piston picture and question

1991notchbackLX · Jul 20, 2008

one of the pistons in the short block im using for my engine build looks like this... how much of a big deal is this?? can i get away with not replacing it? it looks like someone didn't check their piston to valve clearance in this motors previous life... can i run it or not?? everything else on the motor will be completely new, thanks in advance for the advice

Chris

vristang · Jul 20, 2008

How did you purchase the short block?
Did you ever see it run?

It 'looks' like a valve/spring failure damaged the piston... not really piston to valve clearance issues.
just guessing though.

1991notchbackLX · Jul 20, 2008

i purchased the short block from a guy on craigslist, relatively local, it was torn down when i bought it, the guy said he just needed room in his garage for a new project, claimed it had 34k on it and was part of a supercharger setup that was run for three weeks then torn down and replaced with a 351w... seemed like it was in good shape, clyinder walls are smooth and no real carbon buildup on the pistons, i dont know though (???) i only paid $150 so even if its bad i think i made out okay (?)

Vipersix · Jul 20, 2008

This one will be touchy...

What sort of a setup will this be installed on? Compression? Torque output?

If you are building a N/A motor with nothing too terribly extreme, it is possible to utilize this piston. It is by no means the correct answer and it should be replaced immediately, but this is real life and people in real life need to get the most utility from their limited supply of money. So, if you are short on cash and are unable to purchase new pistons then by all means use these ones. However, new pistons should be the first item on your wish list.

The simple fact that the valve failed and contacted the piston face is not necessarily a terrible thing. The picture displays only cosmetic damages and you would, in most scenarios, experience negligible differences in compression and ignition than the other pistons. The thing which worries me is internal cracks and reduced integrity which are hidden from the naked eye. It doesn't appear to have any problems though and I would say it is likely OK to use.

More importantly though, what does the rod look like? Normally the rod is the first to buckle when you experience valve failure. Is it perfectly straight?

1991notchbackLX · Jul 20, 2008

the setup for the motor is in my sig, pretty mild N/A, about 300 horsepower if that... i've just spent so much money so far, i' didn't want to have to go through the rotating assembly as well

i'll check the piston rod today, though the crank turns freely and everything, thanks a lot for the help guys

Chris

5spd GT · Jul 20, 2008

It will be fine based on the information you have given.

Vipersix · Jul 20, 2008

Your biggest issue then will be to ensure the rod is straight. I ran my old 5.0 with a cracked piston for about 5,000 miles a number of years ago with few adverse reactions. I don't foresee you having any difficulties.

oz · Jul 21, 2008

Check how much clearance all the pistons have to the top of the block at TDC. If this one has more clearance than the rest, then the rod is bent. Any bending of the rod will effectively increase the distance to the top of the block at TDC. IF all are the same, then I'd be comfortable going forward with it as is. If not, do it right and replace the rod and piston.

piston picture and question

1991notchbackLX

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vristang

1991notchbackLX

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Vipersix

1991notchbackLX

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5spd GT

"the 5.0 owns all"

Vipersix

oz

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