Running In

[Mrapocalypse]

Hi,

Just had the barrel rebored to 4th oversize and it's back together.

Theres a lot of white noise on the web about exactly how to run a 2 stroke in.

As far as I can see, start it, idle it till warm, then once warm shut down. The let it cool completely.

Then start it and gently ride it until mildly hot.

The cool off.

Then start it and ride it revving through the range but not going too hard or too consistent.

The let it cool.

The start it and thrash it!

Also, I am a bit concerned that my ring gap isn't right. I put them into the bore and there was a tiny gap. Like a hairs width.

Didn't think to measure it.

As mentioned. It's 4th oversized.

regards

Ian

[Mrapocalypse]

It's a 1976 M158 Bultaco Sherpa T 250 BTW.

Cheers

Ian

[eagle]

I like to warm up for a minute or so then you need to put some load on the motor, otherwise the rings wont seat,if you just heat cycle a few times before you put some load on it you may glaze the bore, i run it for about 10mins no more that 1/4 throttle then 1/2 then 3/4 then she's ready to go,well that's how i've been doing it for 35+yrs

[David Lahey]

Just think about what running-in is for. At first there is huge friction between the rings and the fresh bore, which generates a lot of heat. Initially there is too much heat being generated for the available heat rejection capacity of the barrel. This means that if you just start it and ride it normally, the rings and bore may get so hot the oil film breaks down (the oil film burns off)
You can either use a conservative ritual technique for how long to run between cooling down sessions, or run until the cylinder gets up towards the temperature that causes oil films to fail, between cooling down sessions.
If you use a surface measuring thermometer, measure the temperature at the base of the cylinder fins and don't let it go above 110 degrees. A good standby to a fancy thermometer is to put some spit on your finger and when it sizzles wildly as you touch a fin, it is time for a cooling session.
As for your ring end gap, you should definitely take the cylinder off again and measure the gap properly and make sure it is enough gap, before running the engine. Bultaco engine parts are way too expensive to take that sort of a risk

[Jools]

Oooh yep that ring end-gap is critical, you'll have to pull it apart and measure the ring end-gaps and adjust them if necessary. OR risk seizing the motor, thence, possible new piston, rings, rebore etc! Eeeek!

[Mrapocalypse]

Hi,

I think these are the best descriptions yet.

You guys have done the internet a lasting favour.



Cheers

Ian.