Breaking In That New Engine

By June 6, 2012Engine
How to Break In a New Engine

With the cost of engine rebuilds nowadays looking more like telephone numbers, you certainly don’t want to be doing this on a regular basis. And guess what; those first few moments when the beauty roars into life will make all the difference.

You see, the marriage of all those parts spinning around and going up and down is not naturally made in heaven. Everyone gets to know each other intimately, and for this to be amicable all the rough edges of the relationship need to be worked out very gently.

The minister in this marriage is the lubricant. Although oil is always important, on initial start up it’s vital that all moving parts have an adequate boundary layer to shield them from excessive mechanical contact with their partners. But a bit of peer pressure is good, so you don’t want to use any friction modifiers (such as PTFE additives).

Although machined surfaces, such as a piston and honed piston liners, appear to be very smooth; they are in fact surprisingly rough. The reason being, that during the run-in phase the parts actually bed themselves in through controlled mechanical contact. (That’s why it’s common practice to cross-hone a cylinder bore when fitting new piston rings – a glass-like surface will never allow the rings to seat)

If you’re about to fire up a rebuild, it’s best to manually “prime” the top end by removing the cylinder head cover and, using a good old fashioned oil can, apply a liberal coating of oil to camshaft, followers and if applicable, rockers and buckets. As with every other start up in a motor’s life, it’s the top end that takes all the strain while waiting for the oil pressure to build up.

If the engine’s been sitting for a while, it’s not a bad idea to disconnect the HT lead from the ignition coil and just crank the motor on the starter motor a few times – just to give the oil pump the opportunity to lift a good head of oil and send it on its way in a leisurely fashion.

Obviously you also need to make sure the coolant level is correct (bleed the system from the highest point if needed) and all filler caps are secured – it’s no fun trying to mop up after a gusher’s deposited a gallon of 20 W all over the exhaust manifold.

And don’t forget it may take a while for the fuel pump to deliver enough fuel to get the whole plot on song – especially if you’ve rebuilt an older motor with a mechanical fuel pump and carburetor.

When the motor fires up, don’t race it; it’s under enough peer pressure without having to run a race as well! Just let the engine warm up; and warm isn’t the water temp gauge. You want to let it idle a good 10 to 15 minutes before doing anything. In this time take a good look at the engine bay to make sure there’re no leaks or expensive sounding noises.

More modern engines, the ones that use materials that aren’t even on the periodic table, don’t need the same degree of attention. Material like Nikasil and pre-coated pistons take care of most of this startup ritual. Although a bit of TLC for the first few days in a new life are always welcome.

Treat a motor well in these vital times and it’ll return the favor in buckets!

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