This is another of those subjects that crops up on the message board frequently. I am constantly surprised by the number of engine builders - or people who charge other folk for building engines at any rate - that never hand out such an information sheet. It seems pretty daft to me that having taken a wad of money off of a customer for an engine you've lovingly put together, you'd want to help that person get the very best out of the engine. And the running/breaking in procedure is absolutely crucial. It at least ensures no damage is incurred when the engine first bursts into life. A collection of the usual suspects have explained their own methods on the board, along with various others - many of which probably work just as well for them, a few which are down-right dubious. Following is a sheet I administer with every customer engine I build. Most of it is pure common sense, but then that's what tends to get most folk into trouble in the first place! I've been using this procedure for some 15 years now without any problems reported whatsoever. And believe me - when a customer pays out the sort of money it takes to have an engine built, they'll be banging on the door at the slightest hiccup! With that in mind - I'm sure this will work for most. Running in New Engines - the Mintec method.
Install engine. It is absolutely imperative that the cooling system is more than sufficient to deal with any temperatures likely to be produced by the engine. More power means more heat to be dissipated. A standard radiator is very unlikely to be able to cope with a reasonable power increase over standard. Do not fill cooling system yet. Set clutch throw-out and free-play take up. Double-check all connections electrical, oil, fuel and cooling system. Put in engine oil – use a cheap multi-grade mineral oil. DO NOT use either semi or full synthetic oils. They will stop the rings from bedding in. Remove spark plugs, and spin engine over in bursts of a few seconds at a time to pick up oil pressure and prevent starter motor damage. DO NOT start engine until oil pressure picks up. Once oil pressure is showing, check ignition timing statically. Set to figure advised by distributor maker, or if no figures available, set at around 6-8 degrees BTDC. Re-fit sparkplugs and start engine. DO NOT allow to idle under 1,500rpm at start-up - 2,000rpm is preferable. Allow engine to run until cylinder head is warm to the touch, then switch off and allow to cool completely. Fill cooling system and re-start. 2,000 rpm should be maintained for the first ten minutes of running, irrespective of use, to prevent cam/follower damage, and help bed same in. After this period, reduce idle to 1,500rpm on race units, 1,200rpm on road units until engine is run in. After this, race units should not be allowed to idle at under 1,200rpm as valve train damage and premature wear can occur from erratic low speed running, and the water pump is very in-efficient at low revs. Road units, aim for 900rpm as a minimum. All that trying to get the idle down to 600 rpm like uncle Joe used to on his old banger is nonsense - that was Ok when cams barely had lobes! Run engine in using part throttle and low loads only, and keep rpm down to no more than 60% of rpm limit. Use the gearbox. DO NOT put engine under unnecessary loads (i.e. going up hills in top gear just using the throttle to maintain progress). Although the bulk of the engine requires little running in because of accurate building and tolerances employed, the more miles you can achieve the better the ring seal will be. 500 miles is enough. During running in, make sure the engine does not run hot, too lean or too rich. Both will cause premature piston/ring failure. Temperatures over 95 degrees C (203 degrees F) are unacceptable. If this occurs, re-set static ignition timing to 2 or 3 degrees BTDC, re-check carburettor/fuelling settings, and re-check cooling system capability. Once the running-in period is complete, re-torque cylinder head nuts – 50lb ft for the nine main 3/8”AF nuts, 25lb ft for 5/16”AF rocker post nuts and end two 3/8”AF nuts. Re-set valve clearances (see below for settings). Where roller tip rockers are used, DO NOT push feeler blades through from front as standard. The roller tip acts like a panel roller and will draw the blade through irrespective of gap size – even if there isn’t one. The feeler blade must be wiped sideways from one side to the other. Finally re-check all connections, and then have the unit set up on a rolling road. As soon as it’s finished, and whilst still hot, ask the rolling road operator to check the ignition timing at, say 2,000 or 2,500 rpm using the TDC pointer/mark on the timing cover/crank pulley. The actual reading is irrelevant, just a reference point. Make a note of this, and check it periodically in the future. It will also serve to re-set it in the event of ignition component changes/engine re-builds for whatever reason in the future. Carry out periodic compression tests – they can help forewarn of possible trouble. Always do them immediately after competitive use or when engine’s hot, with throttle wide open. Running without an air filter will cause premature wear to valves, guides, seats, pistons, and rings. RECOMMENDED VALVE CLEARANCE: NOTES: In this end section I add obviously the valve clearances I'll recommend for the cam and usage, plus anything particularly relevant to the individual's engine. I believe you simply cannot have enough information, but also realise too much would just swap the recipient. Hence this is short, to the point, and covers all those items that cause hassle when starting an engine for the first time.