Piston pin galling in a drag race engine

Belgian1979vette

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This is not for me, but for a work related case I'm going to work on.

The subject is an expensive drag race engine that ran into problems when being used. My cliënt is a factory that does coatings and was asked to coat a specially made pin, consisting of an aluminum core with an 34CrNiMo6 outside. The coating was an Balinit C with 51 HRc hardness.

From what I already know, the pins were galling.

Untill i have seen the engine in question and can post some pictures, what could be possible causes for piston pin galling.

I'm assuming overspeeding, piston kissing the head, detonation...but what else ?
 
2 most obvious reasons, tolerances too tight or too little oiling. Does it rely on oiling from the piston? Is the small end drilled from the top? Does it have a dedicated pressurized oil feed like an EDM channel through the beam? Why would you use an aluminum piston pin? Cassidium coated pins seem to be the norm nowadays in very high HP applications. the coating gived the pin the ability to survive a momentary starvation of oil which would otherwise cause problems. Even with dry sump systems and priority main oiling it can happen that a pin gets starved for oil, even with a pressurized oil feed.

If the pistons are kissing the head you should be able to see it and sometimes hear it, not uncommon though esp. w/ alu drag rods. Detonation will clearly show up on the piston as pits or even broken ring lands, should not be a direct cause for pin seizing.

Need more details
 
2 most obvious reasons, tolerances too tight or too little oiling. Does it rely on oiling from the piston? Is the small end drilled from the top? Does it have a dedicated pressurized oil feed like an EDM channel through the beam? Why would you use an aluminum piston pin? Cassidium coated pins seem to be the norm nowadays in very high HP applications. the coating gived the pin the ability to survive a momentary starvation of oil which would otherwise cause problems. Even with dry sump systems and priority main oiling it can happen that a pin gets starved for oil, even with a pressurized oil feed.

If the pistons are kissing the head you should be able to see it and sometimes hear it, not uncommon though esp. w/ alu drag rods. Detonation will clearly show up on the piston as pits or even broken ring lands, should not be a direct cause for pin seizing.

Need more details

Thx Marck. I will come back when I've seen the pieces of it.
 
Totally over my head this question but I did stay at a Holiday Inn last night so I'll take a guess; too much horsepower?
Not sure if they is even in the ballpark but a curious answer to a curious question:
I am an automotive engineer. I am presently working on a piston pin bore scuff problem. We have observed that merely sliding a medium Carbon heat treated piston pin 60Rc, into a Hyper Eutectic Aluminum piston pin bore, the pin would lock up and it would be extremely difficult to get the pin out. The clearance between the pin and piston pin bore is approximately 18um (microns). Once pushed out it was observed that bits of aluminum literally stuck, almost like welded to the pin surface. I would like to know metalurgically, how the aluminum can adhere to the steel pin so strongly that the aluminum shears away from the pin bore.

I suspect that the aluminum is actually reacting with the carbon steel and leaving a thin coating behind when you withdraw the pin. All aluminum is coated with a thin layer of aluminum oxide immediately upon exposure to the atmosphere. That is what keeps it from corroding further. Carbon is a strong reducing agent, and given the differing electromotive potential of iron and aluminum, it is possible that a reduction reaction occurs at the contact. Some high tech lubricant used between the pin and the piston might keep the metals suffciently separated if this is the problem, you might want to consider something with molydenum or graphite, avoid silicone.

Another possible answer lies with interstitial migration of the aluminum into the steel. This is possible if the finish on the steel is flawed or if the steel has a coarse crystal structure, both possible with carbon steel. If this is the problem, careful polishing might alleviate it.

Source:
http://en.allexperts.com/q/Metallurgy-2280/Aluminum-Piston-pin-bore.htm
 
You need a zirk fitting with some Moly Buy Sulfide Poly Unobtanium Grease....

take the oil pan off every year and grease the wrist pins....


sorry for the sick humor, just could NOT resist....

:crap::shocking::p
 
I'm surprised that an aluminum piston pin would be used in a high performance drag race engine. I would think aluminum is much too soft. But, maybe I've learned something new!
 
little bit confused....galling or coking ;as in the pins starving for oil and the bit that is there is frying and leaving a hard carbon residue??
c-ya
ToddG
 
I'm surprised that an aluminum piston pin would be used in a high performance drag race engine. I would think aluminum is much too soft. But, maybe I've learned something new!

Yep, my thought as well. Apparently the builder designed them himself.

My thinking is that an aluminum piston pin is subjected to way to much bending and that could lead to galling of the pin. Apparently weight reduction is a concern. If i would have to design an engine around lightweigt rotating parts, i would rather design a piston with a short pin, than to make it out of aluminum.
Also the expansion rate of an aluminum pin is the same as the piston itself, so I assume that in operation and at operating temps the clearance in the piston pin bore would be to small.

Let me get back to you guys when I have actually seen the parts. The survey is going to take place april 8th.

I just wanted to know what the possibilities were on this thing before i enter the arena.
 
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I should mention this is an hemi

On other pictures i got, i noticed that the piston hit the head.

Anyone have any info on the kind of stretch that is to be expected with alu conrods, piston to heads clearance, conrod bearing clearance ? Or a site which has good info on these motors ?

Thanks
 
Last edited:
...Anyone have any info on the kind of stretch that is to be expected with alu conrods, piston to heads clearance, conrod bearing clearance ? Or a site which has good info on these motors ?

Thanks

Have you searched the speedtalk forum?
 
alu rods require about .010 more clearance because of rod stretch.

Are you sure the pin is alu? looks like a coated pin to me. The alu on it is smeared on from the rod?? Those are non bushed small ends right?

I see scuffs above the top ring land, the piston is barrel shaped, if there's a problem w/ it seizing in the bore, you'd see score marks at the pin height first, this is weird. Was there debris above the top ring? I see it's only on the thrust side, is the piston rocking from too much side clearance?

Fractured cap rods, nice :)

Shoot Carl (cnc blocks http://www.vettemod.com/forum/member.php?u=239) a message, he's the most knowledgeable guy here on these things.
 
It appears to me the builder wanted to use a sleeved pin for the lightness and had the od of the pin sleeve Balinit c coated because he read or heard it could be used in a dry application. It appears the coating did survive the heat but the aluminum piston and rod did not, which caused the plasticity and ultimate failure.
He did not correctly consider the loading that the wrist pin would see vs the ability of the coating and aluminum counter parts to dissipate the heat generated that would have been carried away by coolant had it been present.

The light weight pin did not fail,nor the coating, it was the lack of any oil to carry away heat is the root cause of the failure, imho.
 
I should mention this is an hemi

On other pictures i got, i noticed that the piston hit the head.

Anyone have any info on the kind of stretch that is to be expected with alu conrods, piston to heads clearance, conrod bearing clearance ? Or a site which has good info on these motors ?

Thanks

Piston hitting the head is most likely the result of not being attached to the rod.
 
alu rods require about .010 more clearance because of rod stretch.

Are you sure the pin is alu? looks like a coated pin to me. The alu on it is smeared on from the rod?? Those are non bushed small ends right?

I see scuffs above the top ring land, the piston is barrel shaped, if there's a problem w/ it seizing in the bore, you'd see score marks at the pin height first, this is weird. Was there debris above the top ring? I see it's only on the thrust side, is the piston rocking from too much side clearance?

Fractured cap rods, nice :)

Shoot Carl (cnc blocks http://www.vettemod.com/forum/member.php?u=239) a message, he's the most knowledgeable guy here on these things.

It is an alu pin with a bushing over it.
I did sent Carl an email.
 
It appears to me the builder wanted to use a sleeved pin for the lightness and had the od of the pin sleeve Balinit c coated because he read or heard it could be used in a dry application. It appears the coating did survive the heat but the aluminum piston and rod did not, which caused the plasticity and ultimate failure.
He did not correctly consider the loading that the wrist pin would see vs the ability of the coating and aluminum counter parts to dissipate the heat generated that would have been carried away by coolant had it been present.

The light weight pin did not fail,nor the coating, it was the lack of any oil to carry away heat is the root cause of the failure, imho.

That is another possibility also. These picture were sent to me in advance of me seeing the engine. I'm still awaiting all the details on this engine.
 
This thing was discussed over at speedtalk also, and with the help of a very knowledgeble guy, the case is probably cracked.

The first picture of the pistons with the pin (small end side) did it... Just can't believe i didn't see this before.:banghead:

8-4-2011 the meeting is taking place, after that i will give you the details.
 
What's the verdict?

I still don't get why this engine has an aluminum pin. What is it, a drilled alu pin w/ coated chromemoly sleeve? with all the alu smeared over the coated sleeve it seems to me that the pin was flexing, seizing in the small end resulting in a failure. The pin is too weak.
 
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