TOPIC: 1966 35hp wards sea king (chrysler) plugs

motor had/still has champion L86c plugs. manuals mostly specify j4j (replaced by j4c). I mostly run motor wide open or at least half open, no extended idle or low speed. L86c plugs look pretty good, maybe a bit wet, buy motor starts instantly and performs flawlessly. Should I switch plug to j4c? Thanks.

I looked cross ref to NGK.
L86C is NGK B6HS
J4C is NGK B7S

Slight diff heat range, but I would just switch to NGK (better plugs than Champs in my book). But up to you.

Thanks for doing that work.

You might want to look at this PDF Champ plug chart. I just looked this up. To me, shows 2 different plugs. Look in the L/S column. 9th column down is J4C, shows it a cold plug, and 3/8ths reach.
12th down is L86C, shows a hot plug, and 1/2 reach?
If you are 1/8th past the head, thats gonna be a hot spot and a good way to hole a piston. I'd take a second look into this.
Chart link

aftermarket.federalmogul.com/en-US/Technical/Documents/Champion%20Spark%20Plug%20Copper%20Plus%20Heat%20Range%20Chart.pdf

Robbie, thanks again. I'm new so bear with me, but you are saying the l86c could be a problem because it's too hot and fires too close to the top of the piston, right? (especially because it run it mostly wide open?)

Yes. If you don't have a J4C to compare to, just pull one the L86C plugs, measure the thread depth in the head, then the plug. If both same reach, probably OK. If 3/8ths depth head, and 1/2 plug, yank'em and get the real thing.

OK. I just looked reach the NGK equivalent of the 2 Champ plugs (like mentioned before) and THOSE are L86C is B6HS 1/2 reach. J4C is B7S, and thats 3/8th reach. I'd yank and toss the 1/2 reach champs, get NGK B7S. Or J4C Champs. SOON!

Keep this updated here..(I'm gone now, going out in the boat!)

Have fun on the boat. Doing the same later.
Head thread confirmed at 3/8, and had already picked up the j4c so will change to that. I also see the j6c is same 3/8" reach and a bit warmer. When might a warmer plug be good?

Gkopan wrote:

Have fun on the boat. Doing the same later.
Head thread confirmed at 3/8, and had already picked up the j4c so will change to that. I also see the j6c is same 3/8" reach and a bit warmer. When might a warmer plug be good?

I'm back. (Nice to live a private HOA, 104 slip marina block down me, have a 26 foot slip, and take the "rat scooter Marina runner" down there, get in the boat..burn gas in one the boats slipped, as own FIVE!. Or just beers, sit in the boat, BS with the other idiots with boats! But I have a (been wrenching 55 years motors, boats and Harleys) been thinking this today. I have J4C, J6C here in the shop. Both 3/8th reach. Before I forget, if you had 1/2 reach in the last couple threads the plug would be discolored (combustion carbon). Theres gonna be a sharp "thread" edge to get hot and ya get Pre Igniton. Building a motor you want simple "NO HOT SPOTS combustion chamber" Know where I coming from?

Back too the plugs. I got a many smaller OB's here. I looked the used (I never toss anything away!) J4C's, and the J6C's. Seems the J4's, and black carbon the porcelain, but the J6's look fine!

GO FOR IT! And glad to help ya. I still learn something new everyday, even sometimes I think I know it all? (No WAY!)

Link about this, Pre ignition, and Detonation. Good read. Wish the best...Robby

www.contactmagazine.com/Issue54/EngineBasics.html

Been busy,but did get j6c and so far so good, the motor continues to hummm.