One more time, rod side clearance

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peejay
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Re: One more time, rod side clearance

Post by peejay » Sat Apr 07, 2018 1:47 pm

The idea that more side clearance means more oil flows out of the bearings is akin to the idea that putting a 4" exhaust tip on a 2" exhaust system will make it flow more.

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Re: One more time, rod side clearance

Post by pamotorman » Sat Apr 07, 2018 1:54 pm

back in the 70s i freshened a BBC NASCAR engine out of jr Johnson's shop and it had close to .050 rod side clearance. i was concerned so i called my contact at GM racing and he told me don't worry as they all are built like that.

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Re: One more time, rod side clearance

Post by MadBill » Sat Apr 07, 2018 2:01 pm

peejay wrote:
Sat Apr 07, 2018 1:47 pm
The idea that more side clearance means more oil flows out of the bearings is akin to the idea that putting a 4" exhaust tip on a 2" exhaust system will make it flow more.
Well darn; are you saying a fart can doesn't add any power? #-o
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Re: One more time, rod side clearance

Post by Tom Walker » Sat Apr 07, 2018 3:18 pm

I believe Madbills' comment about the effects of rod bearing clearance explains a lot, and if that is taken into consideration, would explain many of the variables and experiences discussed here.

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Re: One more time, rod side clearance

Post by ptuomov » Sat Apr 07, 2018 3:38 pm

Does the oil flow and pressure between the rod big ends and the crankshaft play some role in locating the rods more precisely under the bores?
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Re: One more time, rod side clearance

Post by pamotorman » Sat Apr 07, 2018 3:41 pm

why do builders worry about the side clearance on the rods and oil loss but don't worry about the side clearance on the mains except for the thrust bearing. i would guess this shows that the radial clearance is more important than side clearance as far as oil loss goes. JMHO

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Re: One more time, rod side clearance

Post by groberts101 » Sat Apr 07, 2018 6:18 pm

MadBill wrote:
Fri Apr 06, 2018 8:34 pm
One situation in which more side clearance could result in more oil outflow would be if the radial clearances were large, such that the tight side clearances were effectively doing the metering... :-k
You mean in a scenario when things weren't perfectly toleranced in the first place? Or maybe even when things started to wear out and went WELL beyond acceptable tolerances? Hmmm.. who knew?

Guess it deosn't really matter anyways.. Warp convinced me with all that scientific data and he put forth to help others around here.. as he's well known for because he's always so giving of his constructive criticisms.. learn the real truth about side clearances not making an iota of difference to where the oil flow actually ends up. Don't have a scraper, baffle, vac pump, rod guides or anything fancy with my 5/64-5/64-3/16"" ring package but I think it will be really fast now that I'm running 7lb oil rings with .250 thou rod side clearances. :roll:

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Re: One more time, rod side clearance

Post by digger » Sat Apr 07, 2018 6:34 pm

groberts101 wrote:
Sat Apr 07, 2018 1:20 pm
I never once said it changes the total volume of leaked oil.. only WHERE that same volume of oil is being directed. Big difference there.
i don't see how the clearance changes this. if the rods bunch up to one side on a non piston guided setup its going to be directed to pretty much the same spot regardless of clearance . the clearance would change the speed which it is ejected if the volumetric rate is the same (more clearance less ejection speed)

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Re: One more time, rod side clearance

Post by groberts101 » Sat Apr 07, 2018 7:06 pm

digger wrote:
Sat Apr 07, 2018 6:34 pm
groberts101 wrote:
Sat Apr 07, 2018 1:20 pm
I never once said it changes the total volume of leaked oil.. only WHERE that same volume of oil is being directed. Big difference there.
i don't see how the clearance changes this. if the rods bunch up to one side on a non piston guided setup its going to be directed to pretty much the same spot regardless of clearance . the clearance would change the speed which it is ejected if the volumetric rate is the same (more clearance less ejection speed)
Redirected flow of same or similar volume. Do we prefer to have the oil sharing all the gap space equally?.. to hopefully allow more consistent flow patterns amongst the cylinders directly above? Windage mass and crankcase flow direction variables already push oil volumes around as it is and all I'm trying to get across is this can add to those variables by REDIRECTING EXISTING FLOW VOLUME TO SLIGHTLY DIFFERENT LOCATIONS. Can't be good to aim more volume towards one side of any particular cylinder.. can it? Or the oil and compression rings just don't care?


Or it doesn't matter if the rods pair up together to change where their partially shared volume of escaping oil might end up?

Obviously pressure differentials via oil hole locations has an impact here too and I'm not trying to imply that combined oil flow of bunched up rods will pass through both bearings simultaneously to push ALL their shared volume towards one side only. Just that it tends to want to take the path of least resistance. Push them both to one side of their shared journal as compared to the other and the volume of escaping oil can be redirected towards the path of least resistance.

I'm beat up and tired from auto repair(cop, plugs, injector replacement on Ford v10) and this phone doesn't like my big beat up sausage fingers one little bit. Seem to spend more time correcting my replies than the actual time it takes to rattle it off.

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Re: One more time, rod side clearance

Post by Warp Speed » Sat Apr 07, 2018 7:20 pm

groberts101 wrote:
Sat Apr 07, 2018 6:18 pm
MadBill wrote:
Fri Apr 06, 2018 8:34 pm
One situation in which more side clearance could result in more oil outflow would be if the radial clearances were large, such that the tight side clearances were effectively doing the metering... :-k
You mean in a scenario when things weren't perfectly toleranced in the first place? Or maybe even when things started to wear out and went WELL beyond acceptable tolerances? Hmmm.. who knew?

Guess it deosn't really matter anyways.. Warp convinced me with all that scientific data and he put forth to help others around here.. as he's well known for because he's always so giving of his constructive criticisms.. learn the real truth about side clearances not making an iota of difference to where the oil flow actually ends up. Don't have a scraper, baffle, vac pump, rod guides or anything fancy with my 5/64-5/64-3/16"" ring package but I think it will be really fast now that I'm running 7lb oil rings with .250 thou rod side clearances. :roll:
Now your just trying to adjust the scenario to fit your theory!
What data do you have to refute my (and many others that have actually tested this back to back) findings on this subject?
Not trying to be a dick, but I treat how I get treated......

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Re: One more time, rod side clearance

Post by GARY C » Sat Apr 07, 2018 7:59 pm

What do you guys consider to be a good min side clearance? I was taught the side clearance was needed to keep the rods from growing and butting up to the crank flange? I don't see how side clearance could effect oil usage considering the small clearance restricting oil flow from the bearing surface it's self.

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Re: One more time, rod side clearance

Post by groberts101 » Sat Apr 07, 2018 8:41 pm

Warp Speed wrote:
Sat Apr 07, 2018 7:20 pm
groberts101 wrote:
Sat Apr 07, 2018 6:18 pm
MadBill wrote:
Fri Apr 06, 2018 8:34 pm
One situation in which more side clearance could result in more oil outflow would be if the radial clearances were large, such that the tight side clearances were effectively doing the metering... :-k
You mean in a scenario when things weren't perfectly toleranced in the first place? Or maybe even when things started to wear out and went WELL beyond acceptable tolerances? Hmmm.. who knew?

Guess it deosn't really matter anyways.. Warp convinced me with all that scientific data and he put forth to help others around here.. as he's well known for because he's always so giving of his constructive criticisms.. learn the real truth about side clearances not making an iota of difference to where the oil flow actually ends up. Don't have a scraper, baffle, vac pump, rod guides or anything fancy with my 5/64-5/64-3/16"" ring package but I think it will be really fast now that I'm running 7lb oil rings with .250 thou rod side clearances. :roll:
Now your just trying to adjust the scenario to fit your theory!
What data do you have to refute my (and many others that have actually tested this back to back) findings on this subject?
Not trying to be a dick, but I treat how I get treated......
So, now you see how it feels when the shoe's forced onto the other foot! I mention junk 327 claimer motors and you go full nsscar on me. Lol.

Truth be told you obviously know far more than I probably ever will about some, probably even most, things engine related and I should show more respect. But nobody knows everything and as you said.. sometimes the vibe gets reciprocated in like manner. Plus.. some of the cocky smartassery gets lost in translation and unfortunately I also suffer from minor turrets when face to face too. Not always a personal thing.. just a general piss poor sttitude mixed with witty remarks, is all. My apologies.. been a very long day for my old back. :wink:

All my theories are based on the data I've acquired from near a lifetime of family(gearhead uncles), friends, racers, various engine builders in several states of moving around through the years and first hand experiences. Granted it's nothing like yours or some others posting here, but I'm surely cynical and pessimistic enough to rule out false positives and placebo affects. Just keep the glass more towards full until I have enough reason to empty it and allow something new to be added.

So I have a question related to another comment you made elsewhere around here. Do you guys now run wide rod side gaps without some form of guides to keep them away from one another? How does that work?

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Re: One more time, rod side clearance

Post by Warp Speed » Sat Apr 07, 2018 10:00 pm

groberts101 wrote:
Sat Apr 07, 2018 8:41 pm


I have a question related to another comment you made elsewhere around here. Do you guys now run wide rod side gaps without some form of guides to keep them away from one another? How does that work?
The rods are guided side to side by the piston in the bore. The rod small end has tight side clearance to the piston pin bosses. Typically .004-.006.

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Re: One more time, rod side clearance

Post by Dutchman » Sat Apr 07, 2018 10:14 pm

I could be stepping out on a ledge here,but all the mentions of excessive side clearance causing ring issues,oil control.nothig really said about big end issues.
We all know what happens when it's too tight,so with that said I see it as if too little side clearance will not allow the oil to flow out,overheating it. wider side clearance ensures a steady flow of oil.
Ring issues are just that ring issues. Better honing procedures and better ring types will do what's needed if a problem arises.

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Re: One more time, rod side clearance

Post by Newold1 » Sun Apr 08, 2018 8:05 am

I am not trying to debunk anyone here's knowledge or beliefs about rod side clearance numbers in standard crankshaft guided rods versus piston guided rods. I would however put forward these thoughts and discussion.

In any engine such as the american V-8's we are generally discussing here in this thread the oil system in the engine is operating at a certain pressure and certain installed clearances. The oil is being pushed to the crankshaft and finally to the bearing interface between the rod bearing and the rod journal. Once that oil volume at that pressure and volume is there it protects the bearing and journal surface with a wedge of oil. That wedge should be a constant for good bearing protection and that volume of oil at pressure is pretty much dead headed at that journal and the only real way it has to exit back to the sump and get filtered and cooled is to flow out the sides of the rod bearings. My question of this fact is that if the clearances between rod side flanks is let's say .050" to .200" versus .020" to .025" shouldn't it be easier for the expelled oil to exit from the bearing and rod side surface under pressure easier? This portion of oil pumped to the bearing has to go somewhere correct? It has nowhere else to go since it's the end of the line for that oil volume and if the resistance from flowing out of the big end of the rod is less from greater clearance then it seems by reasonable to presume that more oil by volume can exit there and the spinning crankshaft rod throw and rods are going to sling that oil off as they rotate. If this physical description is wrong and that does not happen as shared here by an obvious Nascar engine expert as they witnessed in their testing then my understanding of oil movement to crankshafts and rods is flawed and there must be an more accurate description of this oil volume at pressure travel to show how this greatly increased oil exit clearance does not result in any increased volume of oil exiting at that location?

I think it would be a real eye opener for someone to show with a observation port window on an oil pan on a running performance engine with those bearing clearances and wide versus standard rod side clearances to actually show if there is any change in the oil volume exiting the rod/bearing interfaces on rod journals. If for example Nascar uses and proved this condition then I would have to assume they did some sort of testing like this and they most likely would or should have used some observation like this and most likely used high speed camera recording to evaluate this finding of no increased oil on cylinder walls and at ring oil control interfaces?

Just some thought and questions for furthur conversations. :?:

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