Definitive 3CX King Pin repair guide

[McSpud]

Guys, do any of you know if there exists a definitive guide for slew/kingpost overhaul & repair on the JCB 3CX?

I've just finished shimming up, and replacing bushes at the bucket end of the boom, so it's all nice and tight now, but since I improved that end, it's really showing up the left/right slop in the boom. With the boom raised, you can even move it by hand, left& right.

I dunno whats involved in going after the problem, or if it's even worth it, or where to get the parts even. What do ye think? It's a 1988 3CX blackcab.

Cheers
MS

[si25]

depends if the slop is in the slew gear or the boom bottom pin and bush? if if is the bottom pin and bush, fairly simple. i'll have a think/look at the slew gear set up as am unfamiliar

[Scooby]

If you get the complete kingpin and carriage repair kit c/w all bushes, seals etc. it will take a little of the play out of the slew. This is because you obviously get new teeth on the pin and the bushes will take out some of the slack at both ends of the pin. But you won't eliminate the slack totally because unless you replace the rack the teeth on that will still be worn.

If you decide to go down the pin and kingpost repair route then you need to know what you are doing. There's quite a bit of weight in there and there's a right and wrong way to do it.

It is not uncommon for the pins to break in half (they will still work for a while even in two pieces) but that will make the slew even more sloppy. Is your pin still in one piece ?

[McSpud]

Hi fellas,
Well, I haven't dismantled anything yet, I'm trying to assess whether its something I want to take on, but as the title of my post says, i can't find written experience of anyone thats done it before.

Theres a little forward/back rock in the kingpin housing but the yellow cap is still up on the top, so I've no reason to think it's broken in the middle, I'd expect it to be inching its way up out of it if it was maybe???

How do I find out whats worn lads, can I take the bottom pan off that slew gearbox and have an eyeball, or is there a danger if the pin is broken, it will fall down out of it?

No doubt this repair kit would cost a fortune I suppose!

What approach do you take removing the back actor, do you seperate it at the top knuckle to make it lighter?

Anyway thanks for your replies lads - Scooby, I recognise you from the DBTC site, I'm wrestling with a pair of Browns too!

[Scooby]

Hi fellas,
Well, I haven't dismantled anything yet, I'm trying to assess whether its something I want to take on, but as the title of my post says, i can't find written experience of anyone thats done it before.

Theres a little forward/back rock in the kingpin housing but the yellow cap is still up on the top, so I've no reason to think it's broken in the middle, I'd expect it to be inching its way up out of it if it was maybe???

How do I find out whats worn lads, can I take the bottom pan off that slew gearbox and have an eyeball, or is there a danger if the pin is broken, it will fall down out of it?

No doubt this repair kit would cost a fortune I suppose!

What approach do you take removing the back actor, do you seperate it at the top knuckle to make it lighter?

Anyway thanks for your replies lads - Scooby, I recognise you from the DBTC site, I'm wrestling with a pair of Browns too!

Hello McSpud,

Even if the cap is still on the top the pin can still be broken. But you should be able to see if it is. Rest the bucket on the ground and very slowly lift and lower the boom. You will soon see if the gap between the top of the kingpost and the carriage does strange things.Do not take the cap off the bottom. The pin could, theoretically, come out and although the boom ram would still be attached the boom AND kingpost could all come away from the carriage.If you're underneath you've got half a day at the undertakers.

Last one I did was in 2005. I always do it my way. The proper plant lads do it quicker.They stick a ditching bucket out at 90 degrees, take the weight of the boom with a jack and drive away. I take the bucket off, then the dipper, (using a tractor with a loader), then get some pallets up to the same height as the bottom of the boom and rest the boom on the pallets. Then slip the pins and boom ram and drive away. Then I lift the carriage off the digger after undoing the Hydra-Clamps and all the pipes.

Then I reassemble the new pin, and seals/bushes into the old kingpost and new carriage while still on the ground. The pin will need a bit of persuasion. You have to be sure that you have the pin and rack "timed" properly. I use a D/A valve on the back of a tractor and work the slew so that you know everything is O.K.

Then you lift the whole carriage/kingpost lump back onto the digger and fasten up the Hydra-Clamps. Then the pipes and then everything else. It's a very satisfying job and the slewing is much better.

Lats one I did I got change from £500 for pin, carriage, and all seals, bushes, etc.

Don't struggle with 2 DBs. What's the problem ?

Regards - Scooby

[McSpud]

Great post there Scooby.
I'm wondering if this is too big a job to take on myself, I've already replaced the bottom boom pin and the ram pin, as there were both broke in the middle. Considering that, it's a fair bet that the kingpin assembly has taken a beating too. I have noticed a kind of forward/ backward rocking motion in the pin housing when you lean / lift the bucket on the ground. I'll try grab a video and stick it on youtube so you can see, it's hard to explain. Do you usually replace the rack too, or could you take a chance on that being ok? I got this machine for very right money, so I can afford to spend a little to tighten it up.

This machine will never be doing any hard slogging for us, in fact you could nearly consider it being in retirement, but I'd like to have it right just the same.

As for the two DB's, they're a labour of love, chasing leaks and the like, we've a 995 & a 1390. The 1390 needs the most attention, a cylinder head cleanup and a clutch job. We have the clutch got for it and all, from vapormatic, I'm making up a dolly to put under it at the moment so we can split it. Theres not enough hours in the day man....

[Scooby]

Great post there Scooby.
I'm wondering if this is too big a job to take on myself, I've already replaced the bottom boom pin and the ram pin, as there were both broke in the middle. Considering that, it's a fair bet that the kingpin assembly has taken a beating too. I have noticed a kind of forward/ backward rocking motion in the pin housing when you lean / lift the bucket on the ground. I'll try grab a video and stick it on youtube so you can see, it's hard to explain. Do you usually replace the rack too, or could you take a chance on that being ok? I got this machine for very right money, so I can afford to spend a little to tighten it up.

This machine will never be doing any hard slogging for us, in fact you could nearly consider it being in retirement, but I'd like to have it right just the same.

As for the two DB's, they're a labour of love, chasing leaks and the like, we've a 995 & a 1390. The 1390 needs the most attention, a cylinder head cleanup and a clutch job. We have the clutch got for it and all, from vapormatic, I'm making up a dolly to put under it at the moment so we can split it. Theres not enough hours in the day man....

Personally I would always have someone helping me although I suspect that proper plant boys would do it on their own although it's much easier lining things up if there's two of you. Good idea if you can to stick the video on YouTube. Get someone to either work the digger or take the video. Take long shots of the whole kingpost and carriage and then a close up of that area that I mentioned. i.e. the gap between the kingpost and the top of the carriage.

I have never replaced a rack, principally because they were never available as an aftermarket item. If it isn't going to be doing much work I wouldn't bother with a rack unless you can get one cheap. The purists will tell you that you shouldn't replace a pin without the rack because you are putting new splines on the pin against worn ones on the rack but it's your choice.

Don't forget to block the front axle on the 1390 when you split it.

Good luck - Scooby

[McSpud]

Hi again Scooby, yep, I'll do that, could be Friday when I get a chance to do that in daylight hours, but you'll definately have no problem seeing the movement anyway. One thing that just struck me, do you need to replace the carraige as well? Or just some bushes top & bottom? I have the service manual for this machine, but theres very little detail about that whole assembly back there.

I'm thinking the newer type slew mechanism is better, since it's just two simple rams and no rack/gear stuff....

Yeah, hope to make a start on the 1390 asap, before it's needed for the summer... Got the whole kit, incl the PTO.
It's got the Sekura cab, looks like it could be trouble tilting it back but won't take long to find out I suppose!
I have another thread running on dbtc with the saga of that yoke... We wouldn't be terribly experienced doing clutches, and heads, but nobody's born a genius!
S

[newjcb123uk]

Heres a pic of a kingpost pin replacement we did a while ago - as you can see it's not a 5 min job and fairly dangerous .

[Scooby]

Hi again Scooby, yep, I'll do that, could be Friday when I get a chance to do that in daylight hours, but you'll definately have no problem seeing the movement anyway. One thing that just struck me, do you need to replace the carraige as well? Or just some bushes top & bottom? I have the service manual for this machine, but theres very little detail about that whole assembly back there.

I'm thinking the newer type slew mechanism is better, since it's just two simple rams and no rack/gear stuff....

Yeah, hope to make a start on the 1390 asap, before it's needed for the summer... Got the whole kit, incl the PTO.
It's got the Sekura cab, looks like it could be trouble tilting it back but won't take long to find out I suppose!
I have another thread running on dbtc with the saga of that yoke... We wouldn't be terribly experienced doing clutches, and heads, but nobody's born a genius!
S

Morning Seamus,

That's a good question about whether you should replace the carriage at the same time. In my experience the carriage comes as part fo the kit and I always assumed that the new bushes wouldn't be a very good fit in an old carriage. If you buy a "new" aftermarket carriage it's actually a reconditioned one and I have always thought that they have been line-bored and then slightly oversize bushes and seals are put in. Never tried new bushes in an old carriage just to see if they are oversize.

I have no experience of the newer type of slewing arrangement.

Not sure if you're right in saying that no one is born a genius. Einstein ? Gallileo ? Stephen Hawkin ? All I know is that I certainly wasn't. You wouldn't believe some of the b&!!s-ups I've made over the years. But my excuse is that the man who never made a mistake never made anything.

David.