I broke an exhaust valve spring on my #2 piston yesterday. When I tore it down I found in addition to a bent valve I also found my piston face was a little beat up.

What is the best method to dress the face of this piston to get rid of the dents and ridges?

 

Same thing happened to me, on my old motor(383). I just left it that way since it seemed most of it was in the middle. Never lost any power and I must have sparyed that thing 100 times(175shot). I'd leave it.

Where did the valve hit the piston at. In the middle, on the sides?
If it hit on the sides better plan on pulling the motor. If it hit on the side of the piston most likely it smashed down on the ring.

 

You're trying to do this with the piston in the motor/bore? You can use a small block with a piece of sandpaper to get down all the high spots. The problem is the grit! I'd get it to TDC and mask around the edges where the piston meets the bore to try to keep the stuff from getting down along the sides. After finishing, it wouldn't hurt to spray the bore down with WD-40 and a clean wrag. Then change the oil!
I still don't like this but that's the best you can hope to do without a r&r.

-Mindgame

 

I'll be real careful when doing this. Is the fine, small particles you need to worry about. They can easily get wedged between the piston and the cylinder walls.

 

Fixing it in the bore, you might try doing it dry with a vacuum cleaner hose in your other hand sucking out the bits.

The sharp edges could form hot spots and cause pre-ignition in that cylinder. You don't have to completely eliminate the dings, just smooth them out and get rid of the sharp edges.

Follow Mindgame's advice.

Good luck.

 

Sorta a combination of what has been said:

bring the piston to TDC, wipe it off well with some carb cleaner or mineral spirits, get it good and dry. Get some duct tape and tape it to the edges of the top of the piston (so nothing can get between the piston and the block) and then mask off the rest of the engine. use a combination of abrasives, I've had good luck with a dremel and sanding rolls and then finishing it off with a nylon brissle wheel. Make sure you get rid of any sharp edges.

 

what about that coating that comes on some pistons?

 

how about replacing it?

 

Look at the pics, it's not that bad. Being realistic, it almost doesn't make sense to mess with. The only reason that I would go as far as I would is that I'm more **** retentive then 99.99% of people.

Leave it alone or polish it up a little if you have to do something, but don't go replacing pistons over this...

 

being **** retentive is a plus when working on engines!

 

WS6 TA,
[ Comments deleted by moderator ]

I wouldn't leave anything that could cause a hot spot on the top of a piston or anywhere in the combustion chamber for that matter. Any raised edge has got to go.

-Mindgame

 

Edited by Moderator

Please no name calling, or unnecessary rudeness in Advance Tech. Thank you.

 

As it turns out I pulled the drivers side head this afternoon and found that two more pistons had dings in the piston face and found that the heads surface did too. I found little bits of metal in the #3 and #5 piston that seemed to be responsible damage to my cylinders. I looked for hard for the culprit and this is what I finally found: guide boss. It looks as if the valve guide boss cracked and a piece fell into the #2 cylinder and somehow pieces of it traveled to the driver side of the motor and caused damage over there. Heads are off and are being shipped out to see if they can be repaired. It looks like the motor is going to have to come out any way to get some new pistons.

I'd like to go to a forged rotating assembly but this was an unplanned event and I don't have the money. I think I'll have to settle for forged pistons and retain the stock crank and rods. Man this broken valve spring is starting to get really expensive.

 

Yes sir,
Broken valvesprings usually cause a whole $$$load of trouble. That's why I spend so much time keeping checks on the ones in my race engines.... street engines too for that matter.
The shrapnel from the little 'drop' ends up back up into the intake where it just migrates to other cylinders.

I don't know your situation but I'd give the KB hypers a good long glance. Inexpensive, relatively lightweight and a good buy at about 22 bucks a pop. Best of luck.

WS6,
[ Comments deleted by moderator ]
-Mindgame

 

94Sleeper- I think that you're looking for a bigger problem then a broken valve spring or valve guide. it's fairly unlikely that something would make it from one bank of the engine to the other. Broken valve guides usually go along with bent valves and/or valves contacting something. One or the other just letting go... well, it might happen, but neither is very likely to cause the other and both happing by themselves at the same time is unlikely. I wouldn't be that suprised if this was caused by overreving the engine or possibly a problem with how the heads were originally assembled.

If a rebuild is too far out/you need to drive it I'd check everything out really well (loose timing chain?), clean up the piston tops and put a clean/rebuilt set of heads on it and just not push it hard till you're ready for the rebuild. If the other pistons are worse or if the damage is near the edge I'd just set it aside till you can do it right to avoid turning the rest of the still usable parts that you have into a big pile of scrap.

Mindgame- [ Comments deleted by moderator ]