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FS-120 Connecting Rod

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Old 07-05-2012, 06:04 PM
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dbacque
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Default FS-120 Connecting Rod

I have just completed the tear down of a 20 year old 1.20 Surpass E. It is in remarkably good shape, even down to the original bearings that still feel nearly new.

The thing that I am puzzling over is the fit between the connecting rod and the wrist pin. Considering that the con rod is bushed and drilled for lubrication, I would expect the wrist pin to rotate in the rod. But the pin is such a tight fit in the rod that it is difficult to drive it in. Then when I reassemble the piston, rod and wrist pin, the pin rotates in the piston instead of rotating in the rod. Is this a correct fit or do I need to replace the rod and wrist pin?

Thanks,
Dave
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Old 07-06-2012, 06:08 AM
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Default RE: FS-120 Connecting Rod

You likely need to clean the wrist pin. It is in an area where it gets hot and fuel/oil residues bake onto the wrist pin. The connecting rod should move freely on the wrist pin.
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Old 07-06-2012, 10:13 AM
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Default RE: FS-120 Connecting Rod

That did the trick. Thanks for the quick response!

Dave
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Old 07-06-2012, 11:14 AM
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Default RE: FS-120 Connecting Rod

Another question, I'm having trouble removing the camshaft bearings. I've got the crankshaft bearings out but try as I might I can't get the camshaft bearings out. I've soaked with carb cleaner and penetrating oil, repeated the heat treatment and still no joy. Any suggestions on how to get these stubborn bearings out?

Thanks again,
Dave
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Old 07-10-2012, 04:56 AM
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Default RE: FS-120 Connecting Rod

The cam bearing in the cover comes out easily with heat and a tap against a wood block. The one inside the crankcase is a bit more difficult. You may need to make a small puller or slap hammer to get it out. Another way is to use heavy grease and pack it into the bearing's center and then ram it with a small dowel or rod that will just fit into the bearing. Pack it and add grease, pack it and add grease. This will also work, but does take a little time.
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Old 07-17-2012, 03:08 PM
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Default RE: FS-120 Connecting Rod

Got it!

I made a puller similar to the one in post #23 on this post http://www.rcuniverse.com/forum/m_6960314/tm.htm . I don't have machine tools so it was made by hand with a Dremel cutoff wheel, minus the hole down the center. Instead of the rod down the center to keep it open, I used a wedge shim made from part of a washer seated between the legs. That kept the legs from closing. Assemble the parts, throw it in the oven at 350 for 15 - 20 minutes and crank down on the nut. It worked great and I finally got the camshaft bearings out. The engine is now rebuilt and ready for action.

Developing the tool took many tries and several days. You should offer a tool for this purpose.

For those hunting for info on how to do this, a longer bolt is better. Earlier versions were longer but I was out of bolts. The tool is made from the largest diameter bolt whose shaft will fit through the bearing but the head won't fit. When the legs of the tool are pushed together it will just barely fit through the center of the bearing. Once seated the legs open up and the feet engage the edge of the bearing. If you try to pull now the legs will close back up letting the tool pull out but if you put a wedge between the legs it will hold. Remember, assemble everything, put it in the oven to heat, then try to pull the bearing.

For pulling the bearing out of the cap, look at post #7 in the thread listed above to see how to use a socket with the puller.

Oh yeah, instead of the screwdriver shown in post 7, I used a couple of nuts locked against each other at the tip of the tool with a socket wrench on them. I should have take pictures but since I didn't and the engine is back together, this will have to do.

Thanks for the help,
Dave
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