any tips on boring a con rod on the mill table?

1940indianchief · Wednesday at 5:25 PM

Does anyone have a holding jig to hold a con rod on mill table, to bore small end parallel with big end?

just Dave · Wednesday at 6:01 PM

I have had good luck straightening with a long rod fit snug in each end ( bush if needed) . With the two 4 ‘ rods it is easy to see when you get it perfectly straight. Use eye for angular alignment and rod end to rod end measurement for parallel alignment. Once straight tie it down and bore. You can use alu. Tie downs if you have very small margins around bore and thick dense paper under to facilitate a thru cut.

john.k · Wednesday at 6:30 PM

Conrods that had white metal bearings always have two centre drill cuts ,just outside the rod bolt bores either side ...........these two cuts are held by two centres on the boring machine ,as is the small end held by a couple of opposed cones.............up to the 1950s,every small lathe had a fixture with two screw in centres to hold rods for boring.

1940indianchief · Wednesday at 11:54 PM

I am working on vintage harley motors. The manual tells you to check for a bent or twisted rod, with a checking pin in wrist pin hole and laying across motor cases. and to straighten bent or twisted con rods by bending rod with a bar. This method does work, but I am trying to get away from that by boring a new wrist pin bushing that is perfectly parallel with big end of con rod. I am just trying to figure out how to make a jig that will hold the big end perfectly square with table. Thanks in advance for any replys.

Dan from Oakland · 2023-01-19T00:11:20-0600

Make a spud with a hole drilled thru the center with the OD the same size as your big end bore. Make sure to face the end of the spud square with the OD. Bolt the spud on the mill table and put the big end of the rod around the spud. A small vise at the other end or better a simple block with two pointed set screws to bite the sides of the small end of the rod ..............hope you get the idea- square up your spindle and you're ready to go.

john.k · 2023-01-19T00:11:47-0600

There is a device that was called a "SeaLion" that goes with every old rod bearing boring setup.........the instructions that go with this device explain testing and correcting bend in conrods.......incidentally,prewar engine rods were made to be bent for correction........basically ,you hand ream the pin bore ,and bend the rod to correct piston alignment .......Ive done this many times with Wisconsins,Ford flatheads,Harleys Indians,etc.

john.k · 2023-01-19T00:21:10-0600

The factory always machined the rod held by the three centres .....one atop the small end,and two on either side of the bigend.....if your jig holds these three points rigid ,thats all you need ....check your South Bend lathe book for conrod bearing boring......Myford also supplied a similar fixture,also in the instruction book.,

just Dave · 2023-01-19T06:26:17-0600

1940indianchief said:
I am working on vintage harley motors. The manual tells you to check for a bent or twisted rod, with a checking pin in wrist pin hole and laying across motor cases. and to straighten bent or twisted con rods by bending rod with a bar. This method does work, but I am trying to get away from that by boring a new wrist pin bushing that is perfectly parallel with big end of con rod. I am just trying to figure out how to make a jig that will hold the big end perfectly square with table. Thanks in advance for any replys.

Like I said you must straighten first for best results.Two long rods makes it so easy.
If you have a fixture great, if not that is a lot of work for 1 bore.

BT Fabrication · 2023-01-19T07:42:03-0600

1940indianchief said:
Does anyone have a holding jig to hold a con rod on mill table, to bore small end parallel with big end?

find a good engine machine shop with a sunnen hone, rough bore 8-10 thou large, then hone within a few tenths.

Servicar rider · 2023-01-19T08:55:21-0600

S&S Cycle sells an accurate checking pin for harley rod alignment. I use that and a Storm Vulcan rod alignment machine for all the Harley engines I do. Sunnen made rod alignment machines too. You can check bow and twist easily and correct any issues.

Erich · 2023-01-19T11:11:09-0600

If you bore out the small end, you need an oversize piston pin. Do they make pistons with oversize pin holes?

greggv · 2023-01-19T13:55:36-0600

find a torbin arprod machine, not only square and parallel bores but equal center to center distance

Dan from Oakland · 2023-01-19T17:04:48-0600

The "sea lion" was made by KR Wilson to be used for checking Ford rods on their con rod fixture- suppose you could use it for any thing...................

1940indianchief · 2023-01-19T17:25:09-0600

greggv said:
find a torbin arprod machine, not only square and parallel bores but equal center to center distance

Yes Sir, I have been looking for a Tobin Arp rod machine for years. The ultimate rod boring machine. They were made in Minnesota, and Sunnen bought them out in the early 80's.

1940indianchief · 2023-01-19T17:51:54-0600

Dan from Oakland said:
Make a spud with a hole drilled thru the center with the OD the same size as your big end bore. Make sure to face the end of the spud square with the OD. Bolt the spud on the mill table and put the big end of the rod around the spud. A small vise at the other end or better a simple block with two pointed set screws to bite the sides of the small end of the rod ..............hope you get the idea- square up your spindle and you're ready to go.

The spud sounds like a good idea, but I need it to expand and lock the rod perfectly square with table. I rebuild 2 sizes of rods, 45" rods and big twin rods. Each time the big end gets sized, The I.D. gets larger, so I need to figure out how to make an expansion spud ?

1940indianchief · 2023-01-19T17:53:35-0600

Dan from Oakland said:
The "sea lion" was made by KR Wilson to be used for checking Ford rods on their con rod fixture- suppose you could use it for any thing...................

I am not familiar with the Sea Lion, but I know KR Wilson was a quality tool maker.

1940indianchief · 2023-01-19T17:55:27-0600

Erich said:
If you bore out the small end, you need an oversize piston pin. Do they make pistons with oversize pin holes?

O.S. pins are available, but not needed with a new W.P. bushing and new piston pin.

1940indianchief · 2023-01-19T18:02:00-0600

Servicar rider said:
S&S Cycle sells an accurate checking pin for harley rod alignment. I use that and a Storm Vulcan rod alignment machine for all the Harley engines I do. Sunnen made rod alignment machines too. You can check bow and twist easily and correct any issues.

I have the S&S checking pin, and the Sunnen hone and dozens of mandrels. I'm just trying to re invent the wheel, if I can make both bores perfectly parallel, then I won't need to bend the rod. Any chance you could post a pic of your storm vulcan rod alignment machine? Thanks

AlfaGTA · 2023-01-19T19:34:38-0600

1940indianchief said:
The spud sounds like a good idea, but I need it to expand and lock the rod perfectly square with table. I rebuild 2 sizes of rods, 45" rods and big twin rods. Each time the big end gets sized, The I.D. gets larger, so I need to figure out how to make an expansion spud ?

You should be looking for a Berco rod mschine. More flexible than the TA.
Uses expanding mandrels to locate and hold rod big or small ends.
Cheers Ross

AlfaGTA · 2023-01-19T19:51:12-0600

Here is a shot of my AB320
Rod mounts vertical (no sag due to gravity) \
Spindle mounts solid boring bars (40 taper)
Expanding mandrel mounts to slide that sets the rod length. Different mandrels cover a size range.
Can hold the rod either way and bore either the big end or the small end.
Bed provides the long power feed

2and photo taken after adding DRO to long feed to control facing cuts (White metal rod applications)

Looks like there is one on bid spotter.....

Berco Model AB-320 Rod Boring Machine, s/n 662B, Minimum Boring Diameter 19/32”, Maximum Boring D

Lot 215 at CENTER DIESEL & MACHINE from Thompson Auctioneers.

www.bidspotter.com

Cheers Ross

any tips on boring a con rod on the mill table?

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