Tecumseh BVS 143 - what spark plug?

[threeeyedjoker]

I have a BVS 143 that needs a new spark plug. I have the owners manual, which has a diagram clearly showing the plug should have a reach of 8mm, and a gap of 0.6mm. It also states to replace the plug with a Champion RJ17LM plug. If I look up this spark plug is has a reach of 9.5mm, and a gap of 0.8mm.

The existing plug has a reach of 8mm, and the engine runs on this - but its very old. And on top of this, I can't find any plugs anywhere with a 0.8mm gap and the same thread size.

Am I ok to use the RJ17LM with a slightly longer reach than what is in there now?

Any help or advice would be much appreciated.

 

[StarTech]

I don't know where that info came from but this is what I have on the RJ17LM plug here. But converting to metrics the specs matches to 9.5mm reach. Just 8mm is very close to 5/16 and I see no Champion with that spec. The .6mm gap is converted .023-.024" which usually gapped at .025". Normally you do have a little leeway on the reach but a not a whole lot; otherwords, you can't go to an 7/16 inch reach.

Now what plug is in there now?


And most time it is okay to install the RJ19LM in place of the RJ17LM.

 

[threeeyedjoker]

Thanks. I've attached the instructions. I think I'll take the head off the engine and see if the thread of an RJ19LM sits flush once its screwed in - if it comes through I'll know I have an issue. And I'll set the gap to 0.6mm and see how it runs.

 

[threeeyedjoker]

Am I getting confused between 'thread' and 'reach'?

 

[StarTech]

Thread is the diameter of the threading. In this case thread is a M14 diameter.
Reach is the length of the thread section and /or the tip. Example M14-1.25 x 8mm or a 9/16-20 x 5/16. Now there is difference in how this measure is done. In you example they are just the threaded section but in the chart I post they are measuring the threaded section plus the tip. I verify this by actually checking a plug here.

In this case the length from the gasket of the plug to tip the M14 threaded section from the gasket to tip or just the threaded section without the gasket. And measurement with gasket can vary a little depending on how much the gasket crushes. So I would say the RJ17 or RJ19 would be safe to use.

 

[VegetiveSteam]

J8C was the standard Tecumseh spark plug for years and years which is basically the same as the J17LM or the resistor equivalent, RJ17LM. I've also used the J19LM and RJ19LM on Tecumseh engines with no issues.