robertbartsch

I read the GM bulletin on fixing piston slap a few months ago. I was surprised to learn that they recommend replacing the top ring only - no honing is done. If I were GM I would recall every last engine and replace them all. This is a serious factory defect.

Obviously, the bulletin states that the same pistons must be replaced in the old bores...

I would have thought that if the bores were out-of-round that GM would have installed a brand new fresh engine under warranty.

Hey, if the rings don't seal I would bet GM will just replace the engine....

As you should know by know, GM cars are crap - just look at the resale. Some of the decisions on warranty or replacement are dicktated by performance. GM is really sucking wind right now - see the wall street journal article today. I'll bet they would have replaced the engine but since they have not been selling any new cars lately, you get the crappy rebuild instead.

Next time buy a Honda.

cyphur

iTrader: (10)

Thats a great idea!!

technical

But how does that translate to setting the motor up "loose" like you were talking about? Sure engines make more power after they break in, but we weren't talking about that.

BBQLS1

After several thousand miles bearing clearances will get looser, similar to running a looser bearing clearance. You will find almost all if not all professional engine builders will run looser bearing clearances for high performance engines. As long as you can keep the bearings filled with oil at pressure, it will make more power because of less loss due to friction. This can and does affect the longevity of the engine.

technical

Sorry, maybe I'm being too thick. I understand how things break-in. What I'm asking is how can you setup a motor loose? You have to stay within the tolerances. By loose are you just saying the loose "side" of the tolerance?

LOnSLO

iTrader: (15)

Yes. A loose motor would be everything set up on the high side of tolerance.

technical

OK, but how much power are we talking?

BBQLS1

Right, sometimes you can even go outside of the tolerances specified by the manufacturer. In the case with main bearings, I have heard of .0035, which is way out there. If you go loose, you have to make sure your oiling system can keep the bearing filled with oil (more volume and more pressure). Also this loose an engine can make more power, but the life expectancy of the bearings goes down. Plus you may not be able to keep up enough volume and pressure at a low idle. It just kind of depends. When you blueprint an engine, you can come in tight for longevity (never go tighter than spec) say around .0015 for the mains (This is probably a little tight it's just for an example) or go loose around .003 which may get you a couple of MPH or maybe 20hp. We are only talking approximate here. That is part of the reason you see many different MPH's on peoples time slips on cars with the same mods. I think you can see even bigger differences when it comes to ring gap. Here you want to run as tight a gap as possible without having the ends butt together and power adders such as nitrous or boost will greatly increase the temperature and force the ring ends closer together and combustion temperature rises.

BBQLS1

If you want to learn a great deal about this kind of stuff, check out Pro Stock racing or Stock Eliminator. These guys are super hard core when it comes to this stuff. Stock Eliminator cars will even run the oil pan dry if they don't shut down after the quarter mile to keep windage down. Hardcore! You can run your oil on the lowside of the dipstick and pick up some power especially if you are running some rpm's. I wouldn't do it on a street car though. I don't think I am that hardcore!

technical

Like I asked before. What does blueprinting and trickery have to do with a motor built at the factory? FWIW, I'm well aware of the things race engine builders do to achieve the competitive edge. But I don't build race engines so that information is trivial at best. If I ever setup a customer's engine outside of the tolerances, then I just bought an engine and lost a customer.

The original poster is asking about honing his *street* car's engine. He is not in the market for a balanced and blueprinted race engine that has to be shutdown every 1/4 mile to avoid being genaded.

BBQLS1

If it gets rehoned, material will be removed and the clearances will change, if this goes out of spec, new sleaves or a larger piston could be required (not likely, but possible). Or the dealer may rehone the engine and pop the pistons in without checking (could be good could be bad). You could be fine without rehoning since this engine does not have alot of miles. The new rings will need to seat in. I don't really think this will be a problem if the don't hone it.

Grimes

iTrader: (3)

some random dealer tech who probably has done one or two hones in his life will do more harm than good. let them put the pistons in, and see what happens.

BBQLS1

Hey if it works it works. If it falls to pieces, you now have a reason to build a 600hp 427 cu in LS1! It's a win win situation!

technical

I vote 434ci.

redrocketls1

damn this is scaring me outta wanting to get a forged shortblock... all these problems honing or not honing.. and depending on what kid.. like eagle or lunati u have to have it honed by a machine shop or osmething no?

BBQLS1

This is for repairs not building. The is issue is wether or not to have the local dealer hone the an engine to just put new rings in. If you are building, have it honed by a machine shop, they will need your pistons and what type of rings they are honing for. Machine shops do it for a living. Usually, a tech at a dealership does not do this very often.