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Well, got my dual sport all back together (or so I thought). Had planned to heat cycle and ride it last night until I started pouring the coolant in... and it just poured out on the floor . Looks like I neglected to replace the coolant plug in the underside of the cylinder I spent an hour or two searching and can't find the plug anywhere.

Anyone know the size of said plug? I know that it's not shown on the OEM part diagrams. I have read on here some where that one person claims it is an M16x1.5 metric plug. I saw on TT that someone claims a 3/8" pipe plug is the size. The 3/8" seems more feasible to me, size wise, but I feel like it probably is some weird metric size. M16 just seems too large, thats bigger than 5/8". Just wanted to see if anyone could tell me for sure? If its a 3/8", I can get one no prob. If its a metric size, I will have to order.

It is definitely a tapered plug. I would be surpised if it wasnt metric.

Just go to the hardware store and get the appropriate sized pipe thread tap and plug and take care of it in a few minutes.

I wish I could remember but it's already been too long since I did mine. I do remember it took a metric allen wrench. Sorry. We need to confirm what it is for sure so others can find the info in the future.

SS109 wrote:We need to confirm what it is for sure so others can find the info in the future.

Agreed, bigtime. Couldn't find the answer anywhere besides two people on TT saying they used 3/8 plugs. I'll grab a 3/8" NPT plug and give it a try in the next couple of days and see how it fits. I would happily order some metric plugs and do some trial and error to find the right size, I just don't know where to begin.

I sent an email to both RB-Designs and FRP Racing to see if either of those experts would happen to know. I don't know where else to turn if not! I guess I will just go ahead with searching for and ordering plugs for trial and error. I will update once (or if) I hear back.

Well. Ron Black is unsure of the size, but he thought it may have been M16 also. He recommended I ask Powerseal USA if they know or have one. Powerseal replied back with "we can weld that hole closed for $20 because it isn't used for anything". Guess I'm going to be buying a whole bunch of plugs and trying to figure out what I need

Just placed an order with Bel-Metric for an M16, M14, M12, and M10 plug. I also am going to get a 3/8" Pipe plug to try.

I'll get to the bottom of this one way or another!

Hey. Just saw this thread!

It is 3/8".


JUST KIDDING! Good luck with it.

I happened to remember that a friend of mine who I met on craigslist (not the personals from selling/trading kdx parts) had several good cylinders in his collection. He is going to let me have one, should be back in business in the next couple of days dont worry, I'll still try to figure out what it is once and for all! Stoked that there are still good people out there that are willing to help ya out!

CONFIRMED! The thread size for the coolant plug on the underside of the cylinder is most certainly M16x1.5. I tried a 3/8" NPT and it would start into the hole but stop. Here is a link to a plug if you need it, got mine from Belmetric, saw that Fastenal also sells them: https://belmetric.com/stainless-taper-m ... P16X1.5TSS

Thanks for the follow up!

Heck yea, hopefully it will benefit someone down the road!

This is incorrect info. It is not an m16x 1.5. My thread gauge proves that at least the thread pitch is a SAE 19 (on the SAE side of the tool with number 19 on the correct key). Not sure about the diameter. I bought the same one and threads are finer on the oem thread plug. Picture of aftermarket plug followed by the oem.

Thanks for the pictures and info!

Where can you find an SAE 19 pitch plug that would fit this? I did a quick google and couldn't find one.

I wouldn't say that the M16x1.5 is incorrect though, my bike has 6 years of fairly hard riding on it with no signs of leakage at the plug. Valid solution in my book!

Tyl3r wrote: 10:19 am Aug 23 2023 Where can you find an SAE 19 pitch plug that would fit this? I did a quick google and couldn't find one.

I wouldn't say that the M16x1.5 is incorrect though, my bike has 6 years of fairly hard riding on it with no signs of leakage at the plug. Valid solution in my book!

Yea I can’t find one anywhere. And technically it’s incorrect but realistically it will work. The m16 x1.5 will thread in and stop just before it’s flush with the surface, this is because the threads begin to bind and not because of the taper. I would use the m16 x 1.5 plug but I would definitely want to use a thread sealer. In reality it’s a one time thing and the plating company I sent my cylinder to shouldn’t have ever removed it, after getting my cylinder back the oem plug is now bottoming out way past flush inside the water jacket of the cylinder. I sent it out with the plug flush with the surface.

Tyl3r wrote: 10:19 am Aug 23 2023 Where can you find an SAE 19 pitch plug that would fit this? I did a quick google and couldn't find one.

I wouldn't say that the M16x1.5 is incorrect though, my bike has 6 years of fairly hard riding on it with no signs of leakage at the plug. Valid solution in my book!

Did you use any sealer for yours? Thanks

As my day job is at a machine shop, I will try to sort out exactly what this plug really is. Makes not sense to me it would be NPT or BSPT on a Japanese bike, but ya never know....... I too have a leaking plug

New rebuild fired right up first kick on Monday, and she's weeping out of the plug......... so plan A is to clean up the original and use a bit of really good PTFE tape, (I hate the paste).......... plan B is to use a 16x1.5 plug I picked up on amazon. Plan C is to use potentially a 3/8" BSPT plug (not NPT, British Pipe Thread) which is actually 19 TPI and a bit over 16mm, Plan D is to use a 3/8 NPT plug which is 18 TPI and a bit over 16mm........... something has to seal, it's not like we're high pressure! Will post results.....

And a good bit of info found here.....
https://trimantec.com/blogs/t/thread-id ... tion-guide

Kawibunga wrote: 02:11 pm Oct 03 2023 As my day job is at a machine shop, I will try to sort out exactly what this plug really is. Makes not sense to me it would be NPT or BSPT on a Japanese bike, but ya never know....... I too have a leaking plug

New rebuild fired right up first kick on Monday, and she's weeping out of the plug......... so plan A is to clean up the original and use a bit of really good PTFE tape, (I hate the paste).......... plan B is to use a 16x1.5 plug I picked up on amazon. Plan C is to use potentially a 3/8" BSPT plug (not NPT, British Pipe Thread) which is actually 19 TPI and a bit over 16mm, Plan D is to use a 3/8 NPT plug which is 18 TPI and a bit over 16mm........... something has to seal, it's not like we're high pressure! Will post results.....

And a good bit of info found here.....
https://trimantec.com/blogs/t/thread-id ... tion-guide

I'm eager to hear your results, as PowerSeal USA seems to have removed mine to strip and clean my cylinder, and never reinstalled it nor returned it to me!

[/quote]I'm eager to hear your results, as PowerSeal USA seems to have removed mine to strip and clean my cylinder, and never reinstalled it nor returned it to me!
[/quote]

OK, so still waiting on a few things, but what I have confirmed is it's definitely not the 16X1.5 metric, which is in agreement with JZ05220r. Which really surprises me. I don't have 19 TPI pitch gauge, that's coming Friday, but you I could see that the 18 was just a bit off, so think it's the 19. I'll stick it on the optical comparator at work tomorrow over lunch as an extra check (forgot it at home today)

So it really does look to me like a 3/8" BPST thread, a few more measurements will confirm.

But I did end up fixing it. Originally I put the plug back in the first time with paste, and I could not thread it down tight enough for what I wanted. When it was flush, I could have still gone another full turn fairly easy. It leaked. So on the weekend I installed the plugs I ordered off amazon. These plugs were slightly longer, seemed to be the identical thread on initial measurement (but still confirming that 100%) With it being longer. I got it to tighten up way nicer while threading in. I also used good PTFE tape instead, felt really nice threading in........... and Bingo, got a good seal, no leaks at temp!

You can see that the plug is orignaly flush, I could have easy went in another turn from here........
Here's the new plug vs original, you can see it's a wee bit taller
Here it's installed, nice an tight (not over tight) and sitting slightly proud. Threaded in nice. After the fact I will now take a few more measurements and report back. But these worked great. Here's what I ordered.......
They call them both NPT and BSSP which is obviously wrong, you can't be both, NPT is slightly larger OD and 18 TPI while BPST 19 TPI and slightly smaller OD.......... it still makes no sense to me that it's not a metric thread, but that's what I've found out so far. More to come once I take some final measurements........

Was just doing a tune up on a 18 hp Briggs and Stratton V twin yesterday. The oil drain bolt was very similar looking to the ones on our cylinders. I doubt it will work but might be worth checking.