Carbureter bent needle grub screw

[Objective]

Another gotcha.
We have a bent needle in the rear carb (1971 2000TC) and a replacement ready. On our twin SU HS8 carbs, can i release the (brass?) grub screws from the dashpot pison (nos. 19 and 21 in the WSM) holding the needle secure in the piston . . . nope.
The screw has already resisted previous attempts and its single slot is a little 'rounded'. The deep well where the screw is located has been bathed in WD40 - no joy. My impct hammer (luckily) hasn't got the reach to get down into the well and locate on the screw head. Ive applied some heat, but still no joy.
I have a garage, some suitable tools and few facilities locally. I could take it to one of the garages locally, but I'm concerned the piston itself could get scored or dinked by over-zealos vice-work.
Has anyone got suggestions ?

 

[sdibbers]

I'm afraid that is the screw you need to remove. Maybe try warming the whole assembly in the oven. Clamp the piston by its base in a vice (wrap with cloth first to protect it) then take a good quality screwdriver, align it with the slot in the screw head and tap it with a hammer. Now push down hard on the screw driver and use a pair of pliers to grip the shaft the of the driver and try to gently undo it. I have had good success with this approach on similar situations in the past.

 

[Objective]

sdibbers - that is good advice - thank you. I have warmed it a bit but not oven hot, so there is a difference; and the use of a screwdriver and hammer sound like a plan - thank you again. I was afraid to use a vice, as I'm not sure what the piston is made of, so afraid of damage.
I have 2 to do, so I'll let you know how it goes. Brilliant!

 

[sdibbers]

I was afraid to use a vice, as I'm not sure what the piston is made of, so afraid of damage.

The pistons are aluminium, so quite soft, so bear that in mind. Protect them with cardboard or fabric when using the vice. I would hold it by the cylinder that’s below the grooved part of the piston. That’ll be happier with the force.

 

[Objective]

DONE !
Combined your excellent feedback and now have extracted both grub screws and needles.
Thanks sdibbers; heated in the oven, hot wrapped in fabric in the (gentle) vice, tap with a (big) hammer, heavy-weight turning with applied pressure and when it didnt work - repeat.
Huge boost to the work!

After my experience, does anyone think a smear of copperslip (other brands available) could help the next time? (N.B. I'm not planning to be the "next time".)

 

[sdibbers]

After my experience, does anyone think a smear of copperslip (other brands available) could help the next time? (N.B. I'm not planning to be the "next time".)

Never had one seize before. My guess is someone over tightened it in the past, or it had gotten damp and not been loosened since manufacture. Either way, anti seize paste would be a good call. Maybe with fresh grub screws if the heads of the original ones are damaged from the work needed to remove it.

 

[Objective]

Someone has had a go, judging by the damage to the original heads before I even started. The tap with the hammer seemed to break through the slot's carbon that had filled its slot. One piston (the rear, with bent needle) was significantly harder to shift that the other. I think fresh grub screws are in order, but I'll use these until I can get some from the UK (I'm in Greece). Does anti-seize paste withstand the heat - must be over upwards 150 C on a hot day, hence the brake-orientated copper slip suggestion.

 

[sdibbers]

Someone has had a go, judging by the damage to the original heads before I even started. The tap with the hammer seemed to break through the slot's carbon that had filled its slot. One piston (the rear, with bent needle) was significantly harder to shift that the other. I think fresh grub screws are in order, but I'll use these until I can get some from the UK (I'm in Greece). Does anti-seize paste withstand the heat - must be over upwards 150 C on a hot day, hence the brake-orientated copper slip suggestion.

The carbs will be significantly cooler due to air flow and fuel evaporation during atomisation, so I wouldn't be too concerned with heat. Normal anti seize paste would be fine (possibly better considering a chance of it making its way into combustion chambers (slim to no chance TBH).

If you're seeing carbon in that area I would look at the spindles and spindle bushes, when they wear you get lots of carbon everywhere due to poor sealing. YOu'll be amazed how much wear you can see on the spindles.

 

[Objective]

Sdibbers, you re a legend. Thanks SO much !
OK, moving to fit the new needles, my supplier corrected my order of a plain needle to one with needle with flang. My old needle is a needle with no flang . . .
A quick call, and they say the part is correct, since you can force the needle out of the flang. They say that SU admit that they used more than one needle on this tag number - the 'only' time this was done. So I should be able to force it out of the flnge and it'll be "exactly the same"
I've force the new needles out of their flang (with hammer) and the root of the new needle is hatched and the diameter is visibly lightly larger than the old needle at 3.2mm - so not "exactly the same".At £24- each its out wih the emery paper to reduce the diameter to the original fit.
(I'm sure this should be easier ! )
I think the carbon content is OK, as the feed from the crankcase has provided ample crud inside the air fliter and carb.

If anybody is interested, I have installed a fluid trap on my crankcase breather - looking to help me assess the volume of blowpast in my cylinders.
Photo attached, after 1500 km since fitting - I have approx 3sq mm of milky crud caught in the trap. I look at this as a good sign of limited cylinder problems on our 55,000 km, 53 yr old engine.

 

[sdibbers]

Looks good on the breather! This was my write up on making and fitting new bushes and spindles near the bottom of this page. Getting back on the road