Jota 120 Rotor disassemlby from Crankshaft

[Claudio57]

Dear colleagues

I am opening the engine on my 120 Jota to access the gearbox. I'm having trouble removing the alternator rotor. It's stuck fast on the crankshaft. I have a well-fitting hook wrench and a suitable internal puller. Can any of you give me a tip on how to remove the rotor cleanly? It seems to me that it requires an immense amount of force. I'm grateful for any input - I dont want to damage anything (tried to warm that thing - no movement anyway).

Cheers
Claudio

 

[sfcpiet]

Insert a M16x1.5 bolt in the centre of the rotor to pull it from the crank. Alternatively, you can use your front axle...

piet

 

[Paul Marx]

Do you need to take it off to access the gear box?
Paul

 

[sfcpiet]

Do you need to take it off to access the gear box?
Paul

Not absolutely necessary, but always a good idea to check starter clutch springs once you're already in there.

piet

 

[Claudio57]

Hi Piet & Paul

Thanks for your prompt reply.

Piet, I have the right screw (bought it sometime ago from Andy Wagner) . I'm taking a cautious approach in this case; after 40 years, the rotor seems to be sitting well. The cylinder head is already off. I've left the cylinder base on. I'll try again tomorrow with more force and patience. Is there anything else I need to keep in mind?

 

[The Sock]

Tighten up the puller then tap the bolt smartly with a hammer, not too brutally.

 

[andre g]

Before you take out the rotor you have to remove the small plate on top with the M5 screw. Then take out all together as one part the sprocket, the generator and the starter clutch.

 

[Andy]

Impact driver on the bolt.
I was told that any usefully-hard hit with a hammer is not good for the bearings.
Mine was well glued on with locking compound, I think from the factory, and it was a real pain the first time I removed it.

 

[chrisk]

Impact driver on the bolt.
I was told that any usefully-hard hit with a hammer is not good for the bearings.

‘Smartly’ doesn’t equate to a sledge hammer at an axe worthy hit.

An Italian machine manufacturers top service guy told me to hit a similar part with a hammer to get the part loosened.

I passed the advice onto our technician. I heard from the upstairs office the sound of something being hit numerous times. Went downstairs and the tech was walking in circles cursing, after the shaft was bent.

While visiting the factory in Italy, I mentioned it to the top service guy, he took me out back and showed me the part and gave it a smart tap with a brass hammer. “All it takes is a kiss”

Our technician wasn’t kissing, he was deep throating it!

 

[Paul Marx]

Is the crankcase open yet?
Paul

 

[Claudio57]

Thank you for sharing your experiences. I was unsuccessful in removing the rotor today. Andy's description seems to match my situation—heating and shock treatment with controlled hits didn't get me anywhere. I've decided to skip removing the rotor and open the housing next week, as I basically want to get to the gearbox and don't want to put unnecessary stress on the crankshaft bearings.

Enjoy the evening

 

[iis_iis]

Overnight or longer with a firmly screwed in M16 bolt, firm tap now and again, tighten a tad more. Perhaps a proper hot air gun ( not your hairdriers ), heat local quickly up to 90C is ok, or dab of oil on the heated inner hub when it just smokes that is hot enough. Dont hit the soft iron magnetic rotor perimeter, if not already aware.

It will come off with careful tried and true f and m techniques, rattle guns are plan Z with cranks, though i do use rattle gun on a crank, properly configured ( undo crank primary drive sprocket, allowing for the roller bearing to take the side measured impact ), no doubt various techniques from owners. HTH j.

*** under no circumstance is fastener adhesive to be used on the taper shaft fit surfaces, Vince will no doubt indicate the consequence.

 

[Vince]

You get to visit the nice man who contains the green smoke.

 

[breganzane]

I have (well I made...) the suitable puller to go on the external thread on the outside of the central boss. The nice thing about that is that you can leave the crank bolt installed but just backed off by a turn or two. Saves exerting pressure onto the small annulus of the crank nose, and more to the point, it means the whole alternator assembly cannot shoot off and fall on the floor - as happened to me the first time I removed the same rotor from my RGA. That thing was on DAMN tight, and I had the puller really well loaded up and stopped to rethink my choices, after about 30sec there was a crack like a gunshot and the thing jumped a metre off the end of the crank and fell on the floor. I was well pleased.

I think the alternator is the same as GS1000 etc, so if you can find one for those I believe it will fit. I probably have the thread specs at home, maybe M38 or so. Pitch is deffo 1.5. I have probably posted copies of the drawings I made for the tool a decade or three back on here, might be searchable.