rod - side clearances

[p.dow]

what is the max side clearance you will accept.
i have had a builder tell me he accepts up to 50 thousandths.
i think that is excessive but do not want to tell the builder he is wrong (maybe he is right !).

i think excessive side clearance would quickly put the crank journal out of perfect round.

what exactly would be the consequences of haveing all the rods with excessive side clearances ?

thanks
paul

 

[TurboTR]

Good question. I remember being surprised way back when (~ '90 or so) at how much side clrnc my factory mill had when it was still nearly new, like < 20k miles. Asked on the list at the time and it didn't get much input. Seems as delivered from the factory it had like 2-3x the spec that was printed in the manual, like on the order of 0.040" if I recall. Guess it maybe doesn't matter that much if it exceeds the spec in reality (?)

TurboTR

 

[TurboDave]

Well, side clearances on stock rods "should" be between 8 and 10thou.
If you're going to be running the motor hard at the track, you might want to look at setting it closer to .006 (6 thou).

 

[at7we2]

I recently had to deal with this issue in the engine in my '87 GN. I had the converter restalled (loosened) and immediately afterwards I noticed a "clattering" noise under the car while idling in park.

I had everything checked out and it turned out to be excessive rod side-clearance. I don't remember what the measurements were off the top of my head, (have them written down somewhere) but it was pretty far out of spec. This is on an untouched original engine with approximately 22k miles at that time.

Apparently, with the re-stalled converter, there's not enough load on the crank to keep the rods from walking back and forth enough to "clatter". I can put the trans. in drive and the noise dissappears.

There's not many options to solve this problem. The best option is to replace the rods, but that wasn't in my budget. Another option was to have the sides of the rods knurled which effectively increases their overall thickness and decreases the side clearance. This also helps the sides of the rods hold more oil, but there's pro's and con's to that.

I ran thicker oil for a while and that took care of the noise, but I've recently switched back to 10w30 and the noise has returned. Now that I know what it is, I'm really not that worried about it. If I was going to make more serious power, I'd probably go ahead and replace the rods, but I don't believe it's a problem for my combination. It is very annoying to hear though. It's not that noticeable, but *I* know it's there!

Rob

 

[TurboTR]

Hmmm... FWIW I never noticed that noise on mine after switching to an AC 9" converter.

TurboTR

 

[750H.P.V6]

Guy's,

from what I've seen factory rod side clearance is usually outside the factory spec when tearing down a used engine. More often than not the side clearance is .015" +. With that said .050" is too much although the biggest problem you'll probably have is some extra noise. If your rod side clearance is somewhere between .010-.020" it will be fine.

Neal

 

[Intercooler]

Good luck trying to get .006 because they never started that good. Also no way to tighten it up. .020" is fine!

 

[at7we2]

just to clarify...

just to clarify...

when I said my engine started "clattering" after loosening up the converter, I didn't mean to imply this was typical for all engines.
I believe it might be typical on an engine with very excessive rod side clearance like mine.

 

[REDS HOT AIR]

stock is typically 15-17 tho ..I prefer tighter just cant get it on stock stuff

at 20 usually the piston cocks in the bore enough to drag the top of the piston on the wall at 30 tho the piston can try to wedge itself in the bore.. the more the piston cocks over the more oval the cylinder becomes to the rings trying to seal also

the more the side clearence the more the bearing cocks on the journal also causing the bearing to prematurly wear on the sides

if it were not an offcenter motor it would not cause these problems

 

[Lee Thompson]

Bingo

Red you are one smart Mother. That explains why my sons pistons and some of the rod bearings looked as you explained. I knew the rods had too much side clearance but was not smart enough to put 2 and 2 together. BTW, a stock rod is .844 in width at the bearing end.

 

[p.dow]

side clearances

thanks for the input.
i am thinking that the clearance measurement is for both sides of the rod as measured to the crank surface...
so with a excessive clearance on each side the rod is quite free to walk on the crank rod journal.

so clearance of 25 thousanths would mean there is a distance 50 thousanths for the rod to move on its journal.

(i am assumeing side clearance is a measure of each side and not the total of both sides !)

i have a hunch that my crank or my rods may have been machined to much. which has caused the excess clearance !
i could be wrong of course. but there is no question ... the rods are sloppy sideways on the journal.

paul

 

[Blown&Injected]

With a new Eagle Crank and stock rods measuring around .841 to .844, my side clearance is about .017.

I have not heard about measuring for both sides. The Book says measure on one side, just push the rod to the far edge and measure what's left.

 

[TurboDave]

Re: side clearances

Originally posted by p.dow
thanks for the input.
i am thinking that the clearance measurement is for both sides of the rod as measured to the crank surface...
so with a excessive clearance on each side the rod is quite free to walk on the crank rod journal.

so clearance of 25 thousanths would mean there is a distance 50 thousanths for the rod to move on its journal.

(i am assumeing side clearance is a measure of each side and not the total of both sides !)

i have a hunch that my crank or my rods may have been machined to much. which has caused the excess clearance !
i could be wrong of course. but there is no question ... the rods are sloppy sideways on the journal.

paul

No, not both sides. Just slide the rod to one side or the other and measure.

 

[p.dow]

measureing it...

ok
measure only one side.
thanks

 

[Ormand]

Push the rod to one side, measure. Then push to the other side, and measure. Add the two measurements, then divide by two. Just joking!!
If you find a way to tighten this up, please share! Some builders don't mind it being "loose", but as Red explained, there are problems from having it too sloppy, in addition to the oil control problem.

 

[Steve V]

Red that's an AWESOME description!!! I wish there was a way too tighten it up,other than an new eagle crank!

 

[REDS HOT AIR]

Re: Bingo

Originally posted by Lee Thompson
Red you are one smart Mother.

lol I been called a smart azz before but never a mother

well Lee I guess thats a down payment on payback from all the things I learned from you over time

anyone have a shortblock handy run a piston up to tdc and measure piston to deck on either side of the piston in line with the wristpin with the rod pushed to one side then again with it toward the other side and you'll quickly see how much effect that little bit of rod side movement makes at the piston

I havent found a stock crank and rod assembly yet that stands the piston strait up

most of the time you dont even need to measure you can see it by eye if you lay a strait edge across the block

 

[ijames]

If you find a way to tighten this up, please share! Some builders don't mind it being "loose", but as Red explained, there are problems from having it too sloppy, in addition to the oil control problem.

Someone else mentioned knurling the sides of the rod but that would scare me - it seems like a forest of stress raisers just begging to become cracks. An engine builder friend told me that he uses pipe solder (this was a few years ago so I'm assuming 50/50 lead tin) to build up one side of the rod so it's a little too high, and then surfaces it back down to the width he wants. The pipe solder is about as hard as the rod bearing material so any wear is going to be in the solder and not the crank, it's apparently a decent bearing material in terms of sliding/galling/self lubrication, etc., and the side loads are pretty small anyway, so he says he has never seen any signs of the solder "squishing out of shape" on subsequent teardowns, as he put it . Besides, the final film thickness is only going to be 0.010" or so on most rods. The melting point is low enough that you shouldn't affect any heat treatment, and he didn't mention any problems with flux so I assume the standard zinc chloride stuff works okay. I don't know how the new lead-free stuff compares, so if I had to do this I'd try real hard to scrounge up some lead/tin.

 

[at7we2]

ijames -

I had mentioned "knurling" the sides of the rods. and I would agree, this seems like it would produce stress risers. I read up on the proceedure in an old engine building manual I've got. After I read your post I got to thinking about it, and the manual pertained to stock type rebuilds and not performance build-ups. The stress risers would probably be more of an issue on a little v6 producing way more than 1hp/cu. in.

I had forgotten about the pipe solder method, I've heard about that somewhere also. Seems like a reasonable solution.

How much is a set of stock type rods these days? I haven't had to buy a set of Buick rods (yet)