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Mixing spark plugs

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ragtop

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The plug in my #5 cylinder fouls up after about 250 miles or so. At that time the engine starts missing slightly and I clean it off and it runs great for another 250 or so miles. Its an oily deposit. Would installing a hotter burning plug in the one cylinder help this out? Can I just place a hotter burning plug in one cylinder and keep regular plugs in the other 5 cylinders? The engine/valves have never been rebuilt and other than this issue the car still runs fantastic. And yes it does blow some blue smoke more so till it warms up. Chris - 69TR6
 
Yup, you can use a hotter plug in just that one cylinder.

Another old time trick that might be worth trying is to file away the end of the ground electrode, so it only covers about half of the center electrode. I don't know why it works, but "2-cycle" plugs used to come that way.

I'd also try running Valvoline synthetic motor oil for at least one oil change. Might not make any difference, but it has cut oil consumption on several engines for me. (Unfortunately not the TR3.)
 
Some mechs have put in Ford valve seals which do stop the oil from fouling the plugs. Can be done without removing head.
 
LarryK said:
Some mechs have put in Ford valve seals which do stop the oil from fouling the plugs. Can be done without removing head.
Click to expand...
True, but that only works if the oil is getting through the intake valve guide. Given that it seems to only be #5 with a problem, plus it gets better as it warms up, I'd guess that the oil is coming past the rings. In which case adding valve seals won't help at all.

Easy way to tell the difference is ask the driver following you to watch when the tailpipe smokes. If it blows "puffs" every time you shift, then it's a valve guide problem. If the worst smoke is when you are on the throttle, then it's rings (or cylinder wall).
 
What spark plug are you using ?
Before I overhauled my 74 TR6 engine, I was using a quart of oil per 400 miles and never fouled a Champion RN12YC spark plug.
 
I once had a Twin Cam MG that I bought new. It consistently fouled plugs from the day I bought it. My solution? I actually had 3 heat ranges in 4 cylinders. As I recall some 44 years later, I had 2 N3s an N5 and an N8 Champion plugs. I got calls from Twin Cam owners as far away as Washington, DC asking me how I got mine to run without plug fouling. BTW, I only kept the car for about 6 months before trading it for a VW Beetle sunroof - but that;s another story..
 
I've been using NGK BP6ES plugs. I've got a RN12YC that I'll put in today. Thanks for all the responses - Chris
 
I had the same problem with the NGK plugs - switched back to Champion and the car runs great again.
 
Does everyone stick with the recommended 0.25" gap? I sort of remember folks using a gap of .30" for some plugs. I went ahead and put all new 12YC plugs in at 0.25" and the engine is missing just a wee bit and it wasn't before. The NGK plugs I pulled out measured closer to 0.30" - Chris
 
Since I am the poster child for Murphy's law, I have had the opposite experience. I could not keep Champions from fouling. I switched to NGK BP5HS, which is one step hotter, set them @ .030 and have ended my fouling problem.
 
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