• If you log in, the ads disappear in the forum and gallery. If you need help logging in or getting registered, send request to: webmaster@southernairboat.com

Hotter plugs

marshmaster pat

Well-known member
On a Lycoming 0-540, if you are running the Champion plugs and want a hotter plug, which way do you switch. Up or down.

Just cannot remember and the fellow at the auto parts store eyes sort of glazed over when I asked.

Red - Where are you at when I need an answer. LOL
If your running D-16's, and want to go hotter, then try D-18's. I've tried D-21's in one cylinder that had oil control issues, but those are to hot in my opinion.

Why do you want to go up on the heat range?
Just curious.
IIRC, Champion goes down a number to go up in heat range.

I will double check this tomorrow, give me a call

(386)418-2010, ask for Chris
Similar reason as yours. A buddy is running an older 540 that is leaking oil through the rings some and fouling plugs quickly on a couple of cylinders. Engine still has decent compression and its oil temperature runs very cool. Not wanting to do a ring job yet at $65.00 a cylinder when it still has good compression. We were talking about options and I suggested running hotter plugs to see if that would help get the oil temperature up and maybe help burn of the oil before it fouls the plugs.

Just could not remember which way to go.

MM Pat, if the engine has good compression but is oiling the plugs, it's possible that the valve seals are leaking. I think those can be replaced without disassembling the engine. Call an engine shop and ask them about that.

Big Feather,

The Lycoming 0540 like Pat has decribed does not have valve steam seals like a car motor.

Most engines that have a poor ring seal or bad rings still test O.K. during a compression test especially if the motor is burning oil because a wet ring will seal better and read higher. The only way to establish the conditions of your rings and bore is to do a leak down test.
Just my 2 cents, :? and maybe I've been lucky or whatever.
I've been running D-9 Champions in my 540 for years.
Cranks good and runs great. Gap about 15.
VernonW (wynnboat) Wynn
Thanks, y'all ... I don't know much about A/C heads, but it was an idea.

Thunder, is there any good reason to put roller rockers in a SB engine if it doesn't already have roller lifters in it?

Thunder - I have been told that the leaked oil can hide bad rings. But we don't have the capability to do a leak down test among the guys I know. I guess that by the time we find a bad cylinder it is really bad.

But the boat still turns up the prop to the same rpms, and hasn't appeared to lost its snap. Just using that and a compression test as a crude measure.

But I have looked at some of the compression gauges that are set up to do that. Any ones that work better than others for Lycomings. Have looked at those made for aircraft, not that really pricey.