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Sat Sep 28, 2019 2:50 pm

I was taking out the spark plugs today on my bus ('74 Brazilian split), and I found this on cylinder 3:

I'm guessing that's a thread adapter because the threads on the head were stripped at some point? Obviously not ideal, but any concerns with this? The electrode no longer sticks as far into the head, so is it worth getting a plug with longer threads?

The plugs that were in there were NKG BP5HS. The replacements I bought are NGK B6RHS and it looked like the NGK BP5ES had threads about a quarter inch longer.

Thanks

Sat Sep 28, 2019 4:20 pm

You will need to come up with a solid insert to fix that, or probably a new head. To start on the former you need to know the size of the hole in the head. This can be done by measuring the end the adapter fitted into the head.

Sun Sep 29, 2019 10:14 am

Thanks for the advice Eric&Barb. Are you referring to something like a Time-Sert? Is is just better because it allows the plug to extend fully into the head, or are there other things that make it fundamentally different than what I already have?

Sun Sep 29, 2019 10:23 am

ryanl wrote: Thanks for the advice Eric&Barb. Are you referring to something like a Time-Sert? Is is just better because it allows the plug to extend fully into the head, or are there other things that make it fundamentally different than what I already have?

Something like a Time-Sert but probably much thicker wall. Without a measurement of the adapter part OD can not tell. Yes, to work well you have to have the plug electrode in the cylinder. With any solid insert, it can be locked in place. Making one on a lathe and drill one edge to pin it into the head to lock in place is not that hard, but requires the head off. Time-Sert has a special way to flair out the end inside the cylinder slightly so it is not likely to just spin out with the spark plug if an anti-seize is used on the plug threads.

Biggest problem is there is not that much space between the spark plug hole and the valve seats. So there is a point one can not just go any BIGGER.

Sun Sep 29, 2019 11:23 am

https://www.dormanproducts.com/p-4934-42002.aspx?origin=keyword

Almost looks like an anti-fouler.

Sun Sep 29, 2019 4:47 pm

That’s what is called a “non-fouler” , they’re installed when the engine is burning oil so it doesn’t foul up the spark plug. It’s probably got bad piston rings. The thread on the head is probably ok, put a new spark plug on the non fouler and run it as is.

Mon Sep 30, 2019 8:48 am

Interesting. I'll do a compression test soon. In the mean time, I'll run with the anti-fouler.

Red loctite on the anti-fouler threads, or just put some anti-seize on the threads like I would for installing plugs?