eallanboggs

iTrader: (1)

Got P0306. Ran EScanPro Mode6. Got nearly 3,000 misfires on #6(all others had 0 misfires or #4 had 30 misfires). Owner said he changed plugs and wires and swapped coil #1 with #6. Pulled plug 6. Side electrode covered w/carbon after only 2 days. Pulled Bank 2 rocker cover. #6 intake rocker NOT rocking. Exhaust rocker OK. Pulled both rockers on #6-OK. Pulled both p rods on #6-OK. Turned crank by hand to measure p rod travel. #6 Intake p rod moves 1" less than the #6 exhaust p rod so #6 intake valve is NOT opening, but that doesn't explain 0 psi comression on cy #6. Also pulled #4 rocker to compare #4 intake p rod travel to #6 p rod travel(just wanted to compare intake to intake instead of intake to exhaust). #6 intake p rod travel is still 1" less than #4 intake p rod travel. So either the lifer has collapsed or the cam lobe is gone(not very likely, but that still doesn't explain the 0 compression reading on cy #6. Out come the borescope and down she goes into #6. See a hole the size of a dime on one side and round scratch marks at the center of the piston crown. Any help would be appreciated. I know how to do the repair. I'm just asking if anyone has seen a hole in a piston with the intake valve not opening?

bww3588

iTrader: (49)

Sounds about right. My guess is, the hole came from the valve hitting the piston. Now the valve won't seal and causing no compression. Or...when the piston broke, the piece came up and got into the valve, and bent it.

joecar

eab, do you know if it was knocking/detonating...?

eallanboggs

iTrader: (1)

It is not knocking. I only looked at the car for under 2 hours. This guy does repo so he gets deals on vehicles. The thing is he doesn't know the history of the vehicle so when I get them they already have problems. He buys them first instead of bringing them to me and paying me to check the engine. He's tight with the cash. It always ends up costing him because he buys vehicles that look good on the outside, but are junk under the hood. I should have mentioned the spring is not broken. The measured height of both valves on #6 is the same. That doesn't mean the intakve valve isn't bent. It just means right now it is being held closed by the spring and it is NOT opening because the rocker is not rocking. This is not an interference motor so why would the valve hit the piston putting a hole in the crown if the spring and retainer are in good condition? That hole in the pistion really makes this a much bigger job considering this is a 4X4. To get the pan off on a 4X4 the transfer case must come out. I don't think this guy can afford this repair. He's going into sticker shock when I tell him the flat rate hours on this job times 80 dollars. The truck looks new. The interior is very clean, but with a hole in a piston I'd sell it as is.

TheWolfMatt

So I'm guessing it's either a 4.8 or 5.3 that detonated a piston? You didn't specify. If that is the case then you could get him another motor out of a junker for around $250-400 at your local yard. Just my 2c.

batboy

iTrader: (6)

A number of things can result in zero compression. I burnt an exhaust valve once which caused this very same problem. So, valve not sealing, broken/burnt piston, broken ring(s), bad head gasket, warped head, damaged cylinder wall, etc. etc. Another thing I've seen is a damaged lifter that is stuck in its bore preventing the valve to close all the way. I know you say the valve height was measured, but it doesn't take much to prevent a valve from sealing. In the end, this requires the heads to be pulled off. Well, I guess you could poke a bore scope down the spark plug hole for a look if you want.

eallanboggs

iTrader: (1)

It is a 5.3 I suggested he find one OR he can rebuild this one. The problem is this is a 4X4 which means the transfer case has to be removed to get the oil pan off. What a pain. The pan has to come off to get that piston out the top. I did use my borescope and found a hole the size of a dime in the crown. Circular scratch marks in the top/center of the piston crown and a dime size hole on the side. It's almost like someone dropped something down inside the spark plug hole and started the engine without removing the object. I say that because the scratches are in the center and the hole is on the side. I'd like to have a look into the pan and see what is in there besides a round chunk of aluminum.

batboy

iTrader: (6)

There are two likely causes, detonation burnt a hole in the piston or it kissed a valve. From what you described, I'd say a valve hit the piston.

bww3588

iTrader: (49)

All ls engines are interference. Non interference means it is impossible for the piston to hit the valve unless something is taken past it's limits. Like a rod breaks or a valve spring breaks letting the valve drop further than it would by the cam opening it.