07-08-2012, 10:37 PM
Join Date: Jun 2011
Location: Detroit Burbs
Total Cats: 3
Main Bearing and Ring end Gap Clearances
I'm doing a stock internal 1.8L rebuild prior to blowing some boost on it.
The block is from a '96 Miata.
The crank is from a '95 Escort GT and has been "polished" by a machine shop (they farmed it out to a crankshaft grinding specialist).
Standard size King bearings.
FSM states main bearing clearances should be 0.0007" to 0.0014" with a max spec of 0.004".
I plastigauged the mains and they are all at 0.002".
Is this too much? I know loose is good, but am I going to have any oil pressure at idle?
Did the polishing take off too much from the crank? Should I just slap it together and not worry about it?
Also - another question - this one about ring end gaps.
I have some Hastings chrome rings. I put them in the bore and pushed them down about half a piston length (loose - not attached to a piston). I used feeler gauges to measure the ring end gap. Both the top rings and the middle rings were in the 0.015" to 0.019" range.
The FSM states top ring 0.006" to 0.012", and middle ring 0.012" to 0.018".
So, it looks like the middle rings are pretty much in spec, and the top rings are really loose. But, is this just a Hastings thing? If the middle rings are close to spec, that means the bore can't be too big, and Hastings just makes the top ring gap bigger?
Maybe this is fine for boost? Do I want an even bigger gap for boost? I'm only planning on ~220-250hp.
Also, one of the Hastings rings was messed up right out of the box. It has like 0.250" ring gap, and you can see where a piece of the ring was broken off somehow. The rings were brand new still in the box, so weird.
I am going to call Hastings and see if they can send me one ring to replace it. I suppose I will ask them about the ring gaps at the same time.