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 Post subject: Reusing a dented piston? (valve failure)
PostPosted: Tue Jun 28, 2005 3:32 pm 
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Joined: Sat Jun 19, 2004 4:31 pm
Posts: 329
I'm about to tear down my engine (stock 1600DP), which had a valve failure of some sort. With the valve cover removed, you can see that the valve is stuck partially open, as the rocker has extra clearance, and the valve never fully closes.

Although I haven't pulled the head yet, I suspect it's identical to what I saw on another car I bought- the valve seat came out of the head, the valve closed on the (now crooked) valve seat, then the piston smashed into it bending the valve stem and pushing the seat into the head sideways. On my other engine, the piston had a ding in it from hitting the valve/seat.

I'm guessing that this will be no different. If there is no damage to the rod bearings, would it be OK to reuse a piston in this condition? Or would it cause hotspots and an eventual failure?

Thanks
- David


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PostPosted: Tue Jun 28, 2005 4:59 pm 
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While I will defer to the experts here, I would strongly advise against it. I once had the brass accelerator jet come loose and make it by the intake valve. Lots of noise so I stopped. Pulled the head off and you could see the scratches in the head and there was brass left in it (which is what clued me into pulling the carb apart to look for the source). The piston looked fine so I put it back together. Sure enough, 3 weeks later, major failure on that hole (I seem to remember that it was the rod bearing that went but not positive)

Brian


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 Post subject:
PostPosted: Wed Jun 29, 2005 4:02 am 
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Joined: Mon Aug 09, 2004 10:15 pm
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If a valve has hit it, its probably junk. You will need to put new rod bearings in it. Usually the force of the impact will crush one side of the bearing. Look it over real good and make sure its not cracked underneath.
If it was mine and it looked ok,I'd probably use it. I've done it before, but it was a nut from the carb on a small block ford. If it was for a customer, no way in hell. Besides stock pistons and jugs are to cheap. I seen them over on the samba for 75 dollars new. Could even goto a set of 87's and have you a 1641.(ZOOM ZOOM)!!!!


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 Post subject:
PostPosted: Thu Jun 30, 2005 10:43 am 
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I hit a piston with a valve in my Baja. Upon inspection I had the same concerns. I decided to go ahead and reuse the piston even though the valve was badly bent. The piston had a bit of a ding but I found no cracking. This car is NOT a street car so if it didn't work I would not be late for work or anything. Point being that the car is fine after 4 or 5 years. Maybe some one could give you a 1600 piston just for your peace of mind.


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 Post subject:
PostPosted: Thu Jun 30, 2005 2:39 pm 
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Thanks for the replies, everyone.

With a stock replacement piston/cylinder set at only $100, it seems silly to not replace them while they're apart... but the problem is that I don't really have the time to give it the proper break-in...

I basically need the car right away (to drive the 150 miles back to school), or I'd need to take something else. Of course I'd rather have my VW!! :D


I'm hoping the rod bearings are OK... if it's splitting the case, I definitely wouldn't have the time to fix it. I'm out of state working, and only have a 4 day window to fix the car when I get back. :(


I'll just have to wait and see what I find when I pull the head!

- David


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 Post subject:
PostPosted: Thu Jun 30, 2005 7:15 pm 
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You dont have to split the case to change the rod bearings. I could do all of this in about 3 or 4 hours. Break in? Whats that? Put them on, fire it up and drive it away and goto school.


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