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#115501 26/05/22 09:34 PM
Joined: Jan 2016
Posts: 7,427
Likes: 135
NormK Online Content OP
SENIOR TECHNICIAN
I'm having trouble removing a couple of blade bosses from Chonda motors. I have cut the shafts off the motors and tried pressing the shaft stub in my press and there is no sign of them moving. On the second one I tried, with a bolt into the end of the shaft, all that did was push the bolt down into the shaft stub. I guess 12 tons will do that. I tried heat from a butane torch but not sure if it got it hot enough. Any other thoughts as I want a boss to fit on a Honda motor?

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NormK #115504 26/05/22 11:36 PM
Joined: Jul 2018
Posts: 2,082
Likes: 80
SENIOR TECHNICIAN
Norm, the luckiest way I have had is sitting it for weeks in thin oil. I would heat the oil on a stove if I wanted to try it quicker.

My other suggestion (which is more dangerous) is to use a weak (ie max 300nm) impact wrench on a 3 legged puller. the jolting will often break the seal.

Wear a full face shield - I don't know if the pullers like impacts. But I have used this method successfully

NormK #115506 27/05/22 01:42 AM
Joined: Sep 2015
Posts: 1,996
Likes: 137
SENIOR TECHNICIAN & HISTORIAN
Hi Norm and Tyler

I would have a lot of trouble removing a seized boss with a 2 leg puller but with a 3 leg puller with a lot of tension ,then
place one side of the boss on a solid bit of metal like an I beam or train track etc,then I use a 3/4 brass drift as a punch,
you hit the brass drift on the opposite side of the boss when it's on the solid metal I beam and a few blows of the hammer
and the boss will move then retension the puller and few more hammer blows will move the boss some more.

The only problem is occasionally if you hit too hard and the boss is cast iron you can crack the boss.

If I don't care about the motor and want to make sure the boss is saved I would just heat the boss red hot with the oxy
then it would easily tap off the shaft.

Seeing that the shaft is cut and the inner thread is stripped ,I'd be soaking the shaft and boss in white vinegar.

Buy a 2 litre bottle of vinegar ($1.40) at any supermarket and soak the crank and boss for 2 weeks in a cut open 2 litre bottle.

I did this to free a rusted V8 gudgeon pin that was rusted for 40 years , it still needed a little heat with lpg but was the easiest way.

Cheers
Max.

NormK #115507 27/05/22 03:09 AM
Joined: Apr 2014
Posts: 219
Likes: 10
Apprentice level 3
I’ve not mucked around with these, I guess it would depend how it is attached to the shaft.

If it’s a plain cylindrical shaft it might be less effort to mount the assembly in a three jaw chuck, face it off, centre drill and then drill out the remainder. If it’s tapered then you’d need to form a tool and use the sliding carriage on an angle to achieve the same outcome.

I do things like this when I want to preserve the hardening or finish.

Another method, if you still have a decent stub of shaft left, is to freeze the whole thing onto a mounting plate for the press and encase the shaft stub in a block of ice also freeze a mandrel slightly undersize. Doing all this in a deep freeze helps. Next day I mount it in the press and, using the mandrel with the whole thing under pressure, heat the outside of the external part with a torch.

The ice blob and mandrel act as a heat sink and the shaft stays cold while the external part expands with heat and the two parts more easily separate.

Another method is to stretch the external circumference using weld shrinkage. I warm up the whole assembly first, get the whole thing red hot if I can without damaging the bit I want to preserve. Then I weld a great hunk of junk of some description with a hole through it that has thermal mass much greater than the part to it using a series of big chunky welds, leaving gaps between.

As these welds and the part cool they shrink and pull the external part back. The gaps ensure the part doesn’t crack. The inner shaft will be free to shrink back to its normal size and should be much easier to remove.

You can achieve similar effects running thick beads longitudinally down a part with gaps between the beads. Grinding the beads off and giving it a spin in the lathe returns the part to normal dimensions.

These are methods I’ve used to fix machinery, tractors and implements. Sometimes spares are well outside the budget and the thing needs to be fixed asap no time to wait for a part.

NormK #115508 27/05/22 09:35 AM
Joined: Jan 2016
Posts: 7,427
Likes: 135
NormK Online Content OP
SENIOR TECHNICIAN
It is a steel boss on a steel shaft and I have had 12 tons on it so any puller is not going to even think about it. I might have to take it to my mates factory and put 20 tons on it. Not sure how I am going to get the other methods to work

NormK #115509 27/05/22 10:23 AM
Joined: Sep 2015
Posts: 1,996
Likes: 137
SENIOR TECHNICIAN & HISTORIAN
I've seen a lot of people damage parts from using too much force when all they needed to do was apply an impact load to free a frozen part. It's the hammering that
loosens the hub if you kept tightening the puller without
Hammering you would just strip the puller bolt or break
the puller bolt.

If you use too much force to push a frozen shaft it can
Expand into the hub you are trying to remove the shaft
From and you would need to drill the shaft out.

Cheers
Max.

NormK #115510 27/05/22 12:23 PM
Joined: Jan 2016
Posts: 7,427
Likes: 135
NormK Online Content OP
SENIOR TECHNICIAN
Got it out finally with hammering,heat and the press only to discover it is a 7/8th shaft I han't checked before because I thought the Chondas had a 22mm shaft same as the Hondas. Anyway live and learn

NormK #115513 27/05/22 09:41 PM
Joined: May 2007
Posts: 23
Novice
One way I have used to get off stubborn parts is one of those rotary hammer drills.If you can angle it right it really delivers a lot of hammer force to the offending part. Heating helps (i use one of those plumbing hi heat blow torches). You can use the sds chisel bit but if you want to reuse the part it can damage it. Sacrificing a bit by cutting off the chisel gives a better impact surface.

NormK #115514 27/05/22 10:08 PM
Joined: Jan 2016
Posts: 7,427
Likes: 135
NormK Online Content OP
SENIOR TECHNICIAN
Hi rollo,
I have always been able to get them off with my puller using a 6 ton jack except one on a Honda 6 months ago. The motor was good so I ended up having to change the plans for it. Now I had these 2 and all have been steel bosses and they have rusted solid to the shaft. What completely blew me away was the fact that the Chondas are using 7/8th shafts not 22mm as Honda does

NormK #115516 28/05/22 08:55 AM
Joined: Jan 2015
Posts: 1,233
Likes: 32
Junior Technician
Morning Norm, last try, soak the part in 50/50 molasses water, it might float some rust off.. for 2 weeks.
then do heat cold.... bang bang.
speedy


........................Keep your blades sharp......................
NormK #115517 28/05/22 09:38 AM
Joined: Jan 2017
Posts: 637
Likes: 3
Senior Contributor
Reminds me of the trouble I had getting the boss off a tapered Victa shaft one time. It had rusted itself on there well and truly. As the motor was beyond repair anyway I resorted to cutting the shaft off and getting it in the vice. Even a large 3 arm puller would not budge it. The only thing that removed it was what speedy just suggested. I used heat and cold, heat and cold, then banged it with a hammer. Blasted thing still wouldn't move. While I was walking over to the other side of the shed to get a big hammer, I heard a plonk sound on the cement. The boss had dropped out! Must have finally had enough bashing.

NormK #115560 04/06/22 11:55 AM
Joined: Sep 2015
Posts: 1,996
Likes: 137
SENIOR TECHNICIAN & HISTORIAN
I measured 3 Chonda crankshafts

.
Originally Posted by NormK
only to discover it is a 7/8th shaft I hadn't checked before because I thought the Chondas had a 22mm shaft same as the Hondas. Anyway live and learn

7/8 is 22 .23 mm ,the ones that I had were 22. 22 mm , 22. 17 mm and 22 mm ,I guess the machining tolerances are
slightly out being cheap Chonda motors.

If it's 0 .2 of a mm loose on the shaft I guess when the shaft gets a little rust the hub would be a snug fit.

Cheers
Max.

NormK #115561 04/06/22 01:22 PM
Joined: Jan 2016
Posts: 7,427
Likes: 135
NormK Online Content OP
SENIOR TECHNICIAN
Thanks Max,
Problem gets worse because I wanted to fit a boss to one of those GXV160 motors that have the blade clutch on them and the bottom of the shaft is 20mm to fit the bearing in the clutch. That one is in the too hard basket at the moment


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