rod bearing clearance

I am having a hard time getting even .020 clearance on my scat 6.7 rods using extra clearance bearings (545 stroker). I am going to have the rod big ends resized. I see online most BBC rod bores are listed @ 2.325", so my question is, should I have the machine shop size them to that size or a little bigger? thanks-glen

Where are you trying to get .020 clearance?

oops, .002 clearance, not .020 ha ha.

I would say the crankshaft is probably on the high limit; do whatever you gotta do.

ok thanks, I'll get the rods measured so we know if they are "tight" or crank is "big"

glenevans wrote:ok thanks, I'll get the rods measured so we know if they are "tight" or crank is "big"

It could be some of both.

probably like you say, thanks for the help guys

How are you checking it?

green plastigage (not the most accurate), but my old bearings do show small amount of heat coloring after running it the last few years, so I am trying to open the clearance up a bit

Plastigauge is not completely accurate for the true dimension but, it is quite accurate when used for comparison sake.

Yes, that's about all I'm doing, by the way Randy, I still haven't put your cam in my EFI 460 yet, but the headers and adj. fuel pressure mods have helped the truck quite a bit.

try a set with .001 extra clearance, King CR808xpnstdx. Clevite makes em too. Also depends on if you're using coated bearings.

69BOSS wrote:try a set with .001 extra clearance, King CR808xpnstdx. Clevite makes em too. Also depends on if you're using coated bearings.

I do this a lot, works fine.

glenevans wrote:green plastigage (not the most accurate), but my old bearings do show small amount of heat coloring after running it the last few years, so I am trying to open the clearance up a bit

did you check clearance with old bearings? Just to compare where you are with the new? You could have other reasons for your bearings looking like that. Plastigage ain't very accurate on rod bearings,IMO.

I did, but like you are saying, it is really hard to do without turning crank, wiggling rod, etc., with old bearings it was less than .0015 on the plastigage, I guess I thought that was ok back in '08 when I first put it together The other problem at the time was the flat tappet cam I was running, the company that ground it said to use 20w-50 oil, then combine that with the tight bearing fit, could have been really bad

The solid ft cam could have been part of your bearing issue.I've had too much top end oiling with solid ft before causing psi drop at high rpm. That doesn't however change your bearing clearance , lol...

I am just trying to get this thing up and running for the Halloween Classic in Boise, first part of October. Then maybe take it to Las Vegas in November (not in any of the fast nitrous classes) Street car race. My car is a 1969 Mach 1, all steel/full stock interior. I bought this car in December of 1982, $2100.00 back then ha ha