(ENGINE) Engine mount nuts
 

Anyone happen to know what size nut fits on the motor mount bolt? I tried all the nuts I have and none of them worked.

M10 x 1.25

thanks

The bolts or studs (found on earlier engines) which holds the front mount to the front cover, is 10mm x 1.5 because it is threaded into aluminum. It is a slightly coarser thread pitch than 1.25.

If your engine is older and uses studsin the front cover instead of bolts, the thread pitch is 10mm x 1.25 on the end of the stud that sees daylight, and the other end is 10mm x 1.5 where it threads into the front cover.

The motor mount pads each have a single stud in the center with 10mm x 1.25 thread pitch.

Incidentally, the only 10mm x 1.5 (coarse thread) nuts on the engine are on the exhaust manifold etc. Stainless steel, too.

Jeff20B - just want to say that you are a wealth of knowledge. Thanks for sharing it here,

You're welcome.

Here's some more bolt info for future reference. The three most common sizes you'll find on a Mazda rotary engine are

6mm x 1.00 with a 10mm head

8mm x 1.25 with a 12mm head

10mm x 1.25 with a 14mm head

The tension bolts are 10mm x 1.00 (very fine thread pitch for that diamter). Judge Ito recommends running a tap in the holes to clean them out for a more accurate torque when assembling the engine. I've tried it and it works great.

The thread pitch of the shifter lever in '81-'85 RX-7s is commonly asked about on this forum. It is 12mm x 1.5; same as the two studs at the bottom of the front plate which holds the AC/power steering bracket (spark plug side of engine) and also the same as engine alignment dowel pins. Peejay used these to make the tall boy shifter mod.

Early shifters were 10mm x 1.25.

All bellhousing to engine bolts are 10mm x 1.25 except for the starter. Since it bolts to the aluminum bellhousing, and part of its housing is either pot metal or aluminum, both bolts are 10mm x 1.5 to hold better in the softer metal. I can't tell you how many times I've seen damaged threads in the bellhousing because some idiot mechanic accidentally tried to install one of the short medium pitch bellhousing to engine bolts there. It happens a lot during clutch jobs because they're the same length. If only they'd spent half a second and noticed there was a difference...

Speaking of clutch jobs, pressure plate bolts are 8mm x 1.00, grade 10, usually 14mm head. Torque spec is around 14ft lbs. If you've installed a light steel flywheel, torque its bolts to 28 foot pounds into the counterweight. For the big 54mm nut, I use a 2 1/8" socket and an air wrench. I'm not sure what it torques to, but it works fine.

Archived!

Jon