Replace #6 piston in situ? Or pull? or ?

#1

Woe is me… In May at Barber, it appears that the #6 intake valve stem broke and the valve head dropped into the cylinder. Needless to say, there was some nasty impact and the piston won the battle. The valve head is now firmly planted at a 90 degree angle into the aluminum head (toast). The head is now completely out of the car.

The #6 piston has fairly significant gashes on the face. This cylinder wall (and the other 5 piston/cylinders) look fine.

I have considered grinding down the scars in the piston and running it. This seems risky since I would then have a piston with reduced mass and possible internal damage. Plus the connecting rod may have been damaged, too. Am I right?

So, the least cost option appears to be replacing the one piston, rings, connecting rod, and bearings. Can this be done with the block in the car? (Oil pan off, on my back, oil in face, etc.) (It would be very nice to have a lift…) Or am I better off pulling the engine out to replace this piston?

Or should I replace this bottom end with another and do a more thorough rebuild over the next few months? (This bottom end is nothing special, some street engine with 150k+ miles. It was running great before the valve failure.)

I realize this is multiple questions, but I would appreciate your suggestions and prior experience with this challenge. Thanks.

#2

theese engines are to cheep to bother spending the time or money required to fix that correctly, get another engine and be done with it!

#3

While it is possible to replace that piston and rod with the engine in the car. If you go that route I think it would be a lot better to pull the engine and do all of the cylinders. If the cylinder bores aren’t worn, they should be cross-hatch hosed so the new rings will seat. And it would be best to inspect the crank and have it polished.

#4

jlevie wrote:

Other options:

  1. I have an old piston you can have for free. Put your bearing in it and drive on. Hell, I have a used head I’d be willing to part with too. I was going to get it rebuilt, but I can always get another head.

  2. Live with the scarred piston face. Put a used head on your motor to get you thru the year and then decide later if you really need to open up the bottom end.

  3. I don’t like the idea of removing material from the piston. If the gashes are serious enough that you are considering machining it’s surface, then you might have to worry about removing enough material that there might be vibration issues. I’d rather have a few gashes in a piston that will fill up with carbon soon enough, then a single piston that was significantly lighter. I’m kinda pulling this one out of my butt tho. I don’t know how much piston weight difference is too much.

And how much material can you remove before the piston is no longer legal? It’s unlikely that folks are going to give you a hard time, given the circumstances, but it’s an issue worth being aware of.

#5

You are forgetting one of the basics…the crank. You can patch the motor but it is not going to make good power and you run the risk of killing the whole motor, including the new head, by patching. I agree with the suggestion that that motor is junk and start over (again:) ) I have been there and hated to pitch the motor but did. Check the cylinder walls carefully to make sure they haven’t been attacked by the errant valve. Start over and be happy!!! Chuck

#6

Good advice from all, as usual. Still pondering my options. Other ideas/suggestions?