Mkiii tacho drive seized screws

Anvill

Anvill

Joined
Feb 26, 2022
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Hi all,

I’m having a heck of a time removing the screws for the tacho drive housing on my Commando. I understand there is a chemical reaction that can happen between the aluminum motor case and the steel screws for these. Does anyone have any tips or tricks they can share to break these screws free with the least risk of damage? I’ve tried heat gun and various penetrating oils with no luck. I currently have the cylinder barrel off so I have good access. I’m afraid I’ll break the screws if I keep going.



Thanks,

Anthony
 
Those aluminium cases will wick the heat away very quickly, you need a hotter heat source so locally the temperature can rise before its sucked away.
 
concours said:
Was the bike out in the weather for years? How rusty/corroded is everything else?

More Heat. Local heat with a propane torch to the aluminum case.

Weasel piss. PB Blaster can wick into the threads. Do it hot.

Impact driver.

Amazon product ASIN B001WHQH0W
Click to expand...
Like concours replied,the basic impact driver is your best bet for those screws especially if they are the slotted head.You have much more control using them than a pneumatic or battery operated ones. I try to get rid of those type screws whenever possible.
Mike
 
Anvill said:
Hi all,

I’m having a heck of a time removing the screws for the tacho drive housing on my Commando. I understand there is a chemical reaction that can happen between the aluminum motor case and the steel screws for these. Does anyone have any tips or tricks they can share to break these screws free with the least risk of damage? I’ve tried heat gun and various penetrating oils with no luck. I currently have the cylinder barrel off so I have good access. I’m afraid I’ll break the screws if I keep going.

Thanks,

Anthony
Click to expand...
Generally, there is no real reaction between aluminum and plated steel. It's stainless steel used without anti-seize that has the problem.

Others have said more heat - absolutely, but try to heat the aluminum of the crankcase, not the tacho drive or the screws (I know, nearly impossible). I use a propane torch but with Mapp gas. A heat gun often will work, but it takes a real long time, and it tends to heat more widely. Heating the tach housing just makes the screw tighter while hot.

Learn to use an manual impact driver and they will usually come loose without heat - put in the screw slot, push down hard and twist hard to unscrew and then hit with a 16oz or bigger hammer. That not only twists the screw but shocks it as well. Usually they will loosen without heat but if not then do it after hearing.
 
marshg246 said:
Generally, there is no real reaction between aluminum and plated steel. It's stainless steel used without anti-seize that has the problem.

Others have said more heat - absolutely, but try to heat the aluminum of the crankcase, not the tacho drive or the screws (I know, nearly impossible). I use a propane torch but with Mapp gas. A heat gun often will work, but it takes a real long time, and it tends to heat more widely. Heating the tach housing just makes the screw tighter while hot.

Learn to use an manual impact driver and they will usually come loose without heat - put in the screw slot, push down hard and twist hard to unscrew and then hit with a 16oz or bigger hammer. That not only twists the screw but shocks it as well. Usually they will loosen without heat but if not then do it after hearing.
Click to expand...
You will need heat. Heat gun will work , toast it all up . Penetrating oil onto the 2 screws , then an impact driver to them to reverse and out , hot . You won't be saving the screws , replacing with Allen key stainless ones . The tiniest micro - dab of anti-seize on each new screw , because you don't want any anti-seize entering the crankcase .
 
concours said:
Was the bike out in the weather for years? How rusty/corroded is everything else?

More Heat. Local heat with a propane torch to the aluminum case.

Weasel piss. PB Blaster can wick into the threads. Do it hot.

Impact driver.

Amazon product ASIN B001WHQH0W
Click to expand...
A manual impact driver is your friend. I started using one in the late '60s with my BSA A65T.
 
Select the best bit for the screw slot. If all fails and you bugger the slot, Dremel the tops of the screws so you can slide the drive up and off and attack as stubs. Really hope you don't get that far. MAPP gas is best.
 
Although it seems counterintuitive, I heat stuck bolts and the like with an oxy acetylene torch with a tip sized to the job, in this case, smallest you have. Screw will expand and contract as the aluminum sucks the heat away. The shock should loosen. Tiny tip will direct heat fast to the screw head without the wide flame of a MAP torch.
 
Used one of my WMD yesterday.
Mkiii tacho drive seized screws
Mkiii tacho drive seized screws
 
Use a parallel pin punch on the head of the screw and strike with a hammer
This can flatten the head of the screw incrementally
And also shock the thread from binding
Then proceed heat etc as necessary
 
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