Tank strainer won't screw into new tank

[twistedtree]

I'm installing a new fuel tank in my '70 280SL.  It's a new MB tank straight from the classic center, though I bought it about 14 years ago.  It has been stored in my shop which is dry and climate controlled.  All appears in perfect condition as I would expect, however the strainer from my old tank won't thread into the new tank.  I can get maybe 3/4 of a turn on it and it binds up.  It threads freely into the old tank.  There are no signs of thread damage, but it's binding up real tight, and I don't want to force it and create a bigger mess.  My plug and strainer is the old style with a brass plus and copper screen.  It's in great shape so I see no reason not to reuse it.

I have encountered threaded bosses like the one on the tank that have become a bit distorted from welding and the threads bind.  I'm thinking that's what's happened here.  In other cases I have chased the threads with a tap and that solves the problem.

Has anyone run into his before?  Any ideas other than getting a bottom tap and chasing the threads?  It will be a big tap and likely hard to find/expensive, so if there is a better solution...?

Thanks in advance.

[DaveB]

If you have one of those thread pitch gauges you could test to make sure the tank thread really is the same as the filter thread. If it is I think you’d be ok to use a bolt with the same thread to carefully tap it out. With grease, back and forth.
I guess you have already inspected the tank thread for damage in the place it’s binding.

[twistedtree]

I checked measurements with calipers and a thread gauge.  It's the same.  The tips of the male threads on the plug appear to be making contact so I'm thinking the threads aren't cut deep enough on the tank side.  I decided to order a new plug and will try that first.  It's a lot less expensive and quicker to get than a tap.  It's an M36x1.5 thread, and I don't have any bolts anywhere near that large.

[ctaylor738]

Yikes! Expensive, but I have had good experience with these folks.

 https://drillsandcutters.com/m36-x-1-50-hss-metric-hand-tap/?gad_source=1&gbraid=0AAAAADyuQN4iVcbcp1rxORzQXL4d_Zsep&gclid=CjwKCAiAtNK8BhBBEiwA8wVt9_vJARkRqMs9jf4Sa0VqKxHnbEbWcOiKLfP3xyKFRy3_oRGvukzn-BoCTNsQAvD_BwE

Good luck on this one,

CT

[twistedtree]

I tried a new drain plug/strainer and it binds up too, so it’s definitely the threads on the tank.   Disappointing since it’s an MB tank.   I have ordered a tap and the next step

[twistedtree]

Just a final update to close this out.  I received my tap - M36x1.5 so it's a big one.  I was able to chase out the threads on the tank and now the strainer plug fits fine.  It's very disappointing to have to do this on a new MB tank.  I bought two new tanks from MB back around 2012, one for a 230 and one for a 280.  I installed the 230 tank without issue, but this 280 tank sat on a shelf until now.  But I can't see any way that just sitting on a shelf could have distorted or shrunk the threads.  So I have to believe it was like this from the factory.  Anyway, it's all working now.