90cc Break-in With Temperature gauge

[magoconnor]

Hello.

Im about to break in my newly re-build engine, I would like to hear to some suggestion/experiences about: heat cycling - max temp - warm up temp - idle speed - Trip distance of the first few rides - Oil changes - Max Rpm - Which main jet to start out with.



After reading extensively on the subject, these few things I have gathered:
Vary the rpms and change the oil often.
Use mineral oil untill you reach 500 miles.
The rest of the process people seems to disagree on.


Gentle break in - Cons:

The rings wont seal propably.
The top piston ring create a ridge lower down in cylinder, because of the engine not reaching a high enough temperature for the crankshaft to reach its full length.
Lower max speed. 


Hard Break in - Cons:

Risk of seizing.
Massive catastrophe.


I would start with some soft acceleration, and go harder from there.
To help seat the rings.

Ensure the engine gets up to temperature, to avoid ridge build-up low in cylinder.
What temperature would this be?

Any suggestion would be greatly appreciated.


Cheers Mag. 


My set up:

Everything is new and assembled correctly.

Naraku 90cc cylinder

Naraku Bvh 23/21

Naraku Heavy-duty crank

20mm carb

[GrumpyUnk]

Well, I can throw some gasoline on the soon to be flame war...

My take is based on what I read years ago about breaking in new piston rings on a 'backyard/garage rebuild' of a Chevy 235-six. "Get into 3rd gear, going about 30. While still in 3rd, floor the gas pedal until you reach ~50mph. Take your foot off the gas pedal, and coast down to 30. Repeat about ten times. Then drive without going to maximum power for the next few hundred miles. Change the oil @ about 500 miles."
The explanation was that WOT, WITHOUT the high rpms, allowed the compressed gas to get 'behind' the compression rings and push them out to the cylinder walls to force interaction which would lead to the rings bedding in short order. High rpms would or could cause a lot of heat due to friction from tight-fitting rings, so lower rpms until the rings had bedded would avoid the heat. Heat could make the rings lose tension and seal like dirty diapers.(leaky)
So, you pays your money and takes your chances. I'd still try to get the scoot up to low 20's, and floor it up to top end, then back off, letting the scoot engine cool, and drawing some oil up onto the rings as they go through their 'high friction' period. Repeat as desired(ten times?). Don't go WOT for any length of time, and if you do, back off on the gas, and let it coast for a while after, reducing the temp and again sucking oil up onto the cylinder.(engine braking vacuum will help pull oil up, and maybe a bit down the valve guides).
And that's about it. Except, don't keep steady rpms for any length of time, such as cruising ten miles straight without backing off on the gas now and again.
Broke in my new car that way driving from Indy to CA, cruised @55, sped up to 65, backed off coasted down to 50, accel back up to 55, and ran with increased speeds, up 5, run, up 5 more, run, back down 15, run back down 5, etc etc etc. Have about 250k on that engine w/o pulling anything due to problems. Long block untouched.
tom

[ThaiGyro]

Grumpy Unk has it...sort of, really! The issues are so numerous. GU explanation of gas loading between piston and rings is good. The problem is, that every single engine has a different loading, different jetting, various atmospheric pressures, different driving.

For my new engines...four strokers, that is...just think moderation in the first few hundred miles. You cannot know what your rings are REALLY doing, so make them happy...easy and fun.

When you get curious as to the performance? Goose it some, but as GU suggests, not alot and not WOT!

Then? Who knows? My Yamaha Mio 125i was a good running engine new. Nicosil alloy cylinder and FI...It did not run GREAT until about 4,500 km. Just ran it to the store. WOT after 4K km, but not for long. UP hills on even acceleration...varied speeds is, what? Driving in traffic? Yep!!

It is primarily an OEM engine with good air flow and FI tuning. It is a good running scoot! Now? It can pull strong off the line and gets near 95 mpg. (Down from OEM tuning, but I am CVT tuned for low end torque)

I say...not to worry my Padawan. Drive it and it will show the way.

[magoconnor]

yes master

Sounds like a pretty sane approach, how long do you guys let it warm up before takeoff?

So you dont do any "real" heat cycling?

Im in middle of hooking everything up again..
My Koso has max Cht setting, and if in case it is reached, it will flash like a siren.
Do you guys know what a safe max cht is?

[magoconnor]

Also what size main jet would be a good starting point?
same with rollers?