Aftermarket piston failure theory discussion

[White Mountain Saws]

I have a ported well known vendors 372 big bore which ran with out a hiccup for roughly ten years. Then a piston ring locating pin failed and took out the piston. I bought an entire big bore kit from the same vendor and noticed the cylinder and piston were different than previous generations from that vendor.

I mismatched the piston into the 10 year old cylinder. With 160PSI compression the piston lasted maybe 5 tanks of fuel before the small end (wrist pin) holes began ovaling. Fuel was 87 octane with name brand oil. RPM was set at 13,800
I have another aftermarket piston in the cylinder as I type. I’m done with aftermarket if this piston fails as well.

Does any one have theories as to why the piston began failing; Beyond metal quality?

 

[Ronie]

If the pin was a little loose in the piston, maybe it pounded it into an oval, just an uneducated guess. What brand of piston was it?

 

[Ketchup]

Old or new wrist pin? Circlips? Bearing condition?

 

[tek9tim]

If the pin was a little loose in the piston, maybe it pounded it into an oval, just an uneducated guess. What brand of piston was it?

Loose tolerance between the wrist pin and piston would be my guess if we're skipping talking about metal quality, especially given middle-of-the road compression.

 

[Stump Shot]

I have a ported well known vendors 372 big bore which ran with out a hiccup for roughly ten years. Then a piston ring locating pin failed and took out the piston. I bought an entire big bore kit from the same vendor and noticed the cylinder and piston were different than previous generations from that vendor.

I mismatched the piston into the 10 year old cylinder. With 160PSI compression the piston lasted maybe 5 tanks of fuel before the small end (wrist pin) holes began ovaling. Fuel was 87 octane with name brand oil. RPM was set at 13,800
I have another aftermarket piston in the cylinder as I type. I’m done with aftermarket if this piston fails as well.

Does any one have theories as to why the piston began failing; Beyond metal quality?

Yes, some of the BB 372 kits of old were quite the runners and yes they are gone like DeSoto's. With the new ones not able to hold a candle to the previous kits.
Poor fit and poor(soft alloy) metallurgy make for a certain impending disaster.
My recommendation is to find a OEM cylinder even if used and a decent piston like a Meteor and good woods port job and you'll forget all about those BB kits.

 

[White Mountain Saws]

Old or new wrist pin? Circlips? Bearing condition?

New wrist pin and circlips which was supplied with the kit. Wrist pin bearing was tight before and after piston failure.

 

[White Mountain Saws]

If the pin was a little loose in the piston, maybe it pounded it into an oval, just an uneducated guess. What brand of piston was it?

Upon assembly the the pin had zero felt movement and the machine fit appeared normal. I don’t want to out the vendor knowing how one online situation can cause major headaches for the business. Especially if my situation is an isolated incident.

 

[Ketchup]

Yes, some of the BB 372 kits of old were quite the runners and yes they are gone like DeSoto's. With the new ones not able to hold a candle to the previous kits.
Poor fit and poor(soft alloy) metallurgy make for a certain impending disaster.
My recommendation is to find a OEM cylinder even if used and a decent piston like a Meteor and good woods port job and you'll forget all about those BB kits.

Some of the 52mm jugs can be used but most of the AM pistons are suspect. Now that the XPW kits are NLA I feel pushed towards 52mm AM.

 

[Stump Shot]

Some of the 52mm jugs can be used but most of the AM pistons are suspect. Now that the XPW kits are NLA I feel pushed towards 52mm AM.

You can't even count on the plating holding on any longer either. I stand by my recommendation for more power that will last.

 

[Ketchup]

You can't even count on the plating holding on any longer either. I stand by my recommendation for more power that will last.

Thinking back, the last two AM jugs I ported, I said I would never do another one…

 

[huskihl]

The wrist pin holes may have been milled at an angle. Or maybe the pin bosses are too wide allowing the bearing to slide too far out of the rod. Or it’s all just junk

 

[Woodslasher]

I have a ported well known vendors 372 big bore which ran with out a hiccup for roughly ten years. Then a piston ring locating pin failed and took out the piston. I bought an entire big bore kit from the same vendor and noticed the cylinder and piston were different than previous generations from that vendor.

I mismatched the piston into the 10 year old cylinder. With 160PSI compression the piston lasted maybe 5 tanks of fuel before the small end (wrist pin) holes began ovaling. Fuel was 87 octane with name brand oil. RPM was set at 13,800
I have another aftermarket piston in the cylinder as I type. I’m done with aftermarket if this piston fails as well.

Does any one have theories as to why the piston began failing; Beyond metal quality?

I'll take a gander and say that the old kit you're referring to is a NWP kit from the company that has the same name as that Irish cream that you add to coffee. A buddy swore by the old kits but apparently the new ones aren't so good. If you haven't run the saw yet I'd say put a Meteor 272 piston in the old jug if you want a quality piston, or maybe you could use a Hyway 272 popup piston if you want to go that route. If you just use another cheapie no-name it's probably just gonna blow up again.

 

[White Mountain Saws]

I’ve tried a 272 piston in the past and found the saw doesn’t run as well. I had skirt length issues with the 272 piston. The ports on this cylinder are at arguably max dimensions for everyday use. I put a aftermarket pop up piston (came in a red box) in the saw Tuesday evening and will be running it until this piston fails. I am stepping down to a 7 pin sprocket to see if gearing makes any difference.
I will be going back to a 50mm cylinder should this piston fail.

 

[Ketchup]

The 272 piston makes the intake duration too long. Some epoxy really wakes it back up.

 

[White Mountain Saws]

What are the thoughts regarding detonation because I was running 87 octane with a 8 tooth sprocket, ported, with 160 psi?

What does detonation feel like in a chainsaw?

I hammer this saw bucking 24-30” oak. Nearly every cut was a full length of bar cutting hard with a razor sharp chain set around .027 depth height.

 

[Ketchup]

Usually the piston crown looks like someone hit it with a thousand tiny hammers after detonation.

 

[wcorey]

Had a friend get assigned to babysit at a manufacturing plant in china involving aluminum castings.
He watched in horror as they filled the hopper of scrap aluminum to be melted in next (un-babysat) line over (someone elses similar product), tossing in cubes of crushed scrap that had all kinds of random nasty things sticking out like lawn chairs with plastic and other hardware still attached.

That's the inherent nature of manufacturing in china, you can imagine if that were something critical like pistons or whatever how one batch to another would vary in quality just a bit, lol...

 

[Mastermind]

Had a friend get assigned to babysit at a manufacturing plant in china involving aluminum castings.
He watched in horror as they filled the hopper of scrap aluminum to be melted in next (un-babysat) line over (someone elses similar product), tossing in cubes of crushed scrap that had all kinds of random nasty things sticking out like lawn chairs with plastic and other hardware still attached.

That's the inherent nature of manufacturing in china, you can imagine if that were something critical like pistons or whatever how one batch to another would vary in quality just a bit, lol...

The Chinese have exactly zero *f-words to give about the garbage they make and sell to the rest of the world.

OEM or nothing on stuff that matters.

 

[White Mountain Saws]

Usually the piston crown looks like someone hit it with a thousand tiny hammers after detonation.

This rules out detonation. The crown had zero marks.