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1985 720 2.4 into 620... maybe? Is there a "f.a.q." link or something?


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Alrighty then.


     All I know about the 720 1980's motors is:

-they have too many sparkplugs 😄

-an L-series head fits (I think?)

-there's more cubes than any L-series


I scored on a 620 (thanks FishyLemons!), but it is w/o motor-vation.

Finding an L20B is like .... getting IMPOSSIBLE now... so I gotta see what I can stick in this thing cheap.


Motormounts are different, or the engine leans or something, and the transmission needs to be gotten with the engine?

Or no?


(Do we have a "what fits what for what years" "cheat list" anywhere? I feel like that could be a holy-grail,)

'preciate the help!

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The L series engine leans 120 to the right side, the Z series about 80 left of vertical so you will need Z series engine brackets. The metal brackets that connect the block to the rubber isolator mount on the frame. The 620 frame rubber isolators might work. 


The Z24 is basically 400cc larger L20B sharing main and rod bearings oil pan gaskets, timing cover gaskets, oil pumps, cylinder spacing, head bolt patterns, flywheels. The Z24 block is 3/4" taller than the L20B.


Because of the engine tilt the transmissions have mounting bolt patterns that match this tilt. Even though the L20B and the Z24 have the same bolt pattern, an L transmission bolted to a Z engine will fight to be almost 200 to the right and the shifter will be in the driver's hip. Never seen it done but if the transmission cross member were modified and shifter bent right, I see no reason why it wouldn't run and last tilted over to the drive's side. If you have the Z series transmission, it's just better to swap it in with the engine.


You'll need to mount the dual coils on the driver's inner fender and, I assume, this is a points (pre '78) truck? Find the switched power wire from the ignition to  the ballast resistor and connect to both coil positive terminals and the lead to the distributor. Trust me you want to run dual coils. (I wish the L series could have them)


I think I used the Z series down pipe and grafted it to my exhaust system. Easier this way.


You could use the L radiator by finding two hose elbows. I had a Z22 rad with the inlet on the right but it's wider and not a good fit at all between the headlights. Absolutely forget the Z24 rad.


The Z24 alternator is internally regulated as was the '78 and up 620. I'm again assuming this is a points truck so the wiring harness should be converted. It's easy enough and more on that later. The 720 alternator is much larger diameter and will be tight against the idler arm grease nipple right below it. I had an SAS so not a problem. The larger 50/60 amp 720 or car alternator can fit. It's just a pain. 


The water temperature sender is on the intake under the top rad hose. So join that one to the 620 wire.


Oil pressure switch is in the same place.


Heater hoses are self explanatory.


You'll need the 720 throttle cable. The two mounting screws are horizontal to the 620's vertical or at any rate you can't use the holes. I just used self tapping screws. The choke heater and idle cut solenoid wires on the 620 will need extending to reach the new carb location... or pick the engine harness apart on the passenger side fender and find these two wires and connect to the carb directly.


The speedometer pinion will be matched to what ever differential is in the 720. Probably a 3.70 or 3.889. There were a few changes in the '80 and up transmissions so the 620 pinion won't work as it is. You may be able to cut a new key way in it with an angle grinder 1800 around and install it upside down. More on that later.


The 620 speedometer cable will fit the 720 transmission.



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I'll add that the Z motor is cross-flow vs the L motor intake & exhaust are both on Left side. Like Mike said, use the Z mounts for engine & trans to position the motor correctly. Neither radiator will be useful, the 620 rad doesn't have the inlet & outlet in the right places, and the 720 rad is too wide for the space. IF your 620 rad is actually in good shape, a local rad shop could relocate the top neck, probably not worth the cost. I'm using the rad for a VW (see my build here 620KC onto 720 frame - Page 2 - 620 - Ratsun Forums ) which fits the space and has the outlets in the right places.

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The outlet (bottom hose is lower right so alright) I had a three core 620 rad. There's more than enough room on the stock one but I don't know if this might be a Camper or HD option, or the radiator was done up at a shop. Looked stock.

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