1987 Wrangler YJ - JeepForum.com
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post #1 of 4 Old 05-06-2010, 08:38 PM Thread Starter
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1987 YJ Wrangler 
Join Date: May 2010
Location: Carlisle, PA
Posts: 3
1987 Wrangler YJ

Hey there, everyone. Glad to be on the forum. Brand new to the site - literally, just signed up.

Let me get right down to it. I just bought an '87 Wrangler YJ about a month ago. After a week, the motor let loose. She had a real bad knock. So out with the old, in with the "new".

I turned around and bought another motor, freshened it up and dropped it in.

I've changed over the intake/exhaust manifolds, various sensors, fuel pump, accessory system (went from a two belt setup to a serpentine system), clutch, flywheel (bought a new one for an '87) onto the "new" motor from the blown one.

The other day, I started it and it seemed to run pretty darn well for about 10-15 minutes and then it just died and won't restart now. I'm getting spark and fuel and it sounds like it wants to start, but won't.

Now, I've done a little homework on the block casting numbers and found that the "original" motor was from '81-'89. The "new" motor I put in is from '75-'79.

What, if any, differences are there between these two, seemingly, identical motors? Specifically, are the crankshafts and/or flywheels different in terms of being internally versus externally balanced? Any help that anyone could lend in terms of the minuscule differences between these two AMC 258's would be GREATLY appreciated. The more information, the better.


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post #2 of 4 Old 05-06-2010, 09:10 PM
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1987 YJ Wrangler 
Join Date: Dec 2005
Location: Canton, Georgia
Posts: 515
When you went to a serpentine belt did you change the waterpump to a reverse rotation waterpump so it doesnt run hot?
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post #3 of 4 Old 05-06-2010, 09:33 PM Thread Starter
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1987 YJ Wrangler 
Join Date: May 2010
Location: Carlisle, PA
Posts: 3
No. The water pump that came on the "new" motor was fairly new so we replaced the gasket and put it back on with the blown motor's pulley and fan clutch and all that. If it's a matter of the water pump. I have the blown motor out in the shed with a good water pump on it. Just swap them? The gauge was bouncing up and down when it was running, but I figured there were bubbles in the coolant system and I was going back and forth topping off the radiator and watching what it was doing. Like I said, after about 10 minutes or so it just cut out and won't restart now.
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post #4 of 4 Old 05-06-2010, 10:09 PM Thread Starter
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1987 YJ Wrangler 
Join Date: May 2010
Location: Carlisle, PA
Posts: 3
I just looked the water pumps up on RockAuto. Crap!!! I didn't realize they were different.

So, basically, I have a reverse rotation pump with the standard rotation belt/pulley. Great...I hope I didn't waste another motor. I guess I'm going to swap the water pumps tomorrow, pull the spark plugs and do a compression test.

Seriously though, if it was only running for 10 minutes, is that enough to overheat that motor to the point of rendering it beat? It seemed like it was moving the coolant. I filled it up as much as possible before starting it and was able to get another gallon or so in it while it was running since everything was pretty much filling back up.
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