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While turning the distributor during diagnosis process your customer noticed the other four cylinders would start running and theoriginal four go dead. Now, since it is a big block I truly understooda phrase that my brother always used: "There is no substitute for cubicinches," because it did actually run on either of the four cylindersets.

In your mind you’re thinking "Great, I’m dealing with another guy whois certainly not the sharpest tool in the work shed," but in theinterest of customer service you entertain the bizarre possibility thatthere is something wrong with the engine and not the ignition system.Finally after what seemed like enough time to grow a beard on the phonewith the customer you agree to take the engine back into your facilityand provide the customer with another one, certainly expecting him tohave the same problem as the original.

A few days and hundreds of tasks later your customer calls and says thenew engine runs great. You wonder how that can be possible and realizethat it is time to get the returned engine on the bench and pull outthe CSI tools and find out what happened. Heads are perfect, cylindersgood, pistons and rings fine, all the bearings look great, the timing gear’s in time – there is absolutelynothing wrong! You see the camshaft lying on the bench and know there’snothing wrong there…or is there? You pull out another new camshaft andlay it next to the one you just removed and scratch your head, becausethe two are very different. First thought, this is simple. Somehow areverse rotation marine camshaft was incorrectly packaged, right?Wrong! Finally you just walk away and right it off to a bizarreanomaly. Then weeks later you read a short blurb about how the firingorder on 8.1L big block engines is different than a normal big block.The 8.1L FO is 1-8-7-2-6-5-4-3 where a 454/7.4L is 1-8-4-3-6-5-7-2 asseen in Figure 1.

Despite the differences, however, an 8.1L camshaft will drop right intoa 454 like it belongs there – but it will only run four cylinders.

So guess who had the elevator that didn’t get to the top floor? Itwasn’t the guy who called up saying that his engine only ran on fourcylinders, that’s for certain. If you’re in the engine business longenough you’ll have those days when you feel like one of those suckersthat you used to get after a shot at the doctor’s office – I think theywere called Dum-Dums.Figure 1 The camshaft on the left (with the red arrow) is for an 8.1L GM. Make note of the lobe differences in comparison to that of a 454/7.4L on the right.

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Roy Berndt
Roy Berndt has decades of machine shop experience. He is the Program Manager for PROFormance Powertrain Products, a PER in Springfield, MO. You can reach Roy at [email protected]