What's happened to my engine?

[Inksta]

No fuel pressure issues, though I agree that it would be nice to know why so much carbon. The engine has always run well, no real troubles at all. It had gradually started using a fair amount of oil (maybe 2 litres disappeared between each 10,000k oil change) - but virtually no smoke out the exhaust, and I put it down to leaky seals.

It's dríven daily and the engine has around 250,000 kilometres on it.

As you suggested, there's no discernible notching on the cylinders, so that's a plus.

[Inksta]

Things looking a little healthier in this shot!
Waiting on rings and bearings to arrive, then the rebuild starts.

Also, I spoke to the machine shop about the carbon - they thought that it wasn't caused by any particular failure, just the result of a high km engine and slow commutes to work. Need to drive it harder more often

[StanTheMan]

how much did you have your deck shaved by?

check protrusion of pistons.
check thickness of head gasket.
when engine warms up parts will expand and also stretch a little at high RPM.

I dont recall what the minimum clearance is any more. just check it though

Ive had my pistons hit the head with a slightly thinner head gasket at 3500 rpm upwards . worked fine with a standard size.

I'm talking about my Old B6 motor....

[Inksta]

Thanks Stan, good point - I'll watch out for that. Going to be using OEM head gasket.

[hks_kansei]

Unless you specifically asked the machine shop to mill it down a lot, or the head/block had a really deep gouge, it wont be an issue.

To start having issues with pistons and valves etc you're looking at having them mill off whole millimetres.

A skim, which is what pretty much every machine shop will do unless specifically asked to to otherwise, is tenths of a millimetre.


And also assuming you're using OEM spec pistons, and havent gone for high comp ones or something.

[StanTheMan]

mmmm Id still tread carefully & check tolerances

My B6 motor had standard pistons which protrude 0.4mm above deck. and that is nothing unusual for B6's. My NB motor didn't protrude out like my B6

I went from a 1.3 standard head gasket to a 0.9mm for extra compression. it was too much. My pistons started hitting the head. Valves were fine.

[Inksta]

Yep they took off four thousandths of an inch (~0.1mm).

I'll keep an eye on it just in case.

[Inksta]

Just a little follow-up to finish this story.

Started it up last weekend, set the timing and went for a test drive. Touch wood, all good so far. Feels like a new engine. Pretty satisfying to have finished the job without any major dramas.

New bearings, rings, clutch, engine mounts, basic head job etc. - this "timing belt job" ended up more time consuming and more expensive than I had anticipated, but on the other hand I've got a car that feels young again, and learned a lot.

Thanks for all the help and advice. It's good to be back in the 5!

[Inksta]

Bonus shot of engine going back in:

image.jpeg

[Red_Bullet]

Well done mate. There's something really satisfying doing stuff yourself and learning learning learning along the way.

[StanTheMan]

Did you work out why your engine was getting stuck?


Sent from my iPhone using Tapatalk

[Inksta]

The fouling was being caused by excessive carbon build up. There was a good couple of millimetres of junk on top of the piston, and my theory is that when the car sat for a couple of weeks while I did the timing belt, some of it shifted - so it became a problem suddenly. You can see some spots (eg the flat bit at 12 o'clock) where the carbon was compressing against the roof of the cylinder:

piston 2.JPG

Thankfully no damage done in terms of bent valves etc.