Building a 318 Polyhead Motor — LA and A Parts Interchange
A lot of parts interchange between the 1962 to 1966 polyspherical A 318 engine and the LA series of Mopar motors (318, 273, 340, 360), including:
- Thermostat
- Thermostat housing
- Internally balanced 273-318-340 harmonic balancers
- Valve springs, retainers and keepers
- Main bearings (NOT 360 though)
- Rod bearings
- Crankshafts (reground 360's included)
- Flywheel
- Starter, both standard and high torque
- 318 LA ring set
- timing chain and sprocket
- fuel pump
- oil pump
- oil pan (not 360)
- distributor pump drive gear
- distributor, standard points or electronic
Though reported as interchangable in several references, apparently the timing covers are not exactly the same.
Jeff
Two pictures show the difference between a poly 318 timing cover and a small block LA cover. The one shown on the right is the poly 318. Notice it has one bolt hole that the other does not, exactly opposite the fuel pump opening. The LA does not have that, and neither do the gaskets that claim to fit all 318's, (poly and LA).
Update May 2008
Gary Pavlovich writes: The missing bolt hole in the LA cover is not a problem for the Poly block as that hole in the Poly block is easily plugged. When I finished up a 402 inch stroker engine I confirmed that we hit water from that odd hole, so we plugged the hole and all was fine.
The only problem on Poly to LA timing cover interchange is with the early 1956 to 1961 Poly blocks that use the cast iron timing cover exclusively and have a unique water pump to those years.
New Mopar Performance LA timing covers are now available through Mancini Racing and other Mopar Performance vendors for the Mopar LA and would fit on a 1962 to 1965 Mopar 318s.
September 7, 2001; Updated May 19, 2008
