Lost part of a piston - Pull the engine to replace?

Post by **vjaneczko** » 22 Jul 2012, 18:16

In the process of trying to stop the noise, I dropped the oil pan thinking it was from old gaskets. I found chunks of a piston in there! Even though I have good compression, it appears that a small part of the piston broke loose, below the ring.

Talking with a buddy, he's thinking we can pull the head off and replace the piston, not needing to pull the engine out of the car. Since I've never dived this deep into engine work, I'm looking for second opinions or suggestions. I just put a lot of parts & time into lifters, valve stem seals, water pump & timing belt, blah blah blah so I'm not looking to get another engine.

Any thoughts?

Post by **JimBee** » 22 Jul 2012, 22:17

If you just need to replace a piston, there's no need to pull the engine.

The first thing that comes to mind is condition of that cylinder wall. If you're lucky which I hope, it won't be scored. If it's just a piece of the skirt then it probably didn't damage anything, but you'll need the head off and probably the piston out to determine that. I've had other engines apart, but the not the 850. If you already have the pan off, you can see how the connecting rod cap can be removed. It might have a "keeper" you'll need to pry away so you can get a socket on the hex bolt. You can turn the engine to get the rod cap at the bottom for best access. I assume you can clearly see which piston gave up the piece.

Before you remove the piston, shine a light up there to check for tightness around the bottom of the piston in the cylinder, and the top, too. Was it slapping that caused a piece to break off? Was that the noise? Check the others while you're in there. If it was slapping, you'll want to mic the cylinder diameter all the way around to make sure it's round and proper diameter.

With the head off, use a stick with a hammer to tap the pisto rod up and out. Tap the rod at he bolt point, not the bearing area. Hopefully, there won't be a ridge that stops the piston from coming out the top. If there is, you can rent a tool to shave it off. I think O'Reilly's and maybe Autozone has one.

You'll be able to see the cylinder wall clearly.

It would be a good idea at that point to mic the rod bearing journal on the crank just to make sure it's perfectly round—just in case...

After you assemble the new piston to the rod, you'll need a piston ring compressor to hold the rings in while you tap the new piston into the cylinder using a hammer to tap a piece of wood (piece of 2x2 or 2x4) on the piston crown. On the big block v-8's I've rebuilt we lubed up the piston, put the ring compressor on good and tight, with everything aligned, give the piston a good wallop with a apiece of wood like I described—to send it into the hole in one shot. That's because if you try to tap it lightly many times, the rings can hang up on the top of the head as they come out of the compressor and you have to start over the with compressor. I don't know if it's recommended this way on the 5 cylinder. Okay, you don't want to drive it too hard so the rod goes smashing down against the crank, just hard enough to get all the rings in at once. NO HANDS should be on the rod to guide it while the piston is being driven in. And the bearing insert should not be installed in the rod, yet.

I would replace the bearing inserts with new while I had it apart and fussy me would probably "plasi-gauge" it.

With the piston rings inside the hole, install the bearing insert in the rod journal, lube it, then the person underneath should carefully guide the rod as a helper taps the piston down the hole, so it slips perfectly onto the crank journal. The rod might need to be turned a bit to perfectly align it. Like I mention below remember the assembly lube part. Install the lower bearing insert in the cap and properly torque the cap back on. Remember the keeper if it has one. Done! Down below, anyway.

Other notes:
While you have it out, I would probably take the rod to a machine shop and have them check it for straightness. They can also press out the wrist pin and back in again with the new piston.

Before you put it back together, make sure you smear all metal to metal moving parts with assembly lube. Autozone sells a tube for about $7.00. Do not put lube behind the bearing shell where it contacts the rod or rod cap; only on the surface where it contacts the crankshaft.

While the pan is off, check around the bottom end for any other shrapnel.

Any seals in there you'll want to replace while you have it apart?

Good luck. Post back how it went.

Post by **vjaneczko** » 23 Jul 2012, 08:21

Very detailed, thank you.

We did pull it part with the block still in the car, easier than I thought it would be - until we snapped a head bolt. I'm ignoring that problem for the moment. I'm sure it's going to be a great project! Just wish I had more time to devote to it. I start vacation Thursday, so I can't take any more days off before that.

Post by **JimBee** » 23 Jul 2012, 09:00

I found your other post this morning—should have looked further before I launched into it. Your writeup is really helpful, especially with the included links. I've got it bookmarked!

Sorry to hear about the head bolt. Is there anything we can learn from how that happened?

Post by **vjaneczko** » 23 Jul 2012, 11:57

I think it was just dumb luck. We used a two-foot long breaker bar to loosen the bolts and it was still very hard - took a lot of grunting with the right hand on the handle while keeping the neck of the breaker bar over the bolt with our left hand. This one just snapped.

Since the bolt is something like 6 inches long and the head is covered with oil, there isn't any way to get PB Blaster to the threads so if you're going to do this, treat it like any other critical bolt; apply steady pressure without bouncing on the ratchet - and keep your fingers crossed!

Post by **rmmagow** » 23 Jul 2012, 12:08

Do head bolts react well to impact wrench assisted removal, i.e. the shock value helping break it free or is this more prone to breaking the bolts? Electric impact wrench, not a million ft-lb air tool.

Post by **vjaneczko** » 23 Jul 2012, 12:33

We actually tried using an electric one and they didn't budge. No real information on the impact except that it's rated for 3.5 amps at 120 volts. The bolts should be torqued to 44 ft/lbs plus 130 degrees. Not sure what that equates to ft/lb-wise, but it's pretty stout!

You're supposed to replace the bolts since the extreme torquing stretches the metal.

gregandterra · Post by **gregandterra** » 23 Jul 2012, 19:16

recently broke head bolt on my burnt valve adventure. Soaked with PB blaster, placed bolt atop broken piece and hit with 2 lb hammer several times. Then used Snap-on left handed drill bit and it backed right out. I was stressed out the whole time worrying I would not get it and have to pull the block and take to machine shop. The key is finding an drift pin that very closely fits the bolt bore to center the punch mark perfectly, and praying! I would not attempt without the left handed drill bit. They will usually back out the bolt as it is no longer "loaded" under torque and really isn't tight in the threads.

Post by **vjaneczko** » 23 Jul 2012, 20:28

I lost about 1 or 1.5 inches of the end of the bolt. It's been soaking in PB since last night and keeping my fingers crossed.