[a.graham52]

I noticed both times iv had the head off the K321 that the plug (old and new) does not protrude into the combustion chamber. As in its too short. Is there a longer plug that works? I though about opening the hole in the combustion chamber but not sure I want to do that to a good original head. Otherwise I feel milling will be required on the outside in order to obtain a good sealing surface. I feel like if the plug was more exposed to the chamber I would have better efficiency and more power. Anyone looked into this?

 

[JDBrian]

Never checked mine! If it's running the recommended plug then it should be fine. You might want to look on sites that tune these engines for pulling. I don't think I've ever read of using a longer plug on a stock engine.

 

[jpackard56]

Never checked mine! If it's running the recommended plug then it should be fine. You might want to look on sites that tune these engines for pulling. I don't think I've ever read of using a longer plug on a stock engine.

This is good advice ! I wouldn't make changes to a head without very specific evidence that it will improve something. Also remember pullers and such will do some modifications that garner them a fraction of advantage that in normal use we wouldn't even be able to tell the difference. They also spend much time tearing down and rebuilding for that extra edge. Im thinking you may have the wrong plug if it truly is not seating well. The companies used to spend substantial monies on designing the "best" plug for an application. Good luck !

 

[grattone]

I believe the older engines were built to work and last, not like the newer ones with built in problems to make money.I agree with the others , check for proper plug first.

Gratton

 

[MiCarl]

I have the NGK Book. The correct NGK plug is B6L.

The book shows that cross referencing to Champion RH10C or RH12, Autolite 3507 and Motorcraft ATL4.

 

[James Bosma]

I just happen to have my K321s head off due to a blowen head gasket

Spark plug is Champion H10C

Plug is flush with head, nothing sticking out

Spark plug is over top of the exhaust valve

Here's a couple picks showing H10 plug screwed in finger tight

 

[JDBrian]

One picture is worth…. ! That should be a big help to the original poster!

 

[James Bosma]

I think there is enough room for the plug to operate properly.

If you ever get a chance to look at a Briggs model A, B, ZZ take the plug out and look down spark plug hole

They use a 7/8 plug but there is only about a 5/16 hole that connects sparkplug hole to the cylinder.

That's the way my 1936 Briggs Model B is

That is one reason those engines need to be 1/2 choked to start when warmed when hand cranking or rope start

 

[classic]

I was surprised when I pulled the plug out of a 1948 Briggs ZZ engine and saw the pre combustion chamber in the head. It's amazing that those engines even fire and I never researched the Idea behind it. I'm thinking it was to help keep the plug from fouling or to help prevent carbon build up. Good point James.