Posted by: Mark Polk | 2014

71 Power Wagon – 318 Poly Engine Start-Up Woes


It has taken longer to get to this point than I expected, but that happens when you have a job and a hobby. I was finally ready to start the rebuilt 318 poly head engine in the Power Wagon. I bought the three deuce Rochester set-up on ebay and the seller said the carburetors were rebuilt and set up for a progressive linkage, but before trying to start the engine I took all three carburetors apart and cleaned them thoroughly just in case. I double checked all my wiring, double checked the timing, checked for fuel at the pump and topped the engine oil and antifreeze off.

With today’s engine oil lacking in the zinc department I decided to use Royal Purple break-in oil and I added a break-in additive from Schneider Racing Cams, where I bought my camshaft. Everything checked out okay so I hooked the battery up and attempted to start the engine for the first time. It turned over but there was no sign of it trying to start so I stopped cranking it within a few seconds. I decided to pull the number 1 spark plug and check the timing again. When I pulled the plug I noticed the electrode on the end of the plug was completety bent over, there was no gap. I just finished gapping all of the plugs for the new electronic ignition so I thought that was really odd. I decided to pull the other plugs and check them. It’s a good thing I did because almost every spark plug had the electrodes bent over. Turns out the plugs were for a LA 318 and not a poly 318 engine. If you are building a poly 318 A series engine be careful when it comes to interchanging LA series and A series parts. I have run into several situations where the parts did not work and it can be very frustrating, time consuming and costly.

Ok back to starting the engine. I replaced the plugs with the correct ones and I tried starting the engine again. This time it popped through the headers and there were some flames at the headers from the unburnt fuel. I didn’t want to crank the engine any more than I had to, so I decided to do a quick compression test on the cylinders to isolate the problem. The test revealed 3 cylinders with zero compression. I used hydraulic lifters on this build and the rockers are adjustable so you need to set the pre-load on the lifters properly or the valves won’t close all the way. I readjusted all of the intake and exhaust valves for good measure. The key to adjusting the pre-load is to make sure the valves are in the correct position when you make the adjustment and as soon as I feel tension on the push rod I stop and then tighten it an additional 1/4 turn. If you keep going until the pushrod stops turning altogether and and then tighten it an additional 1/4 to 1/2 turn the valves won’t close completely resulting in no compression in that cylinder.

Now I was ready for a third attempt, but with good compression readings in all cylinders I felt confident it would start. The engine fired as soon as I hit the key. Unfortunately after running it for about a minute I noticed a leak at the oil filter adapter plate and had to shut it down. As soon as I fix that I can run the engine through a 15 to 20 minute break-in cycle. You want to run the engine at 1500 to 2000 RPMs for about 20 minutes to ensure the lifters and the camshaft break in properly.

I’ll keep you posted on how it goes:

Read next: Mopar Charging System Wiring Headaches

See the full build HERE: 

Mark Polk
Auto Education 101

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