strange bronzing/wear patterns on piston

hey y'all, just was curious if any of you could shed some light as to what is causing this on my piston. It's a relatively new 70cc treats kit on a maxi, less than 3 hours of ride time on it. could it be timing? bearings? halp

Re: strange bronzing/wear patterns on piston

Probably Fred /

Some Blow by but mostly overheating looks like seizing scuffing against the cylinder due to high timing, poor jetting/poor tuning and not being protected by temperature gauge.

Learn how to time!

learn how to jet/tune!

Buy a temperature gauge and keep below 380F

Done

Re: strange bronzing/wear patterns on piston

i bought this bike all built up and when i first got it, and the jetting was a bit rich based on plug chops. however, i opened the cylinder, and it was fine, and the piston did not look like this.

it recently started to get super leaky on the exhaust, could air leaks cause this much temp differential? also, any word on the weird scuffing patterns?

Re: strange bronzing/wear patterns on piston

if it is a stock crank that is the problem. bushing is melting and the piston is not happy.

Re: strange bronzing/wear patterns on piston

is that exacerbated by timing/air leaks? or is it just time to rebuild the crank?

Re: strange bronzing/wear patterns on piston

Probably Fred /

You could be jetted very high and still seize because unchecked timing is what makes the temperature go high.

You need to be at the timing shown on graph at your rpm or you will have unsustaining head/combustion temps and boom

image.jpeg

Do not run your engine even after rebuild unless you time it correctly and run a head temp gauge.

Re: strange bronzing/wear patterns on piston

Yes an exhaust leak can cause you to run lean enough to seize if the conditions are right. But don't just seal it up and call it good, go through the whole build and get it right once or replace kits over and over til you do.

Re: strange bronzing/wear patterns on piston

Ken Roff Wrote:

-------------------------------------------------------

> You could be jetted very high and still seize

> because unchecked timing is what makes the

> temperature go high.

> You need to be at the timing shown on graph at

> your rpm or you will have unsustaining

> head/combustion temps and boom

>

>

>

> Do not run your engine even after rebuild unless

> you time it correctly and run a head temp gauge.

That is the chart for an HPI ignition, and may have absolutely nothing to do with your bike. You haven't stated what ignition you have, stock or otherwise.

Re: strange bronzing/wear patterns on piston

BryAn eurism /

What oil are you running there?

Re: strange bronzing/wear patterns on piston

Probably Fred /

DPC Ryan Wrote:

-------------------------------------------------------

> Ken Roff Wrote:

> --------------------------------------------------

> -----

> > You could be jetted very high and still seize

> > because unchecked timing is what makes the

> > temperature go high.

> > You need to be at the timing shown on graph at

> > your rpm or you will have unsustaining

> > head/combustion temps and boom

> >

> >

> >

> > Do not run your engine even after rebuild

> unless

> > you time it correctly and run a head temp

> gauge.

>

> That is the chart for an HPI ignition, and may

> have absolutely nothing to do with your bike. You

> haven't stated what ignition you have, stock or

> otherwise.

Yes it's a chart for Hpi and it shows what the timing needs to be at 8, 9 10,000 rpm whatever.

If you have static timed/no curve points ignition then you need to be at the lowest you can be and still make power which on a Puch is 14° before top dead center to to run cool at 9000 RPM but anything past that with a high rpm pipe/setup you cannot time low enough in most cases to sustain cool temperatures because you won't make enough power at low rpm to hit that rpm/speed so

that's why Hpi/curve ignition are needed for most performance application with the exception of the mild kit mild rpm set up,

Water or fan cooled engines can help/allow for bit higher timing

Re: strange bronzing/wear patterns on piston

Daniel, Google says bronze melts at 950 f. That's pretty hot. Please say some more on the subject.

Re: strange bronzing/wear patterns on piston

Melt isn't really the right term, it's not becoming liquid. It smears and sticks like an aluminum piston does against the cylinder when it seizes. Picture this, once you start to get lubrication break-down the heat and friction continue to increase exponentially. All that heat cooks off any remaining oil and it'll either seize the bushing, or it'll basically spin or smear it to pieces.

Re: strange bronzing/wear patterns on piston

And bushings melt or smear on the basis of errors in timing and jetting or is there some other factor such as a blocked oiling hole?

Re: strange bronzing/wear patterns on piston

Probably Fred /

I replaced them several times, I saw it happen with well oiled, well lubed, no blocked hole.

Brass bushings were Designed for around 7,000 rpm speeds, At prolonged higher rpm it justs seizes.

Re: strange bronzing/wear patterns on piston

Marc Friedman Wrote:

-------------------------------------------------------

> Daniel, Google says bronze melts at 950 f. That's

> pretty hot. Please say some more on the subject.

Re: strange bronzing/wear patterns on piston

poor break in procedure, poor piston ring gap or piston-cylinder fit. uneven cylinder stud torque and leaking exhaust. cylinder and piston distortion causing scuffing of parts. lack of adequate lubrication.

Re: strange bronzing/wear patterns on piston

Glenn Kuehn Wrote:

-------------------------------------------------------

> Marc Friedman Wrote:

> --------------------------------------------------

> -----

> > Daniel, Google says bronze melts at 950 f.

> That's

> > pretty hot. Please say some more on the

> subject.

>

>

>

glen nailed it. lack of lubrication and susatined high rpms will cause anything to seize, needle bearings will fail if not properly lubed as well... just had a minarelli just about weld the rod to the big end pin from a disintegrated roller bearing. shouldnt ever happen again, got a fancy new crank for it. i love treatland.

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