The IDEAL way to plane the mating surfaces is to torque the intake and exhaust
manifolds together off the vehicle and have them planed as a unit before
installing the assembly on the engine. This will assure good mating and reduce
stress.
Generally, if the manifolds are still bolted together, don't separate them
unless you have to replace the heat riser valve.
Here's my suggested installation procedure:
1) Check all mating surfaces for flatness and plane if necessary. If possible,
plane the assembled intake and exhaust manifolds as a unit.
(At an absolute minimum, make sure all mating surfaces are clean.)
2) Install new gaskets, and make sure all are of even thickness.
3) IF you have previously separated the intake and exhaust manifolds, bolt the
two manifolds together LOOSELY (with a new gasket).
4) Bolt the intake/exhaust manifold assembly to the block LOOSELY, using the
CORRECT washers and nuts (see note below).
5) LIGHTLY torque the manifold assembly to the block (no more than about 5 or
6 foot pounds). (If you have previously separated the manifolds, this will
help align the manifolds so that you can torque the intake and exhaust
manifolds together in proper allignment without stress).
6) IF you have previously separated the manifolds, torque the two manifolds
together with the four nuts. Bring them up to recommended torque in at least
two or three stages to avoid uneven tightening.
7) Torque the manifolds to the block. Bring them up to recommended torque in
at least two or three stages to avoid uneven tightening.
Notes on washers:
1) Any flat washers that bridge a large gap should be very THICK. If you use a
thin washer, it will bend and you will lose the proper torque/stretch on the
stud. If you don't have a thick washer, you can probably get by with doubling
up a flat washer.
2) If you have INTERNAL-TAPER washers, you might want to replace them, since
the old ones may be stretched beyond their usable range. The inside surface of
an internal-taper washer is tapered to match a surface on a TAPERED NUT that
resembles a miniature wheel lug nut. The washer is designed to stretch when a
certain amount of torque is reached, thus helping (to some degree) to prevent
over-torquing and also locking a bit more securely because of the slightly
resilient stretch of the washer helping to maintain a wedging action against
the nut. To get any benefit from these washers, they must be used in
conjunction with the proper tapered nuts, and the mating surfaces between
washer and nut must be clean and smooth.
The most important thing is proper and gradual torquing and alignment.
While there is no guarantee that the cast-iron manifolds will not crack, this
approach will certainly reduce the possibility of stress cracks.
Have fun,
Alan
MVTrucker@aol.com wrote:
> When you mate the two
> manifolds, put a straight edge across the engine side of the flanges.
> I'm pretty sure that you will find that planing the surfaces is in order.
> Also, leave the four bolts that hold the
> manifolds together loose till after you snug the assembly against the
> engine block. Refer to the manual for details.
> Joe Young mvtrucker@aol.com
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