gearbox slipping in reverse

[svgruffalo]

Hello All,
We have a Yanmar 4JHE with a KBW20, raio 2.62.
It's started slipping in reverse a few weeks back and has become so bad i can hold the prop shaft still in reverse.
A mechanic replaced the thrust bearings and seals a few months back in teh UK. He looked at the clutch plates and said they were fine and did not need replacing.
I contacted him and he instructed me to disonnect the lever cables, retest and if the problem persists, adjust the position of the side cover in order to alter the neutral position of the shift fork. I did this but could not improve on it. When fwd is selected, a sharp clunck of the gears is heard and propulsion is instant. When reverse is selected the clunck is only slightly less, but propulsion is much slower to build and when revs are increased slippage soon follows. This seems to become worse as the engine warms up.

Has anyone had the reverse gear slip in these gearboxes ?

Has anyone else made this adjustment to thier gearbox ?
Is thier any tricks to it ?

I'm almost at the point of pulling it out and splitting it to check clutch plates and plate springs ?

If i go down this road, are there any further tests i should do to help diagnose the problem.

Can anyone offer a likely diagnosis of the problem and what parts i need to replace ?


cheers and thanks
Darren.......sv Gruffalo

 

[Bosun Higgs]

We had this problem.

My Yanmar box had a cone clutch with limited movement. As the clutch wears, it gets to the point where it just cant grip tight enough and starts to slip. Whether it slips in reverse or ahead depends only on the adjustment of the gear change lever. The whole problem can be made worse if someone has filled your box with gear oil since this lubricates everything just a bit too well.

In our case I brought the box back from Bilbao in my handluggage ( weak after 9/11 !) and Cellar marine at Porthallow shimmed it for me to take up the wear. They also told me to use SAE 10 engine oil in the box. It worked well thereafter as long as I had the boat but this was with a 2GM. I dont know whether the SAE 10 trick would give a 40HP engine sufficient lube.

The pukka solution is to replace the cone clutch but this is expensive. Cellar marine are Yanmar agents but deal mainly with inshore fishermen so they are used to finding economic ways of repair. Good outfit IMO.

 

[svgruffalo]

Thanks for your reply Bosun Higgs.
I suspected inadequate shimming or the plate springs, but i'm no mechanic and so am happy to hear other peoples ideas. Even happier to see i may not be so far off the mark. Do Cellar Marine have a website / email ? I could not find either. If we could find a good second hand KBW20 or KBW21 at a reasonable price i'd just swap it out and canibalise the other for spares. I think we may well just ignore it for now, sail to the Caribbean and fix it with cheaper priced US parts.

cheers
darren

 

[Ludd]

Thanks for your reply Bosun Higgs.
I suspected inadequate shimming or the plate springs, but i'm no mechanic and so am happy to hear other peoples ideas. Even happier to see i may not be so far off the mark. Do Cellar Marine have a website / email ? I could not find either. If we could find a good second hand KBW20 or KBW21 at a reasonable price i'd just swap it out and canibalise the other for spares. I think we may well just ignore it for now, sail to the Caribbean and fix it with cheaper priced US parts.

cheers
darren

Hi Darren,Sorry to hear you've got problems.Can't help,I'm afraid,but you have my sympathy! Are you in the Canaries,or did you go to Cape Verde Islands?
Kids ok?
Tom (El Viento)

 

[Bosun Higgs]

cellar are on 01326 280 214 I doubt they have a web site - they are down in the bowels of cornwall and the sort of practical engineering business where the boss has greasy hands.

they have done several practical money saving jobs for me and I have bought two engines from them, albeit I havent done business for a few years since my current boat is volvo unfortunately.

P.S. Just had a quick look at the EP barrus site and apart from the ZF gearbox, all the boxes it shows have cone clutches not plate clutches albeit none of them are quoted under the initials you use. If it is a cone clutch and if you have made sure the gear lever is correctly adjusted, I would be pretty confident about the diagnosis. The clutch is slipping and its doing that because it has worn, the surface is now a bit shiny and there is insufficient pressure on the face of the clutch to overcome this and make it grip. To remedy it you either need another full fat clutch of you shim the shafts to take up the wear as an interim cure.

 

[anderson]

gear box slip

if the gear box is driven by a cone clutch system and if you have used engine oil that is for a turbo engine this oil is not suitable for cone clutch drives,the oil helps to polish the cone drive and causes slip.if theis is the case remove the cone and rough it up with a file or rough emery tape.

 

[Bilgediver]

if the gear box is driven by a cone clutch system and if you have used engine oil that is for a turbo engine this oil is not suitable for cone clutch drives,the oil helps to polish the cone drive and causes slip.if theis is the case remove the cone and rough it up with a file or rough emery tape.

This is definitely a possibility and some Volvo boxes suffer the same problems.


The surface finish of the cone is important and too good a polish is not good.

Cellar are good but not sure if they do these engines.

 

[earlybird]

I suspected inadequate shimming or the plate springs,

[/I]

If the KBW20 is similar to the KBW10, it has two multi-plate clutches, but no springs as such. Engagement of the clutches is forced by helical grooves and followers in the shifter plate. The greater the torque, the greater the pressure.
If disconnecting the cable makes no difference, I'd suspect internal wear.
e.g. maximum thickness wear on each plate, according to the Yanmar manua,l is 0.030", difficult to spot by casual examination.
Incidentally, the manual doesn't suggest adjusting the side plate as a means of altering the neutral position, but rather as a means of ensuring proper engagement of the cam with the shift fork.

 

[svgruffalo]

Thankyou everyone for your help

It is a multi-plate clutch with 12 friction disks.

I suspect internal wear also, but it all seems to have been triggered by the replacement of the thrust bearing, so i'm not sure thats the whole story. It developed over a few weeks but the usage over those weeks was very small. Certainly i was less than perfect on oil changes and now it has lovely red ATF fluid. A few people have suggested just sae 30 so that maybe worth a try too.

Adjusting the cover plate seems to have improved it a bit, but it seems to be a bit of trial and error once you have the audiable click of gears. So i'm not sure i have adjusted it as well as it can be.

PS...thanks Tom, yep kids and family fine. Everyone ready to roll.

cheers
darren

 

[Norman_E]

My boat has that gearbox with an 89hp Yanmar (yes I know it should be a KBW21 with that engine, but its a KBW20) It does not slip, and I am amazed that anyone has recommended SAE10 oil. The correct lubicant is ATF, or automatic transmission fluid, not engine oil.