Marc3.4V6

iTrader: (1)

I am in the middle of a head gasket job and when I go to unbolt the intake manfold, over half the bolts on each side I could loosen with my fingers. What does this mean? Back when the car was running, I had an unexplained miss/backfire on and off that seemed like it was coming from the engine bay...possibly the intake I am thinking now. What could this mean? Engine was rebuilt 12k ago.

Also, anyone know what size wrench to use on the coolant hardline on the right side of the head?

wrd1972

iTrader: (12)

15mm or 17mm IIRC.

z28rob18

iTrader: (7)

idk if that was the cause of your miss but i tour down the old motor last week to sell the heads and i had the same thing. half the bolts were very loose and the others were extremly tight

SS RRR

iTrader: (2)

It means you have discovered one of the main reasons why the LT1 is plagued with intake leaks most everyone has encountered at one time or another.
The intake, being aluminum against iron expands/contracts extensively during heat cycles. This causes bolts to loosen and sealant to fatigue. That's why whenever you remove the intake you must retorque the intake bolts after several heat cycles to ensure they remain at torque spec. It's the same thing with aluminum wheels. You should always retorque lug nuts after several heat cycles...

GIZMO

iTrader: (8)

?????

SS RRR

iTrader: (2)

Iron does not contract/expand like aluminum which creates pressure on the weakest links which happens to be the intake bolts. As stated it's the same thing bolting up an aluminum wheel to an iron disk/drum/hub.

GIZMO

iTrader: (8)

All that is true, but all LT1's in Z28's had aluminum heads.

whytryz28

iTrader: (28)

Yes we do.

SS RRR

iTrader: (2)

Yes and over the years there has been discussions about whether or not people actually go through the process of re-torquing the heads after several heat cycles. There are many that do and more that don't. I never have because I figure 17 bolts at 65ft.lbs. will keep a cylinder head in it's place whereas I have re-torqued manifold bolts and most become horridly loose.

monster81

probably unproper bolt torqueing in the time of rebuild

SS RRR

iTrader: (2)

mdacton IM'd me and shed some light on this subject which makes me tend to believe I am completely wrong. I never took the intake gaskets into consideration. I've only ever used GM gaskets because they were easy to port match. Perhaps those who use a different aftermarket gasket will have better luck with the intake staying fast.

Marc3.4V6

iTrader: (1)

thanks guys.