Piston as seen using an endoscope

[nsa]

...as seen down the spark plug hole. The endoscope is just a £10 eBay job. I took more pictures but unfortunately this is the best. All four pistons look like this.



The engine runs fine and compression etc is good and it doesn't use a lot of oil, but I assumed the pistons would be shiny clean. Is the wet patch oil sucked up past the piston rings, and is it worth trying to do something about the brown coating?

[cptsideways]

They will not be shiny, looks sweet to me, you might have a drippy injector though

[226bhp]

If you knew what had been going on in there you wouldn't expect it to be clean!

[TheEnd]

Yea, that's pretty normal.
Check out some pics on google images and you'll see they all have that blacked carbon crud built up.

[nsa]

Great. Thanks. I'll check if the same wet patch appears under the other injectors and investigate cleaning them.

[Rwdfords]

Looks like it is running a little rich somewhere in the rev range, ideal colour is sandy to light brown, light grey is ok too, in NA race engines an optimised burn would leave every surface in the chamber + piston light brown, easier said than done but can be achieved over most of the piston crown and chamber, if this is a race engine you have work to do! either way the AFR needs fine tuning

[shalmaneser]

I've just replaced my heaad gasket, mine were significantly cleaner than that. Maybe running a bit rich?

[Pumaracing]

Rwdfords said:

Looks like it is running a little rich somewhere in the rev range, ideal colour is sandy to light brown, light grey is ok too, in NA race engines an optimised burn would leave every surface in the chamber + piston light brown, easier said than done but can be achieved over most of the piston crown and chamber, if this is a race engine you have work to do! either way the AFR needs fine tuning

I've never seen piston deposits that were anything other than black whether road or race engine. Exhaust valves should certainly be brown if the mixture is correct but those pistons look quite normal to me at least.

[George111]

Looks like a picture of an aubergine in bad light.

[poppopbangbang]

Pumaracing said:

I've never seen piston deposits that were anything other than black whether road or race engine. Exhaust valves should certainly be brown if the mixture is correct but those pistons look quite normal to me at least.

By 700KM our stuff has an even black coating on the crown (the exception being in the inlet valve pocket areas due to fuel wash) and defined ring in the unswept area of the bore. If it had all gone brown I'd be pretty worried.......

OP that looks absolutely fine for a road car motor, don't worry about it.

[PeterBurgess]

Most interesting it takes 700km to 'coat' the piston crown. On and off we have been experimenting with piston crown finish/texture to encourage a rapid 'carbon' coating to act as a thermal barrier (jury out as to whether bhp is better earlier in engine life or not), do F1 piston crowns have any coating/surface finish/texture work from as machined finish?

Re ex valve colours, we find the colour varies depending on what octane booster/lead replacement additives are used above and beyond the brownish colour expected from pump fuels. Millers seems to give a very olive colour which we are lead to believe is a manganese compound.

Peter

[nsa]

Thanks again. I appreciate people taking the time to look. The spark plugs had a nice beige glaze to them as well.

[Evoluzione]

PeterBurgess said:

Most interesting it takes 700km to 'coat' the piston crown. On and off we have been experimenting with piston crown finish/texture to encourage a rapid 'carbon' coating to act as a thermal barrier (jury out as to whether bhp is better earlier in engine life or not), do F1 piston crowns have any coating/surface finish/texture work from as machined finish?

Re ex valve colours, we find the colour varies depending on what octane booster/lead replacement additives are used above and beyond the brownish colour expected from pump fuels. Millers seems to give a very olive colour which we are lead to believe is a manganese compound.

Peter

Why not coat them with Ceramic to begin with?
We're experimenting with it, had four pistons and a head in the oven last week.....



Once it's baked on you can polish it up to a satin chrome finish if you choose.

The Yorkshire puddings tasted better though.


I've often wondered how much can be read and learned from a combustion chamber and deposits left on it, probably useful to some degree, but never seen anything written about it. I'm guessing on a good condition properly running engine clean areas will be from fuel wash and high squish, brown thin coating normal/good and black indicating cooler areas. A good even coating everywhere indicating a good combustion chamber design?

Edited by Evoluzione on Thursday 10th April 10:21

[Thom]

For what it's worth my pistons tops lost their black layer when I upgraded the ignition system. I'm not an expert on the physics involved but I would guess a much stronger spark will help burn most of the mixture more efficiently?

[Evoluzione]

Thom said:

For what it's worth my pistons tops lost their black layer when I upgraded the ignition system. I'm not an expert on the physics involved but I would guess a much stronger spark will help burn most of the mixture more efficiently?

Was the timing altered at the same time?

[poppopbangbang]

PeterBurgess said:

Most interesting it takes 700km to 'coat' the piston crown. On and off we have been experimenting with piston crown finish/texture to encourage a rapid 'carbon' coating to act as a thermal barrier (jury out as to whether bhp is better earlier in engine life or not), do F1 piston crowns have any coating/surface finish/texture work from as machined finish?

Nope just ally. I can't comment on later stuff than 2004 but on the engines we run the crowns are uncoated and have a very finished surface to them. The skirts are DLC or Xylan depending on year/legality.

Worth noting that running GP revs etc. the engines would have come apart again at 400KM so would have very little going on in there by that point.

[chuntington101]

Didn't / don't f1 engines use oil srquirters to control piston crown temps rather than coatings? I thought coatings would add too much weight to the piston to make it worth while.

[poppopbangbang]

chuntington101 said:

Didn't / don't f1 engines use oil srquirters to control piston crown temps rather than coatings? I thought coatings would add too much weight to the piston to make it worth while.

Yes everything we have does.... but squirters aren't really high tech - most road car engines run them too!

[Rwdfords]

Here is what a race piston Should look like, not saying exactly how we achieved this but a lot of work was done on the DCOSP's to greatly improve atomisation to a very high level for carbs, also the mixture was tuned to exactly 12.5 to 13 to 1, mods to the combustion area to keep the fuel in suspension and also get the flame front into the squish areas as soon as possible as the piston travels past TDC and onto the power stroke

If you don't get a burn colour similar to this in a NA race engine you Are loosing power

2.0 pinto tarmac rally engine, the images speak for themselves.

I am sure further modifications could be made and running the top ring even closer to the crown but this is a very good working example, I have yet to see a better burn pattern in a 2V or 4V chamber

Edited by Rwdfords on Thursday 10th April 22:08

[Evoluzione]

chuntington101 said:

Didn't / don't f1 engines use oil srquirters to control piston crown temps rather than coatings? I thought coatings would add too much weight to the piston to make it worth while.

The oil would be heavier than the coating. I'm quite surprised they used them, but it must have been deemed better than nothing, I wonder if piston coatings weren't allowed...