Does this piston need replaced?

[little67stang]

67 Ford Mustang 200ci blown head gasket between number 5 & 6 cylinders, all other pistons look black and have carbon build up.
http://www.cardomain.com/ride/2613961/3

 

[Anlushac11]

EDIT: I am wrong. Replace the piston. What I thought was a valve relief isnt. If you are not missing a valve then that means someone in the past dropped a valve and rebuilt the engine with that piston.

By rule of the thumb I would say yes. Looks like FOD to me. There is a danger the piston is damaged or cracked. A stock cast aluminum piston is cheap.

But...if your short on money then get piston cleaned up and checked for cracks. As long as the piston is not cracked then at the low compression and low rpms the stock motors usually run I would not think it would be a problem.

The oily sooty pistons can be cleaned but it depends on if the engine will need boring to clean up the cylinder walls.

 

[tony1963]

I wouldn't worry about the piston. You can see "20" stamped in the face so it has probably been rebuilt at one time. The other bouncing marks are probably from a piece of valve banking around.

Pistons are pretty durable and a dimple like that won't hurt. Put 'er back together and go.

 

[little67stang]

Thanx for the replies. Another theory I've heard is that that one cylinder has been bore over already and the "20" indicates the amount. It sounds strange to me to only do one cylinder, but for someone really low on cash or someone trying to get rid of a car and make it run for cheap it could be an option. I've owned the car for two years now and 90% of the driving I do is highway 80mph+, so probably replacing the piston will be the way I go. The cylinder walls look great, so no worry there. The head is heading to the machine shop for a valve job and to be spec'd and milled for the proper C/R. Possible new 289 springs if I ever get the money for a hopped up camshaft/headers. We'll see, again thanx for the replies.

 

[rbohm]

8) the piston indicated not only shows some damage from a foreign object, it also shows damage from detonation. cylinders 5 and 6 usually run the leanest of the six, as well as the hottest and thus are prone to detonation. this is probably also the cause of the head gasket damage you have shown. the piston seems otherwise fine though. i wouldnt replace it unless it showed signs of cracking on its skirt. i would however determine what caused the detonation in that cylinder and eliminate that cause.

 

[little67stang]

I have the duraspark II on the car, less than a year old all new parts. So hopefully it not any of that. The main reason I took the head off was because from a vaccum gauge reading it looked like I had a stuck valve, and it was time for a valve job anyways. The dropping vaccum and not being able to time/tune the engine correctly could be the cause of detonation.