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Is this piston okay to use?

Thought I would put this question out to the experts for a discussion.

Found one (1) Mahle piston with a small ding near the top ring land (see picture) which does not affect the piston travel within the cylinder or the piston ring when it is positioned within the ring land.

Piston is in very good condition in all other respects and well within specifications of 94.971mm measured at the skirts.

This car will not be used for track racing, just touring and street use.

Appreciate all comments, and if there is a way to repair this, or should it be repaired "how would you do it?"

Thanks.

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Ed Paquette
1983 911SC
1987 944 Manual (Donated to the Nat. Kidney Foundation)
1987 944 Automatic
Old 06-06-2012, 07:28 PM
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I wonder how that might have happened? It looks to me like it should be ok if there is no other damage like cracks.

-Andy
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Old 06-06-2012, 10:40 PM
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Hey Andy:

I had wondered how this happened as well. My best guess is 1) banged against something upon removal, or 2) some "foreign" object got caught between the cylinder and piston during running maybe?

There are no other signs of damage and no cracks which is good in that respect.
Forgot to mention this piston is from a 3.0L, but you probably already knew that by the measurement given (94.971mm). It seems like a bummer to have to throw it away, so I am glad to hear it can be used again.
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1983 911SC
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1987 944 Automatic
Old 06-07-2012, 12:07 AM
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That looks like a way for combustion and maybe more so during detonation to get down behind the top ring when the go pedal is down. The rough edges look like maybe that was already happening.
I might install it in an old lawnmower if nothing else was around but I wouldn't put it in a Porsche.

I'm not a pro though and I'd like to read what Henry, Steve, Mike or anyone else would say and if anyone's seen that before.
Old 06-07-2012, 11:00 AM
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It's not the skirt you need to measure. It's the top land to ring measurment that will be the critical factor . That Dim wears out much sooner than all others.

No more than .004
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Old 06-07-2012, 11:01 AM
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JFairman and Aaron, thanks for your comments and input. My fault for not posting more information with regard to the ring land clearance/tolerance measurement.

When checked with a new ring, I could barely get the .001 feeler guage in, so that was a positive. Probably the only positive, and I do worry about all the components of combustion taking its toll as suggested.
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1983 911SC
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1987 944 Automatic
Old 06-07-2012, 01:37 PM
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According to this source: Back to Basics: Preventing Piston Problems: Engine Builder

Preignition Damage
A burned piston is a piston that has been subjected to excessively high combustion temperatures. Damage may include a hole burned through the top of the piston or the upper piston land. This type of damage is typically caused by a hot spot in the combustion chamber that becomes a source of premature ignition.

The cause may be spark plugs with too hot a heat range, an extremely lean air/fuel mixture, a hot exhaust valve or even a sharp edge in the combustion chamber. Reading the spark plugs should tell you something about the air/fuel mixture and the heat range of the plugs. If the electrodes are melted or damaged, the plugs are too hot.


Some information on piston wear from Kolbenschmidt:
http://www.ms-motor-service.cn/ximages/ks_50003973-02_web_leseprobe.pdf

Some interesting information from Carrillo on pistons. Note there are also links to cylinder surface finish and ring installation guideline. Maybe not applicable to you, but good information
Piston Tech

You may want to talk to your piston manufacturer and ask for what dimensional criteria is used to qualify a piston. Ring to land clearance is one, but I am sure there are more than that from reading through the above material.

Otherwise, when in doubt, replace. Too much money and time in assembly in putting together one of these engines.
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Old 06-07-2012, 02:51 PM
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Quote:
Originally Posted by JFairman View Post
I'm not a pro though and I'd like to read what Henry, Steve, Mike or anyone else would say and if anyone's seen that before.
I would entertain a guess as to what any one of these gentlemen would say. Let's hope one chimes in here soon with their respective advise to put this question to rest.
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1983 911SC
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1987 944 Automatic
Old 06-07-2012, 07:01 PM
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Quote:
Originally Posted by AlfonsoR View Post
Otherwise, when in doubt, replace. Too much money and time in assembly in putting together one of these engines.
AlfonsoR:

I found the sources of reading criteria enlightening, however, my gut feeling is this was not detonation but "operator" error due to handling when removed, or ring broke on installation. Unfortunately, this piston was not in one of my cars so there are no other facts to provide, such as: whether or not spark plugs or heat caused this issue to surface. There was no signs of heat damage, but also no car history to provide the "what happened here" answer? Hopefully, someone with lots of experience has seen this before.

I must agree with your opinion that "too much money and time in assembly" is one big factor when it comes to decisions being made. But then again, I don't know for sure and this website is the place to ask for answers.
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1983 911SC
1987 944 Manual (Donated to the Nat. Kidney Foundation)
1987 944 Automatic
Old 06-07-2012, 07:15 PM
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put all the numbers from inside the piston here. someone may have an extra one
Old 06-08-2012, 07:49 AM
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Ed,

Those are cast pistons and that damage may have occurred when someone tried to remove the top ring from the piston.

In a pinch, thats certainly usable however that cylinder will always display more leakage than the others. Personally, I would not install that in any engine I build for that reason, alone.

If your expectation is for another 100K before opening the motor, I'd be looking for a better one.
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Old 06-08-2012, 08:55 AM
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rgmrgm:

Thanks for your reply, but I, personally, do not have a need to replace this piston.

There is another Pelican in need and I am trying to help them with a replacement, so I wanted to ensure they could use it.
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Ed Paquette
1983 911SC
1987 944 Manual (Donated to the Nat. Kidney Foundation)
1987 944 Automatic
Old 06-08-2012, 05:26 PM
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Steve:

Excellent.
Thanks so much for your reply with regard to this piston.

In trying to help another Pelican with there project, they can make a decision to use it or not. If it is used for their needs, documenting the life-cycle will certainly help our community here with valuable data.
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1983 911SC
1987 944 Manual (Donated to the Nat. Kidney Foundation)
1987 944 Automatic
Old 06-08-2012, 05:41 PM
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Old 06-08-2012, 05:41 PM
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