Running in

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Mar 21, 2006
Having recently done a top end overhaul on my Mk1 850, I thought the forum would like to know that the running in method advocated by Mototuneusa does work as described. See :-
I fired up initially for 3 or 4 minutes. re-torqued the head and barrel. Did the tappets again. Then went for a blat up the road. After the first couple of miles or so I bravely opened the throttle to about 3/4 in 3rd gear so the revs went from about 2500 to 5000 and then closed the throttle again. I repeated this dozens of times (lost count) and after about 20 miles of this treatment I returned home.
I changed the oil (basic mineral cheap stuff) and filter, retorqued etc and went out again. I still gave the engine plenty to do and extended it to some pretty fast riding.
More oil changes and retorques. (I had to retorque 5 times before it stabilised)
The engine now has full compression, no leaks, burns absolutely no oil, fires up first kick and goes like stink.
This running-in technique must have been known years ago, but possibly not fully understood. In my Velo days we always used to say "run them in fast and they stay fast"
If you every have to do a top end rebuild, make sure your ring gaps are ok and then do as Mototuneusa advocate for the first 20 miles. It works.
Yes very interesting , specially, all the works done to reshape the inlet and making them smaller at 65% of the OD of the valve (for multi-valves heads) , he said that 80% seems reasonnable for 2 valves head, which go in the way of a max 30 mm at the venturi (before the guide). I had heard somebody telling the 28.5mm Commando were better than Combat 32 mm about flowing....going the same route!!Pierre
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