Jump to content
SAU Community

Carbon Deposits On Head Normal?

MerlinTheHapyPig
 Share

Recommended Posts

MerlinTheHapyPig Mentor

MerlinTheHapyPig

Posted
Posted

Now, this is the first engine i've pulled apart so sorry if this is a bit of a newb question.

Refer to pictures, I'm wondering if this carbon buildup on the valves and top of cylinder is normal? (piston surfaces are like this also) I remember helping my dad rebuild a motor years ago, and it was nowhere near this bad. I'm trying to diagnose a possible problem with this rb20det I bought (it apparently had a misfire, but they couldn't figure out what was wrong with it).

Anyway, is this sort of carbon buildup a bad thing? The spark plugs were in similar shape, isn't this ment to mean it was running fairly rich?

head1.jpg

head2.jpg

anyway. like i said i don't really have a clue, but i'd like to have a rough idea of what's going on before i drop it off at the engine builder.....

Link to comment
https://www.sau.com.au/forums/topic/112769-carbon-deposits-on-head-normal/
Share on other sites
Craved Grand Master

Craved

Posted
Posted

hmm the RB30E i just pulled apart was like that, and mad flakes of it on the pistons

my RB25DET was heaps cleaner when i had the head off that, same with the pistons.. pretty much just discolouration not a coating like that.

carl h Proficient

carl h

Posted
Posted (edited)

that engine wasnt DRIVEN like it should have been, carbon builds up when you drive like grandma and dont give the old girl a good flogging once in a while.

when i pulled my head off my block nary a spec of carbon in the head and only a thin coat on the pistons, went well and never had a problem before i blew it.

proly misfired due to the massive ammounts of carbon buildup, hot spots and dieseling occur.

Edited by carl h
Cubes Grand Master

Cubes

Posted
Posted

I recently had 2 heads off an RB30e, one was on gas and perfectly clean, the other was rather dirty and on fuel, no where near as bad as that though.

Shall be interesting to see how the head on mine looks after almost 40,000km's. I drive it like a grandma 90% of the time.

RB30-POWER Mentor

RB30-POWER

Posted
Posted

Way to rich mixtures, nothing more, nothing less. (what caused the excessively rich mixtures would be the real question)

You can get upper cylinder lube/cleaner or carbon clean in a bottle you spray into the inlet manifold and it cleans the piston tops, valves etc, without having to remove the cylinder head.

Water also does a good job, but you have to be very careful, if you don't know what your doing as you can hydro lock it.

You don't want all the carbon in the combustion chamber at all as it can get rather thick in places and cause hot spots that glow and cause the engine to detonate.

You don't usually see modern engines in a state like that, because the ecu's control the injection so precisely.

But you get a backyard racer boys that fiddles with oxygen sensors, fuel pressure regs, injectors etc, without having a clue, you can get the above effect.

carl h Proficient

carl h

Posted
Posted
My guess would be a f**ked 02 sensor.

no way in hell a farked o2 sensor would do that, i didnt run an o2 on my car and had no problem with it.

im gonna guess perhaps bad gas and granny driving did that, but like i said eariler (and this applies to most if not all nissans) you have go give the girl a bit of a go once in a while to keep her happy.

MerlinTheHapyPig Mentor

MerlinTheHapyPig

Posted
  • Author
Posted

intersting...

thanks for the replies, I don't know much about the dude who I bought the motor from, but i believe it was running an aftermarket turbo and higher than stock boost ~180-200kw or so from memory.

No idea if he granny drove it, I'll be curious to see what the head from the rb20det in my car looks like when i eventually blow it and have to change it, because i don't daily drive it, it's a dedicated drift car.

what would be the best course of action to reco the head?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • tsuokun
      Lets play a game - What is causing my oil consumption?

      By tsuokun · Posted

      Yep, so far most have said that it looks like corrosion on the wall from piston not moving. Which then has probably damaged the oil rings and caused those vertical marks. The longest the engine was still after the rebuild, was the winter of 2018 - 2019, plus the boat trip to Japan. When I shipped the car, it had normal gas in the tank but before that winter pause, it had E85 in tank.  In any case, even if either one of those was the cause, it happened close to 6 years ago and the car has been driven something like 30 000kms after the fact. Again, apart from the plugs and the dip stick, there is nothing in the way the car runs that would indicate what has been going on in the engine. I am going to consult a shop and ask their opinion, what would be the best approach. I do have some access to a garage I could use to diagnose further myself, but time is very restrictive. Might end up buying another engine that could be used while this one is being remedied. Without pulling the head, it will be impossible to find out if it needs another bore, but here's to hoping a hone would suffice.  Goddamnit, I would really have preferred this not happening.  
    • 25RBGT
      Got this r31 silhouette flood car to rebuild.

      By 25RBGT · Posted

      Boot is going to be replaced eventually. I just wire brushed what I could and rust converted. Then painted in rust kill primer. the spoiler also got repainted and plugs replaced on the ends. The under side of the bonnet is going to be black also, currently white. But red on the top side, same colour code as the silo to begin.
    • Shoota_77
      Car Rotisserie

      By Shoota_77 · Posted

      Hi guys, has anyone either purchased or built themselves a rotisserie for their car before? I can only just justify the need for one hence why I should just make one but at the same time, if I make one I can kiss another 4 weeks of potentially productive car working time goodbye because I'm building a bloody rotisserie....  I mainly want it for the application of the body deadener.  Cleaning the old stuff off, priming and then colour over the deadener doesn't worry me, it's just the application using the Schutz Gun that I feel would achieve a significantly better finish painting it side on and keeping the Schutz Gun upright.  I don't think they would work well on the side let alone almost upside down for some areas.  If the product I use (Terosun, etc) could work through a HVLP ok then it might be ok to apply without the rotisserie.   I can get one of these style ones for about $1200 which is pretty good value-     I reckon if I made one it would cost around $500 but it's more the time that it would take is more of a killer than the cost.  They look to hold their value pretty well second hand so I could always sell it after using it and realistically only lose $200-$300 at worst.  Or keep it and buy another project when this one finally sees the light of day... Anyone selling one...? Cheers!  
    • GTSBoy
      Stock rb25det neo questions

      By GTSBoy · Posted

      While it is a very nice idea to put card style AFMs into the charge pipe (post intercooler, obviously), the position of the AFM and the recirc valve relative to each other starts to become something that you really have to consider. The situation: The stock AFM is located upstream the turbo, and the recirc valve return is located between the AFM and the turbo inlet, aimed at the turbo inlet, so that it flows away from and not through the AFM. Thus, once metered air is not metered again, neither flowing forwards, or backwards, when vented out of the charge pipe. When you put the AFM between the turbo outlet and the TB, there is a volume of pressurised charge pipe upstream of the AFM and there is a volume of pressurised pipe downstream of the AFM. When the recirc valve opens and vents the charge pipe, air is going to flow from both ends of the charge pipe towards the recirc valve. If the recirc valve is in the stock location, then the section between it and the TB doesn't really matter here - you're not going to try to put the AFM in that piece of pipe. But the AFM will likely be somewhere between the intercooler and the recirc valve, So the entire charge pipe volume from that position (upstream of the AFM, back through the intercooler, to the turbo outlet) is going to flow through the AFM, get registered as combustion air, cause the ECU to fuel for it, but get dumped out of the recirc valve and you will end up with a typical BOV related rich spike. So ideally you want to put the AFM as close to the TB as possible (so, just upstream of the crossover pipe, assuming that the stock crossover is still in use, or, just before the TB if an FFP is being used) and locate the recirc valve at the turbo outlet. Recirc valve at the turbo outlet is the new normal for things like EFRs anyway. In the even of a recirc valve opening dumping all the air in the charge pipe, pretty much all of it is going to go backwards, from the TB to the recirc valve near the turbo outlet. But only a small portion of it (that between the TB and the AFM) will pass through the AFM, and it will pass through going backwards. The card style AFMs are somewhat more immune to reading flow that passes through them in reverse than older AFMs are, so you should absolutely minimise the rich pulse behaviour associated with the unavoidable outcome of having both a recirc valve and an AFM in the charge pipe.
    • joshuaho96
      Rb25det Belts Change

      By joshuaho96 · Posted

      Yep, in my case as soon as I started hearing weird noises I backed off the tension until it sounded normal again. Delicate balance between enough tension to avoid that cold start slip and too much damaging things.
×
×
  • Create New...