Engine build - Miata content

I'm re-building an engine for the autocrosser. I got the rotating assembly together this weekend and it feels awefully tight. With just the crank in and the main caps torqued, everything spun freely. After torquing the rods down, not so much. I did some testing w/ the torque wrench and it's b/w 20-24 lb/ft of torque to spin the bottom end (the head's not on the block yet). My machinist inspected the rods / crank and said that the oil clearances are correct to use with the standard Mazda bearings (which is what are on there). The only thing I can think of is that I went to the 1st factory overbore while I was there, so I've got new pistons / rings on new bores and that's what's causing that resistance. This is my 1st engine, so I'm just trying to make sure I'm doing it right. Is that what sort of resistance I should be looking at? Or does that seem high? really, I'm just trying to figure out if the resistance is just from the new rings / bores, or from the bearings being too tight.

Hmmm. 20-24 does seem pretty tight for a 4 banger. See if you can slide the rod side to side on the crank journals by hand. They should move freely. If not, I'd start by being REAL certain the rod caps are on the correct rods and that one is not reversed. All it takes is one flipped around wrong and to be about .003 off to make it tight, since the average rod clearance is about that.

If the rods move freely, then the bind has to be somewhere in the piston/cylinder area. I saw a rail from a 3 piece oil ring get crossed over the expander but still go into the bore, it was only about the last 1" or so. That one was pretty tight when turning, enough that I got real concerned. I narrowed it down by removing one cap at a time until the motor freed up. It didn't hurt the cylinder bore, thankfully. Got another oil ring and it worked great.

Thanks, I'll try those tonight when I get home. I remember all the caps being correct (my machinist was nice enough to actually use numbered punches and number each cap (ie, you get the marks lined up on one side, and a number (1 through 4) on both parts of the rod (on the rod and on the rod cap). I'll make sure though.

Any other thoughts? Or does that pretty much cover the possibilities? I've got 3 hours before I head home from work :p

So the #1 cap was on backerds. We (my co-driver and I as a collective) are retarded. Good catch facepalm

It might be worth your while to check most, if not all, of your bearing clearances with plastigauge. That'll answer any questions about clearances.

NEVER trust that the machine shop did not screw up. If they assemble an engine and it blows up, they fix it. If they do all the work and screw up but you assembled, you eat it.

That said, an engine rebuilder MEASURES everything when it comes time to assemble.He does this because he knows he will have to eat his (or his machinist's) mistakes.If you are going to make a habit of this, go buy a set of micrometers. $500 will do for what you need.

Grassroots, use plastigage. This will cost about $10 and give you an indication of bearing clearances. Drag while turning with a lever is not a spec you are going to find in any book.

While you are at it, you are also going to need a dial indicator, degree wheel and some way to measure compressed spring load/height. I only toss these last in because you mention you are building a race engine.