Hello everyone,

My first post. Just become a 1986 Ninety Owner in the last month and have been working on the 200tdi engine that has been a replacement for the petrol original. Had some "black smoke" on startup but engine very willing and keen to get going. Some oil in injectors and glowplugs so did compression test (via glowplugs) and had pressures of 370-430 on a cold engine. This seemed reassuring (is it?). Took off cylinder head and when cleaning noticed that the combustion bowl/piston bowl on one piston was smoothly eroded. It's smooth like a pebble on a beach. In the photos its about at the 12 o'clock to 2 o'clock position. I don't have any technical knowledge so what does this mean? Is it a replacement situation? Obviously the volume of the "bowl" is slightly changed and not symmetrical. Just for information the head had cracks between valves on 2 pistons (including the one with the deformed bowl) and between the glow plug and the injector. I think I know that means I need a new head. But what do you make of the piston? Can I get by for a while without having to remove the engine? Any thoughts very welcome.

I am not an expert in this sort of internal engine diagnostics so wait for an adult to come along and give a proper answer. But over fueling can cause pistons to melt. So maybe an injectors issue on that piston if that’s the only one?

Also as a shameless plug. If you do need to replace them I have a good used set of pistons and rods that are for sale. Unfortunalty I cannot help you with a new head.

Don't think you will get a new head, 2nd hand or reconditioned if available.
Puff of black smoke is pretty normal on start up it would seem.

Local heat buildup.

If its one cylinder only then over fueling injector or blocked oil gallery in the piston crown are possible causes, with the latter only relevant if the 200TDI has oil cooled pistons. Local blockage in coolant gallery might be another cause.

Checking the coolant gallery is easy with the head off. Injectors need specialist equipment. Checking the oil gallery in the piston bigger job with crank out.

Deciding to keep or replace the piston depends on how much damage and what appetite for future issue risks.

A while back I saw a two-stroke piston crown with a burnt hole "repaired" by screwing a self tapping screw into the hole...it worked for far longer than it ought have.

Thank you for the responses. It seems like there are lots of re-manufactured 300tdi cylinder heads but not nearly so much choice for 200's : this seems like an option? https://www.autotechcylinderheads.c...reconditioned-cylinder-head-sk0991-00040.html Would there have been any (external) way to tell that the injector was "over-fuelling"?

JohnNinety said:

Would there have been any (external) way to tell that the injector was "over-fuelling"?

Click to expand...

The injector wont be over fueling - the quanitity of fuel is the job of the fuel pump - but if the injector is not atomising the fuel correctly it might not be burning evenly, creating a potential hot spot.

Testing an injector spray pattern really needs specialist tools.

New head gasket, get injectors checked/reconned and crack on, no pun intended!

Cracks in the head between valves are not unusual on 200 engines, mine has had a cracked head for years, no leaks no coolant loss, keep on trucking.

I think even my spare cyl head has cracks in it.

Most likely is what @SimonBrown says in above post. Hot spot due to poor injector spray pattern.
Black puff is the 200's excess fuel start system working, good for getting dirty looks at the supermarket car park.