good info here this is copy and pasted
I've been rebuilding engines for over 30 years, and I'm VERY LEARY of using old bolts in 'Critical' areas.
Head bolts are one of those 'Critical' areas.
(along with rod bolts, main cap bolts, ect.)
Since I've been doing this so long (and owned an engine machine shop that specialized in racing engines for over 20 years) I've learned some things...
STUDS are a MUCH better way to do things than bolts.
Studs have a HEAVY or 'USS' thread on the bottom to grab into the cast iron block,
Then use a FINE or 'SAE' thread on the top to give more clamping power for the same amount of 'Torque' value on the top nut.
(Finer threads mean more 'Gear Reduction', and that means more clamping force for the same torque value)
This also takes much of the danger of stripping the soft cast iron threads out of the block since you aren't MOVING the bolt threads when tightening, and the bolt threads can seat without moving around ruining the seating and holding force.
Put studs in at 15 or 20 Ft.Lbs., just enough to seat them,
and they will EVENLY pull on the cast iron threads in the block as you tighten down the nuts on the top to clamp the head in place.
With bolts, imperfections in the profile of the threads of the bolt or block *CAN* cause a thread to break loose at the root (usually in the cast iron) and that crack will 'Un-Zip' along the cast iron and cause the thread to 'Strip' out.
Since the imperfections aren't MOVING with a load when using studs, you don't run the risk of starting a crack and having problems like you do with bolts.
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DON'T USE CHEAP BOLTS!
Most high quality bolts have ROLLED threads,
That means the grain of the steel is still intact, making for a MUCH stronger bolt,
Where cheap bolts have CUT threads, and that removes the grain of the steel, making for a much easier break factor on any given thread.
(Remember the cracks at the base of threads and the thread 'Un-Zipping' along the root of the threads mentioned above?)
SPS bolts/studs are the best you can use... BAR NONE!
Torque, sheer and stretch loads are usually 3 to 4 times as much with SPS bolts/studs over any of the factory bolts.
There is a reason NASCAR builders, NHRA top fuel builders, ect. won't use anything else but SPS.
They are expensive, but the strength, quality and repeatability are simply unparalleled.
ARP bolts/studs are very good quality, and I don't hesitate to use them in street engines.
Milodon used to make a full bolt/stud kit for AMC engines, and they are just fine for a mostly stock application,
And at about 1/4 the cost of an SPS set, they are a bargain.
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For a good handle on head bolts and their application/installation,
I think we need to cover proper proceedures to install head bolts...
First off,
DO NOT INSTALL A DIRTY HEAD BOLT INTO A DIRTY BLOCK!
Chase the threads with a SHARP tap/die to clean the threads of THROUGHLY!
Imperfections/grit/crud in the threads of the bolt or block will UNEVENLY load the threads, and that can result in cracking the root of the cast iron threads,
Screwing up your torque readings, ect.
Secondly,
DO NOT INSTALL A HEAD BOLT DRY!
Dip the threads in engine oil, let them drain off to where you have an oil film on the threads before you install!
Also, don't forget to oil the underside of the bolt head (Flange) so you get correct torque readings!
Dry head bolts will read 15% to 20% higher torque reading than the bolt is actually giving in clamping force, and that will often result in the bolt NOT clamping the thead gasket firmly enough.
Third,
CHECK YOUR HEAD BOLT HOLES FOR 'BLIND' HOLES OR 'WET' HOLES!
Many head bolt holes in the block deck are drilled right into water jackets!
If you don't use bolt sealer on these bolts, the coolant will creep up the head bolts and leak out under the bolt heads into your oil!
Make sure you check to see if the bolt hole is 'Blind' (Closed bottom, no water) and that head bolt gets oiled,
Or if it's a 'Wet' hole (Into water jacket) then you need to use thread sealer on the threads, and oil under the cap of the bolt for correct torque reading.
Fourth,
TORQUE 'STEPS' & PATTERN.
Very often, people see the 'Tightening Pattern' or 'Sequence' in the manual, but don't understand 'Why'...
The reason is, you have trapped moisture and air between block and head gasket, between head gasket and head,
and you are trying to get two long, flat surfaces to pull together evenly.
You also have to remember that cast iron is VERY soft, and the block will flex as much as 0.010" an inch with V-8 heads, and the head is much less rigid than the block, it can distort as much as 0.035" from head bolt torque load alone!
When you are doing an I-6 head, it's much longer and even more prone to distortion...
Start at the center most head bolt, and work in an increasing spiral pattern outward from the center bolt.
Start your torque loading of the bolts at about 35 Ft.Lb. and work up in three or four steps, working the pattern 3 or 4 times to reach full torque load.
Steps allow the trapped air/moisture in the air to migrate out to the edges of the head gasket and escape.
Working the pattern pulls the 'Wrinkles' out of the head, chasing them out to the ends of the heads where they are eventually pulled down EVENLY with the engine block.
This will minimize the distortion of the head/block when you are done.
Start with about 35 Ft.Lbs. on the first 'Run' thrugh the pattern.
Allow the block to set 15 minutes or so (on V-8, this is about the correct time it takes to set the other head on, get the bolts started, and run the pattern at the same 35 Ft.Lbs.)
DO NOT get into a hurry!
Let the block/head settle out,
Let the head bolts stretch and unload between torque increases!
The colder the room you are building in, the more time you want to give the engine to settle out between steps in torque...
Then increase torque to about 65 Ft.Lbs. and run the pattern again, allowing another 15 minutes or so between a third round of torque so air/moisture can migrate, and the block can recover from being flexed again...
Then run the toque up to about 95 Ft.Lbs and do the patterns again...
After you have allowed the block to settle out,
Then do final torque to 110 Ft.Lbs. or to full torque value for your particular engine.
If you are doing a V-8 engine, NEVER bolt one head on at a time if you can keep from it!
Replacing one cracked head or something like that can't be avoided in some cases, but if at all possible,
Do both heads together so the block gets evenly stressed on both sides as you are increasing torque.
If I'm replacing one head, I usually loosen the other head and toque it back up while I'm installing the new head just to keep things even!
You will often find your intake fits better if you do it this way since the engine isn't getting 'Warped' as you tighten one side all at once!
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I'm sure people will disagree, argue, and flame over this approach, but it's served me well on engines that turned over 10,000 RPM, engines that had three atmospheres of boost, ect. for many years,
And it was a learning experience...
When I first started with low compression farm equipment and 'shade tree' builds I had a lot of failures.
After I acquired the measuring equipment to understand the forces on the engine block, heads, bolts, ect. I nearly never had a failure...
Just trying to pass on experience that was gained at GREAT EXPENSE in both time and money!
