Gentlemen,
Have used both methods its not a hard fast rule, operated 985's, R1300 /1340's, R-1820/30's & R-2800's sometimes i pulled em through by hand if i could reach the blades or had a ground crew available other times used the starter and listened for clutch slippage, never bent a con-rod on any of the aircraft in over 6000hrs of round engine ops, was taught by my dad who in 18,000hrs of radial ops;who had many failures but none attributed to bent Con-rods/ hydraulic lock.
Eventually modified(Darton Inc. had a similar kit for T-28's,think they called it the "Clean Kit") most of our 1820 powered S-2R Thrush fleet with a B-17 unfeathering pump and plumbed the rocker boxes of the lower cylinders and oil sump to return to the Oil tank:-
Before start up open the Fuel/Oil shut-off valve, hit the pre-oil pump wait til 70 psi in the gauge, engage the starter count 9 blades, place mixture in Auto-Lean (Not Idle Cut-off as the book says found that doing so one does not need to blip the primer switch as A/L provides adequate FF while the engine warms up), Prime till u hear fuel running out the supercharger drain ,engage the starter again mags on at the 2nd blade usually it caught on the 3rd blade, and now wait for 10mins while the engine warmed up or the CHT shows approx 150C, a bit messy as all the excess oil went out the exhaust, added a flame /oil deflector to the exhaust outlet to cut the mess, Occasionally if had time i'd pull the blades through by hand and pull the chip detector bung in the sump and let the oil drain, just as effective as pulling the lower plugs,nowhere as messy: only one drain point, must say in the last 5 years of heavy round engine ops i just used the starter bumping method with no ill effects; good overhauls, burned little oil and very few oil leaks, if after inactive for days very little oil pooled in the lower cylinders or exhaust.
The 1820 & 1830 are the largest i have pulled through by hand myself, the worst prop to work with is the 43E50 prop blades abit short and thin, not like the 23E50 or 33E50. Worked overhauling recips and turbines engines for awhile, both engines types need a gentle touch (a dark art which some of our compatriots have failed to master) both in the cockpit and on the ground.
Had an overhaul shop (Avon Park ,FL) claim a 1820 engine we bought from them which subsequently blew up at 3.5 hrs TTSMOH was due to the fact i had pulled the prop through and bent a conrod, plus his warranty was voided as we were running Mo-gas in the 1820, listened to him profess my short comings as an A&P/IA, and that his engines perform flawlessly, shut him up with one simple question: So who in your shop dropped the # 3 cylinder on its base and then hammered out the damage and fitted it back on my engine?, because the skirt cracked and pieces FOD'ed the engine.
In hindsight ,their bad rep was known by most operators, but it was a package deal a customer traded up to a turbine Thrush, figured it was a good trade cash plus his airframe with a fresh engine overhaul, figured they couldn't screw it up as it was a warranty repair, should have listened to my oldman, he said of that shop if "its anything larger than a 985 dont use em or buy any aircraft fitted with their engines cause the engine will only be good for a boat anchor!", how true,found a much better ovh shop, who didn't mind which method i use to check the engine for hyd-lock and never had such shoddy inspectors.
Try fitting the Oil return kit to the 985's it cuts down the hassle, it was a factory option on the 1965 Beech H-18, well thats the drawings & installation i copied to get 337's on some of the Beech 18's we operated. The S-2R's were in the restricted 137 category, my FSDO guys used to let me fit almost anything on a Field Approval.
On a side note, on the 1340 & 1820 was getting between 3000-4000 hrs on the bottom end between overhauls (on condition TBO; plus wouldn't pull the engine until oil consumption in excess of 3gal/hr or loss of more the 10psi of oil pressure in the zero g portion of the spray run which indicated wear of the main bearing), changed cylinders every 300-600 hrs or so, got a 337 to put the R1820 -76 cyl heavy duty 1425HP cylinders from the Sikorsky CH-34, the MTBf went up to 1000-1600 hrs before having to pull a cylinder.
Ag-Pilot Magazine :Sep 1993 or abouts had a article written by Cal Butler and Greg Levya detailing most aspects of round engine ops in detail and touched on the 985 and 1340 was well, both gentlemen have in excess of 28000 hrs operating round engines in the harsh Ag-conditions and it was more of a tutorial to new round engine pilots and answered most of the myths and questions. Graham White's site is pretty useful its linked here at
http://www.enginehistory.org
Have gone all turbine sold most of the round engine aircrafts but still have a 1820 Thrush:- its the second to last built by the factory in 1990,can't bear to part with it, keep it in flyable storage, pull it outside 3-4 times a year and fly it for a couple hours, still only burning 3 qts/hr @ 950hrs TTSMOH and has yet to hydraulic lock even after periods of 3-5 months of inactivity, ground run for 25 mins, then do a power assurance check before doing a full power take-off pulling 43HG and 2500Rpm@126 gals/hr; try to fly it as much as schedule permits; its a guilty pleasure that my accountant and ops manager are beginning to grow tired of ;they keep saying why don't we convert it to a PT-6 or -331 and we could use it daily along with the others instead of being your glorified hangar Queen, i wont just yet and will continue to hold them at bay, if comes to it i may concede and pull the 1820 and hang the Pt-6 ,prop & mount i have sitting in storage.
Av-gas in our part of the world is at $4.25 a gallon, and we quit using mo-gas as the lead quantity has dropped off, after 28 yrs of running mogas it started messing with the diaphragms in the PD-12 Carb, as well as CHTs and EGTs with occassional missing/backfiring of the engine at power settings above 35 hg, tested with fresh Ovh carbs from Precision and other reputable outfits no cure, switching to Av-gas sorted it out, however the Low lead content of Avgas still is a factor. Maybe someone will come up with an Ethanol conversion for Round engines, cause the only reason we went turbine was the cost of fuel - Jet A @ 1.95,Avgas 4.25 do the math - 5000 gals avgas lasted a month where now 8000 gals of jet a which last about 21/2 months, Ok i'll be the first admit the turbines are nice, but they cant replace the glorious smell of burnt oil and deep rumble of a radial, which even after shut down still talks to you with the pings and creaks of the engine cooling down.