MkI carbon deposits

[markus.nikot]

4 riders,
while investigating some noises i've found some carbon deposits which i had never seen before.
The conrod small ends, piston bottom and rockerbox bottom showing this. The latter may explaines cause it is over the exhaust. Small ends and pistons are looking like oil was burned. All gudgeon pins were very tight and i know i didn't fitted them so tight. While trying to ream only carbon came out until the hole was so big that the pins become too lose. I'm running the MkI with SAE50 with detergents cause a filter is mounted. Ignition is correct, oilconsuption was not unusual. The engine did 10k mls since ti've fitted new pistons.
Any ideas?

Markus

[paul.jameson]

It looks as if you are burning too hot. Perhaps this is due to modern petrol. What colour were the plugs?

[markus.nikot]

Paul,
plugs looking always good and clean definitely not white. Running, power output, fuel consumption was good, ignition not retarded.
I use to run E10 petrol wich has up to 10%Ethanol rather the 5% of other sorts. But I cannot imagine this makes a difference.

Markus

[adrie.degraaff]

I use to run E10 petrol wich has up to 10%Ethanol rather the 5% of other sorts. But I cannot imagine this makes a difference.

Yes it makes a difference, it damaged a 1939 engine of Rob's 600.

[john.whiting]

Theoretically,E10 should need a 5% increase in fuel flow to make up for the alky content.I know this may be difficult to arrange with a Solex,you might have to ream the jet/s.On the subject of plug reading,I mentioned this to my next door neighbour,he said plug colors are meaningless with modern fuel.He is young and should know everything.He also works in a dyno shop of the " mine s got more power than yours " kind.I asked in regard to my old ride on mower,which I definitely dont want to stuff up,with the council allways on my back.In the days of racing with alcohol fuel,weak mixture was to be avoided at all cost,with jetting on the rich side a must.So ,is plug reading now meaningless?Regards John.

[Mike Nash]

Rushing in where angels fear to tread, would a synthetic oil be better?
Regards, MikeN.

[johann.patek]

i have seen similar hefty carbon deposits in two mk2 engines. one was using detergent sae50 the other millers sae 40. both used normal 95 petrol unleaded. the carbon depositis were such strong, that one bike had the exhaust valves jamming, the other the inlets. just reaming the carbon out of the guides made them mobile again. reason i guess is unsuitable oil, which burns at too low temperatures. but its only guessing. brings us to the question what type of oil to use in long and hard driven sq4s.
johann

[paul.jameson]

I used Morris's ring Free XHD 15W-40 in my Healey 4 and my MkII. So does Lester grant and so did Bob Brassington. All 3 of us have been known to ride long and hard on occasion. Don't try this oil in a newly rebuilt engine though - use Morris's Running - in oil for the first 800-1000 miles. As the technical expert at Morris's said to me "You will never run an engine in on Ring Free as it is too slippery."

[markus.nikot]

Running 15W-40 oil wrecked my cammy engine - but this is a another story.

Bloody oil discussion they always never end.

A thought - employing a Morgo pump could make it possible running a thinner oil like 15/40 compared to the manufacturer recommended 50?
In my KH with original pump the oil pressure drops to zero when idling filled with 15/40 - SAE50 cures this and is around 10lbs.

But i've no problem with pressure it is the burned oil that causes problems - could that be cured with a thinner oil??

Markus

[john.whiting]

In simple terms,you have "cracked" your oil.To carbon and various decomposition products,which you see deposited on your hot internals.The stability of the oil at running temperature is the problem,not the viscosity.The fact is that motor oils are made for liquid cooled engines,which do not run at such high temperatures.Modern car oils contain about 30% of additives,all kinds of crap to make a cheap base stock act as though it was a quality lubricant.You can investigate this by simply putting an old worn out piston on a hotplate ,heating to running temp,and slowly dripping the oil in question into it.Multigrade oils contain a lot more additives than monograde.I have allways used an oil suitable for 2stroke Detroit diesels in old bikes,but thats up to you.Regards John.