The Stovebolt Site Forums The Shop Area Engine Shop Breaking head bolts

My first attempt to install the head on my 1957 235 snapped off the number 2 position head bolt while trying to torque it to 95 ft./lbs. Ordered a couple of bolts, one long, one short from Chev’s of the 40s. The received bolts were used, long one had paint on it, short one was just a standard grade 8 bolt. I calibrated the torque wrench which was off a little, cleaned off the adhesive spray on the head gasket and tried again just torquing to 90 ft/lb. Again the number 2 position bolt seemed to just keep turning and not making it to 90 so I adjusted wrench down to 80 getting all the way to number 18 (short bolt, original, not the grade 8) and it snapped off. I did put a small amount of oil on the threads and on the shoulder just under the head. Oil under the head would cause less friction and would stretch the bolt more before getting to the required torque I suppose. Anyone have any ideas? Have all these old bolts been over stressed? Should I just go to the tractor supply and get all new grade 8 bolts?
Thanks,
Paul

Hy FarmerPaul, very sorry to read about your head bolt problems. As far as I remember there were two different strengths of head bolts, what markings are on the heads of your bolts? Does your torque wrench have two different calibrations, one for pounds/feet and one for Newton/meters? If your torque wrench has two calibrations, could you be setting your torque to the wrong calibration?

Paul, I would advise to get all new bolts from a reputable dealer. I have never had problems with Chevy's of the 40's but sometimes they and the rest of our suppliers can be snookered by the middle man. Jim Carter is a wealth of knowledge. To be on the safe side I would get one extra and put a sleeve around it and tighten to 90 lbs. or take it to a machine shop and let them test it. Then toss it away after it checks out. doc

I think I would check with AARP. They specialize in high quality fasteners.
Like what 3B says check your torque wrench. That doesn't sound right. Those are some stout bolts.
George

Breaking two bolts in the same hole is one too many, without finding out what's causing the problem. Maybe there's an obstruction in the bottom of the hole that's allowing the bolt to bottom out, or something similar. I'd suggest installing a Heli-Coil in that thread, and making sure that the hole is deep enough to let the bolt squeeze the head gasket properly. The best fix would be to install ARP studs in all the holes,instead of using 70 year old bolts. That's what we did on 1,000+ HP tractor pull engines.
Jerry

All: Thanks for the suggestions. I found the problem, cheap crap torque wrench. Lesson learned, you get what you pay for. I borrowed a torque wrench and tested it on a large bolt on a log splitter and it pulled (clicked) at a lot less effort at the 95 lb. setting. So the third time was the charm and I got all the head bolts easily torqued to 95 ft./lbs.
Thanks all,
Paul

I hope you replaced ALL the bolts. Any one that has been subjected to that inaccurate torque wrench is damaged beyond repair, even if it did not break initially. If you reused any of them, you have created a disaster just waiting to happen with no warning whatsoever.
Jerry

Did Autocorrect get you guys? AARP = American Association of Retired People. Knowing their politics, I'm sure Jerry isn't a member.
I'm sure you meant ARP, which sells high strength head bolts and stud kits.

Good reminder to get your torque wrenches actually calibrated every now and then. Not just checking against how another one feels, but actually putting a known torque load on them.

ARP has a kit P/N 155-4002. Kit for a F--d 427 SOHC 427. You end up with 4 extra short studs, washers & nuts but cheaper than purchasing open stock parts.

Thanks Kevin- - - -that bunch definitely doesn't float my boat, mainly over their 2nd. Amendment policies. All fixed now! I pay a calibration lab a small fee to check my Snap-On torque wrench once a year, as the investigation reports I send concerning wheel loss accidents have the possibility of ending up in court. Anybody who bets his engine job on an unknown torque wrench would probably draw to an inside straight- - - -let's play some high-stakes poker!
Jerry

Sorry about the AARP mistake. I meant ARP.
George

I'm taking Jerry's advice to replace all the bolts, so 'OFF WITH THE HEAD' for the fourth time. Thanks to BC59 for the ARP part number though Summit says not available until January I will search other sites.
Paul

We have several torque wrenches with some being clickers and some beepers. For all of them we have an old beam type wrench we chuck in a vise and put two welded together sockets ( 1/2, 3/8 ) to calibrate the fancy ones. Unless the beam type has been in a fire or the pointer doesn't return to zero it's accurate. The clickers and beepers are handy where the pointer can't be easily seen.

If the bolt bottomed out, the torque wrench would still stop in the same place, not break the bolt.

A good practice is to back off clicker type torque wrenches to zero after use to avoid having the wrench go out of calibration.
Just saying but it is not advisable to oil bolt threads prior to torquing unless the spec value specifies "wet torque".
For this size bolt oil would add another 3000-4000 pounds tensile load to the bolt, possibly exceeding the yield strength...causing clamping failure, particularly for bolts of unknown origin.
On the flip side..make sure internal and external threads are clean..and dry.

In that case, why does every factory service manual I've read over the past 60-something years state "Lubricate threads with 30 weight motor oil before torquing"? Maybe you should share your wisdom with General Motors, Ford, Chrysler, and a few other manufacturers.
Jerry

Jerry
I agree..if it states to use oil then you must use oil, to achieve the preload required, which I referred to as "wet torque" in my post.
I apologize. I did not research any manuals to establish if these bolts were to be wet or dry.
It all depends on the application and fastener coating, if any, to fall in to where you want to be for the clamping load.
I was only trying to close in on what could cause this bolt to fail.

No harm- - -no foul. Lots of people with little or no experience in the automotive trade read these comments and take them as gospel, since "It's on the internet- - - -it must be right!" I've developed my own procedures after building all sorts of engines over the past 60-sometning years. On the ones that develop three or four times the power the manufacturer intended, I use some unconventional techniques such as using studs instead of bolts on cylinder heads, but I also research the proper torque procedures reccomended by the fastener manufacturer, not necessarily what the factory service manual reccomends. For instance, connecting rod bolts on Carrillo rods have a "stretch" specification rather than a torque spec. Some of then require around 90 ft/lbs or so to get the right preload to keep the bolts tight. I'll be using a set of recycled NASCAR rods in one of the 235's I'm building.
Jerry

Got mine direct from ARP several years ago.

Jerry
I have garnered a tremendous amount of wisdom and knowledge from you posts over the years.
Thank You!
I come from years at Grove Crane (engines transmissions and noise control group) then 36 years in the Railroad Braking Industry.
It's important that a 400 pound brake disc rolls down the track with the train and NOT along side of the train.. hence the need for a robust 12 bolt torque design to handle many different external forces.
Threaded fasteners peak my interest! I can't help it.
Sorry to digress.
This is sounding too much like a job interview.
Signing off


Mike

I was wondering if someone was going to point out the AARP goof-up...lol...

When I was a maintenance man for E&J Gallo winery in Livingston California back in the late 1970's one of my duties was operating a 49 foot Grove rubber-tired crane with a 20K pound capacity. Quite a machine! Pretty often, I'd be working out of sight of my load, which consisted of several people in a "man basket", doing maintenance work on pipe systems 40 feet off the ground or more. That kind of situation makes it very important to do exactly what the guy giving me hand signals wants to happen!

About the only kind of transportation I haven't worked on is a train. Cars, trucks, boats, airplanes, construction equipment, etc., yes. Hey, I'm only 75 years old- - - -maybe there's still time left to learn anothe skill or three!

One bit of trivia about a load shared by several fasteners, such as a cylinder head, or a wheel and tire assembly- - - - -the tightest fastener holds virtually all the load, up until the point where it stretches or breaks. Then the next-tightest one takes over until it fails. The mouth-breatiing impact wrench jockey at the local tire store who installs your wheels without using a torque wrench just might be making your vehicle a rolling deathtrap! A lot of the "wheel loss' claims against Firestone, Goodyear, and other franchise tire stores that I investigate involve progressive breakage of lug studs. Guess why!
Jerry

The last guy to touch the wheel did it right ᠁᠁but᠁᠁gets blamed for the last 5 guys that over torque the lug nuts.

Does this kit have a drilled stud or some provision for the drilled head bolt that provides oil to the rocker assembly?

That drilled bolt is only needed with certain early cylinder head/late engine block combinations. It's not necessary for all applications, and it's a very simple task to drill the bolt if necessary.
Jerry

Calibration at home

https://www.finepowertools.com/hand-tools/torque-wrench-calibration/