[LS1] Marks on piston & head

[Brettly-2008]

The carbon at TDC of the bore, not the carbon on the piston.

My first car (last century, when I was young and had enough knowledge to be dangerous ) I did a valve grind and clean up. It went from blowing no smoke, to blowing a lot of smoke after I cleaned that ring.

Interesting advice given they don't come from the factory with a carbon ring...

 

[Skylarking]

If you do clean the top of the piston, don't remove that ring of carbon around the top of the bore.

In old engines with a mechanical pump and an old fashioned carburettor, the result from carbon hot spots could be that the motor would continue running even after being switched off. In such cases it wasn’t just the spark timing that controlled ignition as the carbon hot spots could also set off the bang

Such run on isn’t an issue with modern electronics as fuel and spark is cut when commanded at key off. But it can mean that ignition timing may not always be optimal when the engine is operating if there are carbon hotspots playing funny buggers with ignition.

Thats why carbon build up on a piston, head or cylinder wall can cause hot spots and such isn’t a great thing for any engine and should be removed when opportunity presents itself

If the piston rings don’t seal well after a carbon clean up, and you now consume oil, there are other issues at play and it’s not the decarbonising as the root cause

 

[figjam]

Interesting advice given they don't come from the factory with a carbon ring...

Yep. New engines don't have ring and bore wear.
My advice was was that this ring could help seal the rings on an older engine.

If the piston rings don’t seal well after a carbon clean up, and you now consume oil, there are other issues at play and it’s not the decarbonising as the root cause

Yep, again.
It was an old engine with no pcv valve or such. It had a lot of miles and a valve grind and clean up created issues which were not evident before.

The rebuild was not a result of this, but my need for more HP in the days when a bit of mechanical fiddling brought good results for not much $$.
0 > 60mph in about 20 secs, and 1/4 mile times a little quicker, in the mid'60s was average, and easily improved upon.

 

[Brettly-2008]

Yep. New engines don't have ring and bore wear.
My advice was was that this ring could help seal the rings on an older engine.

Any piston ring, worn or otherwise, would barely touch this soft, petrol-soaked bit of carbon area for less than a micro second at TDC and would surely have zero affect on sealing.

Anyway, it's one of the the first things I clean whenever I have a head off a used engine. In fact, I did it yesterday on my Yamaha outboard - gasket surfaces, piston tops, chamber and cylinder carbon ring... new spark plugs. Cant beat a squeaky clean combustion chamber.

 

[MiKExAUS]

Any piston ring, worn or otherwise, would barely touch this soft, petrol-soaked bit of carbon area for less than a micro second at TDC and would surely have zero affect on sealing.

Anyway, it's one of the the first things I clean whenever I have a head off a used engine. In fact, I did it yesterday on my Yamaha outboard - gasket surfaces, piston tops, chamber and cylinder carbon ring... new spark plugs. Cant beat a squeaky clean combustion chamber.

Thanks for your input. What method do you use to clean the carbon off the piston tops? I was going to just scrape off the carbon in the middle with a plastic scraper after soaking with oil but I think I'll clean the whole thing after being reminded of the issues hotspots may cause.

 

[Brettly-2008]

Thanks for your input. What method do you use to clean the carbon off the piston tops? I was going to just scrape off the carbon in the middle with a plastic scraper after soaking with oil but I think I'll clean the whole thing after being reminded of the issues hotspots may cause.

I just move the piston to TDC and cover every other cylinder and water/oil jacket with cardboard, rags, tape etc. Turps on a rag will clean basic gunk but baked on stuff will need a wire wheel on a drill. The wire wheel has the added bonus of flicking the black stuff well out of the way and it doesn't cause any damage to piston top. Some gunk will end up between ring land area and cylinder but as you move the piston down an inch at a time, wipe away any remnants until at BDC, where you should be able to see if anything else has remained on the cyl wall. Keep wiping as often as required.

 

[Skylarking]

Yep. New engines don't have ring and bore wear.
My advice was was that this ring could help seal the rings on an older engine…

... It was an old engine with no pcv valve or such. It had a lot of miles and a valve grind and clean up created issues which were not evident before…

In an old worn leaky engine full of decomposing decayed cruddy oil, you can find that the crud may help slow/stop some oil leaks. Some say running oil flush in such engines isn’t a great idea as the oil flush can soften the crud which allows it to move and possibly block fine oil passages and thus cause rapid wear in places that get starved of oil. Me, I don’t disagree with such sentiment about using oil flush on an old engine but I really think it’s the engine screaming “rebuild me“ and it deserves some TLC

It’s sort of the same with sealing rings and oil control rings which may be sitting in crud filled slots within their pistons. The crud soaked oil control ring may not be doing its job too well but it may be managing ok. However if you use a liquid to clean the carbon from the piston top, some will soak down into the piston rings and oil control rings. Who knows what the result may be but I’d speculate the crud may be softened and then as the cleaner flasher off it may harden a bit and hold the piston rings and oil control rings in a different position so they may not now be working as good as they was before. This would likely be the mechanisms at play and why an old engine may experience higher oil consumption and lower cylinder pressures post sloppy carbon removal.

So I’d think that removing the carbon ring around the top of the cylinder itself wouldn’t do anything since that carbon ring serves no purpose at all, doesn’t seal anything and may cause air/fuel mixture ignition issues if left.

Guess removing that carbon ring and having problems was somewhat coincidental and could leads one to misinterpret cause and effect…

Me, I’d clean off as much carbon as possible but avoid flushing liquids down the bore of an old work engine.

Disclaimer… I may be wrong and just talking rubbish but it sounds reasonable to me based on my limited engine work when dinosaurs roamed the land

 

[Fachoo]

That's a good guess.

You can clearly see that marks were there from a long time ago and/or many kms as the carbon build up is covering most of the lil indents.

Mark shapes indicate spark plug steel end as @Deuce suggested.

 

[figjam]

Disclaimer… I may be wrong and just talking rubbish but it sounds reasonable to me based on my limited engine work when dinosaurs roamed the land

But, but .... you are 120 years old !
You must have worked on side valves, and Holden Greys, Ford Zephyrs, and ...... umm, steam engines.

 

[Fachoo]

hard carbon build up in heads is tec kne lee good, makes head chamber smaller and increases compression in old low comp dinosaur engines.