DLE 55 Engine Reliability and Performance Tips & Tricks
The DLE line of model engines has become hugely popular due, in part, to their price point. The 55cc version includes ignition system, aluminum muffler, stand-off mounts and throttle arm extension, all for $ 370.00 from Tower Hobbies. Backed by a 2-year warranty. Love ’em or hate ’em, that’s hard to beat. However, these engines do benefit from some blueprinting and parts upgrades.
– Replace the original CM-6 spark plug with a known brand–NGK or Champion–and set the gap to .018-.020 (thousandths).
– Secure ALL fuel line ends, in-tank, tank-to-engine and pulse line from intake manifold to carb pump cover. We like to use a double wrap of .020 stainless steel safety wire and then curl the twisted pigtail into a closed loop to prevent fuel hose and finger punctures.
– Ensure that the prop drive hub nut is properly torqued to the crank. Invest a few dollars in a Zenoah screw-in piston stop–it is a far more humane way to hold the crankshaft than with a pair of old, rusty slip joint pliers on the drive hub and is an essential tool to establish the exact TDC, should you elect to adjust your ignition timing yourself. Anyway, the proper torque of the hub nut is 18.4 N-m or 13.5 lb-ft and use a medium-grade (usually blue) thread locking compound. It is important not to overtighten this nut since the crankshaft threads are cut, not rolled like an 8.8 SHCS, and are thus more prone to yield failure if overtorqued.
– Adjust the base ignition timing closer to the industry-accepted standards 28-30 degrees BTDC. The 55 is factory set at 44 degrees BTDC, which will cause higher operating temps, a rougher idle quality, and is harder on crank/rod bearings.
– Blueprint the reed cage; ensure that the surface the reed petals rest on is flat and smooth. The factory surface is too rough for a good seal and will cause spitback of fuel/air into the intake tract; this is noticed as a burble around 1/2 throttle while in flight. To surface the reed cage, remove from engine and remove reed petals (noting their placement). Using a Sharpie, cover the entire reed surface with color and gently wet sand with 600 grit sandpaper on a surface plate until flat and smooth. Use the marker color as a guide to ensure an even and level technique is being used. Remove all traces of sanding grit, paying special attention to the reed mounting holes. Using medium grade threadlocker, re-fit the reed petals as square and even as possible.
– Replace the stock piston ring with a ring manufactured by Frank Bowman, in Farmington, New Mexico ( email: firstname.lastname@example.org ). The stock rings are junk, in our opinion: they are not round and have excessive end gaps (a built-in loss of compression). The Bowman ring end gap is .002-.003 when installed, compared to .015-.018 stock gap. This is a huge performance upgrade and well worth the added part cost.
The DLE 55 has proven to be a generally sound engine, but it does need a little TLC to extract all the performance it is capable of. We regularly tach our blueprinted engines at 7500 RPM with an APC 20×12 prop on pump gas. We can perform all these upgrades on your engine during a rebuild, as well as some internal porting and port timing if you want to go even further. But I think we can agree that a 7500 RPM bench run is pretty respectable for a Chinese engine!
PLEASE NOTE: (1) Any internal upgrades/modifications will likely void your original 2-year warranty; (2) AeroScott Model Engine Repair Service cannot be held responsible for any DIY mistakes due to the broad range of abilities of aeromodelers. AeroScott does provide a lifetime workmanship warranty on all basic repairs.
Fly Safe — Scott Swirles