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post #1 of (permalink) Old 09-12-2002, 12:07 PM Thread Starter
 
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Blown piston- can it be changed from below?

So... the #1 cylinder in my Comanche's 4.0 no longer has compression. Do to all the oil being pumped out the air filter housing, a hole in the piston is suspected.

I was planning on selling this truck, and don't really want to rebuild or replace this engine. Can I replace just the one cylinder from below? Will it come out with the oil pan removed?
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post #2 of (permalink) Old 09-12-2002, 12:58 PM
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Re: Blown piston- can it be changed from below?

I don't see how you would ever get it past the crankshaft and even if you could, without a machined surface on the bottom of the cylinder, I don't know how you get a ring compressor positioned to let the new one slide back in.
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post #3 of (permalink) Old 09-12-2002, 01:38 PM
 
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Re: Blown piston- can it be changed from below?

No.
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post #4 of (permalink) Old 09-12-2002, 04:02 PM
 
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Re: Blown piston- can it be changed from below?

I think that would be a task only hudini could complete. I'd start pulling the head and oil pan. Also sycho think to complete the project in the shortest time posable. Go pick up a new set of gaskets, oil and a filter, ring compressor and all the tools you will need, find the rest of your tools and set them out then price out a new piston and everything else associated with it, figure out how much pressing the piston pin in and out will run you and set all that money aside some where where it won't get spent. You can complete one project in a short amount of time if you put your mind to it.

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post #5 of (permalink) Old 09-12-2002, 04:27 PM
 
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Re: Blown piston- can it be changed from below?

I have to agree, it can't be done from the bottom. I am going through this with the 302 in my ford truck right now. the question i have is where can I find a place that sells a piston single?... all places I have found only sell sets of 8. I was just planning on buying a new piston, doing a hand-hone job and putting new rings in all eight cylinders, buying a new set of pistons would push the cost of this project more than I want, and I would be thinking about just trying to find used 302 or 351w to swap in the truck.....thanks
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post #6 of (permalink) Old 09-12-2002, 05:12 PM
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Re: Blown piston- can it be changed from below?

Unfortunetly, when you start to blow oil you have but one choice, rebuild the motor unless you want to catch the oil in a Gator Aid bottle.

Good Luck!
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post #7 of (permalink) Old 09-12-2002, 06:23 PM
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Re: Blown piston- can it be changed from below?

You could on a Miller, and it's successors, the Offenhauser and Meyer/Drake engines, and probably a lot of others. The block and head were a single casting. It was Miller's answer to head gasket problems, and it worked. No modern engine will allow it, though. The space between the cylinder walls is a lot smaller than the main bearing saddles. On the old racing engines, overall size wasn't a concern, but today engineers sweat bullets trying to save a fraction of an inch.
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post #8 of (permalink) Old 09-12-2002, 06:27 PM
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Re: Blown piston- can it be changed from below?

1. You may need a ring job due to blow buy... but you may not.
2. Zero compression on a "wet" compression test usually means a burned valve.
3. Unless you're really pressurizing the heck out of the crankcase, then the problem's most likely in the head, not the lower end.
4. Were it I, I'd pull the head first and see if that cylinder's got burned valves.
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post #9 of (permalink) Old 09-13-2002, 11:44 AM Thread Starter
 
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Re: Blown piston- can it be changed from below?

My oil pressure guage reads where 120 would be if the guage didn't stop at 80. I dunno, it could be a busted guage too, at the same time as all this. I do remember touching the oil-pressure sending unit, I think I just brushed it with my hand. With me, that could be enough for it to implode I suppose [img]images/icons/laugh.gif[/img]

I found a '98 4.0 with all the wiring but the computer, and only 29k mile on it, for $450. It's semi-local, and since I've been putting in a lot of extra hours at work I can actually afford it right now. I'm going to pull the valve-cover on my MJ, take a look-see at what's going on there, and if all that looks good I'm picking up a "new" engine....

Then I'll take it all to a friend's house and pay him $100+beer to do the swap with my help. He's got all the tools we'll need... I don't even know where most of mine are at the moment (all boxed up somewhere)
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post #10 of (permalink) Old 09-13-2002, 12:52 PM
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Re: Blown piston- can it be changed from below?

I wish I had a friend like that [img]images/icons/frown.gif[/img]
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