removed my sparklugs and found #5 to be crusted...

[erickmarciano]

Hi All removed my sparklugs and found #4 to be crusted .beige color but dry . from the manual pictures I have of sparkplugs it looks like ash deposit .any of you see this and what can cause this ? all the others are ok
thanks

[abe280SL]

Funny, recently I had one plug like that and metal slightly "burnt" off.  I attributed to leaving the ignition in the on position too long to get the gasoline pressure up before starting the car.  I assumed that when I did that the points where closed to that cylinder...maybe someone could shine some light if thats even possible.
abe

[glenn]

Doesn't sound possible................

[al_lieffring]

in the 280SL's - m130e motor it is not unusual for problems to show up on just the #5 cylinder (or the #4) before the other cylinders, the 2.8 litre motor was designed ca. 1955 as a 2.2 litre motor and over the years was bored and stroked up to 2.8 litres,
this left the cylinder walls very thin between the #4 & 5 cylinders and causes a hot spot in the back of the block. This in time will manifest itself as wear of the bore of these two cylinders before the others wear, higher temperatures in the cylinder head in this area, causing premature wear of valve guide, seals and / or spark plug fowling.

I'd suggest just changing the #5 plug and monitor how long it lasts before it fowls again, and if it fowls frequently check and replace the valve stem seals on the #5 cylinder.

Al

[erickmarciano]

that makes sense .all compression is at 150 but the before last one is at 122
thanks

[ja17]

Hello,

I agree with Al.   Also fuel fouling does not leave crusty deposites, mostly black soot or damp plugs.  Worn intake valves or worn rings will allow oil into the combustion chamber where it will be burned and will leave a crust on the spark plugs.   

[graphic66]

Also make sure to use non resistor plugs. That was the most dramatic "upgrade" to my engine. I am currently using NGK BP5ES in my 66' 230SL gapped at .034. Watch out, they can be hard to find. Parts people kept trying to give me resistor plugs. NGK plugs can denote resistor by an "R" in the plug# like, I think BPR5ES, don't use those. I have also seen some additives like octane booster and lead additive foul plugs with a crusty deposit.