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Installing Recaro seats. Bolt threads issue

25 September 2020
Bellevue WA
I ran into some issues with installing Recaro seat ABE with SoS seat rails.
the problem actually started with the original bolts that was used for mounting original seat.
I tried to screw back in 4 screws in the photos. Front two screws are in. But rear two screws are not going in. I suspect may be threads in the hole are damaged? Please help.


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Need to figure out if this is a bolt problem, a hole thread problem, a part misalignment problem, or a part incompatibility problem, by removing the rails and inserting the bolts on their own.

Were the bolts difficult to remove? Did they feel like they were cross-threading on the way out? Examine the bolts carefully for any sign of damaged threads & replace if so. Small amounts of "crud" can be removed with a wire brush if the threads are otherwise intact. Test any replacement bolts on their own to be sure they thread in easily before you try to attach the rails.

Remove the rails and see if the bolts can be inserted on their own. Try all of the bolts in each of the holes to see if you can identify the culprit bolt(s) or hole insertion location(s), or both. If a culprit is an insert location, you may be able to gently rethread it with a tap, if you have experience doing this. Double check the tap size & thread count. Otherwise, there are thread repairs like heli-coils etc, if you have experience with them.

Once you've verified that all 4 bolts thread into all 4 holes smoothly on their own, gently thread all of the bolts a few threads in by hand with the rails installed before tightening any bolts, then all bolts finger tight, then torque them all - if you tighten any of the bolts before all of the bolts are correctly threaded in, the part may be slightly misaligned and cause the remaining bolts to cross-thread.

Sorry if this is stuff you already know.
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There's probably nothing wrong. The rear seat bolts on the NSX are notoriously difficult. We ALL suffer with them, so don't feel bad. :) This is because the nut-sert sits a good bit below the hole in the metal and it wiggles around. The standard bolts are 25mm long, so it can be a real challenge to get them far enough down through the seat bracket to grab the first couple threads of the nut-sert inside the bolt hole. My solution was to buy OEM 35mm long bolts so that they could reach deeper into the hole and have a better chance of grabbing the threads. You still have to wiggle and spin them to grab the wobbly nut-sert in there. Solved it for me. Part number is:

Thank you both. When I tried all four bolts on the front mount, all four of them are just screwed in fine. I think it’s either issue that Honcho pointed out or my threads in the hole may be an issue. I ordered the parts that Honcho noted. But they are all discontinued and not available. I ordered few from Japan and finger crossed if they can locate some. I will update the thread when I found the solution.
How fancy are these bolts? A special grade? They seem like regular bolt-washers that get used all over the the place, but you certainly wouldn't want to compromise on something as important as keeping your seats fixed in the case of an accident. Could you just use regular flanged steel bolts? @Honcho , could you just put in titanium bolts? They're pretty easy to order in M10 x 1.25 at any length?
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How fancy are these bolts? A special grade? They seem like regular bolt-washers that get used all over the the place, but you certainly wouldn't want to compromise on something as important as keeping your seats fixed in the case of an accident. Could you just use regular flanged steel bolts? @Honcho , could you just put in titanium bolts? They're pretty easy to order in M10 x 1.25 at any length?
I went with OEM because these are safety related and I don't know the alloy. If aftermarket, I'd use Grade 8 steel before titanium.
I had the same issue with a different set of seat rails. Issue was the OEM bolts were too short! Went to Ace hardware and got me longer bolts, worked just fine. I'm going to order the ones Honcho mentioned, OEM FTW! Thx Paul!
I was able to put three screws in today. Same one that I removed from original seats. I have no luck on last one (rear right side). May be thread is thin because I can see some grinds on the bolt. I bought bolt thread repair tool to clean it. Fortunately it made three of four worked. Phew
I bought these bolts and washer and it solved my issue. Yes it was too short to grab the thread in the hole. Thanks guys. You are so helpful.


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Uh oh. DANGER. My engineering work stopped 30 years ago so my knowledge is limited, BUT...

Unless I am mistaken, those are imperial bolts, not metric. Everything in an NSX should be metric. 7/16" = 11.1mm, 3/8" = 9.5 mm - which did you use? It appears from the pictures you used 7/16" bolts and 3/8" washers? The UPC code suggests the 3/8" fastener is a lock washer, which is not used in the OEM.

The OEM bolts are M10x1.25, 10 mm diameter, 1.25 threads, 25 mm long (or 35 mm as recommended by @Honcho

The threads are not clear from your pictures, but I hope those imperial threads for these bolts are close enough to the 1.25 metric threads that the threaded inserts are not irrevocably damaged. The "1 1/4" in your picture is the bolt length in inches, (31.75 mm, close to @Honcho 's 35 mm length recommendation) not the thread pitch. 7/16" fine threads are 20 TPI, which would work out to 1.27 mm, actually pretty close to 1.25 mm, but the label in the picture seems to show 7/16" coarse threads - 14 TPI, which would work out to 1.81 mm. Compare the threads by applying a purchased 7/16" bolt thread-to-thread to an original OEM M10 bolt from the side. 7/16" fine should almost line up with M10 x 1.25? How close are they?

Seat rails are an important safety component, especially in an accident. But what is the safest course forward now? If a 11.1 mm bolt has been installed, the insert threads have likely been damaged by the larger bolts and M10 bolts will no longer be secure. Is the safest path forward to leave the 7/16" (11.1 mm) bolts, that the nutserts have been effectively retapped by the 7/16" bolts to 7/16"? Hopefully the nutserts had at least 1 mm of safety factor. I suspect that, at the least, the imperial bolt should be removed to examine for damage to the threads?
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I purchased
7/16x1 1/4 (perfectly fit in m10x1.25 hole)
3/8 washer
3/8 fastener

It’s secure now. At least now until I may get OEM bolts from Japan. None of dealer has longer bolts in US.

Fortunately the tread in the hole is not damaged. It was just short as @Honcho noted. When I insert the longer bolt, it catches it right away.
I purchased
7/16x1 1/4 (perfectly fit in m10x1.25 hole)
3/8 washer
3/8 fastener

It’s secure now. At least now until I may get OEM bolts from Japan. None of dealer has longer bolts in US.

Fortunately the tread in the hole is not damaged. It was just short as @Honcho noted. When I insert the longer bolt, it catches it right away.
The bad news is if you used a 7/16 bolt in that hole the threads are now destroyed they may have gone in but they are not secure. The original seat bolts are metric not imperial, I’ve also struggled to get the oem bolts in, the key is to make sure they are all started before you tighten any of them down. You may need to take the car to a professional and have the threads repaired now if you did in fact ram a standard bolt into a metric hole.
I don't mean to be an ass, but I don't believe that insertion of a 7/16" bolt was correct, or safe.

If a 7/16" (11.1 mm) bolt has been inserted into the 10 mm M10 hole, the M10 hole has been rethreaded and is no longer a M10 hole. The hole is now larger, and the threads will not match to the M10 x 1.25 bolt, especially if the 7/16" bolt had coarse (1.8 mm) threads. The hole will not "hold" a M10 bolt safely anymore, so inserting the 35 mm long M10 bolt when you get it from Japan is not safe.

Note that the Imperial "x 1 1/4" is not the same as the Metric "x 1.25". One is length, the other thread pitch.
Imperial lists the diameter (7/16", 11.1 mm), then the length (1.25", 32 mm), then the threads (coarse, 1.81 mm)
For the metric bolt you have ordered from Japan:
Metric lists the diameter (M10, 10 mm), then the threads (1.25 mm), then the length (35 mm)

This imperial bolt is only 32 mm long, but still longer than the original 25 mm. But the imperial bolt is 1 mm larger in diameter and has quite different threads, effectively cross-threaded. I think this requires replacement of the nutsert - could a heli-coil be employed? (Need to check the major diameter of the 7/16" coarse vs the drill bit size of the heli-coil.)
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uhhhhhh. At least it is bolted on now. I will try to repair if I get a bolt from Japan. Otherwise this is the only solution for me.
I don’t think you understand that what you have done is not safe. You have surely damaged the threads that are holding your seats to the floor. Getting a bolt from Japan won’t help as the damage is already done. Bolts are not just bolts you can’t just use whatever bolt in whatever hole.
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Yeah you are right. Well it’s in now. I will repair it when OEM bolt arrives. At least it’s not on driver side. It’s on passenger lol. Thx all for your comments
At least 3 of the bolts holding down the seat are OEM ones so not the worst case I've seen. Like Wild Turkey mentioned, when you get the longer OEM bolt, you'll have to fix the threads. Heli-coil would be my go to as well assuming you have enough material to work with.

Even though the new bolt is "in", you effectively have lost quite a bit of thread engagement due to the larger bolt diameter and different thread pitch. Just because something "threads in" doesn't mean it's the correct application. You'll see why when you remove the bolt you installed and try to rebolt it up.

As a pre-cautionary measure, I wouldn't use the passenger seat until your OEM bolt shows up and the threads are repaired. Last time you want is the seat rail coming loose in an accident with someone seating in that spot.
It's gonna be tough to helicoil a nut-sert. The threads on the 7/16 bolt are a little coarse/loose. You might be ok just backing it out and putting the correct metric thread in there. The bolt steel is harder than the nutsert so you are basically bending them back to the metric. Since you have three good bolts in there, the saftey issue is not as severe. I'd try the correct bolt first. If it torques to spec, you're ok. If it doesn't torque properly, then it's time to break out the tap or thread chaser to try and get the threads back to metric OEM.
I can't believe I'm disagreeing with @Honcho , and others on something NSX related, but I'd like to propose a contrarian view. Trying a M10 bolt now might have been reasonable with 7/16" fine thread (although I wouldn't try it myself with the hole expanded by more than 10%), but 7/16" coarse (1.81 mm) is quite far from 1.25 mm and a significant cross-thread:

First, I would not agree that threading in the OEM M10x1.25 bolt and attempting to torque to spec is a good idea. (Likely it won't hold the specified torque anyway, & might remove even more metal while cross-threading.) BUT, even if the M10x1.25 bolt appears to hold the torque spec, a significant portion of the back-torque from the bolt will be from cross-threading on the 7/16" coarse threads and not applied axial load on the bolt being applied as torque via the threads. The bolt will not be adequately tight axially. It might torque to spec, but that is NOT a guarantee of originally specified bolt pull-out strength, although lateral shear strength might be maintained.

But I'm also not convinced that this a good application for a HeliCoil. It's going to be tough to thread a HeliCoil, for several reasons. If the nutsert is loose, it will be difficult to drill the nutsert, even moreso to keep the hole on-axis, and difficult to verify. The HeliCoil tap will be similarly difficult to keep on-axis, as will the insertion of the HeliCoil itself. A top countersink will be impossible to assess. If the HeliCoil jams or breaks going in, you are scuppered.

But more importantly, a M10x1.25 HeliCoil will likely not be structurally sound in this hole because the hole has been expanded by the 7/16" bolt insertion. The nominal diameter of the 7/16" bolt (11.1 mm) is already significantly larger than the M10x1.25 HeliCoil drill-out diameter of 10.25 mm, so you won't have good material to tap the heli-coil threads into, before inserting the HeliCoil. At least 0.43 mm of the threads on each side of the nutsert will be garbage, twice tapped/cross-threaded metal, meaning the HeliCoil will be prone to jamming, may not thread in, and may not be structurally sound even if it does. HeliCoils have no strength; they hold by being wedged between the inner and outer threads. 11.1 mm is almost as large as the major diameter of the M10x1.25 HeliCoil tap (11.8 mm). I wouldn't do it without something specific from HeliCoil that it would fit their specs.

On the other hand, what's done is done. While you still have the problem of cross-threading back torque causing you to stop before the correct axial bolt load is reached, the very-hard Grade-8 7/16" bolt may have effectively "drilled out" and tapped the softer nutsert to a 7/16" coarse thread already. (The coarse thread is stronger than M10x1.25, which is considered a fine thread.) I would remove the 7/16" coarse bolt, seeing how it comes out, and examine the threads. If it comes out axially without seeming to have been cross threaded, and its threads don't look damaged, I would see how that 7/16" bolt threads back in again after being cleaned up or, better yet, a new 7/16" coarse bolt since the 1st one might have been damaged using it as a tap. If it seems to thread in reasonably, without a lot of back torque, it could be reasonable to torque that bolt to the correct SM spec and call it done. That should be at least as strong as a M10x1.25 HeliCoil, as long as the nutsert is still on axis and not crooked. Likely a time where a "feel" by an experienced mechanic would be valuable. If the 7/16" bolt comes out wrecked and cross-threaded, I don't see another option besides replacing the nutsert and using a new M10 bolt-washer, the safest solution.

Is a lock washer, as the OP used, recommended? Is there one on the OEM bolt-washer? Hard to tell from the pics.

Careful documentation is needed going forward that the seat bolts are no longer uniform, and that 1 bolt and nutsert are now Imperial 7/16" coarse thread and should stay that way unless the bolt AND nutsert are replaced, so that someone doesn't just "correct" to the OEM bolt in future. (Thankfully, the bolt color is different, which should give someone a hint in future.) I've seen this done before intentionally when threads were stripped and helicoils could not be used. The next Metric thread was quite a jump in diameter, without enough surrounding metal, but there was an Imperial thread in the middle that could be tapped in (with a tap, not a larger bolt).

I do agree with the others that the car is probably fine to be driven, sans passenger, until this is fixed.
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