What is the main cause of carbon buildup on pistons and valves ?

lack of maintenance

Rich mixture ,and or oil burning. Slow carbon buildup does not mean there is a fault,its just old technology in action. If there is no smoke screen following you around then oil burning is probably not the issue. Rich mixture does dirty up the motor and the oil. This was not so much of an issue in the past when a bit of extra throttle and a short blast could burn off the plug and keep you going. With the change in plug manufacture to suit clean-lean burn modern engines we have lost much of this option and a dirty or watered insulator may not self clean.If your bike is blessed with good carburation you may never have a problem,we are going to have to run weaker and hotter or invent some sort of add on fueling controls. I think the plugs supplied for non motoring applications where FI is not in use may be usefull, I have an 18mm one to try in my Rudge ,but as its running weak and clean it won't prove anything.

It can be either or both.

1) Burning oil will be evident by some blue smoke emitting from the exhaust, especially on the over-run or when the choke is in use. (both scenarios increase the vacuum in the cylinder and inlet tract) Worn inlet valve guides will allow oil into the combustion chamber, which eventually carbons up the rear side of the valve head. You can check this without a strip down as the valves can often be viewed if the inlet manifold is removed. Also the oil consumption will be high (exclude oil leakage) and the plug will look oily too. If it is a worn bore or rings then a compression check will usually produce a lowish figure which can be increased by oiling the bore (through plug hole) to prove whether it really is the bore or leaky valve seats.

2) Rich mixture will produce performance issues such as lumpy running, high fuel consumption and obviously make the spark plug sooty (fluffy carbon rather than baked on carbon)..Traces of black exhaust smoke being emitted will be evident too as well as the end of the exhaust pipe silencer which will be overly sooty but not greasy. Always sort out the main jet size first by doing a flat out "plug chop" and work through the other settings afterwards.

Hope this might help.

Les

Hi,

Further to what has been said, the type of engine oil used and the fuel you choose to run the bike on make a massive contribution to carbon build up.

Older 'classic'oils, (especially the monogrades, but anything with an SAE rating of SF-CG or earlier) often have a high zinc content, and zinc is an unbelievably good carbon promoter. Just 6 parts per million in diesel fuel can quickly lead to coked up fuel injectors!

This is one reason why modern engines, running on modern oils can do 150,000 miles or more without touching the engine other than basic oil and filter servicing.

The fuel used can also make a massive contribution. Some (but not all) minor brand and supermarket fuels have virtually no detergent additives in them, while the heavily advertised 'premium' fuels have a very good additive pack that will keep things pretty clean.

Before the comments arrive that the fuel all comes from the same refinery, the various brand additives are added to the tanker at the fuel fill point, so BP will get the BP additive, Shell the Shell etc.

I know from my years in engine development at Ford that they really DO work, and have only used main brand fuels for years in my vehicles and I really don't have any carbon issues.

Regards, George.

I wonder if ceramic coatings like those offered by Camcoat would maybe prevent the carbon from actually sticking to the head and valves. A light layer of carbon above the top ring was supposed to be left intact at de-coke time to maintain the bore to ring seal when I was a lad LOL

Hi Tony....The API ratings are confusing. The highest API rating you should go to is SJ as it can have a maximum of 1000PM (0.1%) of ZDDP. Later spec oils have to have even less of the anti-wear additive ZDDP ....an additive that suits and works well in old type engines...Unfortunately the API spec is a maximum figure not a minimum so whereas the SG rating has a higher top limit of 0.15% (less cam train wear) it can actually have less than 0.15% if the manufacturer chooses which is why your Silkolene oils can specify the older API ratings of SF, SG, SH, as well as SJ

So the API ratings don't guarantee how much ZDDP you are getting only the highest amount you MIGHT be getting but as your oil is carries the SJ rating it can not have as much potentially as an earlier API rated oil such as SF or SG or even SH...if these oils are formulated and taken to their highest permissable ZDDP content.

This is why you need to know the actual amount in the oil you are buying and why some Classic oil manufacturers will tell you.... Millers Oils do...but you might be tempted to phone Silkolene and ask their technical dept?...If you get the answer please let us fellow NOC'ers know....BTW....Millers regards 1000PPM of ZDDP or slightly above to be sufficient.

As far as oils promoting carbon build up I don't have the facts but current API modern oils have extremely high detergents and other chemicals that can cause problems in older engines...NB: I'm not referring to the detergent action as mildly detergent oils used with internally clean classic engines work OK, it's the way the modern additives react badly in old style engines.

Anyway....at the end of the day, heavy oil carbon deposits in the combustion chamber are caused by a worn engine rather than any current type of Motor Oil.

Les

Hi Tony and George.

It was my typo - I did mean SG not CD.

I think Les has supplied a very comprehensive answer to the other question you asked - I couldn't have answered it better.

Other point about carbon build up is the type of use the bike has. Lots of low speed running around town etc will be worse for build up than lots of motorway running for example.

Best regards,

George

http://www.millersoils.co.uk/pdf/automotive/ZDDP.pdf

Deleted duplicate entry...Les

I am puzzled by the assertion of Miller oils made in this link. It is the case that oils with reduced ZDDP levels are needed by engines which must conform to latest catalyst durability requirements.

However:

These oils, SM, SN, must achieve HIGHER levels of wear protection in the valve train wear tests of the API than did earlier ones. Formulators achieve this by using more effective, and more expensive ZDDP's and supplementary non S and P containing Anti-wear agents. These are often based on Boron Chemistry.

Any oil worth buying will also carry ACEA , (European Engine Manufactures) approvals. ACEA has a low P and S category , C1.C2,C'S, with lower P and S limits but the A1,A2,A3 categories have 'Normal ' levels of ZDDP.

Again they must achieve the same demanding level of wear whether they are A or C classification oils.

No engine manufacturer who has to meet current Fuel economy, emissions, targets would use oils of the viscosity grades which we run in our Nortons. So it is easy to find a Modern, i.e.. better, oil to meet our targets.

It may seem cynical, but the Classic Market is a lucrative outlet for oils which are cheap to produce. No testing to ensure that performance standards are achieved is possible. I have, as yet, seen no evidence of the problems which the Classic oil suppliers claim.

I was for 12 years, chairman of the working group which developed and maintained the current ACEA valve train wear test.

Hi Charles. There are scores, perhaps hundreds of technical articles on the web that say the same thing as regards ZDDP. From what I have read, I deduce that modern oils are designed for modern engines that require a formula that does not pollute the catalytic converter, an oil that can last for up to 30,000 miles and have lubricating properties with a very low viscocity. Modern engines burn less oil and are built to have less friction and lower pressures in the valve train and can therefore use an oil that doesn't give the ultimate anti-wear properties on extreme pressures...it is not required as modern engines don't create it. However modern engines require different protection for their lengthy service intervals and therefore require different additives and are extremely detergent (which also displaces anti-wear chemicals)

I have spoken to Millers technical at length and they can explain things much better than I can. At no time did I get the impression it was just a market con. They said classic oils were not their biggest side of things, in fact they don't really make much mention of Classic Motorcycles as they have modern oils a plenty for them. They were interested in that I suggested they SHOULD concentrate more on selling their classic oil for classic motorcycle and they took my advice on board and will redesign their web-site with this in mind.

From what I have read in the very many articles backed up by Castrol too. I will always use a Classic Formulated oil changing it every 1000 miles or thereabouts. If one should wish to use the latest top spec. fully synthetic oil in their old motorcycle or lawn mower no-one will mind but for an owner TRYING to make his engine last longer, it seems from what I have read there is a definite consensus, so I am happy to use Classic oils and understand from what I have read in scores of articles that high tech oils are not best suited to old style engines. ...Les

Les,

my point is that ZDDP's have been used in oils as both anti-oxidants and anti-wear agents since the 1940's and in some cases earlier. They are very cost effective in both these roles. There are a wide of ZDDP's available with differing costs and effectiveness.

Modern oils are available in the viscosity grades we use, with the ZDDP levels of old and with better anti-wear and better anti-oxidancy than the so called 'classic oils' and their performance is certified by the test monitoring centers of API and ACEA.

At the risk of sounding arrogant, which I try not to be,I too have read many dozens of papers on ZDDP and it's role in both wear and anti-oxidancy. My sources are peer reviewed scientific papers. I first published on Zddp's in the American Society of lubrication engineers journal in the early 1980's and have authored many papers since as well as written invited contributions to special publications of the I.Mech. E., advanced text books examining PhD theses.

The internet is a source of information but not necessarily of knowledge.

The company for whom I worked manufactured ZDDP+ most other additives used in formulating oils and developed about 50%% of the oils in the market place.

P.S. I am pretty sure that Miller oils were/ are one of our smaller customers.

By all means stick to your classic oil but I do wish that the classic oil marketers would present data to back their assertions.