5ug/7

Also any tips on cleaning up the top of the block ready for new head gasket

Thanks Ben

[Crasher]

That piston is too badly damaged for me; I would feel very aggrieved if a customer insisted I put an engine back together like that.

I block off the oil galleries with cloth that I can retrieve with pliers and then polish the top off with a wire wheel and then run gently over it with 80 grit on a flat steel block, the surface must not be too smooth or the gasket will not bite. When I have finished I blow all the water galleries out with an air line and then rinse them out with brake cleaner and also blow all the oil galleries down including blowing the main oil drilling down with the filter off and using brake cleaner to do my best to make sure it is perfectly clean.

[calum]

Hi, Thanks For the reply, Is it a big job to change the pistons?

How do they get removed? Can you remove them with the engine in the car from the sump ??

Any help would be great, Thanks Ben

Engine must be raised to be able to remove the sump, undo the caps on the con rods then the pistons will slide out the top of the block. It is quite involved though so if you're not sure I'd get someone to do it, there are two bolts on the sump that are only accessible when you rotate the flywheel to the correct position for tool access.


Calum.