Piston Cracks

[84 Convert]

Well, I finally got the engine out of my Crew Cab disassembled. Good news is there are no cracks visible in the block or heads that I can see so far. Bad news is that there are small cracks in the pistons. The engine ran fine and judging from the way it started, it had excellent compression. I pulled the engine from the truck to replace the head gaskets and possibly the timing chain. Now I know the chain is as bad as expected. The question is this... are these cracks normal and the pistons serviceable? If they aren't normal how can I prevent this from happening again? I really don't think the motor is being over fueled because there is no black smoke, and the power level is not great, like most stock N/A motors.

Thanks for any and all info.

Gregg

[TimK]

84,

I had the same problem with my Sub when I bought it with 165K on the original engine. I noticed when I brought it home that when the engine was cold it was puffing a little white smoke out of one bank of cylinders. There was also a lot of blow by when taking off the oil filler when the truck idled. A compression check soon confirmed I had low compression in one cylinder. I took the head off that bank and found the piston low in compression had a severe crack, all the way through the piston crown and the piston next to it also had a crack but there was no sign that the crack went through the crown.

I think this could be caused by a couple of different things. When I took my engine apart it appeared to have the original timing chain. There was a lot of slack in the chain. I replaced it with a timing gear set. I think the previous owner was running the timing a little more advanced then normal to compensate for the stretched time chain. The engine also appeared to have the original injectors. It's also possible that I had an injector not functioning to spec and it was causing the cylinder to run hotter then normal or for that cylinder run with more of a combustion concusion as if that one cylinder had it's timing advanced more then the other. I suspect if an injector is opening at a lower pressure it would mimic advanced timing for only that cylinder.

As some of my other posts have noted, I am purchasing a new DSG motor because of a main web failure that broke the block and crank. I told the tech at DSG that I would be running a Banks turbo on the new engine so they could set the injection pump up for me. He said, in order to get the engine warranty, they would need to build the motor with the 6.5l pistons that have a thicker piston crown. He said the 6.2L piston crowns are thinner and would more likely to crack under the additional horse power.

For what it's worth. When I bought the replacement piston and rings for my truck about 25K miles ago, I had to buy a complete set of piston rings. I still have 6 sets of rings that are brand new. I can sell you set if you are only looking at doing one piston. Since my current block is broken I am also going to be scrapping it. However, it has a timing gear set up on it and two pistons in it with only 25K on it. I can probably make you a good deal on those too. With the new motor I am getting, I won't need them. The new engine has a timing gear set and I doubt if the 6.2L rings will ever fit the new motor.

TimK

[john8662]

Tim,

I am interested in the gear set if you want to part with it, you have email reguarding the TH400 cover and the gear set.. Thanks.

[ 06-10-2004, 12:42 PM: Message edited by: john8662 ]

[84 Convert]

Why yes, I would be very interested in the timing gear set and the piston rings. What other parts might you be looking to unload? Of course, I don't want to pull the rug out from under john8662's feet either. I will be buying a gear drive set, one way or another. .

Gregg

[ 06-10-2004, 09:09 PM: Message edited by: 84 Convert ]

[TimK]

Gregg,

I will email you about the piston rings and what else I won't need. I never noticed that you were in the same state. John is helping me out with finding a transmission cover and we are working on a trade for the timing gears.

TimK