Ideas needed for Striker Plate

[SteveJ]

Okay, so after removing the broken bolt and re-tapping the threads, I'm still having big issues with the striker plate in my 260Z. The door closed fine a few times, but then it wouldn't latch completely. I tried adjusting the striker plate, and I noticed that the bolt would not tighten. I pulled the bolt out and noticed the threads were boogered up.

A replacement bolt wasn't getting tight, either.

At this point, I think that re-tapping the threads and using a new bolt probably won't hold well, and I would like to entertain suggestions.

Should I drill out the M6 to 1/4" and tap at 20 TPI for that size? I am afraid that I might have clearance issues with the head of the bolt if I drill out to M7 and tap at that size.

If these don't work, I imagine I'll need to cut a hole in the body to put in a backing bolt. That is the least preferred course of action.

[Zup]

Hey Steve--

Drill and put in a thread-sert or helicoil. 

Least invasive way of getting a new bite. Won't change the bolt size.

A good friend had a very similar issue on a seat bolt attaching the seat rails to the floor through a hidden, inaccessible captive nut that was stripped.

Worked like a charm.

https://www.amazon.com/dp/B00V8398AG/ref=sspa_dk_detail_3?psc=1

or equal--there are several makers of kits.

 

 

[grannyknot]

Those M6 captive nuts are pretty small and thin, not much to bite into,  I would go with a re drill and an M7 tap, if the head of the new bolt is too tall you could grind it down to the thickness of the M6 bolt so it won't interfere. The torque on that bolt is only 6-7 ftlbs so you don't need much to grab on to. 

[SteveJ]

It's not the height of the head that concerns me. It's clearing the top of the striker plate.

I'll have to check when I get home.

@grannyknot Is there a reason for going to M7 and not trying the 1/4" bolt first? I haven't needed to worry about this before, and I want to increase my knowledge.

[grannyknot]

9 minutes ago, SteveJ said:

@grannyknot Is there a reason for going to M7 and not trying the 1/4" bolt first? I haven't needed to worry about this before, and I want to increase my knowledge.

My only reason would be how irritating it is to find an imperial bolt on a metric car and I guess I'm not sure if 1/4x20 is big enough or maybe too big without some testing, whereas with an M7 you know without looking that it will remove all of the old threads.

Edited March 12, 2018 by grannyknot

[SteveJ]

I did the research (aka, Google is my friend). The 1/4-20 cap screw may be a 3/8 or 7/16 head. The M7-1.0 has an 11mm head. Therefore the head on the 1/4-20 could be smaller than the M6-1.0 or bigger than the M7-1.0.

If the M7 seems to clear the top of the striker plate, it seems like that would be the way to go.

The fun part will be digging the door lock out of the door to lubricate it to make sure it rotates without too much effort. I want to eliminate as many variables as possible here.

[Captain Obvious]

If the female threads are pulled through, then I don't think 1/4 inch threads size is going to solve the problem. M6 and 1/4 inch threads are so close to each other that there isn't enough meat to recut the threads. And if you do decide to try... absolutely do not drill first. Just run the 1/4 inch tap into the existing hole. There's no reason to enlarge the existing hole. You'll cut across the existing threads fine. But I don't think any 1/4 size will suffice.

And if the thread pitch for the M7 is different than the M6, that's not the answer either. But if you can find a M7 bolt with the same pitch as the original M6, you could retap to M7. And I would have to look at the drill sizes before deciding if it required a redrill first.

If you're looking for a small diameter head, you might want to consider socket head cap screws? Won't look anything close to stock, but it should have a smaller head than anything else you'll easily find. 5/16 - 18 SHCS maybe if you can't find a suitable metric option?

[SteveJ]

From my research the pitch for M7 is the same as M6: 1.0. It looks like I should use a 6mm bit (I have metric bits, though one very precise website suggested a C drill bit. Is 0.00577 inches difference that important?) before using the M7 tap. (I have to make sure I have an M7 tap. I think I do. Even if I don't, I can get one in a couple of days online.)

[Captain Obvious]

M6 x 1.0 is the one used ubiquitously all over the Z (and all the rest of the Japanese stuff).

I checked my metric set and I've got M7 x 1.0, so it appears that a M7 with the necessary pitch IS a standard and is easily available option. Assuming, of course, that my set has "standard" sizes. (As a point of reference, I've also got both M6 and M7  in a 0.75 for the finer pitch.)

So if you decide on M7 x 1.0, the trick would be to retap it to the larger size, but carefully start the tap so you're cutting the new threads in the same location as the old threads. Taking advantage of whatever remains of the original peaks and valleys.

As for needing to drill out the old hole first or not... If the pilot drill for a M7 x 1.0 tap is a 6mm (.236) drill and you've already ripped the M6 threads out of the original hole, it should be just about .236. 

Whatever you do, just don't break off a tap in the hole. A brand new sharp tap with suitable cutting oil should be pretty forgiving though, and it's not like you're tapping a very deep hole into thick material. You'll only have a couple threads cutting at once. Getting the tap started square (normal) to the hole is important. If you're unsure of your ability to do it freehand, drill a just fitting hole in a piece of wood to guide the tap and keep it perpendicular to the hole.

[SteveJ]

4 minutes ago, Captain Obvious said:

As for needing to drill out the old hole first or not... If the pilot drill for a M7 x 1.0 tap is a 6mm (.236) drill and you've already ripped the M6 threads out of the original hole, it should be just about .236. 

Whatever you do, just don't break off a tap in the hole. A brand new sharp tap with suitable cutting oil should be pretty forgiving though, and it's not like you're tapping a very deep hole into thick material. You'll only have a couple threads cutting at once. Getting the tap started square (normal) to the hole is important. If you're unsure of your ability to do it freehand, drill a just fitting hole in a piece of wood to guide the tap and keep it perpendicular to the hole.

I was thinking along the same lines about the hole. The 6mm bit may clean it up a little, though.

I haven't broken a tap before, but I have broken an extractor...about 24 years ago. My friend and I managed to salvage that day, though.

[Diseazd]

I would take it to a machine shop....they will fix it while you wait for very little cost. My guess is they will keep it stock specs with a heli coil. Some things are best left to the pros!   IMO

[Turn & Burn]

I would agree with the 1st poster and put a helicoil in. There should be enough meat in the old nut and backing plate to take a coil. The major dia on the coil thread is about 7.4mm.
You will end up with a repair that is at least if not stronger than original.


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