Who Checks for Rod Alignment?

[Kohnke Rebabbitting]

ursus,

I have not used the method you describe, but it should be something every student-mechanic does as some point so that they understand what a crooked rod puts the piston through. If I were teaching auto shop, I would set up a dummy engine so that this lesson could be learned in minutes.

Herm,

I have been thinking about my own question since I made my post and embrace your answer completely. The following is based on my experience teaching tool design for many years:

Part I: If one could grind the sides of the beam parallel in a grinder, one could then hold the rod without introducing any change in shape that would come out when the rod was unclamped.

Part II: If one supported the rod on two points on the beam edges near the big end and one in the center of the web near the small end, it would be supported on three points and would be stable. If it were clamped opposite these three points, there would be no change in shape caused by the clamping process. This sort of clamping would easily keep the rod in a fixed position during the machining and, upon release, I would expect no change in shape.

It seems that Ford tool designers beat me to this description by close to a century. The old-style rods with three center holes in bosses on the forging are an elegant version of three-point support of a part being machined. I would expect that later rods that did not have these bosses used tooling similar to what I am describing.

And, I still would check (& straighten if necessary) every rod . . .

Thanks,

Archie

I used to have a Hempy-Cooper rod lathe that held Model A rods the way you describe, it was a good machine, but didn't get the rods any closer then my other machines. You would think it would?

Herm.

 

[Archie Cheda]

You would think it would?

Herm,

I am not sure if I am being asked a question or not . . . i will attempt an answer:

First I respect your experience and am in no way arguing with your statements. The concepts of tool design are one of the corner-stones of manufacturing, which I taught for two decades. These concepts are theory and, while valid within assumptions made, sometimes do not seem valid in "the real world".

One of my life-long hobbies is to reconcile differences between theory and practice -- assumptions of theory may be incorrect or incomplete and what is observed is not always communicated. (Note I do not mean that anyone is in error, just that two people are actually not actually talking about the same thing in some sense.)

In this case, I can believe that your observations are quite valid, but all real parts have tolerances and I believe most rod checkers are somewhat subjective in that they depend on observation of how large gaps are and that the operator makes corrections until the gap is reduced to a very small level -- please correct me if I am wrong about this. I recently measured a bad rod I have and it was out of parallel .018" in the 3-1/2" length of the piston pin and out of plane (twisted) by .034" -- I know that this is a bad rod. What would be a serious tolerance for these sort of measurements?

I agree that it takes a very well designed fixture to hold a part with absolutely no distortion, but I also know that this is the goal of a tool designer. I would hope to hold a rod for boring and have it come out very close to "straight", but there would always be some deviation. This is why I would always check the rod. I do not have a final answer now, but I hope to do some actual test borings and will post my results. My problem rod is junk and if I can hold this rod for boring both ends and come within a reasonable tolerance, I would expect such a fixture to work with any rod.

I'll do it tomorrow and post my result.

Thanks for your patience,

Arch

P.S.: I expect that any rod machine would be designed to hold a wide variety of rod sizes and types, so that some compromises in the method of locating and clamping would be necessary. This would explain your observations.

 

[Kohnke Rebabbitting]

Rods bend much easier than most people realize.
If you take a new rod with tight nuts out of the box and put the small end in a vice and pull on the nuts with a wrench to take them off, you will twist the rod.
When I check rods in my rod checker, I stick a large screwdriver in the wrist pin and pull on it to straighten the rods, they bend very easy by hand.
Off-set is usually not a bent rod but the Babbitt thrust faces are not centered properly. It can be corrected by bending the rod, but it is better to use the rod checker when facing the thrust faces to get them centered properly.

Some shops get the thrust the right width, and there rod lathe has a setting attachment to get all the rods the same width, but there set up, through rod replacement, is never the same, that is where you end up with offset in a before straight rod.

I know from past pourings somewhere if the rod is checked for Alignment, twist and bend, and the off set wasn't checked, the next time the rods are rebuilt, the off set gets worse.

That is where you see a thin thrust on one side, and thick on the other, or the Guy is no good at telling this.

I checked a set of Heavy Model T rods about two weeks ago, done by a shop North of me.

The width should have been 1.500 wide, and it varied Minus .008 thousandths to .037 thousandths. They were supposed to go on a New Scat crank be sides. I let them know, and the owner said straighten them, so I did.

The bore on the std. rod should have been 1.500, and thay varied .001, to.002. How he got them all a different size, must have bored each one by it's self. They had an X groove in there caps faintly with some kind of hand tool, Plus, I would count on the flanges coming off because for a lack of bond.

When setting off set you should only use the top 1/3rd of the rod flange, as that is where it should be held.

Any given rod is not machined on the sides where the babbitt sets, that is why you can only use the top 1/3.

Herm.

 

[KR500]

Herm, You don't favor using your Waterbury/Ammco rod lathes to cut the X grooves, but rather prefer the Storm Vulcan groover?

 

[Ron/IA]

Herm - Are the many drillings in the rod caps done to get the large ends the same weight? If so, would it be possible to take a picture of your weighing process?

I am trying to get the small and large ends of a set of rods I have to weigh the same, but am having trouble getting consistent results. IE. I weigh the one time and get x-number of grams, then weigh it again without changing a thing, and get a different x-number of grams.

I hope this makes sense.
Thanks,

 

[Kohnke Rebabbitting]

Herm, You don't favor using your Waterbury/Ammco rod lathes to cut the X grooves, but rather prefer the Storm Vulcan groover?

Yup, Vulcan's are quicker, I have 3 set up for different bearings, but some rods are way bigger, and some I have to do with a cutter wheel, on a dremel cable.

The largest rod we have ever had was 85 pounds, and the largest bearing insert, 1/2 of was 35 pounds of solid babbitt, 1.250 thick.

Herm.

 

[Kohnke Rebabbitting]

Herm - Are the many drillings in the rod caps done to get the large ends the same weight? If so, would it be possible to take a picture of your weighing process?

I am trying to get the small and large ends of a set of rods I have to weigh the same, but am having trouble getting consistent results. IE. I weigh the one time and get x-number of grams, then weigh it again without changing a thing, and get a different x-number of grams.

I hope this makes sense.
Thanks,

Put several pictures of your set up on here, so I can see what is going on.

Herm.

 

[Archie Cheda]

Experimental results . . .

Herm and all,

I supported a rod as shown in the first two pics and bored both ends in my mill. The rod is supported on two points on its beam edges on a hardened steel parallel -- these points are as near to the big end as possible without getting up on the filet. The third point is on one beam edge as near to the small end as possible and the support is a nut & bolt being used as a machinist's jack. This allows for adjustment to make the rod web as near to horizontal as one wants. I clamped the two strap clamps lightly and took many light cuts -- there was no problem with rigidity.

The third pic shows how I measured the parallelism and planarity (twist) of the rod bore axes. In a one inch sweep along the bores I found .001" per inch error in parallelism and .0015" per inch in twist. While these are not major errors, I think I will resolve to check and finish-straighten rods when I bore them in this manner.

I learned a lot from this experiment, and I want to support Herm's statements. A rod machine has to be able to hold many different sizes and shapes of rods. These rods must be held very rigidly because a business does not have the luxury of taking only light cuts -- productivity and profit are necessary for survival. I fully agree that all rods should be checked before assembly, no matter what has gone before. If you acquire rods from someone whom you do not absolutely trust to have checked them, taking them to a local shop to be checked is as wise as getting a second medical opinion before having major surgery.

The nice thing about my setup is that, although it takes some time, it allows both bores to be done in one setup and total control over the center-to-center distance. It is possible to calculate how much the small errors in alignment actually move the piston out of position in a Model A's engine geometry, but I'll save that for a day when I am snowed in . . .

Archie

 

[J and M Machine]

Herm - Are the many drillings in the rod caps done to get the large ends the same weight? If so, would it be possible to take a picture of your weighing process?

I am trying to get the small and large ends of a set of rods I have to weigh the same, but am having trouble getting consistent results. IE. I weigh the one time and get x-number of grams, then weigh it again without changing a thing, and get a different x-number of grams.

I hope this makes sense.
Thanks,

Ron: If your scale is electronic you have to warm it up before using it.
also you need to zero it out each time for it to be accurate.

 

[Kohnke Rebabbitting]

Well,...if you have a Sunnen Rod checker, you can do Model A rods.
You need the "TN-120 Midget Attachment"...

BTW,...you always check the rods.

Do they make them today, or years past.

I have a 1948-48 Catalog that lists one, that will do a rod 1.125 to 1.500.

Herm.

 

[Kohnke Rebabbitting]

Re: Experimental results . . .

Herm and all,

I supported a rod as shown in the first two pics and bored both ends in my mill. The rod is supported on two points on its beam edges on a hardened steel parallel -- these points are as near to the big end as possible without getting up on the filet. The third point is on one beam edge as near to the small end as possible and the support is a nut & bolt being used as a machinist's jack. This allows for adjustment to make the rod web as near to horizontal as one wants. I clamped the two strap clamps lightly and took many light cuts -- there was no problem with rigidity.

The third pic shows how I measured the parallelism and planarity (twist) of the rod bore axes. In a one inch sweep along the bores I found .001" per inch error in parallelism and .0015" per inch in twist. While these are not major errors, I think I will resolve to check and finish-straighten rods when I bore them in this manner.

I learned a lot from this experiment, and I want to support Herm's statements. A rod machine has to be able to hold many different sizes and shapes of rods. These rods must be held very rigidly because a business does not have the luxury of taking only light cuts -- productivity and profit are necessary for survival. I fully agree that all rods should be checked before assembly, no matter what has gone before. If you acquire rods from someone whom you do not absolutely trust to have checked them, taking them to a local shop to be checked is as wise as getting a second medical opinion before having major surgery.

The nice thing about my setup is that, although it takes some time, it allows both bores to be done in one setup and total control over the center-to-center distance. It is possible to calculate how much the small errors in alignment actually move the piston out of position in a Model A's engine geometry, but I'll save that for a day when I am snowed in . . .

Archie

Archie, I would like to see the rest of your shop, looks good, and some nice tools.

Thanks for doing that test, Interesting, that is the only way to answer questions.

Herm.

 

[KR500]

Archie, That is a sweet looking Hardinge lathe you employ!

 

[Archie Cheda]

Off Topic -- my shop . . .

Herm & KR,

Thanks for the kind words. Below are a few pics of my 800 sq.ft. shop, pre-Model A. The plan was to buy a Model A that was a driver and continue to work on the 14x54 American Pacemaker lathe that I am restoring. I am in the middle of scraping in the bed that can be seen in the panorama -- it was worn .015" in the 88" length of its bed. Near the end of rough scraping, the bed is well within .001" and is ready for finish scraping. It is on the back burner until the A is roadworthy. Even further on the back-burner is a K&T 2CH universal mill which is in parts, with its bare column waiting for paint. The next project after that is a 100+ year-old Ames planer which will not come apart until the lathe & mill are operational.

All the other machine tools are operational -- from left to right in the panorama:

B&S 10N Tool & Cutter Grinder
Covel 6x18 Surface Grinder
American Pacemaker Lathe Bed (in front of pallet rack)
K&T 2CH Universal Mill (column next to pallet rack)
Lincoln Weldor & Plasma Cutter (gas welding rig somewhere)
Ames Planer (five-foot table stroke)
Hendey 12" Tool Room Shaper
Cincinnati Bickford 24" Drill Press
Hardinge HLV-H Tool Room Lathe
SBL Turret Lathe (hiding behind tool rack - shown in second pic)
Marvel #8 Bandsaw (traveling head - 18x18 capacity)

There is another pallet rack inside, plus two outside (covered) -- not shown is a Yale electric forklift. Everything, even the pallet racks & most of the machine tools, can be relocated by the forklift or the pallet jack.

Most of what I do is use my machine tools to make parts for my machine tools . . . Now I can make Model A parts as well. I am more than willing to consult with anyone who is doing interesting custom work on a Model A. Visitors to my shop are welcome, especially if they arrive driving their Model A's.

Archie

P.S.: I will not be straightening rods in my lathe -- I'll make a mandrel to put in a bench vise. Hopefully minimum straightening will be needed.

 

[KR500]

Archie, Its a shop like yours which keeps us guys out of trouble.You have my same affliction, one machine is never enough, and ten machines isn't either!