Head Bolts

I need to replace some head bolts in a AC G tractor . Are head bolts special or would grade 5 or grade 8 be ok?

Grade 5 would probably strip before tight and grade 8 might stretch a fair amount. I suspect your looking for grade 10.
Others far more intelligent should chime in shortly.

You should find salvage yard bolts at best , maybe a gasser is not that critical.. but , Grade 8 Will not hold a Case 188 Diesel ,,. Guess how I know

(quoted from post at 21:55:55 12/20/19) Grade 5 would probably strip before tight and grade 8 might stretch a fair amount. I suspect your looking for grade 10.
Others far more intelligent should chime in shortly.

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Oh, for gosh sakes, let's not get too carried away here, this is a little low-compression flathead gasoline engine putting out less than 3 HP per cylinder, and there's 17 head bolts to keep all that power under control!

To the O. P., grade 5 will be more than adequate, take a close look at the length of the threads to be sure it matches the originals.

That being said, head bolts can have some special characteristics, such as a reduced diameter between the head and the threads to give a specified amount of stretch/clamping force, and using the correct replacement bolts is never a bad idea, but for this little low compression, low HP engine I can't imagine having any problems using common bolts so long as the length and length of threads is the same as the originals, just my humble opinion.

that statement makes no sense at all. bob is on it.

There are various companies that list nuts, bolts , studs and washers of every type and then some . Fastenall is one that comes to mind

Do you have a service manual that lists the torques And clearances ?

Bruce, i am real curious what diameter bolts does that 188 have??

Just for kicks Call the local Agco dealer

Here ya go

Allis chalmers g head bolts

why not it is not a racing engine just a simple little engine low compression ect. Just clean the threads in the block an use some oil.

Get the right bolts redoing an engine and using the wrong bolts is being Penny Wise and Pound (Dollar) Foolish.

Just for general information, and not for an AC G, when I was getting work done on my F-350 6.0. The shop owner showed me the difference between ARPS and OEM bolts. It was impressive. I rebuilt a 50 year old high performance engine last year, coming out with significantly higher than stock compression. I converted from bolts to studs, and went with ARPs in order to hold the higher compression. I am not suggesting this for the AC G.

I'm pretty sure the factory bolt are nothing special. MH pony is almost the same engine. I rebuilt mine a number of years ago.

Now I would recommend some sort of sealer on the threads, some of the holes are wet.

I would run a good tap into the hole and maybe get another thread or two if possible. Then if using any bolts that are not AC I would use a complete set so they all stretch or not the same and maybe cut them longer if thread depth allows.

Well many years ago i put together many higher then stock compression engines and we used FACTORY HEAD bolts and ya how what they all stayed together . My 390 i hand built from new and when i say new was a NEW BLOCK bare new heads bare and new main bolts head bolts , as a matter of fact all bolts were factory new . And the pistons with the heads used came up with 13.5 to 1 compression ratio on steel shim head gskt. This engine ran seven days a week and three days a week if i was not working was getting the bag run off it on the drag strip for two and half years . The last big power engine i put together for myself was a 385 block Ford that i never did the math on compression ratio but i can tell you this i could not personally hold a compression gauge into the spark plug hole So i had a buddy who was way stronger then i TRY and hold it and on the first compression stroke it shoved him off the step stool and pegged the gauge a 300 PSI and ya know what we used stock 460 Ford head bolts on that one and ran that engine for five years and no problems holding the head on . Sure you can spend big money and get your ARP studs and feel all warm and fuzzy inside . The old engines did use studs on some makes and the ones that did you learned to hate when you had to pull the head and start the clean up fighting your way around each stud . More labor involved when ya have to do machine work on the block , the fun of getting all the studs out of the block , the extra room required for pulling a head over top the studs . And on and old A/C G engine ya could darn near get away with grade two all thread , But a good quality grade 8 would be fine . And un plated Just a plain old Black finish bolt , Now if they used a heavy flat you may run into a problem finding one close to what they came with . Even if your pushing one horse power to one cubic inch myself i would not worry about it . Only engine i had some what a problem with was my Small cam 855 Cummins and on that one i could count on a head gskt failure and stretched head bolt around 50-60000 miles as i may have had the wick turned up a wee bit to much along with the 68 PSI boost the VT 1710 injection pump build . And the fact that we hauled vary heavy . Back then the object of the game was to run fast haul heavy and look light , so you had to be able to plum smoke a freight box on the hill while having more NET in the wagon then they had Gross.

(quoted from post at 09:58:23 12/21/19) I would run a good tap into the hole and maybe get another thread or two if possible. Then if using any bolts that are not AC I would use a complete set so they all stretch or not the same and maybe cut them longer if thread depth allows.

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"if using any bolts that are not AC"

The engine is NOT an AC, it's a little N62 Continental, so it's certainly possible some of the antique Continental engine parts suppliers might have them.

Hey tractor vet, thanks for being concerned for me spending so much money on the ARPS stud kit, but I had to save up for just two weeks because it was only $25.00 extra.

I just semi-restored a Kohler 4 cylinder 12 HP 60 CID flathead generator engine, circa 1965. It had 4 striped head bolts, grade 6. I had never seen 4 striped bolts before. I posted pictures on this forum and someone was kind enough to send me an image from a page in an old bolt catalog that showed the 4 striped bolts.

Head bolts need to have just a little bit of stretch. I would worry that grade 8 would be too hard and stiff. Plus my experience has been that the harder the bolt the more likely it is to snap from fatigue.

I would be afraid to buy a head bolt kit unless it came from the OEM. With so many parts coming from "The Land of Almost Correct" you never can tell what you might get.

Make sure the head is flat. My head was warped real bad. It had to be machined. Also, use oil when torquing those head bolts.

Some oil is good just so long as your torque spec is for oiled and not dry :wink:.

I would agree that that a square flat
Block and head , clean dry threads and relieving the top thread of each threaded bore and proper torquing .
Without those no fastener can properly apply clamping forces .

Don't see the big deal here. We replaced the studs or bolts been over 30 years ago on an old dodge flathead. The old bolts/studs were not looking so good so I just put in some regular grade 5 bolts were a bit longer so added an extra lock washer to them. Like I say been over 30 years ago never had a problem with it.