Vintage Mustang Forums banner

1 - 20 of 24 Posts

·
Registered
Joined
·
1,774 Posts
Discussion Starter #1
You know that feeling as you are tightening down a bolt, waiting for the torque wrench to click... just a little tighter... a little tighter... then the bolt starts to turn easier! That was the feeling I had torquing down the cylinder head bolts on the inline six in my wife’s 66 tonight. I stopped immediately, thankfully as the bolt started to yield I felt it and stopped turning the wrench.

This is the second time this has happened. I bought a complete head bolt set to replace the original head bolts thinking they were spent but while torquing the first new bolt in it yielded before I got to 70 ft lbs (torque spec is 70-75 ft lbs). I checked the torque of the existing bolts and they all clicked at 65 ft lbs. I then went to 68 ft lbs and was getting nervous as some were turning and not clicking so I stopped. I plunked a new bolt in where I stretched the first one, cranked it in at 65 ft lbs and called it a night before I made a mess of it. The attached pic shows the old bolt on the left and the new stretched bolt on the right.
759927


What gives? Are the 200 inline six head bolts torque to yield bolts? Is the book torque spec wrong? Can a torque wrench go totally out of spec when you increase it by only 5 ft lbs? My torque wrench has been quite reliable up to this point, so I trust it hasn’t changed. I don’t know what else could be causing this... it seems weird.
 

·
Registered
Joined
·
3,033 Posts
Dave, where did you get your new bolts ? They have the wrong shank size, and the shank looks like pretty crappy material. I'm certain they aren't TTY bolts, at least they SHOULDN'T be for that vintage of engine. Send them back to where they came from and call ARP and get some good bolts. LSG
 

·
Registered
Joined
·
6,068 Posts
I'm in the same exact boat right now. I'm building a 302, Edelbrock top end kit, so alum heads, intake, new cam, lifters, etc. I followed their directions- lube under the bolt head and on the threads only- none under the washer to head surface. I buttoned up the right side, no problem. The left however..... Murphy's Law- the last bolt snapped just before 72 ft lbs! It's one of the absolute worst feelings one can experience! So, assuming I was going to be drilling, extracting, tapping, I zipped out all the head bolts including the broken one. As I lifted the head off, I heard a thunk on the floor- the broken piece dropped out! It broke at such an angle, that it must have hooked itself and unthreaded right out. My lucky day, right? Then I realized- the ARP bolt hadn't been seized and broke, it had to have been cracked or weak in the first place. After a few calls to Speedway, Edelbrock, and ARP Bolts, they actually sent me a new headset and bolt at N/C, no questions asked. It sucks I have to wait a week or so, but excellent customer service none the less.
759947
 

·
Premium Member
Joined
·
6,957 Posts
Are the bolts the correct grade? PIcture of the top?

When I worked for a company that supplied defense systems, one of our major problems was counterfeit hardware. Common plain "soft" bolts that were made to look like Grade XX bolts. A bolt supplier would have records of purchasing 100000 correct bolts, but the manufacturer would show they only bought 2000.

I cannot find the picture, but years ago, there was a Southwest airlines plane shown coming into land with an engine hanging (they only have 2 on a 737). IIRC, there are 3 bolts, 2 front, 1 back, and the back one had failed, and it turned out to be counterfeit.
 

·
Registered
65 Mustang GT
Joined
·
122 Posts
Shouldn't a head bolt especially ARP be able to easily torqued to twice the spec without breaking? This seems more than a little alarming. I would want to change all the headbolts you got that were run in that same batch.
 

·
Registered
Joined
·
136 Posts
You know that feeling as you are tightening down a bolt, waiting for the torque wrench to click... just a little tighter... a little tighter... then the bolt starts to turn easier! That was the feeling I had torquing down the cylinder head bolts on the inline six in my wife’s 66 tonight. I stopped immediately, thankfully as the bolt started to yield I felt it and stopped turning the wrench.

This is the second time this has happened. I bought a complete head bolt set to replace the original head bolts thinking they were spent but while torquing the first new bolt in it yielded before I got to 70 ft lbs (torque spec is 70-75 ft lbs). I checked the torque of the existing bolts and they all clicked at 65 ft lbs. I then went to 68 ft lbs and was getting nervous as some were turning and not clicking so I stopped. I plunked a new bolt in where I stretched the first one, cranked it in at 65 ft lbs and called it a night before I made a mess of it. The attached pic shows the old bolt on the left and the new stretched bolt on the right. View attachment 759927

What gives? Are the 200 inline six head bolts torque to yield bolts? Is the book torque spec wrong? Can a torque wrench go totally out of spec when you increase it by only 5 ft lbs? My torque wrench has been quite reliable up to this point, so I trust it hasn’t changed. I don’t know what else could be causing this... it seems weird.
The new stretched bolt appears to be longer than the original, maybe more than the stretch could have done. Is it a case where the new bolt is just long enough to have bottomed out on the hole? Are the new bolts the same length as the old?
 

·
Registered
Joined
·
2,278 Posts
I think webstang got it... it looks longer in photo, but that could be camera angle.
 

·
Premium Member
Joined
·
3,965 Posts
Some of the difference may be in nominal thickness of the OE style head gasket and the modern type. But I believe that bolt on the right is all kinds of wrong.
 

·
Registered
Joined
·
653 Posts
You should always buy new head bolts, regardless whether they're torque-to-yield bolts or not.
Evey rust pit, nick, etc., can be the start of a fracture.
I never used to do it, but I learned my lesson through other people's accidents.
 

·
Registered
Joined
·
1,774 Posts
Discussion Starter #11
Thanks for the reply’s folks. The new bolts are made/supplied by a company called AMK. A lot of the Mustang parts houses sell this companies hardware. They are advertised as grade 8 bolts. They are also a smidge longer and slightly different shank design than the originals, but neither of those should cause them to fail. Remember, I stretched an OEM bolt too.

I’m going to bring my torque wrench to work and compare it to our regularly calibrated torque wrench so I can rule it out. It would make sense that I’d be breaking bolts if my torque wrench was way off... I can’t explain it otherwise.
 

·
Registered
Joined
·
2,324 Posts
When I was racing circle track we’d have ARP head bolts on and off the engine at least a few times a season to cheat it up inspect and replace the “stock” parts. :eek: You need to clean and chase the fasteners and the block threads each time they come off. I lube head bolts with motor oil before I reinstall. AMK is the gold standard of reproduction fasteners. It would be odd for them to supply the wrong fastener if they said it was for that vehicle.
 

·
Registered
Joined
·
5,011 Posts
+1 for wanting to see a head stamp.
When you 'unload' your torque wrench, do you just go to the lowest setting, or do you go past it? If you go past it, that can loosen up the cinch nut and mess up the calibration. I've seen this mostly on older Craftsman models from the 80's-90's.
 

·
Registered
Joined
·
3,257 Posts
The new stretched bolt appears to be longer than the original, maybe more than the stretch could have done. Is it a case where the new bolt is just long enough to have bottomed out on the hole? Are the new bolts the same length as the old?
It does look longer, but regardless if it bottomed out or not, it should not yield at 70ft*lbs.
 
  • Like
Reactions: coupster

·
Registered
Joined
·
3,377 Posts
I would definitely verify your torque wrenches before going any further. I just bought one of these for just that reason:

By the time you sent a torque wrench out for testing a time or two, you have just as money in it as buying a new one. So this will give me a decent double check.
 

·
Registered
Joined
·
1,611 Posts
Torque wrenches need to be calibrated from time to time...I had one fail once when tightening down a camshaft sprocket...stripped out the bolt hole and ruined the camshaft.
 

·
Registered
Joined
·
1,774 Posts
Discussion Starter #17
Whelp, found the culprit... my torque wrench was WAY off. The calibrated wrench we have at work was only a 1/4” drive so that wasn’t gonna work, so I ended up on doing it the DIY way with a little bit of math and quite a few lead fishing weights. 😉

With 82 ftlbs of torque applied the wrench stopped clicking at the 60 ftlbs setting!!! No wonder I was breaking bolts... I was probably applying well over 90 ftlbs of torque to those bolts!! Doh!

I recalibrated the wrench to be dead nuts on at 82 ftlbs. At 41 ftlbs load the wrench stops clicking at 47 ftlbs... a 15% error but it’s on the safe side. At 106 ftlbs load the wrench stopped clicking at 100 ftlbs... a 6% error on the unsafe side. I was reaching the limits of my test bucket and couldn’t go higher than that. Anything I work on that needs a torque higher than 100 ftlbs I couldn’t break without a cheater bar anyway. So it’s good enough for now... WAY better than it was, that’s for sure.

Oh, and apparently a 7/16” bolt starts to yield somewhere near 90 ftlbs... FYI 🤪

759986
 

·
Premium Member
Joined
·
11,772 Posts
I have two 1/2" drive torque wrenches, an old deflecting beam style and a clicker. I welded two old 1/2" drive sockets together with the square ends opposite each other. I set my clicker at 100 ft/lbs and test it with the deflecting beam. As long as the deflecting beam is at or close to 100 ft/lbs when the clicker clicks I figure they are close enough.
 

·
Registered
Joined
·
2,324 Posts
It’s a reason to get something like a good midrange CDI rather than the entry level wrenches. While every wrench will need to be calibrated at some point the better the wrench the better the calibration and better it holds it better. Having a reference wrench is a good idea as is the meter in the post above. If you’re a tool truck customer you can get your wrenches checked on the truck.
 

·
Registered
1965 Ford Mustang fastback T5 Ncas 9in Locker
Joined
·
587 Posts
A lot of people do not know what a deflector style torque wrench IS let alone know how to use it properly, not trying to insult ANYONE. This is why I will reuse head, main bolts. They have proven themselves over the years, sure i will chase threads or double check them. I use to do QC and we had a Rockwell machine to pull apart materials and I never had a failure with what I tested. For those not knowing what a deflector or floating style torque wrench is best description is like a teeter totter... when torquing down you " float" the handle, so that the grip is NOT touching the bar, you take the reading from there. NOT saying this is what happened HERE. I agree counterfeit stuff (junk) is out there. BE AMERICAN BUY AMERICAN. Again not trying to offend ANYONE. Education is pricless! If you learn from my mistakes GOOD for you, If I dont tell you about MY MISTAKES, bad for me.. It is only a mistake if YOU fail to fix IT. NO HATE INTENDED.
.
 
1 - 20 of 24 Posts
Top