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Bsa Mercury stuck piston head

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#1 Billsno1

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Posted 13 November 2010 - 10:33 AM

Hi all. Friend of mine brought round his old mercury for me to look at. Think its a mk4 (ZC). Got the piston out but the head remained and is stuck fast in the front end of the cylinder. There appears to be no way of removing it. Could try a drift through the transfer port but hole is so small and could get damaged. Any ideas?

#2 raygun

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Posted 13 November 2010 - 01:37 PM

Try soaking it in a bit of penetrating oil/diesel.

It sounds like your going to have to be a bit more brutal though. You could try breaking it up with a long screwdriver and hammer. I'm guessing the buffer washer has come out/turned to cheese.

Sounds like the roll pin has failed if it's left the head behind.

Another way would be to braze a wood screw onto a piece of bar and try screwing it into the head so you can pull it out.

Both the above supposes it's a plastic head. abiggrin.gif


#3 yamkid360

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Posted 22 December 2010 - 07:31 PM

I`ve had this problem with an old Mercury, I put the air nozzle on my compressor at 120 psi , came out with quite a bit of oomph ! must patch that hole in the roof while I remember !

#4 flatrajectory

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Posted 26 February 2011 - 11:46 AM

This is a common problem with the BSA`s fitted with the nylon piston head ,as they are prone to swelling. My usual method of removal is to drift it out by placing a suitable length of steel rod through the transfer port and tap it down the cylinder with a few taps from a hammer. Spray lube down the port first will help to `unstick` it.
When replacing the piston head obtain the aluminium version if possible , this will prevent a recurrence of the problem. Also if you have to use a nylon piston head , discard the wire `piston ring`, if fitted , as this only adds friction and does nothing for the power.


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