1990 2GM20F issues - HELP!

Ken Cross · Jun 20, 2020

We have a 2GM20F on our 1989 Hunter 30. Wot is about 3,300 rpm on our 2 blade prop. We usually get 6 kts at 2600 to 2700 rpm.

I'd never pull the head unless I had first checked the compression and had one or both cylinders low. (Assuming there isn't a valve problem).

Checking and adjusting valve clearances is an easy DIY job.

As for difficulty starting, these enjines are known to take 5 to 10 seconds or even more of cranking with the throttle pretty high to get them to start cold. After the initial start that day, throttle idle and just bump the starter. Away she goes.

Could it be an injector issue?

And I agree you may be over propped. I'll look at my records and tell you what our prop size is.

Ken

Ken Cross · Jun 20, 2020

15. / 12 RH 2 blade

Ken

RoyS · Jun 21, 2020

With regard to hard cold start (only), some Yanmar engines have an optional Thermostart (not a misspelling) device available. My Yanmar 2QM15 has one. That device uses diesel fuel ignited inside the intake manifold to heat the incoming air to help start the engine. Made for engines without glow plugs. If available for your engine you can determine if it will help starting by directing a heat gun (hair drier will do) into the cold engine intake and then attempting to start. If it helps to have warm air at the intake and the Thermostart device is available you can proceed in that direction. Device is not expensive and is used mostly in Yanmar tractors. Some wiring and plumbing required. Takes 15 seconds to heat intake manifold air. I have used mine for years without any problems. This has nothing to do with the RPM issue, only cold starting.

Ken Cross · Jun 21, 2020

Wow, that Thermostart looks interesting. I googled it. Thanks
Ken

RoyS · Jun 22, 2020

RoyS · Jun 22, 2020

Thermostart above utilizing injector return line to keep reservoir filled.

RoyS · Jun 25, 2020

Good work!

jtm · Jun 26, 2020

I have had a H28.5 for 33 years. it had the 2gmf (not the 20). That engine was also on the 33.5. the 28.5 and 30 are shorter and relatively stub-ier goin thru the water than the 33.5. - more water to ply. I found the sweet spot at 2650-2850 rpm. With heavy wind on my nose or oncoming seas i might go to 3000-3100 rpm but beyond that i felt it was diminishing returns and prolly cavitating.

the prop seems like the likely culprit but the engine would have suffered from an under or oversized prop.

while you are down under - take a measurement of the clearance from the top of the prop closest to the hull to the hull. it could be another indicator if you have the wrong sized prop. that distance is important as it could be causing cavitation if too little separation from hull. i doubt you will be able to read the etching on the prop hub while down under- alittle antifouling paint and its pretty much covered over.

if the engine was suffering from low speeds( read carbon buildup) from prior owner and compound that with poor maintenace and improper oil type/viscosity + The crapped out elbow is another tell that the rusting in the elbow caused constricted exhaust and backing up of carbons in the cylinders. you could have crud deposits in and around the injector and that impairs the atomizationflow of the injected fuel- then it unburnt fuel and exists as black smoke.

I'd try several cycles of 50% heavy duty injector cleaner in your fuel filter cup to see if you can leach out the crud and improve injection atomization. while you could eventually replace the injectors, Id want to try clean the cyl head of carbon crud, as the atomization would be impaired. id pull an injector of 2 to see what thry look like before i did that so id have a bench mark.

let us know the end of the story.

Art12050 · Jun 30, 2020

BOSSailor.....you’ve had quite an ordeal with your engine, sounds like you may be getting close.
We’ve owned our 92 Hunter 30 for 21 years. The original prop was a 2-blade, probably made out of polypropylene. I replaced it 10 years ago with a 3-blade bronze Campbell Sailer made by West by North. Made a big difference. They have all the specs. to match up the props, so they’s not guess work.
Also, motoring in and out, I usually run between 2500-3000 rpm. At slack tide we get about 5.5- 6 knots SOG. This is rare as we always seem to be fighting a foul current in the channel.

heritage · Jun 30, 2020

My H27 was repowered with a 2gm20f. The prop is a 3 blade 13x11. I can get about 3300 rpm at max power in gear and 3600 in neutral. No smoke. 5.5 kts at 2600 rpm.

Robert580 · Jul 1, 2020

I agree with Benny, a little research before head job, fresh fuel etc.
1.8 knots is not far enough off the mark to worry.

Tally Ho · Jul 20, 2020

Glad you have it figured out, and thanks for sharing the solution.

Gref

RoyS · Jul 21, 2020

Good work! Where did you have the injector pump overhauled?