Someone mentioned on another thread that head bolts should be retorqued only once after the initial installation. I have never heard this before. Does anyone else have any evidence that this is a good practice? It seems to me that if they loosen up after running the engine, they should be re-tightened.
One reason I'm asking is this: I recently rebuilt an engine for a friend and ran the engine for a while in my shop, then took the car for some test drives. I initially torqued the bolts (used ones) to 50 ft/lbs, then, during that break-in/running time, I retorqued them twice more. I let the engine cool each time, and some of them turned just a bit each time to get back to the 50-lb. mark. (The block and head were both milled, so they were flat.) The owner drove his car away from my shop about 60 miles to his home. I suggested that he check the torque on the head bolts, and he snapped two of them trying to get them to 50 lbs. He has now ordered a set of NEW bolts and will go through the fun experience of removing the two stubs from his block.
So is there something to this "retorque only once" rule?
Some of the nickel head bolts a couple years ago would not pull 50 ft. lbs. I do not know if that is what was on them but I would retorque every head till it holds 50.
When I install a new head gasket, or re-use an existing one, sometimes I torque head bolts, sometimes I just tighten them. In any case after the engine has warmed up and run a bit, I let it cool off and re-tighten the head bolts. After that I don't mess with them unless I have a problem.
If you snap any head bolts at 50 pounds, the bolts are are junk, or the torque wrench is off, the bolts weren't oiled, or some kind of gasket cement wasn't used for lube, and or sealent, the threads weren't taped, bolts were to long, or the bottom of the hole was not clean.
We Retorque head bolts at least 5 times on the average.
If you oil your head bolts and torque to 50 ft lbs you are asking for trouble. Bolt torques are specified for unlubricated bolts. With lubrication there is less friction and bolt loads can be considerably higher.
Ted, stick to something you know about, what ever that is, don't be a Dumas.
As my Aunt Ann said,you must realize that those of you who think you know everything are sometimes very obnoxious to those of us who do.
bolt loads would be considerably lower, an oiled thread takes several re-tightening to achieve max torque value, also this should and is done with the engine hot.
Only alloy heads apply the correct tension after the engine has been warmed up and allowed to cool down.
I have been around engines of many types for over fifty plus years, but I have NEVER heard that head bolts should be retorqued when hot, no matter what material the heads or blocks were made from. That just doesn't make sense to me. Am I missing something? JMHO. Dave
See in the 'NOTE'
Any gasket used that is thick like Model T's up, to the time they made head gaskets out of thin metal that don't shrink, had to be retorqued.
David, you were in the new, no retorque era.
okay... can someone go through the whole process or putting an aluminum head on a car? does a z head need a special High-comp gasket?
No, but put small machine washers on the head bolts.
Follow the instructions with the 'Z' head for install...
Clean the bolt holes well, then mount the head without gasket, and let it be loose on the cyl block. Turn over the engine with hand crank. If the Z head jumps up, the pistons are contacting the very small squish area. You have to remove some of the inside of the Z head in this case.
Then mount with gasket in place and test again. All should be OK
Use copper gasket (best) and use Copper Coat spray on both sides of the gasket. Install, fit gasket correctly, add the Z head. Fit new bolts with the stainless washers that come with the Z head, the washers prevent galling as you seat the bolts. Use care in snugging the bolts, follow the instruction for torque if you use a torque wrench.
At the Mountain T Tour in Hendersonville NC last week, a T'er with a Z head got water in the engine, all there on site figured the gasket went.
But, after trailer back home the owner found the Z head was damaged with a hole in the combustion chamber, leaking coolant into the motor. The old motor still had Ford two-piece valves. A valve head flew off, split the Z head, or maybe the coolant force too, as that chamber filled-up.
Didn't get any pictures of the damage, but anyway, only minor piston top damage, which a replacement piston will fix, along with a valve job to replace all those old Ford two-piece valves!
awesome! exactly what i needed. Thanks!
Herm, read my post again. I said that I have never heard that they should be retorqued when HOT. Dave
Yes Sir, and then you said: no matter what material the heads or blocks were made from. That just doesn't make sense to me. Am I missing something?
I'm not a proponent of torque wrenches and the plug-n-play torque tables. #1, the average Joe doesn't know that torque wrenches of average quality are maybe accurate to 15% out of the box and lose another 10-15% once they have been dropped once or twice. #2, standard torque tables are based on something called "dry" and dry is naked as in acetone dipped and dried and no one does that....so the average Joe will wind up over torquing everything anyway.
There is a #3 and that is that I would go nowhere near 50 anyway, not without full Helicoils or inserts anyway. But that would be me and I'm wierd.
However, can you do me a favor? ask your buddy where they let go? I'm curious and have been working on something. Shearing at the first full thread engaged means one thing...shearing at the second means something else...and shearing lower means something else again! Also, new bolts? Full body shank or reduced body shank? Thanks
George -- My friend is away for a few days and will work on the car when he returns. Since the new bolts are in shipment, he couldn't do much on it till he gets them anyway. And since you asked, I'll post what I hear as the job progresses.
Shearing the bolt while tightening it is a pain, shearing it when it bottoms out is a much greater pain, pulling the threads out of an early cast iron block is a disaster.
The original Ford headbolt shanks are slightly smaller because they used a rolled thread. A bolt is not likely to fail in the shank.
What I'm actually really trying to determine in my own Don Quixote way is that I think perhaps after all these years the first active thread in the block just may be a 'dead' thread. A bolt can't shear on a dead thread unless the thread itself has a burr...no burrs, shears on the second thread...bingo, dead top thread!
That in turn causes some other thoughts since Joe Galamb cheated us in the first place on thread engagement and losing 1 out of maybe only 7 (which should have been 9 to begin with and also structurally allowing for a top thread to go dead in time with still room to spare) just might be more significant than one might think.
Our T needs all the thread it can get...or the results are the same as short nutting a regular nut and bolt, gets you by most of the time, but always makes you wonder by just how much
Rule of thumb for cast iron is threads should have 1-1/2 diameters of engagement. I don't think we get that much on Model T head bolts.
You should limit retorquing to once because every time you apply force to the bolt you will cause it to rotate further. There is no need or reason to retorque more than once. Constantly retorquing will eventually cause a problem. More is not better. This does not just apply to Model T head bolts, it is good practice on any head bolt on any engine. The gasket crushes a certain amount, and the bolts yield to apply the torque. You can damage the bolts and / or head gasket by constant or repeated retorquing.
Do it once, and then don't fix what is not broke.
I doubt the retorqueing was the problem.
I recently installed the head on my 1915. It was the third retorque before they stabilized and required no furthur torqueing.
FWIW I think its silly to go straight for 50 lbs torque. I've read too many posts here where that last twist to 50 ft/lbs on the wrench was the one that stripped the threads in the head.
Suggest you chase the threads in the block first, using either a bottom tap or one you've made from a good bolt with sharp threads - like this ...
Blow out the holes and measure depth with a caliper.
Then torque to a more moderate level - say 35 lbs. Drive car, let cool (totally) and retorque again. Repeat until they maintain that torque level. If you have leaks, retorque to 40 ft/lbs and so on. Until you reach a minimum torque setting that does not allow leaks. I started at 35 because I have an older block with poorer metalurgy. (I also stopped at 35 because it was enough for my engine - no leaks, good compression). Newer cars with better blocks might start at 40.
What's the sense in torqueing immediately to 50 when that may strip a thread or break a bolt, when torqueing to 40 or 45 (whatever) may have been sufficient? Maybe you need 50, but maybe not. Remember Ford never specified a torque value.
The only torque valve is the amount the average man could pull the the original wrench. There is a reason that wrench is the length it is, same with regular wrench sets. I think the biggest killer of bolts and threaded holes in a Model T is the use to torque wrenches.
You state, "You should limit retorquing to once because every time you apply force to the bolt you will cause it to rotate further."
The bolt will no longer rotate further once the gasket settles in and the torque remains constant. The wrench will simply reach 50 ft-lbs and click with no actual rotation occurring. It's not like you get it tighter and tighter every time.
When discussing torque and re-torque the subject thread can go never never land real quick and usually does. My own engineering view is that Galamb planned on equal to 32-34 ft-lb, and found out that every now and then he needed 10-15% more.
I think I now have a new answer for folks that ask me...
Forget the 'why', just do as Bud says, you should be good to go! (A Z will require a little more)
Bud has it. Cleaning out those holes is a major must. I don't know how that crap gets in there in the first place and actually I've only done 3 heads but damn those holes were loaded! Personaly I work up to 50 in about 3 passes, heat it up and the next day re-torque to 50. They say to do it again after 500 miles. I never did though.
First you should listen to someone that is doing this all the time. Kohnke is right on the money. You can read all the books you want, listen to guys at the bar, or someone that put a holley carb on his 67 Nova, what do they know. Dry bolts will not tightened the same all the time. They want to gall and they you are reading the force on the threads and not the streach on the bolt. Retorquing hot is a joke. Metal grows when heated. The hotter the more growth you get.
Retorque in the morning after it has cooled all the way down. A motor is a motor and the same rules apply to all of them. Its just nuts and bolts. No magic because its says " T " on it. Scott
It will be a lot simpler if you pitch the torque wrench and just tighten the bolts. More Model T head gaskets have been installed without torque wrenches than with them. Cleaning out the holes as Bud suggested is a must.
After stripping two threads in the block, I bit the bullet and heli-coiled them all. When when I broke the crank, I put in a replacement block that was in the '25 C-cab i have. Didn't want to have a similar problem, so I heli-coiled them first off.
I decked the bock and the 'Z' head. When I started to torque the head. I was about @ 20 and this bolt didn't feel right. I backed it out and found this. It came out of a box of grade 5 bolts. I guess it was only Grade 0. Went to Tractor supply and bought another box and spent a while making sure the lengths were right and there was room at the bottom.
I prefer to lube the threads and between the washer and bolt head. Then I tighten to 25, start the engine and run at a medium idle till the engine is at running temp. After the engine has cooled, 4-6 hrs, run the torque up to 30 and take 10 to 15 minute ride with out high power settings. Next i take a normal ride @ 35 and usually the re-torque will only show one or two that actually move.
My thoughts are I can run @ 35 because most of the torque is put into stretching the bolt and not overcoming variances in the friction of the thread interface.
As I was getting ready to post this note, I forgot to say, This is a 'Z' head.