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I'm in the process of rebuilding the 5.4L engine out of my 1999 Ford F250. I'm going to replace the pistons (and rings) because the black (teflon?) coating on the piston skirts is worn off and there is some grooving on the pistons that I can feel with my fingernail. Since I am replacing the piston and rings I will at least hone the cylinders. The cylinders themselves look good, I can see the factory crosshatching. I think the measurements might be telling me a different story, but I'm having a hard time understanding the specs in the Ford factory manual. The only specs I see related to the cylinder bore are as follows, and I don't really understand what the different grades mean:

Cylinder bore diameter

  • Grade 1 90.200mm - 90.210mm (3.55118in - 3.5515748in)
  • Grade 2 90.210mm - 90.220mm (3.55118in - 3.5519685in)
  • Grade 3 90.220mm - 90.230mm (3.5519685in - 3.5523622in)

Additionally I would expect to see a taper and out of round spec, but I don't. So the question is, with the measurements I have provided do I need to bore my cylinders and get over sized pistons?

enter image description here

The spec is 3.5520 (I think), but that doesn't match what the manual says. The differences in measurements is what really matters at this point though. I highlighted all measurements that were not exactly the spec. enter image description here

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2 Answers 2

If you are having to replace the pistons anyway, get the block bored (as long as it's an iron block, which is an assumption on my part). Not only will this give you more displacement (which will equate to more torque for your truck), but will ensure you have perfectly round cylinders as well, as well as symmetrical top to bottom. It will also save you in the long run if "just honing" is not going to work.

This process needs to be done in conjunction with your machine shop. A good machine shop will be able to tell you what is best for your specific block, what costs to expect, and which way to go with parts, etc. Working with your machine shop will produce the best results. Also, when they do the honing, ensure they use a torque plate during the final honing process. This ensures the cylinders will be right when you bolt the heads back onto the block.

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I'd recommend that you bore, but I'm not sure that block CAN be bored. Some can't - the water jacket is too close. Sometimes, even, those that SAY they can actually cannot because of a casting inclusion or bubble. If boring breaks into one, the block is suddenly complete junk.

Given that it's a '99, and the entire drivetrain has been subjected to a LOT of miles of wear, and I don't have tons of faith in the electronics in any '99 vehicle lasting much longer, I'd suggest just honing instead. I don't think you can realistically expect to get another fifteen years' use out of that truck.

If it was a '79, I'd say take the chance - bore it, and if you break through into the water jacket, get another block & rebuild THAT. If it was a '69, I'd even urge you more strongly to do that. Not for a '99, though.

So... my vote is for a honing. If your measurements are actually correct (there's ALWAYS some question of that), you're still within a thousandth of an inch nearly everywhere. That's a HUGE lot less wear than a lot of motors I've had apart for reasons OTHER than full-up rebuilding, not even enough to make a good ridge. I'm betting you didn't even have to ream the tops of the cylinders to get the pistons out.

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