I've started the pre-assembly on my 383 and I've found that the connecting rod side clearance is out of specs. Well, specs for a 350, that is. It should be between .006 to .014", but mine is about .020 on every journal. What the heck do I do now? I'm using Eagle 4340 H-beam 6" rods, and a Scat 9000 crank, if that makes any difference.

 

Wish I could give you some great news but I can't. I have been scratching my butt on this one for years and still have yet to come up with an answer. Maybe one will finally come up. If you measure your connecting rods you should find they are about 0.005" narrower than factory rods. This adds about 0.010" per pair. Hence 0.010" (nice and tight) becomes 0.020" (loose). I have discussed it with a few machine shops to only get a blank stare and sometimes a response that 0.020" is fine. I spent a few hours on the phone once to find an answer. The best I could come up with was a simple statement that the aftermarket rods need that much clearance. The only thing I could think of to support this was that typically aftermarket rods have a wider face where the rods contact each other. So perhaps when running they maintain orientation better with the wider clearances. If this is the case they might need the extra clearance to help lubricate these surfaces. At the same time I can think of several pro engine builders that limit themselves to .014" even with aftermarket rods. I also know that factory 4340 big block rods have less than 0.020" side clearance. So it isn't a matter of rod material.

So in short, live with it. All of the aftermarket rods I have measured came up narrower than factory. I haven't had any problems in SBC's with as much as 0.025" side clearance. If everything is new and assembles that way live with it. The only other thing I can think of is to see if Eagle's SIR rods have a stock width big end. If they do that will solve your problem. Personally I try to stay with stock rods to eliminate just this problem.

 

They're designed to be used with a crank that is ground
with large journal corner radius' ( radii) the same rods and bearings on a crank with narrower journal radii will spread more when you measure it with a feeler guage between the two rods.
You can try getting different rod bearings.
Personally, I wouldn't loose sleep over it.

 

I wouldn't worry about it... of all the clearances in a motor, that one is probably the least crtitical, If material has been removed from the sides of the cranl journals, there's no way to put it back, except welding up; nobody ever does that. As long as it can't move so far that the piston pin contacts the cyl wall, it will be fine.

 

but... there is a downside. Oil pressure at idle will be somewhat lower bc of the leakage.

I had a couple that were in the .020" range and even with a dynagear HV pump, my motor idles at below 20psi when hot.

 

When I assembled my current 355 I came up with .025" rod clearance on all of them.I run the matching Summit/Pro Line (same as Trick Flow) 4340 crank & rods.I maintain at least 23psi oil pressure as hot as it can get outside.Assemble it and don't worry about it..it's fine as long as the other clearances are good.I have over 6,000 miles on my motor with plenty of juice runs on it

 

Im having the same issues with my scat 6" h beams and 4340 eagle crank...guess its normal tho...curious tho this might sound stupid but the locking tangs for the bearings in the rod are supposed to face the oil pan rails and not twoards the center of the block...correct?

 

Run it and don't worry. I put 15-20 thou in everyone I have built with no issues.

 

I hope you're using chamfered berings on that aftermarket crank. Clevite 77 H series or equivalent.

 

Yup clevite H series nobody got back to me on if the lock tangs are supposed to face twoards the nearest oil pan rail (99 percent sure supposed to go that way but its slipping my mind right now) or if its supposed to be facing the crank...

 

If you've ever torn down a very used engine that fed a manual trans that had a heavy pressure plate, you'd probably have seen lots of side clearance. The thrust surface (especially on a 400 SBC) is almost inadequate for the task, so some of it gets "controlled" by the rods, unfortunately. This could be part of the reason the aftermarket rods start with a bit mre, to prevent thrust load on the rods. Just a guess, though.

 

ya i think the most i had was like 22 or 23

 

I haven't done a SBC in many years but the theory is still the same. The bearings will only go on the rods one way (lock tab). The chamfer of the bearing is towards the outside against the fillet of the crank. The surface on the side of the rods that are against each other is flat (no chamfer).

The specs I found in one of my books says.

Excessive side clearance can cause high oil consumption by allowing too much oil to be deposited onto the cylinder walls. With steel rods, .015 - .020 is prefered in a high performance engine while a street engine can generally run with much less. Measurment is between the rod pairs.

If side clearance is too small, the sides of the rods can be sanded to increase the clearance. If too wide, another set of rods is needed.

I'd say let it run the way it is. At least you've checked it and you know they're not too tight. When in doubt, contact Eagle and ask them what's allowable for their rods.

 

right so the lock tabs are facing twoards the sides instead of twoards the middle

 

The way i was taught was that the tangs face out not in towards the center. I built my 355 with this arrangement and all of my connecting rod side clearances were within tolerance. -Bob

 

THe tangs face down, away from the cam.

In fact, early small blocks had a little oil spurt hole in the cap surfaces facing the cam, to give the cyl walls and everything a littlel shot of oil as it passed over the feed passage in the crank. That's why alot of rod bearings still have the little half-moon shape missing out of the end opposite the tangs.

 

ya k what i thought