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cmarty123
01-10-2011, 06:34 PM
I have a 95 Maristar. The female thread on the engine block is stripped where the knock sensor is installed. Any advice on how to rethread? Should I install a helicoil? It looks like I only have about 7 in. to get a drill and bit in there. Do I need to use a right angle drill and a short bit?

I searched the site and did not find anything about this. I would have thought I would have seen this same scenario as it seems like a bad design. After the knock sensor is removed for the season, condensation will sit on the threads and corrode them. After 15 years of this, the threads finally gave out. Thanks

Slinkyredfoot
01-10-2011, 07:12 PM
Is it actually stripped or are the threads just real rusty? I thought I had a stripped hole on my block but realized the threads were crudded up so bad they just needed to be re threaded which I did. I was lucky.

Typically the threads can be chased with an NPT (National Pipe Thread) tap, depending on the size to clean up the rusty threads, probably 1/4" or 3/8 NPT. Be careful and take it easy when you start, spray WD or some other rust stuff in the threads and let set for a bit. Screw the tap in easily to see if it takes, if it does, keep turning a bit at a time and the back the tap out, spray more douch and keep threading it in and backing the tap out.

I am not saying this will cure your ills but it just might clean the threads up for you. Maybe worth a try.

As always, as I have learned, whenever your take a water plug out anywhere to drain, lube your plug up with pipe dope before re inserting. ;)

CantRepeat
01-10-2011, 07:41 PM
I agree with slinky. The first thing I'd do is get a bottom tap and chase the threads by hand at first.

oldairboater
01-11-2011, 03:24 PM
Chase the treads first before anything else. I would be doing this every season and be anti-seizing the threads.

Spork
01-13-2011, 01:01 PM
I would not use pipe dope on the knock sensor threads as it could cause the sensor not to read correctly, just use a good anti-seize lube.

CC2MC
05-19-2015, 09:23 AM
I had the same issue with mine being rusted after leaving the plug out all winter. I bought a 1/4" - 18 tap from Harbor Freight and that did the trick on my 2003 210 with the Predator engine. The rust came out very easily and I put a new plug in with never seize on the threads. Problem solved.

mikeg205
05-19-2015, 09:31 AM
agree with all of this.. had the same problem 5 years ago.. now I keep a light coating of anti-seize - and no trouble since.

etduc
05-19-2015, 09:44 AM
I bet, you can solve the problem, with chasing the threads. Done all the time with aluminum threads.

Two caveats. 1) Getting the tap, square to the surface.
2) Put anti seize( or grease) on the tap's threads, and a little in the tap reliefs. (Usually, the excess anti-seize on the threads, will fall into the reliefs, with debris...but I always put just a tad in the relief.) This will aid in chasing, and catch metal savings. Cleans the threads, as you back out.

gr82bgreen
05-19-2015, 02:03 PM
I would hope it is fixed in the 4 yrs from the original post.

mikeg205
05-19-2015, 02:08 PM
I would hope it is fixed in the 4 yrs from the original post.

holy thread revival

etduc
05-19-2015, 03:48 PM
Didn't even read the post date.

Willski
05-30-2017, 04:57 PM
I'm gonna revive this again! I have this issue. This is the second boat I have had trouble with. I tried retapping, and still can't get the plug in. It seems like it threads in, then just falls out. I'm kind of at a loss right now.

Table Rocker
05-30-2017, 05:34 PM
I'm gonna revive this again! I have this issue. This is the second boat I have had trouble with. I tried retapping, and still can't get the plug in. It seems like it threads in, then just falls out. I'm kind of at a loss right now.
Something like this could be a solution if you drill and tap to a larger size:
https://www.shopcross.com/sites/default/files/styles/product_image/public/images/products/7944350-23.jpg?itok=VVEN0h3b
Brass Pipe Bushing

waterlogged882
05-30-2017, 05:51 PM
I'm gonna revive this again! I have this issue. This is the second boat I have had trouble with. I tried retapping, and still can't get the plug in. It seems like it threads in, then just falls out. I'm kind of at a loss right now.

Maybe too little too late.... Are you tapping with machine screw tap or a pipe thread tap? Use a thread pitch gauge to make sure of the thread use.

Willski
05-31-2017, 03:23 PM
Maybe too little too late.... Are you tapping with machine screw tap or a pipe thread tap? Use a thread pitch gauge to make sure of the thread use.

1/4 NPT.

Willski
05-31-2017, 03:24 PM
Something like this could be a solution if you drill and tap to a larger size:
https://www.shopcross.com/sites/default/files/styles/product_image/public/images/products/7944350-23.jpg?itok=VVEN0h3b
Brass Pipe Bushing

I may have to go that route. It isn't rocket science, but it is not easy to work on either. Drilling and tapping would be tough in the location it's in.

Table Rocker
05-31-2017, 04:11 PM
I may have to go that route. It isn't rocket science, but it is not easy to work on either. Drilling and tapping would be tough in the location it's in.
Yes, it would.