Stroke it Out: Running-in Four-Stroke Outboards

TLC Required

All outboards sold in Australia from 2019 onwards will be low emission engines, with the bulk being four-strokes, which means more care is required when running them compared with carbie two-stroke outboards.

The running-in process with most carbie two-stroke outboards was made easier by being able to double (or with Yamahas quadruple) the fuel/oil ratio for the first five to ten hours. The additional oil provided a level of protection even when owners were less than careful with the running-in procedure.

But not so with four-strokes. While the running-in procedures are nowhere near as regimented as with older models some care is needed in the first three hours where WOT is not recommended.

Before trying out your new investment for the first time I recommend buying a few items that will make the running-in procedure easier. One is a cheap wall clock from the Reject Shop or similar, the next is a nine-litre plastic bucket from Bunnings and finally a notepad and pen. The total cost of these items will be around $10.

The little made-in-China wall clocks run on a single AA battery and keep accurate time for a least a year before needing a new battery. Place a towel 

in the bucket to absorb engine vibration then fit 

the clock on top of it at an angle. This way the running-in period can be easily seen and time recorded using the notepad.

Before getting afloat a few items should be checked such as sufficient fuel and that the engine sump oil level is where it should be. Also check the prop is firmly attached so it won't deep six when you go astern. 

The Procedures

It's easy to understand that lot of people skip reading the owner's manual in the excitement of new machinery, but I was surprised to learn from a Yamaha YouTube clip on running-in new four-stroke outboards that this is actually quite common. This is a shame as owner's manuals are a great cure for insomnia. Sleep guaranteed!

After warming the engine in neutral at idle for three minutes in warm climates and five minutes in cold to fully circulate lubricating oil, idle the engine in gear for around 15 minutes. Then for one hour and 45 minutes increase the rpm to around 2000 (or one third throttle for engines not equipped with tachometers). During this time vary the rpm every 

10 to 15 minutes to help the piston rings bed in. 

The only way to do this is by subjecting engines to varying amounts of load.

Some manufacturers recommend taking the engine to 3,000rpm (half throttle) from the first to second hour but all are adamant that WOT should not be used in this period. Again the rpm should be varied every ten to 15 minutes.

From the second to third hour the rpm should be increased to 4,000 (two thirds throttle) but again not using WOT. The rpm must be varied as with the earlier running-in stages.

After the third hour the engine may be operated at WOT for up to five minutes at a time but reduced back down to 4,000rpm for “cooling” periods of 15 or so minutes, right out to the first 10 hours. At this time it's vital to check that the rpm reaches the upper part of the manufacturer's recommended WOT rpm range. For example, if the WOT range is 5,000 to 6,000 the engine should reach 5,700 to 5,800rpm with normal hull loading.

The reason for under propping is the engine must reach its peak torque band quickly to supply the “grunt” needed to get a hull out of the hole. From then upwards to near WOT the engine is under less load. Fuel injected outboards will benefit under these conditions because the electronic control unit will only inject as much fuel as is needed, normally resulting in excellent fuel efficiency from planing to around 5,000rpm. 

So if your new outboard doesn't reach the upper part of the recommended WOT range the prop must be swapped for one of finer pitch. And on the flip side if the rpm limiter frequently engages (indicated by rough running as the ignition system is interrupted) a coarser prop pitch is needed. These changes need to be done ASAP, not when the engine is taken for its first service, usually at 20 hours. 

An exception to the under propping rule is when an outboard is mounted on a displacement hull. The hull doesn't have to climb out of the hole, so slight over propping at WOT won't be detrimental provided the engine is mostly operated at three quarters throttle opening or less. For example, an Aqualine F2.5 achieved only 5,000rpm at WOT on my 3.8-metre Fairlite Gull sailing dinghy, even though the recommended range is 5,250 to 5,750. But at three quarters throttle opening the rpm was still 4,500 with fuel consumption half of what it was at WOT, indicating the engine load had fallen right off. Hull speed fell only six per cent from 6.5 to 6.1 knots.

The wrap

Always follow the running-in procedures outlined in owner manuals and don't be impatient to get through the running-in procedure. Ten hours of TLC are peanuts compared to the thousands of hours of enjoyment possible from a four-stroke outboard.

Life is a constant learning curve and the countless number of outboards I've borrowed and owned, run-in and evaluated over the past 50 years have all increased my knowledge and enjoyment afloat!