I was looking to replace a spark plug on a lawnmower. The plug for the machine is an NGK-BPR5ES. I cross-referenced on 2 different web sites that say an acceptable replacement is a Champion RN12YC. Everything looks identical except for the fact that the side electrode hangs about 1/8 inch longer than the NGK. Everything else is the same, including the thread length. I'm just concerned that the electrode is going to interfere with the piston. I'm not that experienced but I would expect that an acceptable substitute would occupy the same amount of space in the cylinder. Am I ok with the Champion?
#2
cpurvis
Should be OK. It crosses from NGK to Champion and Champion to NGK.
Thanks. It's always cool when you can use something you already have on the bench.
#4
7394
You could always have plug removed & with a pencil, carefully place it in spark plug hole when piston can be seen as near TDC,
aka Top Dead Center. Rotate engine by hand in both directions w/pencil to see the highest point, mark the pencil & check the depth against the Champ plug.
Using a depth gauge you have to subtract about .030" from the distance.
This is to allow for stretch when the piston goes to tdc at high speed.
With motorcycle engines we generally put a dob of plasticine or an old piece of plastigauge.
Then screw in the plug & rotate the engine. remove the plug & check for the plasticine being flattened.
Generally .030" clearence on a low compression engine is considered OK and .040" to .050" for a high performance engine.
However the champion isa direct replacement, but now you know how to check unknown plugs.
