water pump mounting threads

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   I think this is straight forward, but wanted to ask in case I was missing something (and since I made the mistake of not taking shop in school).  The bottom mounting bolt on my 92 SN water pump will start to tighten up, but then release just when you think it is getting snug.   Bolts look fine (original), guessing the pump mount threads are stripped or cross threaded.   Have also noticed that when the bolt is started into the mount, it drops in about 4 threads worth before making contact. Have been relying largely on the top bolt the past two seasons, with the bottom one snugged to just before it releases.  Want to fix this off season.  Pump works fine, so replacing seems like overkill.
Original bolt is a 5/16-18, so thinking of drilling it out and tapping the mounts for a 3/8 bolt.   Have done taps in steel, but from what I read, brass should not be any more difficult.   Wasn't sure whether 3/8-16 or 3/8-24 would be stronger.   The 3/8-16 bolts in a 3/8-16 seem to have more slop, but guessing stronger??

Viable solution?   Recommended thread count?

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davidaha Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: May-13-2020 Location: Kansas Status: Offline Points: 48	Post Options Post Reply Quote davidaha Report Post Thanks(0) Quote Reply Topic: water pump mounting threads Posted: November-08-2023 at 6:32pm
	I think this is straight forward, but wanted to ask in case I was missing something (and since I made the mistake of not taking shop in school). The bottom mounting bolt on my 92 SN water pump will start to tighten up, but then release just when you think it is getting snug. Bolts look fine (original), guessing the pump mount threads are stripped or cross threaded. Have also noticed that when the bolt is started into the mount, it drops in about 4 threads worth before making contact. Have been relying largely on the top bolt the past two seasons, with the bottom one snugged to just before it releases. Want to fix this off season. Pump works fine, so replacing seems like overkill. Original bolt is a 5/16-18, so thinking of drilling it out and tapping the mounts for a 3/8 bolt. Have done taps in steel, but from what I read, brass should not be any more difficult. Wasn't sure whether 3/8-16 or 3/8-24 would be stronger. The 3/8-16 bolts in a 3/8-16 seem to have more slop, but guessing stronger?? Viable solution? Recommended thread count?
	92 Ski Nautique

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11112	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: November-09-2023 at 5:57am
	Assuming that it's the original Sherwood raw water pump, the threads you're talking about are in the cast iron part of the pump (the pump body that holds the bearings) Only the impeller housing is brass There's not a whole lot of meat there for drilling out, but I'd probably get a 5/16-18 helicoil kit, drill it out and install the helicoil and then use a stud in there so that you're never having to disturb those threads again. Some loctite on the stud would be good. Just slap it in the mounting bracket and use a nut on the stud I'd probably loctite a stud in the other mounting hole too I'd also not worry about which threads are stronger in this application.

67 ski nat Members Profile Send Private Message Find Members Posts Add to Buddy List Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1194	Post Options Post Reply Quote 67 ski nat Report Post Thanks(0) Quote Reply Posted: November-09-2023 at 9:23am
	Perfect solution

davidaha Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: May-13-2020 Location: Kansas Status: Offline Points: 48	Post Options Post Reply Quote davidaha Report Post Thanks(0) Quote Reply Posted: November-10-2023 at 8:34am
	It is the original Sherwood. It is painted gray all over and I had assumed all brass. Using a helicoil and stud is a much better approach than what I was about to do. Thank you.
	92 Ski Nautique

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11112	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: November-10-2023 at 10:33am
	Another thought Dave.......since the hole and adjusting slot in your bracket are big enough for a 3/8 stud to fit, you could save the helicoil part of the job and just tap the hole like you planned and then put in a 3/8 stud. If the threads in the other hole are good, I'd leave that one alone and put in a 5/16 stud or use the bolt that you use now. Kinda a combination of ideas I have no good idea why PCM has the bracket sized for 3/8 holes and they use a Sherwood pump that uses 5/16 mounting bolts Here's a picture of the bracket and the 3/8 slot and hole.

davidaha Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: May-13-2020 Location: Kansas Status: Offline Points: 48	Post Options Post Reply Quote davidaha Report Post Thanks(0) Quote Reply Posted: November-14-2023 at 9:56pm
	I had already purchased and opened the 5/16 heli coil kit, so just did that with a stud and loctite. Was easy to do and seems strong. Agree it is odd how much slop the is between the bracket and the pump. Thanks again. Now I have to find another off season therapy repair project....
	92 Ski Nautique

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11112	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: November-15-2023 at 7:04pm
	You made quick work of that

water pump mounting threads

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