Retorquing Intake Manifold Bolts - Necessary?

[patrickt]

I posted this in the FordFE.com forum, but so far no replies. My 428 FE was completely rebuilt last year, burned in on the dyno, and now has about 500 miles on it. Any need to retorque anything, such as the intake manifold bolts? The heads are Edelbrock, intake is Blue Thunder. If a retorque is in order what ft. lbs. do you recommend and is it necessary to loosen the bolt first before retorquing?

[Woodz428]

I prefer to re-torque all the aluminum stuff between 500 and 1000 miles, then check about every 5000 afterward, others may not. Always loosen and then re-torque, in the same sequence as normal and one at a time.

[sidewaysinthird]

While I don't go as far as Woodz with the situation I do at least re-torque everything aluminum after a few heat cycles and again after 1000 miles. He is correct that you do need to break each fastner loose and re-torque in the correct order/pattern. I've just never thought it was required after 1000 miles or so.

The Chevys I've run in the past always had the intake bolts work loose in those first few heat cycles.

Most every car and light duty truck out there now has an aluminum intake and most (especially on V6 or V8's) have some sort of leak occur later on due to this issue.

Mike

[Woodz428]

It may not be neccesary to check them every 5000 miles as I do, however I discovered a couple decades ago while working on 510's,Alfas and Fiats that it seemed to be the trick for preventing what were inevitable leaks.

[olddog]

Not be critical, but two questions come to mind.

One, we generally torque bolts well lubricated. Over time the oil goes away. Loosening and re-torquing (if that is a word) may eventually end up with a dry bolt, resulting in less stretch in the bolt. Don't you risk making matters worse?

Two, each time a bolt is loosen and tightened, it is unstreched and then stretched again. A bolt is only good for so many cycles, especially a head bolt.

However if you have less problems by doing this, who am I to argue against good results, but it does seem questionable to me, at least in theory.

[olddog]

I guess I always heard that the reason to re-torque bolts was that the gaskets crush down after some time and heat cycles. After that they pretty much stay put.

In the newer engines some manufacturers went to a smaller diameter bolt that you torque then give another 1/2 turn or so to yield the bolt. The purpose is to turn the bolt into a spring - so to speak. Use the bolt once and pitch it. In the modular ford they went to a metal gasket that does not crush much at all. This set-up seems to solve these problems. My 92 crown went 13 years and 155K miles without ever being touched and it never dripped one drop of oil on my garage floor.

[Rick Parker]

The key to the puzzle of most gasket failures it to keep the fastener (bolt/stud) stretched enough to maintain the elastic forces upon the gasket.
If the fastener is stretched beyond its yield point it will fail structurally and as a result will be unable to maintain clamping force. Many of the gaskets being used in OEM (other than head gaskets) are plastic framed with a rubber ring that has two small raised lines that provide 2 effective seals. This design works very well on freshly machined clean surfaces, and dissimilar (sp?) metals. The resilence of the rubber is more effective in providing an effective seal without followup retorquing required with aftermarket fiber gaskets. Overheating will damage OEM type gaskets, where fiber type can accept more heat but initially require retorquing.

[badrich]

What is the advantage of backing the fastener off before retorquing it? Rich

[patrickt]

Originally Posted by badrich

What is the advantage of backing the fastener off before retorquing it? Rich

Torquing aficionados point out that you get a cleaner, more accurate torque reading when you back off the fastener and then bring it back up to the correct number. I did not do that when I re-torqued my intake manifold and each bolt, as I recall, turned about 45-90 degrees before it "clicked off." Had the bolts clicked off without moving at all then I probably would have redone them with the "back off" method.