3gmd pounds when put in gear

[ron finnen]

Yanmar 3GMD idles fine but hammers and pounds when put in gear Motor smooths out after a few minutes. but duration lasting longer and longer Motor mounts appear to be as they should be and I checked the prop shaft for play when I was on the grid this spring . Could this be a problem with one or more injectors . I doubt they have been tested in the past thirty years

[Compass790]

Does the exhaust smoke? If so what colour? Is the smoke different when the engine is warmed up?
Are you sure the problem is not in the gearbox?

[lockie]

Sounds suspiciously like the transmission cone clutch is slipping until it eventually grabs. Do a search in this forum and more widely, plenty of threads and advice.

The long-term cure is to remove and disassemble the tranny, deglaze the cones and reinstall. Not a terrifying task if you are handy. Some people claim short-term success by replacing the oil with various things like a very low-viscosity oil or ATF.

Cheers, Graeme

[Compass790]

Originally Posted by lockie

Sounds suspiciously like the transmission cone clutch is slipping until it eventually grabs. Do a search in this forum and more widely, plenty of threads and advice.

The long-term cure is to remove and disassemble the tranny, deglaze the cones and reinstall. Not a terrifying task if you are handy. Some people claim short-term success by replacing the oil with various things like a very low-viscosity oil or ATF.

Cheers, Graeme

Yes +1 for this being the most likely cause.

[ron finnen]

Many thanks for the input .I will check out the gear box and recondition it or have it done .Thanks again
R

[roverhi]

I'd jump in the water and have a look at the prop cutlass bearing before R&R'ing the transmission. Rule out the easy stuff before before the big expensive things. Doubtful that it's the prop if it goes away but you won't know till you look. In any case it's doubtful that it's your engine though a sticky injector will make the engine run rough and may go way as the engine warms up.

[Compass790]

Originally Posted by roverhi

I'd jump in the water and have a look at the prop cutlass bearing before R&R'ing the transmission. Rule out the easy stuff before before the big expensive things. Doubtful that it's the prop if it goes away but you won't know till you look. In any case it's doubtful that it's your engine though a sticky injector will make the engine run rough and may go way as the engine warms up.

Yes +1 for this too. If folding prop[ isnt opening properly you can get the same symptoms. We have to put ours in reverse sometimes to get it fully open.
Agree always start with simple first. You will pay a kings ransom for a yanmar gearbox rebuild I'd expect

[Celestialsailor]

If it's a fixed prop, maybe a bent shaft or something caught in the prop.

[ron finnen]

Thanks for your input I did check the prop cutlass bearing when on the grid this spring and there was no play at all. The shaft is short ( about 2 feet )and I detect no bend. It is a fixed prop and not fouled so maybe I will have to consider the possibility that the problem is in the gear box . The motor starts well and idles smooth at any speed with no smoke so likely it is not a problem with the injectors .
Cheers

R

[lockie]

Don't be too freaked about gearbox reno. They are very simple devices. You may well find the biggest trauma is from trying to undo frozen bolts. Start now spraying them repeatedly with your choice of goop - WD40 or whatever the local brains trust suggests. Weasel piss comes highly recommended (50/50 acetone and ATF),

Cheers, Graeme

[ron finnen]

I have made the determination to do the gear box reno I have had success with a number of previous mechanical repairs .I will take photos as i go. Is there a certain grit I should use to deglaze the cone clutch? Thanks again
R

[lockie]

Ron;


Sent you a pm including deglaze procedure. It's not perfect (I didn't write it) but pretty good. As before, search this forum for a few relevant discussions. I refurbed my KM2A a few years ago (bearings and seals cost about A$250) works great ever since.



According to my manual you will have a KM3A. I can help with workshop manual if required.



Cheers, Graeme

[skipperpete]

I’d be interested to know the condition of the drive plate, pay close attention to it.... and the flywheel bolts when you withdraw the transmission. Or even better, take a peek through the little grid window on the flywheel/gearbox housing if your 3GM D has the window, you should be able to see if any bad stuff is going on in there with a good led flashlight.
Pete.

[Searles]

Sounds like the engine idle speed drops to low causing low idle hunt ,check rpm when g box is engaged these things need to be adjusted from time to time ..just maybe .⛵️⚓️

[Martkimwat]

Originally Posted by Celestialsailor

If it's a fixed prop, maybe a bent shaft or something caught in the prop.

My thoughts went immediately to a bent shaft or excessively worn cutless bearing, a sticking blade on a folding prop may cause a similar issue but as far as I know, apart from the Brunton autoprop, all folders have a gear mechanism so they open and fold symmetrically, same for feathering props. That being said a broken gear tooth could cause the same symptoms until the blade jumps back into position.