Threads on VST Schrader valve wont engage with fuel pressure gauge

[jkscarab]

Merc 250 EFI 1998 (0G509105)

Background: Helping a buddy replace HP (high pressure VST pump).

In Looking to ensure proper fuel pressure via the schrader valve at the VST, we “tried” to hook up a fuel pressure gauge to find out the treads on that schrader valve will not engage with the pressure gauge (one thread starts but will not fully thread). To diagnose we tried the schrader valve on the other motor (starboard/twin engines) and the pressure gauge threaded on perfectly/fully. So the threads on the pressure gauge seem to be fine but the threads on the VST port motor are “bad”.

I took pics to see if I could see if the schrader threads got mangled previously or whatever and find out the threads look perfectly clean. Confusing, as if Merc put the a bad schrader valve on the motor (which would inhibit them from checking fuel pressure).

Possible next steps:

1. purchase a .305 x 32 die to try to correct the existing funky schrader valve threads.
2. Just forget about the schrader and if the motor runs well just forget it. I hate when stuff doesn’t work properly though …makes diagnosing future fuel pressure issues impossible. So Id like to make it right if a reasonable fix is possible.

Edit: I now see there IS a schrader valve kit from Merc #809059. So, plan B is to get this kit Plan A try a die to "fix" the funky threads on the current shrader valve.

Or am I being stupid and should forget about the die and just replace the valve? Anybody have any experience with this??

Thanks in advance

[Savage]

I would fix the threads with a small fine triangle file from a hobby store. The first two threads are probably damaged from taking a hit at some point.

[Rick H]

My kit has several different size options. Can't say I see much wrong with the od threads.

[EuropeanAM]

I keep a tap just for this very purpose. As long as it's only the first and/or second thread, you should be able to clean it up and have a good connection.

[jkscarab]

I think the die is the right solution for me...thanks Don!! ,Rick H and Savage for your solid input.
Happy Holidays !!