ORIGINAL: Pete Bergstrom
All the engines have been run at the factory.,Â* that being said, if your pinch at the top of the stroke is as tight as you describe, give your self a tank or two on the ground as a break-in to get some of the parts to work together.Â* As always with an ABC engine, the break-in should be done at a needle setting that is just into the 2-stroke range.Â* You need to create some heat and allow things to expand (liner and piston) for the break-in process to work at all.Â* Please don't run this at a rich 4-stroke as a break-in process, all you will do is damage the rod.Â* Most of the time when an engine has a slightly better pinch at the top of the stroke you will find the engine to continue to get stronger through the first two gallons of fuel and will run really well for a long long time.
Thanks for the info Pete.
I may have missed it, but I didn't find any break-in procedure in my .60NX owners manual. It may be worth putting your procedure into future manual printings.
Over the years I've had many different ABC type taper-bored engines. If I buy any brand of APC engine and find it seems unusually
tight at the top of the stroke, I first chuck it up to my little engine test stand. Before its first start up I grab my heat gun and apply heat around the top of the cylinder head area. Applying a little heat always works to loosen it up a little.
I also personnaly believe in NEVER
allowing a new ABC engine to run in a rich 4-stroke needle position. Besides doing possible rod damage, using a cooler 4-stroke needle position, the engine will usually never break in properly and will never become a strong performer. It's got to have heat during break in !
Just my two cents and some observations over many years.