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TR2/3/3A Retorquing the Cylinder Head after the initial torquing.?

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K

karls59tr

Obi Wan
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Is there a consensus on when to retorque the cylinder head after the initial torquing of a new head gasket? Seems like there are many different views on when to do it. This would be with "Non" ARP studs Then there is the whole "hot" retorque thing. The mind boggles.o_O
 
I let the engine go through at least one full heat cycle...up to temp and back down. Then I retorque and re-set the valve lash. After that, I only retorque annually when I change oil and check valve lash. My engine was rebuilt 7 years ago...so the bolts haven't budged on a retorque in 7 years, LOL. But I still check.
 
Assuming iron block and iron head, retorque at 1000 miles and never again. You can skip the 1000 miler if inclined. Do the nuts one at a time; do not loosen more than one at a time. When you back off a nut to retorque loosen just enough to break away the nut (no half turn stuff!). Use the torque pattern in the manual.
Bob
 
I've never heard of loosening bolts for a re-torque. The point is to check for looseness, which is a sign something is giving way...like the head gasket or cracked bolt/stud.
 
John-
Until your post above, I had never heard of not backing off to retorque. Our BMC dealership practice in the mid 70s was to do so when retorquing for the PDI and 1000 mile. Looking around on the net, I do see a divergence of opinion. In a BCF thread started by Banjojambo on 11/17/18, Randall Young opined for backing off and explained his thinking.
Bob
 
CJ is on the mark here (IMHO). Did my first one in 68. Never a failure on one that
has been run a few miles , let cool to 70deg and re-torqued. But it is also helpful
to use new studs/nuts(ARP).....Do it once,do it right,drive it like your 19 again!!
Mad dog
 
Interesting. I'll check my mechanic's "Bible"...a shop manual from the 1970's, when mechanics used real tools instead of computers to work on cars!!
 
CJ my torque wrench is an old torsion bar style for 69......re-calibration ? we DONT need no stinkin
re-calibration.
Mad dog
 
mctriumph said:
CJ is on the mark here (IMHO). Did my first one in 68. Never a failure on one that
has been run a few miles , let cool to 70deg and re-torqued. But it is also helpful
to use new studs/nuts(ARP).....Do it once,do it right,drive it like your 19 again!!
Mad dog
Click to expand...
Does the valve train not get in the way of the re torque?
 
You were going to re-set the lash any way.But I think if the valve cover studs are out, its
OK to leave the rockers in place.
Mad dog
 
Yes, Karl, it does...that's why it's a good time to do both...the torque and valve lash. If you just remove the entire rocker shaft, the lashes should remain unchanged when you bolt it back down, though.
 
The existing routine is alloy head, let cool before retorquing, cast iron head, retorque once warm.
 
bobhustead said:
John-
Until your post above, I had never heard of not backing off to retorque. Our BMC dealership practice in the mid 70s was to do so when retorquing for the PDI and 1000 mile. Looking around on the net, I do see a divergence of opinion. In a BCF thread started by Banjojambo on 11/17/18, Randall Young opined for backing off and explained his thinking.
Bob
Click to expand...
In the TR7 service manual it details both the bolt sequence and procedure of one flat I believe and retorque one at a time. This is of course an alloy head and iron block where gasket failures were perhaps mire likely.
 
A fastener that has been in place can take more than the torque exerted to put it there, to undo or tighten - the theory is by breaking it free with the one flat and then retorquing to spec you avoid thinking it is good when it isn't.
 
Billspohn is correct. It is called "sticktion". The torque required to break the sticktion may be higher than the required torque - leading one to believe the head is torqued to the right value. To avoid this you need to back it off 1-3 flats before retorquing.

Bob
 
Well...let' go one step farther. Why is torque always shown with a range of values? Why not just one value? I have always torqued to lower, and checked to higher. If it doesn't move, then you are good.

I also have to ask what your reference is for "loosening". Have you seen it in a manual anywhere? I see it is rampant all over the internet, but so is a lot of mis-information too.

I looked in my Stockel "Auto Service and Repair" manual, which was the teaching source for tech schools in the 1960's through the 80's. It goes into detail in every operation. Under "retorquing", it only says that, "some assemblies should be torqued after a certain period of time". It does not say loosened and retorqued...just "torqued". I find loosening any gasketed part to be problematic. You go to great trouble to torque the part in the proper sequence and ramping up in thirds to prevent warping or cracking. Why would you ever want to loosen a bolt unless removing the part and discarding the gasket?

I have a degree in Engineering Mechanics, and was taught how to determine bolt size and torques vs. materials. We were taught use lubrication on all bolts for installation and torquing, unless contamination was a factor. I was never taught to loosen a bolt to check torque. I never heard of loosening a bolt to check torque until the internet became common.

Not trying to pick a fight..just trying to learn. What reference have you guys seen to recommend loosening bolts to check torque?
 
A good friend once had a Tr7 roadster he had driven since new.Well maintained and trouble free
till 217 K miles. If he had ever re-torqued the head it would have made 300 K. The club helped
with the autopsy , and several of the head bolts were little more than finger tight.Needless to say
blown head gasket.Quite a shame as this engine used no oil and was is set to make the Guinness Book
for Tr7's running for more than 25 years.
Mad dog
 
What holds a bolt is the stretch you put on it. The stretch puts the bolt in tension, so it cannot loosen. For rod bolts I always torqued to an amount of stretch, measured with a micrometer. Head bolts have one side blind, so you cannot measure the stretch. A dry bolt gets a lot of drag on the threads, making it harder to get an exact stretch...and that is why lubrication is important.

For most head bolts I lubricate with sealant, since they are "wet". ARP bolts come with a packet of high pressure grease. If you don't have any high pressure grease available, then a few drops of engine oil will work.

With the proper stretch, the only way a bolt can loosen is if the gasket compresses, or if it is overloaded to stretch it even further (like over-revving rod bolts).
 
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