Peanu_Keeyes
Peanu_Keeyes GRM+ Memberand New Reader
2/25/24 11:28 p.m.

Rookie here. This is my first engine rebuild and so far things have been going ok, just taking my time and doing as much research as I can. Yes. It's a Miata  :) -- NA 1.8. 
 

This is a mostly dedicated track car, with sights set on a Spec Miata build sometime next year. The engine has been honed, line bored, decked and cleaned. I've got ACL race bearing installed, and I reused the pistons after having them cleaned up and checked. The cylinder honing barely made a difference in the bore and they measured out as standard. Ordered Mazda oem rings and checked the gap. Top rings measured between .008 and .010 while the second rings were similar, .010 to .012

I staggered the oil rings at 11 o'clock, 1 o'clock and 10 and 3 for top and second ring. Ring compressor was used and a tiny bit of engine oil on the cylinders. The engine turns but it requires that I apply a good deal of force on the crank from the bottom. I can't turn it by hand from just the crank bolt. Is this normal? -- also, there is a trail of oil being let through on cylinder 4. Again, Is this normal or should I remove the piston? Thanks everyone

porschenut
porschenut Dork
2/26/24 9:18 a.m.

not sure about the oil trail but yes the fit is tight and in my experience it can be tough to rotate.

Peanu_Keeyes
Peanu_Keeyes GRM+ Memberand New Reader
2/26/24 10:51 p.m.

Ok, thank you! I reached out to my machine shop and they verified that this is all normal. Starts off easy to turn while in the float stage, gets harder near the center of travel and will allow oil to pass through the ring gaps. New engines don't do well on a leak down test until after bedding in the rings and breaking in the engine. 

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
2/27/24 8:02 a.m.

One thing to bear in mind that with a rough hone the ring gaps will open up .003" or so because of how much the cylinder walls abrade the rings until they smooth out.  Starting tighter is a good idea.

 

IMO this is why direct fit rings seem to have such a wide gap when new, they assume that you won't be honing the bore.

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