1989 Raw Sea Water pump 7.4L Bravo 1 - Stripped thread on pump housing

[Fastrack]

Hey.

I have a Formula 7.4L Bravo 1, one of the engines sea water pump housing is melted (0C320740). The engine already had an aftermarket Sierra pump housing installed. So the multi-piece original housing is long gone. (Ran without water so it quickly melted)

I just purchased the Merc Kit 46-807151-A14. It comes with the housing, stainless wear plate all the bolts and o-rings.

Before assembly I tried to find the torque settings. Old manual said 30ft/lbs. ClubRay has a screen capture from Mercruiser that said 15-20ft/lbs. Another service manual (#23 I think) says 120 in/lbs (10 ft/lbs). I settled on 15ft/lbs. I should've just used my gut and tightened them snug using a 1/4" ratchet and I wouldn't be in this mess.

All was great until the thread stripped RIGHT out of the pump housing - I wasn't even close to 15ft/lbs! The only bolt that doesn't go through the metal stamped bracket.


The local mechanic suggested I drill the bracket and pass the bolt through the hole and nut it.

However the supplied bolts with the kit & the old sierra bolts only go halfway into the nuts! They are 5/16 3.25". I'm not sure should I purchase 5 x 3.5" bolts?? I can't figure out why the mercury supplied bolts are so short. I would expect at least a few threads protruding out of the nuts!


Options:
- I'm thinking of buying 3.5" bolts drilling through the bracket and calling it a day?
- The bracket is almost 1/4" thick, I could almost tap a 5/16x18 hole in the bracket instead of using a nut??
- Helicoil kit, described below leaves very little "meat" once the hole is tapped larger. It would be the BEST repair I'm just concerned with the leftover meat in the aluminum housing once the hole is tapped.

Only issue with drilling all the way through is the bracket curves slightly. A little bit of work with the dremel and the nut will lay flat though.


You can see the 2 nuts in the background, those bolts are fully threaded into the nuts!


Shows the "curve" on the bracket


I purchased a helicoil kit. But the tap is 3/8" (requires a 21/64" hole). The wall thickness around the stripped threads is only .126" Granted that's 3/8" "threaded" not a 3/8" hole.


Ben

 

[wrvond]

I have found that when a manufacturer uses a mix of through bolt holes and blind holes there is usually a reason. I'd go with a timesert rather than helicoil, though.

 

[Fastrack]

I have found that when a manufacturer uses a mix of through bolt holes and blind holes there is usually a reason. I'd go with a timesert rather than helicoil, though.

I spent a lot of time deciding on the helicoil or timesert (which look amazing btw). There's so little "meat" in that area, I decided against drilling/tapping the hole that large.

I bet it's because of the way they manufactured the bracket as it was curved in that area, plus they probably drilled the holes first (or punched) and the bending process would've distorted that hole.. so they used a shorter bolt. I've drilled the 5/16" hole through the bracket using the old plastic housing as a guide.

Using a Dremel flattened the area. Looks good! 3 coats of Tremclad are currently drying. I also gave the pump body a nice coat as the previous owner scratched up the pump body pretty good. I'm still thinking of picking up some slightly longer bolts (3.5" vs 3.25"), there is only 1 thread that isn't "threaded" though.

Ben

 

[alldodge]

Could have it welded up, then drill and tap to original size

 

[Scott Danforth]

Helicoil and go boating

 

[Fastrack]

Helicoil and go boating

Well as above I decided on the hole through the stamped steel bracket

As I didn't think there would be enough aluminum left after the 27/64s hole was tapped for the helicoil, strength wise.

Ben