Defective head bolt

Thu Apr 11, 2013 11:55 am

I went out and bought some Grade 5 bolts to replace my head bolts. I torqued them all to 20 flb and started over to take them to 40. The center bolt tightened to 40 and I moved on to the second bolt in the sequence and it snapped off. So either the bolt was defective or I should be using grade 8s. The bolt in question was a Hillman Grade 5. I already drilled and extracted the broken bolt. Should I get a set of Grade 8 or do they not have enough stretch?

Re: Defective head bolt

Thu Apr 11, 2013 12:57 pm

Those are 3/8 bolts, and according to the chart in the front of the service manual torque on a grade 5 bolt is maximum of 37 ft lbs.

Re: Defective head bolt

Thu Apr 11, 2013 2:27 pm

HMMM.. So the replacement bolts on Farmall forever are grade 8 SAE J429, but if you look those up on a torque chart max torque dry install is 44 ft lb. The head specs say 45 ft lbs, so even with factory bolts we are at max torque?

Re: Defective head bolt

Thu Apr 11, 2013 4:21 pm

that is the way I read it. don't forget to use some thread sealing compound on the threads to prevent water leaks, which also acts as a lubricant so you need to use less than 45 lbs for torque, max 40 or a little less.

Re: Defective head bolt

Mon Apr 15, 2013 8:08 pm

I went to my local Case IH dealer today and spoke with their Mechanic about replacement head bolts. His advice is to reuse the old bolts. He said any head work they do on older tractors they either reuse the existing head bolts or find used replacements. He said none of the newer manufactured stuff today is up to par with the original bolts.

Re: Defective head bolt

Tue Apr 16, 2013 9:44 am

I used to reuse the old bolts, that is what my IH mechanic told me to do a number of years ago. Clean em up, put never seize on them and re-install. I will no longer do that. 60 + year old bolts have done their job and time to retire them. I can get exact length replacements from my local fastener supply house that I have dealt with for almost 30 years. Grade 8 bolts. Reusing old bolts does have a few risks .... in my book not worth taking. I redid the head on my '48 3 times. The last time I put in the new head bolts.

Re: Defective head bolt

Tue Apr 16, 2013 10:15 am

Aren't the head bolts supposed to be grade 9?

Re: Defective head bolt

Tue Apr 16, 2013 10:13 pm

You have 2 options with new bolts....either use Grade 8 and drop the torque back to 40 ft-lb, which works just fine, or go with Grade 9 and keep the torque at 45 per the book. Reusing head bolts on a 50 year old engine is more risky in my book than using modern bolts. I went with plated Grade 8 with washers on my last build and so far it's doing just fine. I also did NOT retorque after running the engine.

Re: Defective head bolt

Wed Apr 17, 2013 3:50 am

I have a tractor that came with a professionally rebuilt engine. It was weeping coolant. I replaced that head gasket and re-torqued- no problems. 15 years ago I rebuilt my 52 and same procedure and no leaks. I run it with a pony tank so it only takes a few minutes.

Make sure your aftermarket bolts are trimmed or use grade 8 washers. Too long and the threads extend into the coolant and they will be a bear to get out someday. I like Rectorseal PTFE paste for sealing the threads to prevent coolant weep up the threads. Others use Indian Head shellac with good results- choose your poison, but choose one for sure! I agree with using grade 9 at 45 and grade 8 at 40 ft-lbs. Original bolts were clearly better than grade 8.

Re: Defective head bolt

Wed Jun 19, 2013 5:47 pm

I bought my grade 9 bolts from McMaster Carr for my 1950 engine work. Grade 9 are significantly stronger than grade 8 and because of the higher tensile strength, the heads of the bolts are thicker. I need to trim all the bolt just a little so I was making sure there were enough threads on the bolt. When I had them side-by-side, I noticed the IH bolts had the same head thickness as the new grade 9's. For comparison, I put a grade 8 in the picture. I am ONLY using grade 9 bolts as replacements for IH head bolts. The IH torque spec exceeds that of grade 8 and the extra thickness of the head of the bolt clinched it for me.
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Re: Defective head bolt

Wed Jun 19, 2013 6:09 pm

I have never had any problems re using the original head bolts providing they were not pitted or rusted. It is very important to clean the threads on the bolts plus in the block. On all the cub engines I rebuild I torque head bolts to 45 then after a couple hrs running I re torque them to 45. With heat the head gasket seems to shrink. I do know the new bolts are not like the originals. Failure is high with the new bolts. Even grade 8. It also depends on where the bolts were made. USA made is pretty good but anyting from china or japan is junk. Tractor supply has a selection of bolts but most are china junk.

Re: Defective head bolt

Wed Jun 19, 2013 8:40 pm

That's a great comparison Bob. My concern has never been the bolt strength. I lube the bolts with some type of sealant which reduces the torque required to achieve the same tension. My concern has always been the threads stripping out due to the limited engagement area and the soft cast iron threads. I've Heli-Coiled every bolt hole that secures the head after stripping out the threads on one hole torquing the head.

Re: Defective head bolt

Thu Jun 20, 2013 9:04 am

If I had read this post 2 weeks ago I would have went with grade 9 bolts,used grade 8 from fastenal,Torqued to 45 and used sealant on threads on this restored 48 Cub,Head gasket was seaping antifreeze down side of engine causing paint to lift.

Re: Defective head bolt

Thu Jun 20, 2013 9:34 am

If you did not feel the bolts yield when torquing, you should be OK. I had a weeper just like you described and found at least one bolt was weeping coolant right up the threads. I made sure to re-torque after running it up to full temperature and cooling it down and the bolts did take up a little more. High and dry since.

Re: Defective head bolt

Thu Jun 20, 2013 11:43 am

Being a engine builder for drag racing back in the early days I delt with high compression highly tuned engine idling between 1,200 to 1,800 rpm. Can cause problems with over heating if we don't assemble it correctly.

Here's my assembly process on every engine;

1. Wire wheel every head bolt squeaky clean.
2. Apply the high tac red spray sealer to both sides of the head gasket.
3. I cut the head .010" to make sure it's flat. I also check the deck of the block for flatness too with a starret straight edge.
4. I apply permatex #2 to each head bolt thread so the threads are sealed and the coolant can't weep up past the threads. Of you look closely when disassembling the head bolts the factory during assembly did this too by the old sealer caked on the head bolts.
5. I then follow the torque specs specs and I add 10lbs. Of torque to the specs. Then I run the engine then retorque in a few days after some operation.

I learned this though experience. Bill