My first set of alum. Summit 2.02 heads on a small block chevy . What are the torqe specs?
Not off topic at all with all the Chebby engines in Jeeps now days...
MUCH more to the point and 'On Topic' than the pissing contests about this or that and the soft core porn that's passing for avitars and stuff here!
Same torque specs as cast iron heads,
You SHOULD NOT use BOLTS on aluminum heads,
You should use STUDS and HARDENED WASHERS with aluminum heads.
See, Cast iron won't take a fine threaded bolt without stripping the hole out.
The composition & grain of the cast iron won't allow for a fine thread to stay intact,
So you have to use 'USS' or 'Coarse' threads in cast iron.
Use a good brand of studs,
SPS, ARP, Milodon... IN that order, and torque them to about 15 Ft.Lb. into the block.
Use 'Blue' thread locker or sealer if you think they will loosen or leak, but stay away from the 'RED' thread locker on head studs.
If you tighten more than 10 or 15 Ft.Lb., you WILL crack the block in the blind holes.
If you attempt to torque to 85 Ft.Lb. or what ever the torque spec is for bolts with the stud bottomed out, it's going to crack the block, and there just isn't any two ways about it...
(I did this for 20 years, and I've seen many a cracked block where STUDS were over-torqued when they were bottomed out...)
Bolts don't bottom out, so you CAN torque them to whatever,
But with studs, they WILL bottom out, so stick with just enough to hold them in place, and some thread locker 'Just In Case'...
Personally, I skip on the thread locker and use 'Thread Sealer' Goop with Teflon.
The resistance from the thread sealer is enough to keep the stud in place,
And it's enough to seal things up without getting crap everywhere!
Now, the studs will be USS thread on the bottom ends to fit in the block,
But the top ends where the heads go on will be SAE, or 'Fine' threads.
The more turns per inch of bolt, the better clamping power you can get (just like gearing, it's gear reduction with more turns per inch).
With the stud ANCHORED in the block, those USS threads don't have to rotate,
They are pulled up into contact with the block EVENLY, and they will hold MUCH MORE clamping force than if you have to turn them...
When turning them, imagine anything, speck of carbon, metal shaving, bolt sealer, ect holding the threads up off each other...
And a crack starting at the point where the load is redistributed to...
Once a crack starts in a thread, It's DONE!
There is no saving a cracked thread in cast iron! That crack will proceed no matter what you do!
If you SEAT the studs in the block, then use the FINE THREADS of the stud and nut to load the cast iron EVENLY pulling on it (no rotation),
You stand a MUCH less chance of starting a crack and having a bolt/thread failure!
So, now we have USS threads in the block,
SAE threads at the heads,
We have STEEL stud with STEEL nut as fasteners, and we have pretty much taken the cast 'Weakness' out of the cast iron...
IT's time to take a look at the HEADS...
There are THREE things you have to remember with Aluminum heads on cast iron...
1. Aluminum expands roughly TWICE as much as cast iron at the same temprature.
(If it's a High Nickel racing block, expect nearly THREE times as much movement of the head than the block)
That means for every 1 Millimeter of expansion the block does,
The head will do AT LEAST 2 MM of expansion (and contraction)
2. Aluminum expands and contracts roughly THREE TIMES AS FAST as cast iron.
So, even as the block hasn't warmed up enough to move yet, the aluminum head is on the move like gangbusters!
3. Aluminum heads will 'Point Pressure' or have 'Pressure Points' where the fasteners are.
Answerers to 'Issues' #1 & #3...
If you use regular nuts on the heads, as the head expands and contracts, the edges of the nut will eat into the heads,
And do HORRIBLE things to the head,
Along with making clearance in the aluminum under the nuts, usually resulting in leaking head gaskets or worse...
You need to SPREAD OUT THE LOAD from the nut on the stud...
Do this by using as large of a HARDENED WASHER as you can under the nut.
The larger the washer you can fit under the nut the more you will spread the load out on the aluminum,
The Steel Washer won't dimple or be pushed out from under the nut.
Answer to 'Issue' #3,
Use 'O' ringed head gaskets.
'O' rings will keep the head gasket from leaking as the head moves around on the block like crazy.
DO NOT use hard setting sealers!
Use Fel-Pro Head gaskets with the 'Blue' Teflon surface coating so they allow the head/block to move independently of each other,
But still seal up the water passages.
Those head gaskets have Copper Cored, Stainless Steel 'O' rings built into the head gasket so the cylinders won't leak.
They work GREAT, are reasonably priced, and soak up a BUNCH of the problems associated with heads we used to have to 'O' ring groove, and use copper wire in to seal up the cylinders.
Good set of 'O' ring head gaskets,
Good set of studs with washers,
And some care when you put things together should make for a good, and long lived, install!
You wouldn't believe how many broken and/or useless heads/blocks I've seen ruined by people using plain bolts or studs/nuts without HARDENED washers!
The other thing is,
Before you install the studs, Run a SHARP tap through the block bolt holes to clean them/straighten them out,
And flush the holes with something like brake cleaner,
Then dry throughly before you install the studs...
Factory block threads leave something to be desired...
They were usually cut by a dull tap, so they aren't FULLY formed,
Most of the time they are 'Warped' or 'Wobbly' and they are ALWAYS full of crud.
The studs will be FULL thread engagement, and they will have STRAIGHT, usually ROLLED threads on them,
And the cleaner and straighter the threads in the block are,
The more contact area you will have.
DO NOT use choke/carb cleaner, it leaves a residue that will effect the usefulness of the sealer or thread locker you use.
Go easy on the sealer or thread locker, and apply it to the STUD THREADS ONLY...
You don't want a liquid in the bottom of the hole that can 'Hydraulic' and interfere with the torque reading, or even crack the block!