Yanmar 3Gm30 Gearbox probs

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Jabamusic

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I have asked on here before about a problem I am having with the above (and followed some helpful advice).......the difficulty is that the engine struggles to engage either forward or reverse, sometimes being hesitant to go into gear from neutral but then going in with gusto and with a bit of a clunk.
Adjustment of the cable length by screwing up or down a threaded block was the suggested way to go, but this has not eradicated the problem and in fact it now seems to getting worse.

I was wondering if anybody had any experience of similar? an/or other thoughts, ideas, suggestions?

Thanks

Jaba
 
3GM30 Gearbox Problem.

Do you have a fixed or a folding prop ??

By the way, I think the idea of operating the lever on the gear box (see above) instead of the remote with a long length of cable is a good one.

Alan.
 
The idling revolutions of the engine may need to be checked from the Yanmar Manual to make sure engine is not fast idling?
 
bikedaft said:
does it work (engage fwd/rev) if you move the lever on the gearbox itself with the cable completely disconnected?
Click to expand...

Yes, I believe it engages Ok -but I was so busy making small. incremental changes to the thread length that I never actually tried this.

Do you have a fixed or a folding prop ??
Fixed prop.

The idling revolutions of the engine may need to be checked from the Yanmar Manual to make sure engine is not fast idling?

Idling at usual revs, couldn't be exactly sure what they are, but no noticeable change.

Jaba
 
Sounds like the idle speed revs are too high.
The idle speed of the engine should be controlled by the idle speed adjusting screw on the side of the injector pump and not the cable adjustment.
Try slackening the throttle cable off . if the revs drop , keep adjusting cable length till speed doesent change, the try the gears again.
The gearbox should only engage when the engine is idling.
 
HunterWanderer said:
The gearbox should only engage when the engine is idling.
Click to expand...

yanmar dealer (geo hulley) told me exact opposite - that the revs should rise just before engaging gear (3gm30f)

our fwd/rev and throttle lever is knackered at the moment, so currently the fwd/rev is on a seperate wire. the gears will engage at idle or higher revs, but with a bigger jolt at idle, so generally try to avoid it.

back to the OP (sorry!) if the gear lever on the engine works without cables attached then the problem is with your cables or throttle lever etc. at least its cheaper to fix. on ours its a very definite engagement, just like a cars if you've ever had a g'box off and played with the lever on the box.
 
g/box

You need to start from scratch, disconnect the cable at the box and check the revs on tickover with the engine warm, They should be between 750 and 850m try engaging the box by operating the lever, if the problem is gone then the issue is with the cables and linkage, if its still there the problem is internal in the box.
The dealer was right and wrong, the revs should increase but only after the gear is engaged, if you engage gear the prop turning will drag down the engine rpm so as soon as you engage the cable should be set to allow for this decrease, you may not think there is any difference but the prop is turning and the engine revs are the same as tickover, or this is the way it should be.
if your engine is currently ticking over at 6-700 then this is too low, it needs to be at least 100rpm higher, this will not be helping and needs to be corrected before doing anything. Its the stop bolt on the side of the pump.
 
Update

I have now figured out the following:

Gearbox is kn*****ked ! - Box fails to engage in either forward/reverse when manually changing gear without using the morse controls.

Gets worse when oil is hot.

The gearbox is a Hurth KM3P Model number 25775.

Clearly now needs stripping out and reconditioning.

Questions (if you would be so kind (bearing in mind budget is limited :-( -
Can I get this box reconditioned? If so, where would individuals recommend?

Is a gearbox removal a job only for the professionals (and contortionists). I live in the North West of Ireland so it might be that I have to get it somewhere to have work done.

The boat is coming out in the next few weeks so sudden ingress of water won't be a problem !
Anything else advice wise would be gratefully received.
Many thanks for your forbearance.

Jaba
 
Gearbox removal needs about 2-3" of space so depends if you can slide the shaft back or not. Otherwise it's just remove flange and bolts (8 IIRC) from engine and it slides off.
Just a thought - how old is the oil and is the level correct?
 
there were a few boxes on ebay last i looked, although my problem turned out to be the control lever in the cockpit

bummer, hope you get it sorted
 
awol said:
Gearbox removal needs about 2-3" of space so depends if you can slide the shaft back or not. Otherwise it's just remove flange and bolts (8 IIRC) from engine and it slides off.
Just a thought - how old is the oil and is the level correct?
Click to expand...

Thanks that is useful.............Oil not old and is at correct level.

So, I might be able to remove it, the question now is to where do i send it?

Any ideas?

Thanks
 
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