Yeah, it's like that, it can be felt without looking for it.

Piston 3 is doing the same thing as piston 4, however, it reaches full TDC unlike piston 4, but when you start turning the flywheel, piston 2 starts to drop, but 3 stays up, and then you can push it down by hand as well. Just like 4 when 1 starts to drop.
The techs here think that the score could be a result of something being loose in the bottom. They also think a quick dingleberry hone could take care of it.
However, technically, I could strip the blocks down to nothing but crank, pistons, and rods, take the bent rod out of my '95 block, swap in one of the piston/rods from the MSM block since they are the same, and then swap everything else over from the MSM block to my '95 block (the coolant/oil ports on the MSM block actually exist on my '95 block as well, I use the oil port now, the coolant port has a plug in it). Replace the piston rings and rod bearings on all 4, and be done with it for now. Then I'll have a block with a score in one of the cylinders, but that doesn't matter because when it gets built, it will be overbored anyway.
The only thing that concerns me is that Rosenthal lists 2 different oil pan end seals for 94-00 and 01-05, meaning that the pans might be different and the MSM pan may not fit my '95 block. I need to confirm compatibility before I even really consider swapping anything over to my '95 block.
Ben, if you don't mind, I want to take the pan off the MSM block on Monday (it'll have to be after work on Monday), and see what's causing the issue. If it's something as simple as something being loose or the bearings, I'll let one of our machinists look at the cylinder wall and see if I can get away with a quick hone. If so, I'll keep and run the MSM block, because I need to get this car back up and running asap. And then I'll have my '95 block to build up on an easier time schedule and when I have the money to do so. And we don't have to invest any more time hauling blocks around. :)

On the MSM motor:

I had my 99 block doing the same with piston not reaching top and waiting a bit before starting to come down when rod bearing was completely gone. Rock the crank back and forth when all pistons are halfway and you should see good pistons move with smallest crank movement and worn ones stay stationary. You might even hear a click.

Quicktime video and photos from my motor can be seen here:
http://russmarshall.com/v/cars/cmc7/power/99+engine/

hrk

The 01 style pan does swap into the earlier BPs. I sell the swap kits on a some what regular basis. They end up in the $300+ range with the pan, plate, gaskets, and hardware.

You'll need a B541-10-427 and B541-10-428, and of course the gray silicone stuff for the sides.

The old one is a known quantity, vs. the new one with its scratch and the TDC issue. If you absolutely have to have it done right now, is it really going to take that much more time to swap parts over to the old block and get it back together?

No. Which is what I was getting at in the first place.

Thanks for the info Ben. So it's only the end seals that are different?

No, the pan itself is some what different, as it accommodates the MBSP. But it does retrofit to older BP blocks.

You may find this thread of some interest
http://forum.miata.net/vb/showthread.php?t=291637
(Rich got his set up from me)

Maybe the low #4 piston was mazda's way to protect that cylinder from detonation ;) A little less squeeze means a little less bang.

Just to update on the MSM block, the rod caps on 3 and 4 were loose, apparently from the factory. 4 was to the point that the rod bearings are mush in the oil pan, the rod, cap, and crank are scored beyond repair, and the whole area around the crank and bottom of the rod is scorched black. So no go with that block. Going to exchange for another one.

I remember reading that along with the rods, the piston rings are a weak point inside the Miata engine. At this point in my rebuild, I'm sticking with the OEM rods and pistons for now (just to have my car running again) and will be working on a forge build later when time and money permits. But I figure that having better rings would be a good idea. That being the case, where is a good place to source a set of "superior than OEM" rings?

I just bought a set of Federal Mogul Sealed Power rings for my engine. They are chrome rings and about $50 cheaper than the Mazdaspeed member price on OEMs. I got them from O'Reilly's for $98.99. You can also get them from Summit Racing for about the same price.

I dont see much point in building an engine and not putting stronger rods in it, considering the price of them now. Even my N/A enigine has ETD's. Just hate to see you have the same problem twice, and its cheaper to build an engine 1 time.

If I had the money and time right now to do that, I would immediately. But I'm trying to do what I can with the tools available to me here at the shop, which is basically a rebuild with the OEM parts. Plus I'm about to start a new job and lose my current form of transportation, so I need the car running ASAP. Waiting on parts to get here, trying to find a good machine shop, and waiting for them to do the work I need won't work with my time schedule. That's why the spare block that will come out of all of this will be the one that gets built up into a monster.

OK, well I will be starting my new job before the car even has a chance to get back on the road, so thanks to a kind forum member here, I have a set of CAT rods on the way to me. Going to aim for a mild build here: forged rods, OEM pistons, better rings, new OEM main and rod bearings, and ACT head and main studs.

I was going to reuse my stock pisons, but the piston on the bent rod has a small chip missing out of it, right where it curves down into the skirt. I didn't find the piece, so no telling how long it's been like that, and I haven't pulled the other ones yet. After some research, I found that my '95 actually has an 8.8:1 CR. So now it's off to find some similar or 9.0:1 pistons. Keith @ FM was incorrect about the MSM CR, it's actually 9.5:1, otherwise, I'd use those since I already have access to them.

Ben, thanks for trying to call dibs on those free pistons and rods for me, that would have worked out well for me for the pistons.

And in case anyone is wondering about CRs (for those that don't already know), this is only what the research I have done has clarified (for late NAs anyway):
94-95: 8.8:1
96-97: 9.0:1

Also, I know that the CAT rods will have to be machined to accept the wrist pins, but does anything have to be done to prep them for use with the OEM rod bearings? I'm new to the forged stuff. :)
(I did read on here somewhere that a member took a brillo pad on the end of a pen and ran it through and got the wrist pins in and to move freely, is that even adviseable?)

Just like the "A" -Team...."I love it when a plan comes together."
Good luck man... ;)

you want to have a macine shop to hone the small end. Doing it "with a pen" is asking for alot of trouble. Have a machine shop machine all the clearances and then assemble.

Yeah, that's what Ben just finished telling me. I'm a forged noob. :)
And I'm just going to use the 9.5:1 pistons from the MSM block. As Ben explained to me, faster spool and better efficiency should be a result. Just have to ensure that it is well tuned.