Outdoor Power Equipment and Small Engines - spark plug question

I have a number of small engines that take a Champion CJ8 spark plug.
I came across a Champion 5843 plug in my tool box that says on the package its a replacement for the CJ8. I'm questioning the physical difference in the two plugs. The threaded section on the 5843 is longer than the CJ8 which would put it deeper into the cylinder head. Should i be worried about the piston coming up and slamming into the 5843?

Thanks

about how much longer? if your worried, i'd just go get another cj8 equivalent.

Besides the piston possibly hitting it, if left in for too long it would get carbon biuldup on the exposed threads inside combustion chamber and stand a good chance of wiping out the threads in an aluminum head upon removal.
Mike

The 5843 is a replacement for a CJ8Y, but is also listed as a replacement for the CJ8 but I don't necessarily think it should be. The threads shouldn't be longer rather the core and electrode should be. What is it that you are installing the spark plug in? The 5843 is a fine electrode spark plug and is generally a better plug for cold starts.

I measured the the threded section and found out its the same length as the CJ8. Overall,the 5843 is a little longer,buts its the insulater top section.
I checked out a spark plug reference chart and found that the 5843 is supposed to be a better plug and yes,its interchangable.
I'm using the CJ8 in a Toro ccr2000,2 stroke, snow blower that came with the machine,but the package stated the 5843 was a replacement. I like to keep a replacement on hand.

I have another question for you all. I have a new toro recycler,6.5 H.P.,self propelled lawnmower. The stupid owners manual says to contact a Toro dealer for the spark plug type. The engine is a tecumseh. Anybody have a
plug # for a Champion,or Tecumseh?

Thanks again

Overhead valve will be a RN4C and flat head will be a J17LM. And you're right, the 5843 will work fine in the thrower.

Thanks puey61..