Yanmar 3GM

[pacerow]

I have a 3GM aboard my Morgan 323. I have the hand crank to start it manually. I move the two decompression levers back, but I still have a compression that I can't pull the crank through. I assume that the engine should free-wheel until I activate the decompression levers. Am I doing something wrong, or is this 70 something body showing it's age?

[four winds]

Does the 3gm have only two levers?

3gm30f has three.

[lockie]

The 3gm has 3 cylinders, so you have one more lever to go.

Mind you, you'll be a special person if you can hand-start it. It might be possible if you have adequate room to use your muscles to swing the handle, but my 2GM is cramped. I'm sure I'd strong enough if I had the space, but so far I haven't managed a hand-start.

Cheers, Graeme

[pacerow]

Only two levers and rated at 20 or 22 hp

[Pendragon35]

Is it possible you have a 2gm? I have a 3gm30 and it's got three cylinders, three injectors, rated for 27 hp.

[pacerow]

Plate says 3GM, have three injectors but only two decompression levers.

[four winds]

Hey Jim, the 3gm is a completely different engine from the 3gm30f. The OP said it was 22hp (2gm 18?) and has been down in there with a hand crank getting some exercise. Seems like he should be aware how many levers it has.

But I find it curious it has two on a three cylinder.

Though if I get caught with a weak battery I open one of three on my engine and fire it up. The third cylinder comes online by itself after starting.

So maybe there is some rational for only two levers on this older design engine. And could explain why it appears to still have compression during hand starting.

May have to Google 3gm images.

[four winds]

Originally Posted by pacerow

Plate says 3GM, have three injectors but only two decompression levers.

Well there you go. Not quite senile yet, huh pace. :- )

But you still have one cylinder in compression then. Never tried hand starting yet on mine. No crank lever on board, and the fitting is somewhat blocked on the freshwater version of my engine.

[hugosalt]

I only know about my 3GM (and the half dozen i have seen/worked on in the last 30 years.)
...and I can assure you that my 3GM 22.5 h.p. raw water(made between 1983 and 1985)
has 3 decompression levers.
Jim's 3GM30 is a later version of the same engine with bored out cylinders producing 27 h.p.
Never even tried to hand crank as crank handle blocked from full resolution and
have never heard of anyone hand starting a 3GM, (maybe a 1GM or 2GM) but never a 3GM.
Sure if one needed a hand crank some 3GM owners would donate one, including me.

[four winds]

Yes, in fact it was the earlier 3QM that was a completely different design from the 3GM and later the bored out 3GM30F.

Point of correction, the 3GM was made from '80-'83, and the 3gm30f from '83 to 2005.

That most aft lever sorta hides back there by the breather assembly. Not nearly as out in the open as the others. Maybe the OP will spot it upon closer inspection.

[RaymondR]

I found even with a fairly flat battery I could usually get the starter to spin up the engine and drop one valve lifter to get it to start on one cylinder then drop the other two. Never even tried to hand crank it, far too ambitious for me.

[Rhapsody-NS27]

Originally Posted by hugosalt

...and have never heard of anyone hand starting a 3GM, (maybe a 1GM or 2GM) but never a 3GM.

I've only been able to manually start my 2GM after my rebuild AND after the engine was already warmed up. (haven't tried a cold start yet)

But, that is still a very hard workout to crank this engine even when it's warmed up. I know I've seen 1GMs start manually, but haven't heard of anyone trying it on a 3 cylinder engine.

Best of luck to anyone who tries.

[pcmm]

The 3gm isn't really meant to be hand cranked. There is a reason they bolted a cover over the hand crank boss.

[hugosalt]

[QUOTE=four winds;2235513]Yes, in fact it was the earlier 3QM that was a completely different design from the 3GM and later the bored out 3GM30F.

Point of correction, the 3GM was made from '80-'83, and the 3gm30f from '83 to 2005.

Thanks for correction. Have to start checking my recall/memory.

Somewhere on line is history/time line of Yanmar marine motors
is either on Mack boring or Torrenson web site...(recalled from my questionable memory!)

[four winds]

I use the pdf from Mack Boring attached.