The NRV on my Primus 210 is stuck, the end is buggered and can't be removed with my less-than-perfect tool so I have decided to remove the pump assembly to replace it. And rather than ruin a fairly nice stove i decided to practice on my war-worn, dented, basically junk-pile Primus 51. With my Mapp torch I have successfully removed the pump assembly, NRV, etc., without melting off any other parts and am ready to reassemble with a new NRV. In Bernie Dawg's excellent video on this repair he suggests (and shows) using a tap to chase the threads of the part that the NRV threads into to insure that all goes back in good form. My question is- what size tap do I need for this? Thanks for the help. If I have success I will post pics of the results Tom
https://classiccampstoves.com/threads/nrv-thread-size.18069/#post-185150 Have you considered using firearm bore brushes for cleaning the threads? https://classiccampstoves.com/threads/primus-optimus-burner-14mm-thread-pitch.27020/#post-275479 Best Regards, Kerophile.
As many times as a tap can help, a tap will also cut. And cutting may result in oversized threads. Clean it first. If it does not fit, it may be the NRV thread that is wrong.
I agree @snwcmpr If a previous owner had replaced NRV and or possibly over tightened in the past the threads could have become "pulled" out of spec. to some degree. If at this point a tap is used it could cause an oversize condition that will be prone to stripping out even with a lower torque on the NRV. Use care and if necessary the tap can be used but not to its full thread depth diameter. Just a kiss is all it takes.
I suggest you send Gary "Bernie Dawg" Adams an e-mail and ask him directly. bluewater_stove@comcast.net Ben
I am not questioning Garys advice. But that application does not always apply. Check the NRV before you tap the hole. Gary also wrote about the bad threads of recent NRVs.
Hi all You do practice on a Primus 51 and threads seem to be or could be different of the one on Primus 210. Three months ago, I did replace the NVR on my 1933 Primus 210 with one from Juliands and it fit perfectly. I have also kept the pig holder that was in the old 210 NRV and used it in the new NRV because it is a quality one and fit perfectly. Here the old one and the new one from Juliands Hope that Help Have fun Open old NRV pig holder New and old pig holder Old pig holder with new NVR Old and new NVR threads Note- I think it is very important to know that your new NVR has the thread you need for, if you tap for a new NVR thread that is not original when you can have one original, you simply put yourself is trouble. I like @snwcmpr advice, clean the thread first.
Tom, Sorry to hear of the challenges, congrats on getting as far as you have. Kerophile answered accurately & quickly, an answer that included (also from Gary iirc), boring brass brushes and the use of dental tools... +1 w/that and a soak. Installing a "new" NRV <--- that is often a quality/fit issue vs the original threads. JP2 and Tom, Tom "ya done good" choosing the 51. I am certain I have been advised that the rebuild parts for 210 and 51 are the same (51 has longer pump asm.). That said if the 210 & 51 are years apart that may be a compatibility issue I'm unaware of. (Sorry I'm yackin' here, it had seemed to me you got your answer in 1st comment?) best of luck, thx omc
Berniedawg has updated the description below the video to indicate the correct thread sizes to use to chase pump tube end block NRV threads as well as NRV barrel threads. Ben
A suggestion for a tap that will not cut is a roll tap. They were designed to 'form' the thread rather than cut the thread. A larger hole was drilled and after the roll tap was used the hole was the correct size. If you used a roll tap you would be less likely to cut too big. Look closely at the threads of new NRVs. They may have burrs left after machining. Using them in that condition can result in unwanted results quickly. There are several threads here about that. I posted close up photos. Also check the pip in the new ones also. They can be hard as an old one.
Another trick is to use a smaller tap with the same thread pitch to clean up threads, e.g., 1/4 - 28 tap to clean a 1/2 - 28 thread. You use it hand held, so you can feel how much you're removing or reshaping, and where. Murph
@Marc, @snwcmpr, happy to help! My grandfather taught me that trick, put a fine thread tap in the crossfeed of a lathe and use a flute as a multipoint cutter for fine internal threads in large diameter holes / parts, cut them in one pass. Murph
@Greeley G'day Tom, here is a good discussion https://classiccampstoves.com/threads/primus-nrv-m8-thread.36786/#post-381559