One of the technologies that has been implemented for many of the
engines today is the configuration of the block. Many of today’s
engines are using “bedplates” (see Figure 1).
The block is split at the main bearings or the crankshaft centerline so
there are two distinct pieces to the block; an upper part that houses
the cylinders and the lower portion, thereby eliminating main bearing
One of the distinct advantages to the bedplate is the increased main
bearing housing material in the lower half of the engine with a
distinct main web bulk head not only in the upper block but the lower
bedplate as well. This major increase in the volume of material around
the main bearing and increased support of the crankshaft allows for an
increase in cylinder combustion pressures while operating at a maximum
of efficiency of trace detonation.
Another benefit to the rigidity around the crankshaft is the dramatic
reduction of NVH (Noise, Vibration and Harshness). In addition, this
design gives the ability to have bosses and mounts designed into the
engine block for various accessories, transmission mounts/braces and
even chassis strut/support mounts in some cases.
Bedplates and their installation bring some very unique challenges.
First, with regard to the basic handling, they need to be treated with
the utmost of care. Whether they are aluminum or cast iron, they cannot
be abused because any dents and dings will affect their ability to
seal, and maintain main bearing housing bore dimension and, of course,
crankshaft clearance and bearing crush. They are also typically very
complex in their design, housing oil passages, transfer grooves and
possible “O” rings for oil sealing (Figure 2).
They also have many bolts of various different sizes and lengths and
different torque procedure and sequence. The day of dropping on main
caps and using a torque of sixty-five foot pounds does not apply to
bedplates. If you do not use the OE recommended procedures you will
find yourself in trouble in a big hurry, either in bearing clearance or
sealing. There is no maybe with bedplates – it has to be correct.
There may also be oil passages that are within the bedplate itself that
are plugged, whether with pipe type plugs, soft plugs or steel balls,
but they must be removed and these passages cleaned of any debris or
contaminants that may be reintroduced into the engine.
The mating surfaces between the bedplate and block are critical and
should never be cleaned with a steel scraper, sanding pad, refinishing
discs or any method that may remove material or alter the mating
surface. These surfaces must be perfect on both the block and bedplate.
The ultimate would be a large lapping table and a very fine lapping
compound but that is not likely to be feasible so utmost caution needs
to be adhered to. Chemical cleaning would be the preferred method for
bedplates and any contact surface debris that may need be removed
should be done with a “soft” scraper only, especially if it is
aluminum. If damage appears to breach the sealing face an epoxy may be
the way to fix that; welding would cause too much heat and distortion.
Anaerobic sealer is considered to be the best sealer for the mating
surface between the bedplate and block, however there are some OE
engines that recommend the use of RTV sealer. I will leave the decision
up to you but my money is on anaerobic since RTV could potentially give
you thickness that may change clearances and bearing crush. If you have
not gotten it by now let me just say it plain and simple “the integrity
of the mating surface condition is critical.”
By now you are probably certain that I have gone through a lot of
musing about bedplates – and you’re right. The payoff from this article
is that if you have a bedplate leak it is the nightmare of nightmares:
you cannot stop it and you cannot fix it in the chassis. To repair a
bedplate leak, you’ll have to take the engine out of the vehicle and do
a major lower end disassembly to repair the leak. That is going to cost
you a whole lot of time, money and ill will. So I suggest that you
treat bedplates like you’re taking out your best friend’s sister … with
the utmost of care.