Can the cams be interchanged?
Poly 318 vs. LA 318
- Thread starter Oldmanmopar
- Start date
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xLURKxDOGx
"An angel fat, at satan's feast"
LA and poly cams will physically fit in either block, but the cam for one won't properly operate the valves for the other. For one thing, poly intake and exhaust ports are evenly spaced; LA center center ports are adjacent, so put the cam in the wrong motor and some of the intake lobes would be operating on exhaust valves and vice versa. Also, the valve angles are different from one motor to the other, so put the wrong cam in and even the lobes working the right valve wouldn't do so at the right time.
Timing chains and distributors, however, do interchange between poly and LA. As do rods and post-61 cranks. In fact, the first 273 LA motors used the 318 poly crank, rods, timing cover, timing chain, damper, fan and crank pulleys and alternator bracket. (Early 273 alternator brackets had two sets of mounting holes; one set for the 273, the other for the 318 poly. Same bracket for both motors.)
Timing chains and distributors, however, do interchange between poly and LA. As do rods and post-61 cranks. In fact, the first 273 LA motors used the 318 poly crank, rods, timing cover, timing chain, damper, fan and crank pulleys and alternator bracket. (Early 273 alternator brackets had two sets of mounting holes; one set for the 273, the other for the 318 poly. Same bracket for both motors.)
@Bighead440 has cleared this up once. Maybe he'll chime in again. But no they cannot be interchanged.
PRH
Well-Known Member
About 10-12 years ago I needed a cam for a customers poly 318.
Got one from Sealed Power.
As soon as I took it out of the box, I knew it wasn’t correct.
LA motors have the 2nd and 3rd lobes from the rear sitting basically parallel with each other.
Poly motors are not that way.
The part number on the box matched what was stamped on the box, which was listed in the catalog......... so it wasnt boxed wrong.
I called down to the warehouse where I got it, just so happened he was sort of a Mopar guy......, so I explained the situation.
He grabbed an LA cam off the shelf, I told him about the two lobes being lined up....... he saw how that was....... then I told him the Poly cam isn’t like that.
I needed him to understand what the problem was, so he could have someone at the Sealed Power warehouse do the same thing.
As you could imagine....... it’s not a very popular item, and Sealed Power only had a couple more in inventory........ which were also ground on LA cores.
Would have made for a nice little solid cam for a mild LA build.
There were no correct Poly cores to be had at the time, so I ended up getting a reground stock cam from Delta cams in Washington state.
Since that time, I know at least one cam grinder that had new cores available...... Cam Craft.
Got one from Sealed Power.
As soon as I took it out of the box, I knew it wasn’t correct.
LA motors have the 2nd and 3rd lobes from the rear sitting basically parallel with each other.
Poly motors are not that way.
The part number on the box matched what was stamped on the box, which was listed in the catalog......... so it wasnt boxed wrong.
I called down to the warehouse where I got it, just so happened he was sort of a Mopar guy......, so I explained the situation.
He grabbed an LA cam off the shelf, I told him about the two lobes being lined up....... he saw how that was....... then I told him the Poly cam isn’t like that.
I needed him to understand what the problem was, so he could have someone at the Sealed Power warehouse do the same thing.
As you could imagine....... it’s not a very popular item, and Sealed Power only had a couple more in inventory........ which were also ground on LA cores.
Would have made for a nice little solid cam for a mild LA build.
There were no correct Poly cores to be had at the time, so I ended up getting a reground stock cam from Delta cams in Washington state.
Since that time, I know at least one cam grinder that had new cores available...... Cam Craft.
Think about the cylinder layout is with the Poly's The intake runners and exhaust ports are evenly spaced where the LA has Siamese center ports. Nope. Won't work.
Thanks . I had a friend that asked and I told him I would find out.
Krooser
Building Chinese Free Engines since 1959...
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