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For about the 10th. and final time could someone please give me the size and all the particulars of the head bolts I need for the 66 model L? Ive got the jug on now. And I'll soon be ready to put this smooth head on.

I dont know what to do about the sideways pics, they are not taken like that, they dont appear on my computer like that but it somehow just happens when I post them.
 

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For about the 10th. and final time could someone please give me the size and all the particulars of the head bolts I need for the 66 model L? Ive got the jug on now. And I'll soon be ready to put this smooth head on.

I dont know what to do about the sideways pics, they are not taken like that, they dont appear on my computer like that but it somehow just happens when I post them.
Pretty sure they are 5/16-24nf. I don't remember what length either but most of the holes are through. You could take a pencil and stick it through the hole until it bottoms, mark it and measure for length. Make sure you use grade 8 bolts, and never seize.
 

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Discussion Starter #3
Good idea about the pencil, thats how all this happened because my bolts were to long and they went down and cracked the fins atop the head. So I removed the .0030 over 6.6 jug from mine and am using the jug from a 7.6 LI parts tractor I bought.....thank God
 

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The bolts are NC, not NF.

The lengths have gone by multiple times; I don't have them off the top of my head, but if you dig through back threads, you'll see them.

A thing to remember: None of the castings on gravelys are super accurate. 1/16 or even 1/8 difference in the head bolt length may or may not be absorbed by variations in the castings.

Partly due to that, partly on general principles, test fit bolts before torquing! That's good practice on any machine, but especially important in this case, because of the casting variations. If you have bolts which are a bit too long (ie, they're bottoming out against the fins) you can put a washer or two under the head.

Just don't assume they'll all fit perfectly. Test fit, and pay attention while torquing. It'll turn out fine :)
 

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From an earlier thread on this topic:

The bolts are 5/16 NC. When I remove them, I usually find the 10 short ones are 1-3/16, and the 2 long ones are 1-11/16.
 

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Daryl G
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Mark,
Take a look here: https://www.gravelymanuals.com/pdf/Conv_76_IPL_19720315.pdf

page 1/2 describes the shorter bolts which are 5/16-18 X 1 3/8" (see part number 57) - 10 are needed
page 3/4 describes the two longer bolts which are 5/16-18 X 2" (see part number 12) - 2 are needed

Tractor Supply carries the 2" long bolts but not the shorter 1-3/8" long bolts. I went to Fastenal and ordered the shorter ones. I am really glad that you are back on this project!!!!
 

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Daryl, I see the parts list, and it does say 2". My caution is that all the ones I've ever taken apart (or put together) have the two end bolts 1-11/16 or 1-3/4. That's 1/2" longer than the rest. That 1/2" is exactly the length of the spacer, part number 13 on page 4.

[Later]

Ok, I think I found the discrepancy.

I measured the height of the threaded holes in a 7.6 jug and a 6.6 jug. The newer jug is a different casting, with what would have been the top two fins cast into one, and the threaded hole extending through both of them. On the 6.6 jug, the threads only go through the top fin. IOW, the holes on the new jug are deeper, thus they want longer bolts. (The key here is the jug, not the model year of the tractor)

So the bolts spec'ed in that IPL should be fine.

I'll repeat my earlier caution: Regardless of what measuring and figuring you do, test fit before torquing. It can save a world of frustration :)
 

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Discussion Starter #8
Thanks everyone, and I do need to not just assume they are right because in a 50+ yr old machine I should have been more carefull for sure, and thats what happens when I get in a rush to. Heck the first cpl turns/rotations I felt something was afoul and it just didnt feel right.
Im goin over to TSC tomorrow because they have the fasteners alright and I can toss what I need and how many I want/need in a bag and they weigh the bag and thats that.
Theres a Fastenall a mile away to but if you just want bits and pieces a body needs to go elsewhere. I know because I worked at two wholesalers for 16 yrs. and they dont like to be bothered with someone wanting 3 of these and 4 or 5 of these and so on.
Oh and P.S. what is with the NC & NF ? Whaaaat?

Heck I cant find the 4 nuts for the jug bolting on, but there's a pretty fine thread on those studs coming out of there
 

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Discussion Starter #9
Daryl, I see the parts list, and it does say 2". My caution is that all the ones I've ever taken apart (or put together) have the two end bolts 1-11/16 or 1-3/4. That's 1/2" longer than the rest. That 1/2" is exactly the length of the spacer, part number 13 on page 4.

[Later]

Ok, I think I found the discrepancy.

I measured the height of the threaded holes in a 7.6 jug and a 6.6 jug. The newer jug is a different casting, with what would have been the top two fins cast into one, and the threaded hole extending through both of them. On the 6.6 jug, the threads only go through the top fin. IOW, the holes on the new jug are deeper, thus they want longer bolts. (The key here is the jug, not the model year of the tractor)

So the bolts spec'ed in that IPL should be fine.

I'll repeat my earlier caution: Regardless of what measuring and figuring you do, test fit before torquing. It can save a world of frustration :)
Not to horn-in but Im paying attention to it to and am gonna be extra carefull doing this, Im out of jugs lol!
 

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NC and NF are National Coarse and National Fine. Standard US thread gauges.

Your 4 jug hold-down nuts are 3/8 NF. One of the few fine-thread fasteners on the machine.
 

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Discussion Starter #11
NC and NF are National Coarse and National Fine. Standard US thread gauges.

Your 4 jug hold-down nuts are 3/8 NF. One of the few fine-thread fasteners on the machine.
Thanks, I knew they were finer than the threads on the other bolts or studs on it. Incidentally I did find the bolts a little while ago but Im gonna try to get some new ones tomorrow while Im at TSC and if they dont have them I can reuse the old ones but they need about a .25 cal. brush on the end of a small driver I got ran thru the inside of em.
I have a new tap & die set but Ive never used one before and it seems like they could easily be messed up but w/all those options Im certain I'll get something thats right.
I also found 4 split-washers with the hold down nuts is that correct or did they come from somewhere else. They were with the nuts.
 

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Discussion Starter #12 (Edited)
What a waste of time, I went over there to TSC and couldnt find squat, they didnt even have any Grade 8 stuff unless it was the cadmium yellow or whatever and everything else was Grade 5 w/3 marks on head of bolt.
Not to mention I had to sneak out of here as to not let my crazy dog know I was leaving and forgot to write down what size head bolts were close to. Im just gonna go to JG's and see what I can get because I need all kinds of nuts and bolts.
Oh crap I meant GT's..Galen & Todd I recon..


Wow cant believe I can still edit this. But looks like I'll be searching for bolts and nuts I removed awhile back and trying to reuse them cause I aint having any luck finding any anywhere.
But they got to be round here somewhere.
 

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Cad-plated bolts are fine.

For this application, grade 5 are ok too. You're only torquing to 20 ft/lb. Even SS will take that :)
 

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Discussion Starter #15
OK Thanks both of you, I have a bunch of cad bolts I bought last year somewhere but I was afraid of causing some of that electrolisis (sp?) or "galvanic action" where two dissimilar metals meet meaning the cad bolts and the CI heads and jug.
Thanks again I can run w/that info.
I guess it wouldnt happen unless I used cad bolts and another type of nut or something like that.
 

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I guess it wouldnt happen unless I used cad bolts and another type of nut or something like that.
Nah. Cad plating has been around for years as an effective anti-corrosion treatment.

The place where you get dissimilar-metals corrosion is between metals with significantly different electrochemical characteristics, in the presence of an electrolyte. Bolting untreated steel to untreated aluminum and dipping it in salt water is ideal, which is one reason why aircraft that go in the ocean are often junk when you pull them out. But you can demonstrate the effect by wrapping copper wire around a nail and dropping it in a bucket of water for a while.

Your cad-plated steel bolts going into an iron casting are fine. They'll outlast all of us.

I say stop worrying, find your bolts, test fit them, torque to 20 ft/lb, button that baby up, and post a video of her running!
 

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Discussion Starter #17
Nah.

Your cad-plated steel bolts going into an iron casting are fine. They'll outlast all of us.

I say stop worrying, find your bolts, test fit them, torque to 20 ft/lb, button that baby up, and post a video of her running!
Sounds good, I think they had some of those that would work.
Had I knew I would have got them, instead I walked out w/a Bush craft book that costed $32 ! And a pr. of nut splitters.
If any of you read "Backwoodsman Magazine" I have letters and gun pics in there now n then, In the last issue ( not the one that just came out 2 days ago) but July/August 2019 on pg. 10 these's a few of my .22 mags in there.
Oh well thanks again for the wanted and needed info as usual.
Mark
 

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Old Tractor Enthusiest
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JRD - read through this thread and the advice. Bolt length sounds about right. In light of the various quirks between different versions of jug castings etc, unless you know for sure the entire history of your Gravely, it's better to err on the side of caution. That being, test fit each and every bolt in each location before snugging them down. If you use bolts that are too long, the bottom of the bolt will bottom out on a cooling fit and the torque setting on the bolt is more than enough to snap off the fin from the main casting.

On the bolts - grade 8 is definitely the way to go. The reason being they will retain their strength at elevated temps where some "normal" bolts may soften up over time due to the heating/cooling cycles over time - especially on the exhaust port side. The cyclic heating/cooling is what also contributes to loosing of head bolts with time.

Lastly, didn't see any mention of the proper procedure to tighten the head bolts. After confirming the length is correct at each spot, snug them down with a socket starting from the middle and working out in a star pattern (alternating left to right), but only snug - not tight. After they are all snugged down, then and only then torque them down - again starting with the middle of the head and working out in a star pattern.

After everything is all set up and running again, check the torque after a few hours of operation and/or a couple of heating/cooling cycles. Always check the torque when cool. Good luck.
 

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Discussion Starter #19
Mark,
Take a look here: https://www.gravelymanuals.com/pdf/Conv_76_IPL_19720315.pdf

page 1/2 describes the shorter bolts which are 5/16-18 X 1 3/8" (see part number 57) - 10 are needed
page 3/4 describes the two longer bolts which are 5/16-18 X 2" (see part number 12) - 2 are needed

Tractor Supply carries the 2" long bolts but not the shorter 1-3/8" long bolts. I went to Fastenal and ordered the shorter ones. I am really glad that you are back on this project!!!!
I dont know what to do now exept mow my grass so I can cool down ( mentally speaking) but Im sick of the head/heads on this thing.
Now after buying a dozen bolts literally 7 or 8 times I think Ive got some I can use and now they go thru the head and hit threads on jug/casting and STOP! And Im not about to force them in, it feels like its a totally different thread. My bolts are x 18 ( threads pr. inch I presume that means).
If I walk away from this thing again I dont know what I'll do, just buy my son a decent mower I guess because I said I'd find him one but why I picked a 50 yr. old one Im beginning to wonder.
What the h311 could be wrong now?
 

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With the head and gasket out of the way, try spinning a bolt into each of the holes in the jug. They should go in with not too much effort, finger tight or maybe a little more, but not much.

If one takes much more effort than that, stop, take it out, and make sure the threads on both the bolt and the jug are clean, then try again.
 
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