Melted Wrist Pin Bores?

joefarmer

joefarmer

MR. Supreme Overlord
Joined
Jul 31, 2006
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Had a little problem disassembling the race truck pistons. Apparently the wrist pin bores galled since the last build. Each of the wrist pin bores is discolored and slightly porous at the top of each bore. If 12 o'clock is vertical, it's 10 o'clock to 2 o'clock by ~1/4" wide. Is this something common that I don't know about? #6 was the tightest. Followed by 1, 5, 4 and 3. #2 was the easiest and needed ~6 taps with the deadblow before it was out.

Is this common? Anything tricks I need to know regarding the bores? Machine 0.002 out of them and coat them with something like PolyDyn DL Coating?

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Do you think it could have been caused by all the crap you had in your oil? I remember you posted an oil analysis a while back, wasn't the viscosity really low?
 
GRotman said:
Never seen that! What kind of egt's did you have?
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Really hot. It left the line ~950 and was >1750 most passes.

Muddin_dude06 said:
Do you think it could have been caused by all the crap you had in your oil? I remember you posted an oil analysis a while back, wasn't the viscosity really low?
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I didn't think of that. There was a bunch of fuel in the oil and that could have been the culprit. The bearings look virtually new.
 
Humm.. I was really curious as to what you would find in regards to piston wear Brandon. I Kind of suspected side loading of some sort.
This is strange. Do you think it has something to do with lack of cooling oil to the pins? Your block uses the saddle jet nozzles I assume?
 
joefarmer said:
Really hot. It left the line ~950 and was >1750 most passes.



I didn't think of that. There was a bunch of fuel in the oil and that could have been the culprit. The bearings look virtually new.
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I think you are using the wrong lubrication. At the temperatures you are running this may be better. Soak your pistons in it for 4 hours before each run.
 

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RonA said:
I think you are using the wrong lubrication. At the temperatures you are running this may be better. Soak your pistons in it for 4 hours before each run.
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Piston basting, the secret to succulent pistons. :hehe:
 
Typical with high heat engines that utilize cast pistons. Heat distorted the pin boss, in addition to lack of/poor grade lube caused the galling. Coating would have helped to some degree, once the boss is distorted localized pressure will wear the pin bore in a moments time.

Coating the crown and skirts with Thermal and Anti friction coatings will minimize the effects (piston growth/distortion) of heat related failure's in cast piston material.

OEM's such as Duramax have gone to a bushed piston AND coated skirts for that reason.
 
Garland said:
Typical with high heat engines that utilize cast pistons. Heat distorted the pin boss, in addition to lack of/poor grade lube caused the galling. Coating would have helped to some degree, once the boss is distorted localized pressure will wear the pin bore in a moments time.

Coating the crown and skirts with Thermal and Anti friction coatings will minimize the effects (piston growth/distortion) of heat related failure's in cast piston material.

OEM's such as Duramax have gone to a bushed piston AND coated skirts for that reason.
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Those pistons were top and side coated IIRC


Looks like a lot of heat and beating from nitrous Brandon...but of course I may be biased since I helped persuade you in your tuning:hehe: :hehe:

Chris
 
if the pistons are coated i would suggest that you do it to reduce the heat on the piston and the oil. also you might see if you can get a bushing and slide it in there so that if they wear again you can just replace the bushings instead of the pistons
 
Pistons are top coated, but the sides aren't. I'm guessing I'll take these and cleanup the wrist pin bore to reuse them. Probably go with lower EGT's next season and see what happens.
 
Looks like the pistons shrank from heat. I have rebuilt a few engines that stuck pistons or melted the top and the pins had to be pressed out.
 
joefarmer said:
Pistons are top coated, but the sides aren't. I'm guessing I'll take these and cleanup the wrist pin bore to reuse them. Probably go with lower EGT's next season and see what happens.
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I was thinking the sides were teflon coated as well...sorry about that!

Lower EGT's is a nice goal for next year Brandon...but you know as well as I do you'll just turn the wick up farther ;) ;)

Chris
 
I believe that is timing related. Its "nailing" at low speeds
 
Got another set of calibrated tools on them (thanks HotrodTractor) and the wrist pin holes are egg shaped. I'll be hitting up Jeff Mumau to get another set ordered Monday.
 
joefarmer said:
Got another set of calibrated tools on them (thanks HotrodTractor) and the wrist pin holes are egg shaped. I'll be hitting up Jeff Mumau to get another set ordered Monday.
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I'm assuming you used a dial bore gauge. I am going to check my new pistons when they come in. They welded on them and i have been concerned with distortion. How much out of round did you measure?
 
Jason said we'll re-check them with a set of snap gauges when I get a chance next week. I don't trust my measurements.
 
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