Do I need to have the block bored?

Think I maybe experiencing a little bit of piston slap on #3 and #4 cylinders in my 4.0L HO engine. It is in a 2000 Cherokee. Do I need to rebore the cylinder oversize, or am I able just to hone the cylinders with the engine and crank and cam shafts still in the engine and the engine still in the vehicle? Any thing I need to look out for or be aware of?
Thanks,
Bill

First, piston slap comes from having too much room between the piston and the cylinder wall. Honing the cylinder just makes more room between the two.

Second, honing not only removes material from the cylinder walls, it flings that material, and the abrasive used, all over the place. You don't want any of that inside your engine when it's time to put it back together.

A little piston slap won't kill your engine. Drive it 'till it drops!

What does it sound like, where is the sound coming from, and why do you think it is piston slap.

I have read that true piston slap is caused by a broken skirt on the bottom of the piston (IIRC it is called the skirt).

Check this out:
http://www.youtube.com/watch?v=V9PQI5n3iwk

I have had that same exact noise on two of mine, 87 and 89, and it was not a busted piston skirt, it was sticky valve lifters, because running the engine at 3800 for a minute in park got rid of the noise by unsticking the lifter, by making it rotate again. A busted piston skirt will not repair itself.

Ecomike said:

I have read that true piston slap is caused by a broken skirt on the bottom of the piston (IIRC it is called the skirt).

Click to expand...

Here is some more reading for you: http://www.pistonslap.com/whatisit.htm

I have tore down engines with stretched rod caps, wiped cam lobes, non-existant wrist pin bushings, piston rings in too many pieces to count, cylinders that I could see the egg shape at the bottom. I'm still waiting to see a cracked or broken skirt.

Hypoid said:

Here is some more reading for you: http://www.pistonslap.com/whatisit.htm

I have tore down engines with stretched rod caps, wiped cam lobes, non-existant wrist pin bushings, piston rings in too many pieces to count, cylinders that I could see the egg shape at the bottom. I'm still waiting to see a cracked or broken skirt.

Click to expand...

Nice link, and good info! This was informative!

Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.

Click to expand...

Interesting that the PS noise can also leave as the engine warms up. I know mine that I had for years was not piston slap because it is now gone. But it sounded like piston slap at times mixed with valve train noise. But it took years and miles, and lots of oil changes and repeatedly running the engine at 3800 rpm for 60 seconds when it did make the noise to free up the sticking lifters.

Mine still has a slight sewing machine ticking (not laud at all, very quite, even on a 32 F start up this week, which was when it use to sound like it would explode at any time) at idle that is worn rockers from the parts wearing on the rocker contact points (wearing on each other). I also discovered recently that part of the noise was some of the rockers not being centered over valve stem and lifter rods. I straightened them out when I recently changed some valve stem seals (oil leaking onto the plugs #1 and 2 recently got excessive, now fixed) on my 289,000 mile 87. It is now quite as a mouse after 60,000 miles and 7 years that I have had it. And it finally has most of its full new engine power.

On my 99' The guy that owned it before me had a gash in the lower radiator hose, he drove it till it quit running. Blew the head gasket... we had the head milled and put it all back together and i drove it for quite a while like that till the piston skirt broke off enough that it could rock in the cylinder. It ended up coming up and knocking #2 spark plug out. Apparently it is common on the later model 4.0s to have thses sub- par pistons in them though.
Pic of the piston...

Hypoid - Honing Cylinders

I thought that you had to hone a cylinder when replacing piston and piston rings so that the rings would seat correctly. Am I wrong in my thinking?

That is correct.

You need to take the pistons out, and measure the cylinder wear before spending money on new rings or pistons. If the cylinder wear, or taper are out of tolerance, you are just throwing good money after bad.