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post #1 of (permalink) Old 06-11-2000, 12:12 AM
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calling amc engine guru\'s

how is the wrist pin in an amc 360 held in place?can it come out?is this a common amc
problem?what noise does it make if it does?would it immediately damage the sleave?and how is it
fixed?thanx a bunch.

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post #2 of (permalink) Old 06-11-2000, 01:34 AM
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Re: calling amc engine guru\'s

The piston 'wrist' pin is held in place with what is called a 'Press Fit'.
That means the hole in the connecting rod is slightly smaller than the piston pin, and has to be 'pressed' in place in the rod.

Actually, no one presses them in anymore... The small end of the rod is heated so the hole expands, and the pin is chilled to make it smaller, then the two just fall in place. When the temperatures equalize, the expanding pin is 'grabbed' by the shrinking rod.
Then when the engine heats up or cools down, both the pin and the rod expand or contract together, so the rod keeps a good grip on the pin.

This pin can be forced out of the rod, mostly if you rev the engine too high, or if the pins aren't installed in the rods correctly, or if the rod holes are oversized.
Where these side loads come from, I have no idea, and I've been doing this for 25 years.
When a pin walks out, it WILL DESTROY the cylinder wall.

There is what is referred to as 'Full Floating' piston pins.
They use a 'C' clip arrangement in the ends of the pistons to keep the piston pin in place.
With a full floating piston pin, the pin slips in the rod and the piston, and can just be dropped into place when assembling the engine.
Unless the locks are installed absolutely correctly, these piston pins can get loose too, and the result is the same, destroyed cylinder wall.

If you don't know EXACTLY what you are doing, DO NOT ATTEMPT TO DO THIS YOURSELF...
This is a critical procedure in the assembly of your engine, and will cause catastrophic failure of your engine if not done exactly correctly.
Press fit pins are hard enough to do correctly with steel rods, but if you are using stock AMC rods, you have CAST IRON RODS.
Cast iron rods take special precautions and special procedures to do correctly.
I advise you to seek a qualified engine building shop to do this part of assembly.

Don't forget to replace the connecting rod bolts if your rods still have the stock AMC bolts.
This too is a critical procedure that requires special equipment or catastrophic damage will result.
And don't let anyone talk you into oversized bolts for cast iron rods, ever...
Good quality rod bolts are already stronger than the rods, and removing rod material to install an oversize bolt will only weaken the rod.
(Again, cast iron rods take special handling procedures... See what I mean?)

If you decide to relieve the rod beams, make sure you keep 'Waves' out of the metal.
Waves, and removing too much material will cause failure.
Watch for overheating the rod when you are grinding it also. That will make hardened spots in the surface of the rod, and may even cause heat cracking or heat checking...

Like I said, cast iron rods take special care and handling.
Be careful, and select a good rebuild shop before starting your project...
If they can't or won't answer your questions, go somewhere else.

Hope this is the info you were looking for...
You asked for a 'Guru', but it looks like you are stuck with me...[img]/wwwthreads_images/icons/wink.gif[/img]

Later, Aaron.

"I Have The Body Of A God... Buddha"
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post #3 of (permalink) Old 06-11-2000, 02:17 PM
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Re: calling amc engine guru\'s

Wow thats a very thorough answer,thanx.I'm not even sure that this is my problem,its just that I have a noise that resembles the sound of a noisy lifter,but it doesnt show up at the times a noisy lifter should(cold starts,then quite's),but rather it comes and goes at will for no aparent reason,when I listen with my stethascope,it is noisiest in the RH exhaust manifold,a machanic told me that it could be a wrist pin,thats why I am curious what that should sound like,but if its pressed in and slides over,it should be a constant noise,becouse it would be held there. no?

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post #4 of (permalink) Old 06-11-2000, 09:35 PM
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Re: calling amc engine guru\'s

If you are hearing it on the right side, it could be a lot of things...
1. Slop in the piston to wall clearance. When you start the engine, the piston is cold and small...
As the engine warms up, (aluminum pistons expand roughly three times the rate of steel or cast iron) the piston expands and takes up some of the clearance...
It's still slapping, but not nearly as much when hot, that would explain the knock with the stethoscope...

2. Could be a rod bearing. Stops the loud knock when the oil pressure comes up, and internal engine heat tightens things up.

3. Could be severe cam shaft ware. Real likely in older AMC engines.

4. How about broken rocker arms or malfunctioning lifters...

5. It could be slop in valves. Heat expansion and rising oil pressure will quiet these down also.

It could be a lot of things...
Your best bet is to take it to a good engine shop, and have them check it out...
Chances are it won't cost too much to have the locate what ever the problem is, and then you can tell us, and we can give you options depending on what is wrong...

"I Have The Body Of A God... Buddha"
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