running in two stroke power tools

[srp]

I guess this is a good group to ask.. I want to know if you are you generally supposed to "run in" small two stroke engines ? I ask because I have bought a chainsaw and a brush cutter over the last year or so. The chainsaw (Huqvarna 137 ) manual makes no mention of any running in. However for the Brushcutter ( a rather OTT Stihl FS80 ) the user manual advises 'not to operate on full revs. with no load for the first 5 tanks'.. Now why would you do that anyway ?

I wander if the chainsaw was run in at the factory since it shoudl be used at full revs all the time. As normal I only read the Bruscutter manual fully after using the thing all afternoon.. Oops.. Still I guess I can take it easier with it next time ? I rather thought it sounded a bit on the metalicy/ clanky side on tickover , but fine at speed. Anyone here got one and tell me what it sounds like?

[6]

With technology advances in fuels, oils and metals these days it's hardly worth worrying about on such small engines. If you feel like "running in" the machines just follow the advice on the strimmer for both.

[The Natural Philosopher]

Basically things these days are machined to very tight tolerances and on a petrol engine slathering in oil lie a 2-stroke, there is no real need.

If it bothers you, double up on oil for a tankful and let it idle its way to empty.

[srp]

ok then thanks for the reply. thinking back to my old DTR125 bike..which siezed up whilst flat out on the dual carriage !

[Sylvain VAN DER WALDE]

It's not the tolerances that matter, but the finish on the machined surfaces. I, personally, would always run in all new engines and avoid maximum revs during that period.

That's no good. An engine needs to run under a gradually increasing load to become "run in".

Sylvain.

[Sylvain VAN DER WALDE]

[srp]

Also thinking about it. you get less lubrication at tick over on a two banger

[AJH]

Isn't wear related to peak piston speed? High idle will be several thousand rpm above peak power and there's no good reason to be there.

Most two strokes rev limit themselves by 4 stroking, i.e. the mixture is set to be correct at ideal revs but exceeding this causes the mix to go over rich. The revs are limited by the load of the cut with a chainsaw and high idle can be as damaging as nearly stalled. It's quite possible to seize a chainsaw by overloading it as this cuts the air from the cooling fan, which will have a cooling effect that is a related to the cube of the fan speed. So most modern chainsaw carburetors have a fixed jet to prevent them running too lean. Older saws could be tweaked to give a bit more power but this resulted in higher NOx.

I'd run it in by using the correct mix (don't increase oil content as this affects the mixture strength and fouling) and making short full load cuts with "blipping" the throttle rather than long periods of full load, high idle or idling.

AJH