I haven't had much luck with this. Last time I did an engine swap, i busted *two* bellhousing bolts. This time, I've got an m12x1.5 rethread chaser (not a tap, i understand the dangers there!) to clean the threads out from the block before I try to torque them.

All the same, I'd like to get some brand-new steel on there. One of the ones that broke last time broke in the block, not sticking out either end, and it's nearly impossible to recover. The other one fortunately came out with vise grips.

Anyway, I have hunted down thread measurements and I know what size bolts I'm looking for. The larger bolts are m12x1.5x60 and x75, with 20 and 40mm shanks.

If I figured this correctly, that means they have 35-40mm of threading. A typical partial-threaded bolt from fastenal or similar has 26mm of threading. That's a big enough difference that I don't want to order and find out it's a no-go. Also, the best I can do with fastenal and similar is a cap screw and a washer - they don't make m12x1.5 flange bolts.

Anyone have any ideas on this? Dealer doesn't sell them, said "it's a standard bolt" - not so in my experience. Maybe I'm paranoid, but I really don't want to use the remainder of my bolts or get junkyard bolts after having them snap so easily. (Yes, I used a torque wrench and did so correctly...) Any input appreciated, especially helpful input. Thanks.

Also, any idea if buying fully threaded bolts would hurt anything here? I could easily do that and a washer if it's kosher, it would fix the threading problem entirely.

 

Contact partsgroup.com

 

Thanks, but I'm trying to source new bolts.

 

Just in case anybody else has this problem:

This youtube video has the thread specs: youtube.com/watch?v=nDDPAMwAiqw You need m12x1.5x60 and x75mm bolts, but the threading needs to be longer than a standard partial thread (35-40mm instead of 26mm)

Rosenthal Mazda has them, just not online. If you call them up, they can find a part # that supercedes the old one, and with a little digging, they'll get them to you for $3.60/bolt.

 

Guys, use the Mazda parts diagrams, found in many places, including .pdf files from Mazda Motorsports Development. This diagram is not from them, but diagrams like these will allow you to order anything for the car, just type any one of those part numbers for bolts into a Mazda parts website, and they pop right up, for cheap too.

Just FYI so you don't have to rely off of calling someone, although it does show Rosenthal's customer service.

 

That is good to know, I should have thought of that. Still ended up being the same price, fortunately.

 

I'm reviving this old thread
Hello Dustin, where did you find those diagrams / pdf files ?
I cant find any.

In fact I'm trying to figure out where on the bellhousing the clutch line bracket and Starter harness bracket are bolted.

On my 2001 miata

 

From https://did-it-myself.com/removing-a-miata-engine/

On my 97 it was 99796-1260 (need 6 of them), 99796-1275 (need 2). You can also buy their nut if you’d like for the one through-bolt (99940-1201)

I believe its the same for nb1/2

 

You can kind of decode most of the part numbers into actual bolt dimensions if you're looking for "standard" bolts.

Miata.net's garage section has a bunch of parts diagrams available for download, as well. Miata.net/garage





In this picture from a 2000 engine parts diagram, you can see the bolt numbers are 99796-1275 (x2), and 99796-1260 (x6). These are what I call "standard" Mazda part numbers.

We're looking at 2 x M12x1.25mm x 75mm long bolts, and 6 x M12x1.25mm x 60mm long bolts. The first two numbers denote the thread size, the second two the length in mm.

You can then go grab parts from the hardware store, or, take that information over to my favorite site in the world, McMaster.com, specifically the JIS Flange Bolt section, and you're looking for bolts that they don't unfortunately carry in this exact spot, but they do in other head styles; they just won't be the special 17mm head flanged JIS bolts on the Miata.



Here's the oil pan/rear main seal/dust plate parts and you can really see what I'm talking about. Got a couple of M6x1.0 x 20mm long oil pan bolts, some M6x1.0mm x 20 long and M6x1.0mm x 16 long for the rear main seal retainer, and so on. McMaster p/n 95735A221 and 95735A216, respectively.

 

Great thanks! :-)