MOON shaped Dents in MY pistons??

[mitsubluetalon]

hey guys, alright i'm replacing the head on my turbo dsm because i was an idiot and did the timing wrong and bent all of the valves on the intake side. my question is that there is probably going to be those little moon shaped dents in the top of my pistons, and i can't remember where i read it but someone was talking about using a ball peen hammer and a dremel tool to fix them. is this feasable? pound the dents back into shape and then use the dremel tool to clean it up?

i was also thinking that what if i were to just grind the dents a little more and then clean them up instead of peening them, make the moon shapes a little deeper, meaning i would basically have a non-interference engine. is that a stupid idea or would that work? how essential is it to keep the original shape of the pistons. thanks guys....

Jason.

 

[shifty01]

i dont know much about these dsms (on here to try and fix a friends car) but id imagine you would do more damage with the hammer then if you just left the dents in there. they cant be too bad, maybe just use some fine sandpaper to it if there bad and have a lotta charp edges (make sure you get all the dust outta there too). and i dont think you can make it non-interference that easy.

 

[green machine]

Honest opinion, since your have the head off and the block chillin you might as well do a piston upgrade. That or basic maintenance like new rings. I'd just wait and do it the right way and know nothing bad is going to happen then chance it and have to do it all over again.its what I did and I have no problems with my internals now. Don't go the dsm route and use the duck tape and zip tie method, at least not on something this important.

 

[GTM]

...
and i can't remember where i read it but someone was talking about using a ball peen hammer and a dremel tool to fix them. is this feasable? pound the dents back into shape and then use the dremel tool to clean it up?
...
make the moon shapes a little deeper, meaning i would basically have a non-interference engine. is that a stupid idea or would that work? how essential is it to keep the original shape of the pistons. thanks guys....

There aren't too many people around here that know what a peening hammer is for much less used one. I do seem to recall reading someone suggesting using a Dreml.

http://community.webshots.com/photo/315249027/315254767rosYAY

Unfortunately I don't have an after picture but these were all peened so there were no sharp edges, no mushroomed portions, a soft wire brush in a drill motor will show you your progress. You don't want to make them any deeper nor any larger, just take all the sharp edges off.

I wrote a reply last week for the same problem which I can't find at the moment, if you don't have a small peening hammer you can use the sides, corners, and edges of a good quality deep well socket maybe on the order of 12mm - 17mm. To give you some idea of how much force to use try for about 2 strokes per second. It's just a matter of encouraging the metal to go back where it belongs when possible. The metal will be a little more dense in those areas and thus less prone to act as a source for pinging whereas if you start removing metal it gets thinner and hotter plus lowering the compression ratio.

Cheers,
GTM

 

[mitsubluetalon]

Once again GTM you've saved the day. i've had a lot of other questions on this site and you've probably answered most of them with accurate, clear and concise information. i would like to thank you again.............so thanks.

Jason.

 

[GTM]

Once again GTM you've saved the day. i've had a lot of other questions on this site and you've probably answered most of them with accurate, clear and concise information. i would like to thank you again.............so thanks.

Jason.

You are always welcome. That stack of Canadian virtual beer is mounting. hic, belch.

If you have a camera take some pictures just to show how nice it comes out.

Cheers,
GTM

 

[Defiant]

make the moon shapes a little deeper, meaning i would basically have a non-interference engine.

You're not going to be able to cut them deep enough. If you don't hit oil, you're going to be making such a thin spot that combustion temperature will shortly, and you'll have significant costs in compression ratio.
I don't recall hearing of someone peining a piston crown. Just sand/file/grind.

 

[GTM]

...
I don't recall hearing of someone peining a piston crown. Just sand/file/grind.

Now now now Defiant you really got to get out of the house more. I don't remember beautiful downtown Galt being the sports car capitol of the world.

I've posted this process at least a half dozen times here over the last 3 years and ain't nobody ever said it caused problems or didn't work. By peening you don't loose any mass, you don't introduce sanding grit into the cylinders alongside the piston and rings, and less opportunity to have hot spots. Since I've been woring on overhead cam hemi engines where it is common for valves to kiss pistons you would think in 40 years I would have learned it was wrong. Any shade tree mechanic can grind them out, only a professional will peen them.

When rings come through the top of the piston and chew up the combustion chamber it's the only way to make a proper repair unless you want to drop the compression ratio and have a lumpy tick over.

Cheers,
GTM

 

[mitsubluetalon]

You are always welcome. That stack of Canadian virtual beer is mounting. hic, belch.

Yup. anytime your in Lethbridge Alberta Canada! and thanks for everybodies replies. they are all appreciated.

Jason.

 

[mitsubluetalon]

Hey one more question, i've never peened anything before, so i would like to know if there is a proper technique to follow, or if there is a link anybody could give me, to get the pistons back into shape. thanks.........

Jason.

 

[GTM]

Hey one more question, i've never peened anything before, so i would like to know if there is a proper technique to follow, or if there is a link anybody could give me, to get the pistons back into shape. thanks.........

Jason.

You will start with the raised edge and imagine a slight angled glancing blow, you will be trying to drive this back into the V so you will have to work at say the outside of the semi-circle and then the inside in the other direction. You will then retrace what you did but at a steeper angle, you will then use the side of you tool more down into the V. It's not going to seem like you are doing anything at first but then you notice after 5 min that it's startin to fill in. It will look better than the pockets the factory made, use the wire brush for it will help you to see what you are doing such as high spots. You will get the hang of it in no time.

Cheers,
GTM

 

[sherwinz28]

I thought those marks on the pistons were suppose to be there? I have four of those half moon shaped dents in all 4 pistons. Is it ok for them to be there?

 

[Defiant]

I thought those marks on the pistons were suppose to be there? I have four of those half moon shaped dents in all 4 pistons. Is it ok for them to be there?

Yes, the valve reliefs are mandatory.