Connecting rod big end sizing issue

[CRE2004]

Its not the amount of power. Its the kinetic energies exerted on the rod in proportion to the strength of the metal and the rods design. If you have a really strong rod and have .0025 at the parting line at 8000rpm your probably just fine. Now cut the rods weight by 40% and turn it 9500rpm and see how much more clearance you need. Now, cut the rods weight by 70%, thin the bearing up by 25%, make it out of aluminum, use 3/8 bolts and twist it 10200rpm.

It sounds to me as the rod big end distorts more (higher loads, less mass) that more parting line clearance is required than the bearing itself can provide. The rod bore is going oval under load in the clearance direction and the added eccentricity in the rod bore is keeping the rod from closing up completely in the parting line direction. For what most of us build, we'll not likely see those types of loads as we don't need flyweight parts turned to insane rpm with unbelieveable loads to keep up with the major PS programs. We're usually trying to build max hp with strong bottom ends to live a while in the customer's hands.

[Darin Morgan]

I've had this problem before and would like to get advice on how to correct this from people who do this more than I do. I seem to have a problem with a set of rods when sizing from time to time, even after they have been cut on the Sunnen cap grinder, and all torqued and ready for the hone the parting line is too big, like .001-.002" too big, cut them again, same deal, even though the top and the bottom are undersized and ready for honing. I've been shown a few tricks over the years for this, but rather than cloud anyone's mind, I rather hear from folks how they tackle this problem.
Just so you know, al the rods equipment is Sunnen (hone, rod gauge, cap grinder), all in good condition and the gauge and been double and triple calibrated to rule that out. The rods are Carrillo with Carr rod bolts. Any help would be greatly appreciated. Thanks.

Your correct " awesomebill", I guess I should answer the guys question first. There is nothing wrong with being .001 to .002 big at the parting line on a set of rods so long as you still have adequate crush and the housing bore is perpendicular to the shaft and horizontal to the pin bore with no bell mouth or taper. Race them. They are fine.

[Dave Koehler]

I plan later to discuss some things I have learned about stock OEM rod resizing but for now this:

1: Rod resizing 101 only asks that the rod be the right size at 12:00 and at approximately 10:00 and 2:00. I tend to lean toward 2:30 and 9:30 (or as much of a circle as I can get).

2: Making a large hole smaller will always leave a parting line shadow. No way around it. This was previously demonstrated by a gentlemans graphic.

3: The shadow has no consequences as far as bearing crush.

4: I do not do angle milling. It only covers up other problems and creates more problems such as nut seat spot facing, etc. I leave this to the mass production guys.

5: I suspect that anyone that does line boring thinks this discussion is somewhat pointless as you can't make material reappear in the low spot.

6: IF the shadow is of no consequence and you need to visually please a customer, ball hone the big end and then take the last 2 or 3 tenths out.

7: While I have been aware of the the out of round method I have not run into a situation that called for such a trick to be implemented. Maybe someday.

8: I don't think one can worry too much about a little shadow. There are rods out there that purposely have a large bevel on the edge of the cap and rod thus creating a shadow on purpose.

9: I do sand a light bevel/champher on the edges to avoid a lip forming and pushing on the bearing after the cap has been on and off a couple of times. I think most of you have seen this lip appear on some rods. It probably comes from movement of the cap and rod (distortion?) and for sure a little detonation will aggravate it.
I believe that this potential for a lip to form is more of a problem than a shadow. The lip can push in quite a ways squeezing the bearing.

10: Dead perfect at the parting line while perhaps being desired by some is not needed or warranted. I guess this statement and some of the other points work for both sides of the discussion.

Dave Koehler
www.koehlerinjection.com

[Barry_R]

Since I worked for a good sized bearing manufacturer I can actually add a bit to this post - - as opposed to my normal behavior of reading and trying to learn the best I can... I may be not a true bearing expert - - but am certainly a reasonably well trained bystander. This is kinda long, but not too painful...

We generally made the bearings to go into a round hole. That does not mean that that is the only - - or even the right way - - to do it. It just "is". This becomes more relevent later.

Crush is press fit. Its the the result of a bearing assembly having a larger OD than the hole it goes into. You can't measure it easily in the "relaxed state" because the split halfs are not round. Crush will be increased in a few ways - - a larger OD, stronger steel backing (deforms less), or thicker steel backing. When you squeez the two bearing halves together they will set up "hoop stress" - - the load that creates the press fit. Thicker or stronger steel backings will tolerate more hoop stress and hence tolerate greater amounts of crush before they deform. One very sharp bearing engineer once told me that racers would be well served if they could go to .040 under bearings because the steel backing was thicker.

Now that we have briefly covered crush, we need to be aware that not only will the rod bore impact the bearing - - the bearing will also deform the rod bore. A high strength bearing in a stock rod will measurably deform the rod.

Now a few thoughts on the ID of the bearing. Everyone talks about eccentricity. Fewer folks realize that there are about a million different eccentricity profiles - - they are near to head ports. F-M race bearings used a continuous eccentricity profile where the bottom portion was roundish, and it steadily moved away from the crank as we moved toward the parting line until it reached the "parting line relief". Other bearings use a eccentricity profile that is very round at the bottom and then tips away more abruptly on an angle at a firm given point in the diameter of the shell. Some GM bearings are dual concentric where they are round at the bottom, and then near abrupty go to a larger full round diameter instead of moving at an angle.

The parting line relief was an area about 1/8 - 1/4 of an inch below the split where the profile was tipped in to agressively moved away from the crankshaft. This was to reduce potential oil film and bearing distortion problems caused by rod deformation at the part. At the very edge of the bearing shell if a teensy (very technical term) chamfer - - the parting line chamfer - - to prevent introducing a sharp edge into the hydrodynamic wedge. Too large a parting line chamfer, or to large a eccentricity area when "viewed" from the side, and you get low idle oil pressure due to the size of the leakage path. Thats the reason for the GM dual profile - - it gives a smaller window than an angle does.

Lets close this up. What Darrin is doing with the ovoid bore is providing greater functional eccentricity and a greater amount of parting line relief to the bearing. The same thing could be handled by the bearing company BUT they cannot really afford to make a unique profile for each application. And every application and every rod design/material will have unique needs. So he and others use the rod bore as a means of tuning the profile to meet their specific needs. The impact on crush is nominal since that value is really dependent on the ID length of the rod's big end hole - - a few tenths is not going to have a meaningful impact on that. And the rule of "good enough" certainly applies here - - if it works leave it alone...

[Darin Morgan]

Barry_R,

Thank you for that info. It is greatly appreciated! As far as I knew there where only two profiles. I had no idea there where more than that. I only knew that the "P" passenger bearing has a less pronounced eccentricity than the "H" high performance bearings. Are there other eccentricity profiles that are more pronounced than the standard "H" bearings? I know Warren had some Main bearings made with a large eccentricity profile but how many main bearing profiles are there?

[V Remian]

I was shown how to remove shadows at the parting line(and mic marks) with a sheet of emory cloth wrapped around the mandrel. works pretty slick IMO.

[CNC BLOCKS]

Over the years we have had quite a few sets of old cup rods Lentz and Carrillo and we have seen a few sets the were upto .001 over size and there were some rods with the bearings still in the rod and nothing but a Clevite H bearing that looked like new.

I would rather see a rod housing bore big at the parting line then tight which would tend to scrape the oil off the crank surface cause a bearing failure And we have also seen the housing bores on the main lines of some cup block that have been over size as well and no issues.

In one of my old old engne building books they recomended to shim between the rod and the cap .004 hone round then cut the cap and hone to size the proper size.

[awesomebill]

Barry_R,

Thank you for that info. It is greatly appreciated! As far as I knew there where only two profiles. I had no idea there where more than that. I only knew that the "P" passenger bearing has a less pronounced eccentricity than the "H" high performance bearings. Are there other eccentricity profiles that are more pronounced than the standard "H" bearings? I know Warren had some Main bearings made with a large eccentricity profile but how many main bearing profiles are there?

I do agree if it works for you use it. The abiltiy of the main or rod bearing to withstand the stress of the load of what it is seeing is all we need to stay ahead of. We had a customer about 5 years ago hurt and engine and needed it back quickly. Upon checking his aline bore, it was perfect in size but the bores were not in line. I told him I would have to send it out because at that time I did not align bore. He said just put it together. I said no. I did tell him being the bores were perfect I could oversize a set of .010 bearings back to standard which his crank was. It is a little messy but I aline honed the main bearings. All the mains were multi colored and looked a mess. There were the cheap Engine Tec IROC bearings. I got the align bore back perfect with no taper at all on the parting line. I made a perfect hole as the crank would see it. Took about 1 hour and most of the time was spent on cleaning the stones. I assembled the engine and the crank clearance was a mere .0027. The crank spun like it was on glass. He was a bit concercned because he could see the cooper color in the bearings. I told him this would not mean a whole lot being the oil used and the crank did not have eyes to see it. He ran the engine for the rest of the year and only brought it back after it split a cylinder wall. Upon taking the NOS 400 SBC apart, the bearings looked exactly like we sent them out the door. I was amazed. Now the imbediment material was gone in most places, the bearings were perfect along with the aline bore. If it would not of split the cylinder wall he would of never fixed it. I know this was not the correct repair, but was the more correct of the 2 choices I had. With that said, and the ability of the filled 2 bolt main block to withstand 600 real hp and 350 added with the juice tells me in this case the perfect align bore even with no taper worked very well for the mains. I would not try this with rods.

[Barry_R]

Sorry it took me so long to get back to this.
Federal-Mogul and Clevite use different eccentricity profiles for each bearing - - usually tweaking something that they already know will work based on common journal diameters, etc.

I suspect that - if you get to the right guy - either one would make you up a "special" set in the prototype lab. The profile is either broached or bored into the bearing after all the backing is roll formed, so its not really that hard for them to do. The plating layers are deposited afterward.

Darrin - - a Pro Stock team might have the necessary "glamour" to get this done - - PM me and I'll provide a contact name if you want to try it. Obviously I can't make any promises since I don't work there anymore...

[Darin Morgan]

Sorry it took me so long to get back to this.
Federal-Mogul and Clevite use different eccentricity profiles for each bearing - - usually tweaking something that they already know will work based on common journal diameters, etc.

I suspect that - if you get to the right guy - either one would make you up a "special" set in the prototype lab. The profile is either broached or bored into the bearing after all the backing is roll formed, so its not really that hard for them to do. The plating layers are deposited afterward.

Darrin - - a Pro Stock team might have the necessary "glamour" to get this done - - PM me and I'll provide a contact name if you want to try it. Obviously I can't make any promises since I don't work there anymore...

Do the rolling Die's and Broaches tend to wear out over time and make the bearings look as though they have a wavy surface? We have been getting some of these lately. It seems about every six months or so we get a small run of them like its the end of the dies cycle and they want to push out that last thousand pieces.

[Barry_R]

They sure do.
Your on the edge of my knowledge base here - but I know this much:

The profiling tools travel through the bearing from one side of the bearing to the other parallel with the crank direction.

You need to keep the tools sharp or get smearing or changes in size from one end of the bearing to the other - when the bearing shows taper due to material bunching up as it cuts.

If the tooling is not properly held you get "broach bounce or chatter" where there is a "fan or splined" look to the bearings once worn. This can also be caused by machine maintenence as a bad bearing in the machinery will reflect in the product surface.

When you see that appearance its a bad bearing - nothing in your work causes that.

[BRENT FAY]

In the late seventies I hired an eldery gentleman that had done mostly crank grinding and rod resizing.

He had told me that as long the rod bore was round from (looking at a clock) from about 3:30-8:30 and 9:30-2:30 you will be all right. Never had any problems. He said why do you think the bearings are thinnner at that location. I didnt know? I was young and willing to learn! But he really couldnt explain either, but it worked!

But now over the years I have learned that the way the rod is made and rod bolt strength is, you will get some elongation or none on the rod bore but that depends on engine speed,weight and rpm,ect,ect,ect. Brent

[defrag010]

bumping this thread up, and pertaining to the original poster's original question - I had a guy who used to do work (resizing rods, among other things) for a successful local machine shop that goes by Lucito's give me some advice on fixing a wide parting line.

I do mostly production stuff, and if something is wide more than .001"=.0015" at the parting line, I would chunk it. However, I had this gentleman come in and show me a "trick". He took a rod that was about a thousandth and a half wide at the parting line, cut the cap to where the "12 o clock" was about .0035-.004" tight. Then, he torqued the cap down, and took the rod over to the piston pin press. He put the big end vertically under the press, and just squashed the big end aof the rod a little bit until the parting line was just a few tenths on the low side of size. By then, the "12 o clock" was about 2 thousandths tight, and he just honed it out and ended up with a perfect circle. Guy said he did that alot, and never had any problems. There were no problems with rod bolt alignment, side load, nothing. At first, I couldn't believe it and thought it was extremely ghetto, but after reading some posts on here, it sounds like just another way to get to Chicago.

[TRN]

There is a real good reason for a round hole. If the hole is oval, as described, it concentrates the radial pressure that results from crush at the parting line. This has an impact on thermal conductivity from bearing shell to the surrounding metal. This might not matter, depending on application.

[Wolfplace]

There is a real good reason for a round hole. If the hole is oval, as described, it concentrates the radial pressure that results from crush at the parting line. This has an impact on thermal conductivity from bearing shell to the surrounding metal. This might not matter, depending on application.

=
Say what???