The Ford Barn

40cpe · 01-13-2016, 10:20 AM

When I tore my Mercury engine down the clutch was held on the flywheel with 3/8 bolts without a shoulder. They did have the recess in the head like the pan bolts do, so I'm wondering if they are correct/sufficient. Threads found by search indicate ford stopped using the shoulder bolts around '50. Test fit of the bolt in the pressure plate hole does have a small bit of wiggle. The flywheel has an area for a shoulder before the threads start. Also, O'reilly's has a set with the shoulder and if I do need the shoulder bolts are O'reilly's the correct bolt or is the Ford bolt something special? The engine, flywheel, and clutch is balanced so I don't want to screw it up at this stage. Thanks for any help.

rotorwrench · 01-13-2016, 11:19 AM

The Mercury cars with the Borg & Beck clutch cover do use a special bolt to hold the cover to the flywheel from 49 thru 51 but I'm not sure about the later Mercury cars. The 3/8" shank is a 32th over 3/4" long and the shank is only threaded part way. The non threaded portion is about a 32th over 5/16" from the head to the threads and they are thick head bolt as many FoMoCo bolts are. The head size is 9/16". They use a split type lock washer to hold them on and it is about 3/32" thick. I think of a shoulder bolt as one that has a larger OD on the non-threaded portion than it does on the threaded portion and I don't recall seeing them used on the mid-century Mercury cars. There may have been substitutions made somewhere over the years since I have not seen the ones with the recess in the head like oil pan bolts have.

I'm sure you can use ARP 3/8" bolts for this purpose or maybe even some short grade 8 bolts but you would have to modify some to make them similar to the OEM bolts.

51 MERC-CT · 01-13-2016, 11:59 AM

Last time I needed a couple I just duplicated what was original by cutting down some Grade 8's that were 1-1/2" long to 3/4" long,

JSeery · 01-13-2016, 12:07 PM

Balance shouldn't be an issue as long as all the bolts are the same. If you are going to make bolts, you could weight them to be sure they all match weight.

40cpe · 01-13-2016, 05:21 PM

I got bolts with the unthreaded portion under the head. I learned at the Fastenal store that a shoulder bolt is a different animal.

The parts store bolts were an inch long and I would have to cut them anyway, so I took '51 Merc's suggestion and cut some grade 8 bolts to length.

JSeery, my concern is getting the pressure plate centered as there is a little "slop" in the holes with a threaded bolt.

Thanks for all the suggestions.

JSeery · 01-13-2016, 07:05 PM

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Quote:

Originally Posted by 40cpe

I got bolts with the unthreaded portion under the head. I learned at the Fastenal store that a shoulder bolt is a different animal.

The parts store bolts were an inch long and I would have to cut them anyway, so I took '51 Merc's suggestion and cut some grade 8 bolts to length.

JSeery, my concern is getting the pressure plate centered as there is a little "slop" in the holes with a threaded bolt.

Thanks for all the suggestions.

I agree, I was just commenting on the balance aspect. I would use the bolts you are using. If you are cutting them it might be worthwhile to weigh them if you have the proper type of scale.

40cpe · 01-13-2016, 08:00 PM

I don't have a way to measure anything that light. I just used a digital caliper to get close over-all length. My shop is more like a blacksmith shop than a machine shop.

JSeery · 01-13-2016, 08:08 PM

Quote:

Originally Posted by 40cpe

I don't have a way to measure anything that light. I just used a digital caliper to get close over-all length. My shop is more like a blacksmith shop than a machine shop.

LOL, doubt it will be a big deal, I'm just into balancing.

01-13-2016, 10:20 AM	#1
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,120	Mercury clutch bolts When I tore my Mercury engine down the clutch was held on the flywheel with 3/8 bolts without a shoulder. They did have the recess in the head like the pan bolts do, so I'm wondering if they are correct/sufficient. Threads found by search indicate ford stopped using the shoulder bolts around '50. Test fit of the bolt in the pressure plate hole does have a small bit of wiggle. The flywheel has an area for a shoulder before the threads start. Also, O'reilly's has a set with the shoulder and if I do need the shoulder bolts are O'reilly's the correct bolt or is the Ford bolt something special? The engine, flywheel, and clutch is balanced so I don't want to screw it up at this stage. Thanks for any help.

01-13-2016, 11:19 AM	#2
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 17,411	Re: Mercury clutch bolts The Mercury cars with the Borg & Beck clutch cover do use a special bolt to hold the cover to the flywheel from 49 thru 51 but I'm not sure about the later Mercury cars. The 3/8" shank is a 32th over 3/4" long and the shank is only threaded part way. The non threaded portion is about a 32th over 5/16" from the head to the threads and they are thick head bolt as many FoMoCo bolts are. The head size is 9/16". They use a split type lock washer to hold them on and it is about 3/32" thick. I think of a shoulder bolt as one that has a larger OD on the non-threaded portion than it does on the threaded portion and I don't recall seeing them used on the mid-century Mercury cars. There may have been substitutions made somewhere over the years since I have not seen the ones with the recess in the head like oil pan bolts have. I'm sure you can use ARP 3/8" bolts for this purpose or maybe even some short grade 8 bolts but you would have to modify some to make them similar to the OEM bolts.

01-13-2016, 12:07 PM	#4
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Mercury clutch bolts Balance shouldn't be an issue as long as all the bolts are the same. If you are going to make bolts, you could weight them to be sure they all match weight.

01-13-2016, 05:21 PM	#5
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,120	Re: Mercury clutch bolts I got bolts with the unthreaded portion under the head. I learned at the Fastenal store that a shoulder bolt is a different animal. The parts store bolts were an inch long and I would have to cut them anyway, so I took '51 Merc's suggestion and cut some grade 8 bolts to length. JSeery, my concern is getting the pressure plate centered as there is a little "slop" in the holes with a threaded bolt. Thanks for all the suggestions.

01-13-2016, 08:00 PM	#7
40cpe Senior Member Join Date: May 2010 Location: Star, MS Posts: 4,120	Re: Mercury clutch bolts I don't have a way to measure anything that light. I just used a digital caliper to get close over-all length. My shop is more like a blacksmith shop than a machine shop.