Motor mount to frame bolt size?

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81GrandPrix383

Greasemonkey
Dec 14, 2010
243
2
0
Ontario, Canada
I bought new motor mounts to replace the ones that are welded on my car but they don't come with bolts. Does anyone know the size or specs of these bolts?

The welded ones are way to tall which explains why the previous owner cut a hole in his hood.

Thanks.
 
I guess the dealer should be able to answer this question. Hopefully they can get the bolts too.
 
I can't remember off the top of my head, but I'd guess they're 7/16" dia by 1.5" long. Why not just go to a hardware store with the mount, see what fits the holes, estimate the needed length and buy them in grade 8? I'd get hex flange nuts too if they have them. It will save you a ton of cussing. Can't beat the hardware store for fasteners & cost of them.
 
G-Body_Vet said:
I can't remember off the top of my head, but I'd guess they're 7/16" dia by 1.5" long. Why not just go to a hardware store with the mount, see what fits the holes, estimate the needed length and buy them in grade 8? I'd get hex flange nuts too if they have them. It will save you a ton of cussing. Can't beat the hardware store for fasteners & cost of them.

This is exactly why I didn't want to call the dealer.
I have to cut or grind off the existing mounts. Its a little tough to estimate the length right now as the motor is in the car and the mounts are welded to the frame. I suppose I could get the diameter from the holes on the new mounts but thought the holes in the frame could be a different size.
I just don't want to stop and run for parts once I start this. I want to have everything ready so that I lift the motor, cut out the mounts, bolt in the new mounts, lower the motor, bolt it in place and my fan lines up in the shroud and my hood closes.

Very good tip about the flange nuts. I have heard it before and already planned to get them.
Thanks.
 
Along with the flange head bolts I'd also get the locking flange nuts to go with them. They're the type of nut that has an oblong looking hole that lock onto the bolt.

The length shouldn't be very long. I believe I used 7/16" thread and somwhere around 1"-1.5" long bolts.
 
I'm fairly certain I only used 3/8's threaded bolts on mine.
 
I called the dealership and instead of asking for my 81 I said 87 because I knew the 87 I am parting out came with a 305. in case anyone else is curious, they said the bolt size is M10 x 1.5 x 25.
I stopped at Part Source after work and picked up some M10 x 30 flange bolts and flange nuts to fit.

They are grade 10.9 so I'm sure i will be good.
Thanks for the help.
 
I stay away from metric bolts and nuts for something like this....metric stuff is way over priced
 
pontiacgp said:
I stay away from metric bolts and nuts for something like this....metric stuff is way over priced

Ha ha, everything at Part Source is overpriced.
Too late, they were the only place open at the time and I already bought them.

Fastenall is a great place for nuts and bolts but they close at 5:00. Hard to get there if I work until 5:00.

I'm hoping that I can cut out the old mounts and install the new ones on Thursday.
 
you missed my point...anywhere you go they overcharge on metric bolts so for something like engine mounts a 3/8 flange bolt and nut is what I use
 
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