What would cause this?

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sscamaro70
Posts: 3
Joined: Thu Mar 10, 2011 11:03 pm

What would cause this?

#1 Post by sscamaro70 » Thu May 26, 2011 10:29 pm

What would cause this damage to the pistons on only half the engine cylinders 1,3,5,7 on the lifter valley side of the piston. It is a BBC with JE nitrous pistons
Image

71Hellride
Posts: 80
Joined: Sat May 30, 2009 7:35 pm

Re: What would cause this?

#2 Post by 71Hellride » Thu May 26, 2011 11:55 pm

Are you running Nitrous? Looks like it with the torch marks. Do all the pistons look the same or is that the worst one?

sscamaro70
Posts: 3
Joined: Thu Mar 10, 2011 11:03 pm

Re: What would cause this?

#3 Post by sscamaro70 » Fri May 27, 2011 4:58 pm

Yes i use nitrous. all 4 pistons look roughly the same. only one side of the piston is marked like that the other sides dont even have a scratch on them.

want-a-be
Posts: 189
Joined: Tue Feb 05, 2008 11:04 pm
Location: Southern Illinois

Re: What would cause this?

#4 Post by want-a-be » Fri May 27, 2011 6:58 pm

2 things come to mind for me.

How much piston to wall clearance do you have? How straight are the cylinder walls?

Could be a lean condition also.

Don

71Hellride
Posts: 80
Joined: Sat May 30, 2009 7:35 pm

Re: What would cause this?

#5 Post by 71Hellride » Fri May 27, 2011 8:30 pm

Usually the when the piston looks like it's been "nibbled" on like that it's from too much timing. I'd say for whatever reason (possibly too much timing) the rings gave up and let oil in the chamber. When that happens it does exactly what you see. Looking at the piston I'd assume you have a conventional headed motor, what kind of tune up did you have in it and what was the timing?

sscamaro70
Posts: 3
Joined: Thu Mar 10, 2011 11:03 pm

Re: What would cause this?

#6 Post by sscamaro70 » Fri May 27, 2011 10:30 pm

it is a conventional head. from reading the plugs it showed the engine was on the rich side and timing mark was just before the bend on the electrode side of things. i ran the engine at 37 degrees and on nitrous i pulled out 12 degrees for a 350 tune up

71Hellride
Posts: 80
Joined: Sat May 30, 2009 7:35 pm

Re: What would cause this?

#7 Post by 71Hellride » Sat May 28, 2011 10:04 am

The timing is a little more than what I run. Being rich over time will take the rings out as well. Rich and over timed seem to go hand in hand. If nothing mechanical happened, like trash in the system, I'd say the tune up got it.

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