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Tooling to make split bushing

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
So sometime back i posted about a machine that i got back into service. Its a Tobin Arp cylinder head cam bearing line boring machine. (overhead cam heads)
Project was done to finish a set of DOHC heads for a V-8 50's Spanish car :Pegaso.
The project included finish boring the housings for the head cam bearings.

https://www.practicalmachinist.com/...chine-mer-up-running-394768/?highlight=Pegaso

Well the project continues. Final step in getting the heads finished is to make the required bearing shells that carry the cams in the head. (fits to the bores finished in the above work)

At first glance this looks like a simple job of making bearing shells.
Issue is that the shells are split in two half's so they can be installed ...
There are two ways to make this sort of bushing and i have used both methods for making all sorts of bearing shells for main bearings etc.....
The first process is to make the shells oversize on the OD and small on the ID.
Cut them apart, clean up the cut edges and carefully soft solder the half's together, re-chuck the assembly, finish the OD/ID then break the two half's apart.....

The second method requires double the number of parts be made , cut apart, slightly long on one side, then carefully clean the parting face to exactly half the OD of the bushing.

The first method takes longer to do, but saves material.
The second method requires the wasting of half the bushing material (recycled). I opted in this case for method #2.

I opted to make a fixture to make the machining of the bushings easier.
The parameters were that i wanted a repeatable holding setup, that could locate the half's for trimming at the parting face and allow cutting in clearance notches on the shell sides to clear the cap studs,
and drill/ream the shells for locating pins.

Here is my solution:

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Bushing fit to fixture. Bushing finished both ID , OD and length , Bore touched on the hone to give better finish.
Tool used without locating pin to drill /ream hole in bushing and cut in reliefs on the sides to clear the bearing cap retaining studs.


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Bushing completed, first step. Locating hole drilled/reamed, clearance notches for cap studs cut in.

Cheers Ross
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Here is how the tool works:

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Allen bolt bears on the end of the toggle that pivots on the pin and applies pressure on the bushing .
End of the toggle has a formed piece (held in place with a bolt that is both round and spherical. Done on the lathe to copy the pivot curve of the toggle.

Toggle and end piece made from pre hard ETD 150. (RC30ish)

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After the first operation a locating pin was added to the fixture. Made with a through bore to allow removal of the pin if necessary.
Shells loaded into the fixture and cut in half on the band saw using a fence setup to control the cut position. (angle iron clamped to the saw table)
cut made taller on the side held in the fixture.

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Cut off and saves shell half's

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Here is the setup for finishing the parting faces of the shells. Locating pin visible...

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And the finished product......Holding running clearance of .001-.0015"
Fixture pretty repeatable. Parting line finished in two steps. First cutting (rough) using an endmill , then finished using a fly cutter.
Fixture allows tool to pass over the part without any interference....
Shell can be removed and gauged for height (surface palate and indicator clocking the back of the shell for height and parallel.....
If needed shell can be returned to the fixture and re-cut (If too tall)

Cheers Ross
 

ballen

Titanium
Joined
Sep 25, 2011
Location
Garbsen, Germany
Hi Ross,

Thanks for posting this! As always, it's very interesting to see your methods and work. One of the main things that I have learned from your posts is to invest time to make special fixtures and jigs, even for one-offs. In the end this actually saves time and makes it possible to do work repeatably and well.

I have a stupid question. It appears that the mating faces of these split bearing shells line up with the mating faces of the clamping caps that hold the shells in place. Wouldn't it be better design to rotate the split shells, so that the mating faces of the split bearing shells were 90 degrees from the mating faces of the bearing caps? Or would that make it impossible to assemble everything?

Cheers,
Bruce
 

thanvg

Hot Rolled
Joined
Mar 3, 2015
...

I have a stupid question. It appears that the mating faces of these split bearing shells line up with the mating faces of the clamping caps that hold the shells in place. Wouldn't it be better design to rotate the split shells, so that the mating faces of the split bearing shells were 90 degrees from the mating faces of the bearing caps? Or would that make it impossible to assemble everything?

Cheers,
Bruce

"clearance notches for cap studs cut in." , I think it would need an extra indication step in order to do the notch at an angle, not sure though...
 

jariou

Cast Iron
Joined
Jan 20, 2008
Location
Cary, NC
Bruce,

If it was done "your" way. it would mean that the installation of the camshaft would have to be done with maybe 8 hands holding the shells on the shaft as you lower it into position. I'm sure someone could come up with a clever way to reduce the number of hands needed, but still it would be a hassle.

The way it is now, you just put the bottom half shells in, drop down the cam shaft, then add the tops halves leisurely, one at a time.

At least, that is how I see it. Please slap me upside the head if I am completely wrong!

And, once again, Ross demonstrates his beautiful artistry of everything mechanical! Thanks a lot Ross. Super cool!

Jacques
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Bruce:
Assembly is the issue with "clocking" the shells opposite to the cap parting line.
Remember that there is service involved with this. It is required to service the cams and followers and account for valve and seat wear...his involves removing the cams from a head that is fully assembled to allow removing and installing shims that control the valve lash.(clearance).
.Now when removing the cams some of the cam lobes will be opening valves and thus under strong tension. Its required to use the cap retaining studs to carefully wind all the cap nuts out to allow the cam to rise and release the tension of the open valves (allow them to close.)

Further the loads here are when the cam opens a valve or allows it to close....force (considerable) it trying to lift the cap. Having the parting line in line with the force of opening the valve would tend to break the oil film
where its most needed....

There are additional reasons. Its possible to give the sides at the parting line more clearance (this is routinely done on connecting rod bearings where the shells are thinner at the parting line)
This is done to give more space fro the oil to collect and to offset any position error in the cap (offset)

In the case of a plain bushing like shown above, the extra side clearance can be created by boring the bushing slightly larger in ID than needed. Then shrink the dimension opposite the parting line slightly to give the
desired clearance. The result is a slightly oval bushing giving more side clearance.....Remember is pressure fed lube like this the bushing never touches the rotating journal except at start up...so a perfectly round
bushing is not required and in some cases not the best for the application....


Cheers Ross
 

ballen

Titanium
Joined
Sep 25, 2011
Location
Garbsen, Germany
Hi Ross,

Thanks for explaining, particularly about oil film and the valve springs. It reminds me that mechanical systems are usually designed to take into account many different factors. If one is not familiar with all of those (ie, an expert) then it's usually mistaken to think that it can be improved upon with minor changes. I've only taken one car engine apart and reworked it (1098cc, 1965 MG midget) and that was 40 years ago!

Cheers,
Bruce
 

mattthemuppet

Hot Rolled
Joined
Apr 22, 2016
Location
San Antonio
that is beautiful work and a pleasure to read. I was thinking that was a lot of work for a small number of bushings until I saw the pic with all the blanks :) I love seeing these posts about car restoration/ rebuilding.
 

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
"Machinery" magazine around 1960 published a detailed article how
one of the major manufacturers (in Cleveland) made their crank bearing shells. IIRC similar fixturing, and boring in a fixture mounted in an automatic lathe.
 

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
Bruce:
Assembly is the issue with "clocking" the shells opposite to the cap parting line.
Remember that there is service involved with this. It is required to service the cams and followers and account for valve and seat wear...his involves removing the cams from a head that is fully assembled to allow removing and installing shims that control the valve lash.(clearance).
.Now when removing the cams some of the cam lobes will be opening valves and thus under strong tension. Its required to use the cap retaining studs to carefully wind all the cap nuts out to allow the cam to rise and release the tension of the open valves (allow them to close.)

Further the loads here are when the cam opens a valve or allows it to close....force (considerable) it trying to lift the cap. Having the parting line in line with the force of opening the valve would tend to break the oil film
where its most needed....

There are additional reasons. Its possible to give the sides at the parting line more clearance (this is routinely done on connecting rod bearings where the shells are thinner at the parting line)
This is done to give more space fro the oil to collect and to offset any position error in the cap (offset)

In the case of a plain bushing like shown above, the extra side clearance can be created by boring the bushing slightly larger in ID than needed. Then shrink the dimension opposite the parting line slightly to give the
desired clearance. The result is a slightly oval bushing giving more side clearance.....Remember is pressure fed lube like this the bushing never touches the rotating journal except at start up...so a perfectly round
bushing is not required and in some cases not the best for the application....


Cheers Ross

Ahh, yes the wonder of adjusting valve clearance on bucket follower heads

Gotta watch that you tighten the caps correctly and the thrust surface lines up while tightening the cams down.

Ask me how I know....

Lucky for me cams were no doubt much cheaper and easier to get than these are

bronze bucket liners,hm, always saw steel
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Jag used iron for cam bucket liners. as did Coventy Clymax. Cosworth DFV's use aluminum sleeves in the mag cam carriers.
Alfa has always run the followers directly in the aluminum head casting as does Offenhauser Miller and Bugatti (T55 & T57).........
Not sure i have ever seen "Steel" liners for cam followers.
These are re-pop heads, but the bronze liners are as original...Cam bushings however are aluminum in the original...I opted for the bronze shells to make them a bit easier to make and a bit more
forgiving when running. Aluminum makes OK bearings except for low oil conditions... Lots of makers run the cams directly in the aluminum head castings without any replaceable bearing shells.
Cheers Ross
 








 
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