Pulling a cog. Any tips ?

[tom52]

Hi Chaps,

I am trying to pull the drive cog off the shaft of my raw water pump. Its off the boat and in the garage.
I am putting the claws of the puller under the cog, tightening the forcing screw onto the centre of the shaft and then giving the forcing screw a wallop. Repeated many times but the bugg%r won't shift.
Any tips ? Heat ? Cold ? Or just keep bashing and hope ?
Help !

 

[Superstrath]

Try putting the whole assembly in the oven, then rush it to your garage and retry the puller/bashing thing. The oven will get it up to a nice, consistent temperature without danger of of warping, weakening or bending anything. Avoid blow-torches and such as they will create local hot-spots with the opposite effect, and obviously don't do it at all if there are any plastic or rubber components involved.

If it's oily, wait until the Mrs. is out, as it will smell a bit and she won't like it.

 

[neil_s]

Just bashing and hoping will end up with damage, probably to you and the pump. Check that there is nothing else holding your cog on the shaft, like a concealed grub screw. Reference to the service manual springs to mind. Heat can be helpful, especially if the cog and shaft are of dissimilar metals. If they aren't, you need to heat up the cog and not the shaft to get any advantage. You might need a stronger puller, too. I am in this position, trying to extract the cylinder liners from my Bukh DV20!

Neil

 

[Lakesailor]

Pop down to the local (proper) garage and get them to stick it on their bearing press.

 

[VicS]

[ QUOTE ]
Pop down to the local (proper) garage and get them to stick it on their bearing press.

[/ QUOTE ] A very sensible suggestion

BUT do be absolutely certain that it is only pressed on and not fixed in some way. A grub screw has been suggested but a pin is more likely. If there is a plain shoulder clean that up thoroughly and look at it carefully as that is where a pin or other fixing is likely to be.
I'd expect a gear of any type to be fastened to its shaft not just pressed on.

 

[fisherman]

There's a chance that you've spread the end of the shaft already. Bound to be some sort of fastening as above, some Jabscos have a roll pin. Try dangling cog in boiling water.

 

[savageseadog]

[ QUOTE ]
Try dangling cog in boiling water.

[/ QUOTE ] Or better still boiling oil.

 

[tom52]

It is a Jabsco but it definitely a press fit with no other mechanical fastenings.

 

[James_Calvert]

[ QUOTE ]
Just bashing and hoping will end up with damage, probably to you and the pump. Check that there is nothing else holding your cog on the shaft, like a concealed grub screw. Reference to the service manual springs to mind. Heat can be helpful, especially if the cog and shaft are of dissimilar metals. If they aren't, you need to heat up the cog and not the shaft to get any advantage. You might need a stronger puller, too. I am in this position, trying to extract the cylinder liners from my Bukh DV20!

Neil

[/ QUOTE ]

When I faced this, the guys at Bukh UK said they whacked out the liners with a lump hammer using a piece of hardwood (like a chairleg) against the end of the liners where they project into the sump. This worked for me too- but the wood splintered away in the course of the job. It's the crud that's deposited on the outsides of the liners which makes it a hard job; this gets scraped off inside the engine casing as the liners are removed.

James

 

[VicS]

[ QUOTE ]
It is a Jabsco but it definitely a press fit with no other mechanical fastenings.

[/ QUOTE ] Then Lakesailors advice is good. A decent press, even a mechanical one as opposed to a hydraulic one, will exert a lot more force than a puller.

A local gearbox re-builders would help probably

 

[santeana]

If not a grub screw or pin then a keyway. I don't know your application but a "drive cog" or pinion would normally have something of the sort. I guess you've checked if the shaft is tapered or at least the bit that carries the pinion. If all draw a blank then it can only be an interference fit (like often on bearings). Heating the pinion not the shaft is needed probably together with a press. Making lateral stikes to the boss of the pinion can help separation if still struggling after applying heat. If that fails try sticking it the freezer overnight then reapplying the heating pressing process.

 

[PaulJS]

Just for the record, unless the shaft material has a much greater co-efficient of expansion than the cog, then it won't matter if you heat both up at the same time, or indeed cool both. The reason is that a shaft expands or contracts diametrically, but an annulus expands or contracts along the length of the mean circumference, i.e. pi times D.
I know that this is a theoretical ideal, but true enough anyway.
Is there any sign of a keyway? If so it might be worth a few drops of release oil, not WD40, to soften any rust on the key. If not, the best bet is the decent garage bearing press.
Good Luck! /forums/images/graemlins/smile.gif

 

[santeana]

You're quite correct Paul but we don't know the materials. Improving the heat differential is to the good especially when lacking professional equipment. Freezing the parts is also a technique for helping break any corrosive bond as well improving subsequent heat differential.

 

[macd]

What Superstrath forgot to say was that you should turn the oven on. Even if you become homicidally frustrated with the damn pump, they are not susceptible to gas poisoning. In that case beating it with a heavy blunt object is the most rewarding strategy, although you'll probably need a new pump.