ClassicCar

54Hollywood wrote:

Our Hornet needs new plugs and I usually install Champion H-10C's because I can't find H-11's. Are the H-12's a closer heat-range match for the Hornet or what other plugs would any of you recommend and why? Thanks.



Tim in Wisconsin

Walt here. Go to any lawn mower store or Target or K-Mart and you will find your H-10 spark plugs. Do not install those hot plugs as todays gas burns hot and you can burn your valves and melt the plugs. If you just drive to the corner store, it's OK but not for any long trips.

I've always used H-10's on my Stepdowns, except for maybe back in the early 80's when H-11's were still around. I never noticed a difference going to H-10's from H-11's. I would think that since the plugs were always dry& tan colored when pulled, that they are in the right heat range for the mostly highway driving I did.

If a hotter plug looks whitish and the electrode rounded/ melted looking , it's too hot. The next hotter range was usually only recommended if the driving was limited to short trips, stop & go driving, especially in cold weather, due to the richer mixtures from the accelerator pump, and partially closed choke(s).

I agree with MOST of what has been posted here. To add my thoughts...The heat range of the plugs is a function of the distance from the electrode to the cylinder head. It is not a measure of the combustion chamber temperature, nor does it have much effect on it. That is a result of the mixture and fuel formula. If the electrode extends further into the combustion chamber, the heat has to travel further to be cooled by the contact with the head. Since the heat has to travel further, the electrode will operate at a higher temperature. That does help to reduce fouling of the plug. Too high a PLUG temp will burn the plug and cause it to fail to burn the fuel. So as Dave53-7C said, an engine that has a lot of oil mist or a mixture that is too rich, needs a hotter plug. An old rule to remember is. A cold running engine needs a hotter plug, and, a hot running engine needs a cooler plug. If you make a lot of short trips and don't get the engine up to full temperature, Have a rich mixture, use a hotter plug.

Just changing the heat range of a plug to address the burning or fouling of a plug is only half the equasion. Reading a plug is a little more difficult today since the fuels have been reformulated. Perhaps the carburetor mixture needs to be adjusted? Also, to get a true reading on a plug, A new plug should be installed, The engine brought up to temperature by driving it at highway speed for several miles. Disingage the clutch, shut off the ignition and after pulling to the side of the road, remove the plug and read it. Just the few seconds of ideling the engine after a run, will skew your results. Most Hudson carburetors have worn metering rods and are running way too rich. It's a lot more difficult to adjust the high speed mixture than it is too change plugs, but is the correct way. Just don't lean the mixture out too much. That CAN raise the combustion chamber temperature to a point where the exhaust valves can't transfer their heat and then you WILL have burned valves and seats. Given a choice, I would run a little rich and set the valves a bit loose as Walt does.

464Saloon wrote:

I run NGK's, I have always had good luck with them in all my cars and bikes.

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What number ?

54Hollywood wrote:

As always, some terrific information from the Hudson clan! Thanks for all your responses. The car does run a bit rich and I don't do a lot of highway driving which is why I thought maybe an H-12 might work, or be more appropriate for a Hornet, instead of the H-10C. But I think I'll stay with the H-10C's and trouble shoot the carbs. The Twin-H on our 308 has the 968S carbs and I don't have a uni-syn (yet) so it'll be twice as much fun playing with the dual Carters. Thanks again.



Tim in Wisconsin

Set your floats to 5/8" instead of the 1/2" in the book..That might help s rich idle problem with the new fuels.

With all the Twin-H Hornets out there, has one of our enterprising folks come up with an accurate way to check the metering rod height? Even having the factory dimension doesn't help a lot without the exact shape of the lower end of the factory gauge. I tried to buy an original gauge not long ago, and the supplier wanted something like $40 for it. A gauge for the WDOs and WGDs would be welcomed as well.