The goal with any propeller used in conjunction with a Yanmar 3GM30F is to achieve max RPM 3,600 plus 150 RPM or 3,750 wide open throttle, no wind-waves-adverse tides, on flat water with an unladen boat. It doesn’t matter what propeller brand you use so long as you achieve these parameters.
We ran a propeller experiment with our 2 bladed fixed Michigan Wheel Sailor propeller, altering it from 16x11 to 16x12, which drop the RPMs down to 3,600 max and went from no smoke to black smoke at max RPM. We dialed it back to 16x11 and it has been smoke free since.
There are a number of people who subscribe to over proping and running at lower rpms, near the peak of the torque curve, believing max torque at lower RPM will make their engine last longer, not so; these little Yanmar engine are high RPM screamers, if you load them up at lower RPMS, they tend to load up with carbon, blown head gaskets are only one of the symptoms you will experience.
We service and repair a lot of these little Yanmars in the San Francisco Bay Area, we service and maintain our 3GM30F and never had a breakdown on the the water:
Before starting your engine, open the engine compartment and do your pre-run checks, check engine and transmission fluid levels, check all hoses and fitting, looks for fuel, oil, water leaks, fix before running.
Start your engine and idle it at 1,000 rpm until warm, prevents shaking your boat to death when it is cold, it’s easy on the mounts, propeller shaft and packing gland.
Look for the sweet spot when cruising under power, ours is from 2,750 to 2,900 RPM, it run free and smooth. If you listen to your engine it will tell you if it is working to hard or being under worked.
Operate your engine for 4 minutes at max RPM at least once a month to blow out the carbon, it won’t hurt it one bit and it will pay you back ten fold in longer engine life.
When you return to the dock, let your engine cool down for 5 minutes, then in neutral, raise the RPM to 1,700 for 4 seconds, burns off the carbon without re-heating the engine, then drop it back to idle and let the engine smooth out, then stop the engine.
Pet Yanmar problem areas:
The U-shaped cast iron exhaust mixing elbow: water and exhaust passages are small, prone to clogging. The water gallery will clog where the water enters the elbow, in early stages, you can remove the pipe fitting and dig around with a screw driver and clean it out. Annually remove your exhaust hose and look up into the outlet of the exhaust elbow with a bright flashlight and a mirror, check for restriction of both exhaust and water galleries, don’t attempt to clean, replace it; don’t expect more than 4 good years of service, expect less if you are consistently running at lower RPMS. Just because there is water coming out the transom thru-hull fitting, it doesn’t necessarily mean the elbow isn’t restricted, if you push the limit on time in service, eventually carbon or corroded metal will shed and block the outlet, engine will blow black smoke at lower RPMS, eventually it will not start. Run your engine until warm, place your bare hand on the top of the elbow, it should be cold to
the touch, if not the water gallery is clogged or restricted, replace it. Look for rust water stains or cracks, if so replace, remember for optimum performance, even if you think it still works, chuck it and buy new, your engine will thank you with many more years of good service.
Pickle your seawater cooling circuit with white vinegar every year to reduce mineral build up. Run your engine till warm, shut off the seawater seacock, disconnect the hose and put it in a bucket of white vinegar, restart your engine and pump in white vinegar, let it sit over night. The next day, reconnect the seawater inlet hose, open the seacock and run till warm, flush out the vinegar. There are other chemical that will do the job in less time, but white vinegar is non-toxic to you and your environment, besides, what ever you spill won’t eat thought your boat and it also kill mold.
Fuel system: All small Yanmar diesels tend to shake loose the banjo fuel fittings on both sides of the fuel lift pump and from the pump to the secondary fuel filter, annually tighten up these fittings, not to tight, we just don’t want them to leak. When you can’t snug them up, don’t over tighten, replace the crush washers, 2 per fitting, remember your tightening steel banjo bolts in aluminum body, it is easy to strip them out.
Fuel lift pumps, as noted earlier, below the large round section of the pump body (diaphragm & valve body), you will see a 1/4" diameter round circle of metal on both sides, this is the exposed ends of the pivot shaft, axle, that the pump lever pivots on, the shaft is staked into place with a punch at the factory, to keep it in place; as the pump wears, this axle will tend to slide out one side and drop out of position, causing the pump lever to cock in the pump and rupture the diaphragm, resulting in pump failure or diaphragm perforation and fuel in the block. Preventive maintenance is key to preventing failure on the water, we replace ours every 4 years and forgo the headache, its better to replace it while it’s working than to deal with the issue of worrying about it condition or worst yet dealing with a failure.
Black dust on the front of the engine: All rubber products biodegrade and wear out over time, even v-belts, ensure your spares are not getting to old, chalking, cracking. Renew your belts when they start to ride down into the pulleys, keep your belts properly tensioned, 3/8-1/2" deflection in the middle of the belt. Look for any signs of wear, cracks, shiny sides means it’s slipping, slipping belts cause rubber to shed, black dust, take a cheap chip paint brush and knock the dust loose while you suck it up with a vacuum, your air filter will love you for this.
Cycling your spares: Use your spare parts to service your engine, buy new spares to store for future servicing or emergency spares, rotate your spare stocks. If a spare rubber product is chalky chuck it in the trash, you’ll be glad you did, as old spares fail prematurely.
Renew your air filter every year when you do your annual service, impeller, oil & filter, transmission oil and fuel filters, depending on hours of operation, v-belts can last 2 years depending on hours and proper tension, do not exceed 150 hours between oil changes, never go more than a year between oil changes even if your hours are below 150 per year to prevent moisture and acid build up.
Look for leaks, sweating hose to barb junctions in the cooling circuit, drain systems, replace hoses, use good clamps ABA or AWAB non-perforated clamps, they don’t tear up the hoses, they cost more, but they last longer, careful, these clamps can be easily over tightened.
Seawater pumps: Yanmar seawater pumps are disposable assets, unless your cruising and you have no other choice, replace it, don’t rebuild it, when the shaft seals start to leak. Most seawater pump run a stainless steel shaft, the seal runs on this shaft, cutting a tiny grove in the shaft, a new seal will only last for a little while running in this groove before failing. By the time you have to replace the shaft, bearing are not far behind, the cost of repair is to close to the cost of a new pump, again unless your cruising and you have no other choice but to rebuild, just throw it away, you’ll be glad you did.
Anti-siphon valves: Always install a good quality anti-siphon valve in you seawater circuit, usually between the heat exchanger and the exhaust mixing elbow, height of the valve should be 8-12" above the waterline and on center-line with the boat. We use to use Vetus anti-siphon valves religiously for years, they had a 5/16 hose barb to attach a vinyl drain hose which we ran to the bilge in case it spit salt water as it opened and closed, lately they have doubled the price and we are seeing more failures, leakage while running and have stopped using them. Since the price of the Vetus is so close to the Groco, we have gone back to using the bronze Groco valves with the 1/8 NPT female threads in top of the valve, install a hose barb and run a 5/16 vinyl hose to the bilge; you can take these valves apart and soak them over night in white vinegar to clean them up and replace the rubber flapper valve for $15, darn things nearly last for ever. Remember to apply a little water proof
grease on the cap threads when installing, it makes it easy to remove the cap for future servicing.
Corrosion: get rig of any signs of corrosion, sand, wire brush, convert minor corrosion with a chemical to turn minor pit corrosion to iron phosphate, prime and paint, yes use Yanmar paint it looks better. Corrosion, frozen bolts can add 30% or more to the cost of repair. When your remove your seawater pump to replace the impeller, grease the bolts that hold the pump on to the engine, grease the full length of the bolts as these tend to weld them self’s to the timing cover, this repair is expensive, requiring drilling thought the timing cover from below, through the bolts to remove the cover, in most cases the engine has to be removed to to this.
Invest in drip-less packing material for your packing gland. The manufacturer suggests alternating synthetic rings with drip-less packing. As an experiment, we deleted the synthetic rings and use 3 rings of the drip-less packing (IE.green goo), the shaft runs cool, minimal seepage, almost none and our bilges stay dry, using a conventional packing gland. Another alternative is the PSS drip-less packing gland, note the term is “drip-less”, not drip free; Yanmars, especially when cold or at lower RPM tend to jump around the engine room, this upsets the seal in the PSS gland, making it drip, at higher RPMS it is virtually drip free. The only thing we don’t like about the PSS glands, is having align the engine, fighting to push the shaft back while taking measurements. If you have to remove the transmission, you will have to release the set screws in the SS rotor and slide the shaft back through the rotor to allow room to remove the transmission, you also need to tie back the coupling
to keep tension on the PSS to prevent the seal from unseating and pouring water into the boat. With the Spartan conventional packing gland, we just clean the shaft forward of where it exits the packing gland and slide the shaft back, simple. Use ABA or AWAB clamps on your packing gland, slight drips eat up perforated conventional SS clamps in short order.
Finally, install an R&D Flex coupling between your transmission and propeller shaft couplings, it reduces engine movement transmitted to the propeller shaft, reduced propeller shaft packing wear and leaks, reduces loading of the transmission bearings, reduces or eliminates damage to the transmission in the event you strike something with the propeller, if nothing else, with reduced vibration transmitted to the hull, you butt will thank you.
From max prop to total engine care, who would figure? Diesel mechanic rantings.
Marty Chin, BCC Shamrock