Soft Seize at 300 degrees?

GIlardoni kit, slight seize at the exhaust, 75 jet on a 15.15, temp gauge read 300 when it happened. running 60:1 Dominator.

Literally tiny marks on piston and cylinder still was enough for my engine to stop though.

Why would this happen, so i can take precautions?

Thanks

Re: Soft Seize at 300 degrees?

Re: Soft Seize at 300 degrees?

Jack Rutherford /

What temp gauge are you using?

This one

read 80-100F too low.

Re: Soft Seize at 300 degrees?

Jack Rutherford /

post a pic of your piston

Re: Soft Seize at 300 degrees?

Overpriced Parts /

It could happen and even a lower temperature if it’s not the right letter piston to cylinder letter, if it’s not broken in, air leak/hole in case, jetting way off or timed to high,

Aluminum expands very quick and with a new kit the piston to cylinder clearance is very tight until it’s broken in not allowing for a good gas oil mix cushion between piston and cylinder,

Running 60 to 1 is dumb on a new kit (don’t tell me you’re running saber!) and almost any 2t engine but a Weedwhacker to begin with,

Almost every kit manuals says run 2% synthetic two cycle oil which is 50 to 1, I run 40-50 to 1 on most everything, only time I ran 60 to 1 was on puch polini when a service bulletin came out about it but I stopped doing it, I run the same mix for everything now.

You Could have bad sensor and or Didn’t remove crush washer off the spark plug so wrong reading too,

Post your entire setup

What ignition are you running? what timing? what pipe are you running? what filter?

What carburetor are you running and what is the jetting? What gearing etc.

Re: Soft Seize at 300 degrees?

Im running Amsoil Dominator, I am running that gauge,

the piston was the one that came with the kit.

My set up is 15.15 Sha with the 3d printed slide and free flow filter.

Estoril Pipe geared at 13-28 Morini M1

Timed lower than stock requirement of 2-2.3 MM Im at 1.8

Piston Seize.jpg
Cylinder Seize.jpg

Re: Soft Seize at 300 degrees?

Jack Rutherford /

I'm going to say lean or air leak and that your actual temperature was much closer to 400F than 300f.

Re: Soft Seize at 300 degrees?

Boom! 3d printed slide.

The mid throttle on these is super lean. If you are moving fast on WOT and then back off to a mid throttle position, it will lean out a whole bunch. This carb needs to be rich on WOT for the mid range to be more where it needs to be.

These slides are tough to tune, and will end up being air flow tuning to get it dialed in. I ended up pulling out my printed slide for a stock one while working on tuning my new build. Once I get it dialed in I will throw the 3d printed slide in and retune to that slide. But it will probably just need a little more air restriction to be perfect.

I have also found that these slides do not do well with reed setups.

Re: Soft Seize at 300 degrees

Overpriced Parts /

1.8 is what 21° before top dead center,

If you want to go by MM static timing not with a light it’s probably way more than that

Man that’s nuts high for a air cooled kit static,

Some times you got to keep lowering timing until you’re not making power and then pick it up a bit at a time for sustained temperatures on long Full throttle runs otherwise you could have high temperatures in a second and seize in that second,

Yep timing and jetting welcome to the world of tuning

Re: Soft Seize at 300 degrees?

Im gonna lower the timing to 1.6 and go from there. Are these slides really that finnicky? should I throw on the stock airbox for a restriction?

Re: Soft Seize at 300 degrees?

I was running the 75 when it happened, the 76 is suuuuper blubbery at the bottom.

Re: Soft Seize at 300 degrees?

If the 76 was blubbery try messing with the screen pack. Remove a couple screens and see how it does. I would maybe even bump it up to a 78 and take out some screens.

And yes, a sha is not an easy thing to tune to a kit. Not that it cant be done, but you have to tune it to WOT and not for the low end. If you were on a stock setup I would say you could do more low end tuning.

Just keep an eye on those temps, yeah it only takes a second, but if you see the temps going up by 10's back off right away. And if you are getting over 350, start backing off.

Re: Soft Seize at 300 degrees?

Regeared to 11-28.

Timing to 1.6

Jet still at 75

76 is literally unrideable.

Re: Soft Seize at 300 degrees?

Also if that temp gauge is faulty, why does it read the correct outside temp when its "cold".

Re: Soft Seize at 300 degrees?

Jack Rutherford /

Separate sensor for outside temp?

Re: Soft Seize at 300 degrees?

Nope just the spark plug wire.

Re: Soft Seize at 300 degrees?

Do those half bridges in the exhaust port get crazy hot? Especially with more retarded timing?

I’m asking because I don’t know but, based on what I’ve heard about two strokes, it seems like something to consider.

Maybe that design holds way higher temps right on those pointy bits. Which you’d never see on the head temp. I realize they are supporting the ring and necessary and I have nothing to offer but food for thought.

Re: Soft Seize at 300 degrees?

> Papa _ Wrote:

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

> Do those half bridges in the exhaust port get crazy hot? Especially with

> more retarded timing?

==================================================

"... excessive spark lead is the most frequent cause of detonation, which is a real engine killer. You can't stop advance-produced detonation with a cold spark plug, nor with anything but a wildly over-rich mixture.

The worst, most destructive, combination of mistakes we see begin with two widely-held assumptions: first, that a cold spark plug will help fend off that old devil detonation; second, that more spark advance -not less- is the thing to try when reaching for power. Try to use a too-cold spark plug and you very likely will have to jet for a lean mixture to avoid plug fouling - and as you lean an engine's air/fuel mixture down near the roughly-14.5:1 chemically-correct level it becomes extremely detonation-prone. Excessive spark advance is even worse in its ability to produce detonation, and when combined with a lean mixture it's enough to quickly destroy an engine.

It's impossible to separate the question of ignition advance from the primary evidence of spark plug overheating, which is most strongly shown on the plug's center electrode. If you inspect this electrode's tip with a magnifying glass and see that its edges are being rounded by erosion, or melting, then you know there's overheating. You should also have a close look at the tip of the ground electrode, checking for the same symptoms. Finally, inspect the condition of the insulator, which should be white but with a surface texture about like it was when new; a porous, grainy appearance is evidence of overheating. If the signs of overheating are confined mostly to the center electrode you can bet you're using too much ignition advance. Retard the spark timing in small (two or three degrees) increments and as you get close to the optimum advance you'll find two things happening: first, the whole plug will be running colder; second, the center electrode will begin to acquire a film of fuel deposits extending out from the insulator nose toward its tip."

http://www.strappe.com/plugs.html

Re: Soft Seize at 300 degrees?

Was all That suppose to address my concern about hot bridges in the exhaust port?

I am aware that delaying ignition timing helps avoid detonation. It also causes a delay of the complete burn of the fuel. Which puts more heat into the exhaust port.

Unless I dreamed that up. Pretty sure I read it somewhere.

What I was hypothesizing, is that those bridges may get to be glowing hot right next to an aluminum piston since they might lack the size to transfer heat away fast enough.

But I’m just taking shots in the dark.

Re: Soft Seize at 300 degrees?

> Papa _ Wrote:

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

> Was all That suppose to address my concern

> about hot bridges in the exhaust port?

No, to address the apparent connection of heat to "...more retarded timing."

Scroll down, look for the bold italics.

> It also causes a delay of the complete burn of the fuel.

>Which puts more heat into the exhaust port.

???

> Unless I dreamed that up. Pretty sure I read it somewhere.

I would like to read that source. Please find us that link.

Here's a useful one I found.

http://www.strappe.com/plugs.html

Re: Soft Seize at 300 degrees?

I’m not gonna post a link to every forum on MA where people have countless times given advice to retard timing to move heat into the exhaust and out of the chamber.

Why you gotta be so rude?

The important part (maybe) that I was asking about is if THAT heat (caused by retarding timing) places the hottest part of combustion right on top of those protruding exhaust bridges that are helpless to shed heat due to their size and location.

And if those bridges were to get super heated, they would melt a piston like the pictures. Even though the bike is jetted right and CHT is fine.

Maybe I’m crazy to suggest it. Thought someone would chime in to address the concern about hot bridges.

Re: Soft Seize at 300 degrees?

> Papa _ Wrote:

> Why you gotta be so rude?

==================================================

https://drive.google.com/file/d/1Mz464_v8oehbDqavrZ6XrA2nkOsP-3KC/view?usp=sharing

Re: Soft Seize at 300 degrees?

> Den 23 Wrote:

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

> > Papa _ Wrote:

>

> > Why you gotta be so rude?

>

> ==================================================

>

> https://drive.google.com/file/d/1Mz464_v8oehbDqavrZ6XrA2nkOsP-3KC/view?usp=sharing

EDIT: Fixed the link. Sorry.

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