Marin Shock swap - Help!

I am in the process of trying to swap the rear shock on my 2001 single pivot X frame Marin, but I have a couple of issues and would really appreciate some help from someone who has done the same.

First problem, how do I remove the existing shock? I have removed the nuts on the lower mount and the Allen studs on the upper mount, but what next? Do I hammer out the pivot shaft? On the lower pivot can I remove one nut and keep tightening the other to pull the shaft all the way through?

Second problem, my bike is a 2001 Shore Line Trail (I think) and the fitted "Shock Works" is 175mm. The Replacement I have is 165mm is that just a result of the American aversion to the metric system or have I gone wrong?

Third problem, this one is a two parter.. the bushes fitted to my new shock are obviously unsuitable. Will I be able to remove the bushes from the Shock Works and retro fit them to the new shock or do I need to buy new. How would I remove the bushes already fitted to my new shock?

Re:

There are several threads on here about removing shocks from Marins. Don't just hammer them out.
If the shock fitted is 175mm that's what you need. The 165mm shock will fit but your BB will be a good bit closer to ground, more chance of pedals hitting ground and you will have less suspension travel. The less travel might not be a big problem but you will definitely notice your pedals hitting. How do I know this? Well, I temporarily fitted a shorter shock to my wife's Wild Cat Trail till I could get another correct length one. She is not particularly adventurous on an MTB but she complained about pedal strikes.

Thanks OCP, I didnt realise how much difference 10mm on the shock would make to the BB height. A quick and rough measure looks to be double at 20mm. A little frustrating as I have yet to find a 175mm air shock for sale.

I thought I had read every thread on here with Marin in the title, looks like I need to amend the search parameters, or just try harder.

Re:

Just read your posts on Treker's thread about his Rift Zone. I see that the 175mm shock is really a 185mm.
It had occurred to me that 175mm was wrong and that it was more likely 185mm. Had meant to post in this thread to ask you if you were sure the shock was fully extended but you've sussed it out yourself. Here's a post I wrote on another thread about removing the rear shock mount pin/bolt,

"I removed a very stuck shock mounting bolt on the swing arm of a Marin.
Like yours the alloy spacers either side of shock eye were corroded to feck and stuck.
Liberal spraying with WD40 plus leaving to let it soak in overnight with more applied before I then tried to remove it.
I took off both nuts then put several washers onto end of mounting pin on one side leaving a nuts depth of threads.
Put the nut back on and started to tighten it to pull it one way, when it moved sprayed more WD40 so newly exposed part of pin was wet. Transferred the washers and nut to other side then kept repeating this until I could pull it all the way to one side and out. Took time and effort to get it to move more than a few mm at a time.
Just make sure you haven't mashed the end of the threads on one or both ends of pin because then you're never going to get it through the spacers or shock eye.
Extreme violence then required to remove it."

As I said earlier don't just batter it with a hammer. I laid the bike on it's side and sprayed the WD40 in where the pin is, left bike on it's side to let it soak in overnight then did same with other side. If you can't just push the pin out, the rear bolt/pin is more than likely got the mounting spacers corroded on to it as they are aluminium. If they are corroded on to pin they are toast anyway. But if not the way to get them out is to clamp one side in a vice, not too hard, or grip them with pliers or Molegrips then try to turn them in the shock. They are in 2 halfs fitted from either side of shock eye. To remove the front pin takes a bit of finesse as you cannot pull it using nuts. The tiny bolts can be used to pull it if you are careful. I actually found another bolt that I didn't mind breaking to do this, with both bolts out take off the alloy disc and turn it round so that recess for bolt head is facing in the way, put washer under head of bolt and screw it into thread in pin, when it starts to move remember it will only move as far as the depth of the recess in disc. Once it's gone this far move it over to other side of frame mount and do the same. Of course you've liberally soaked it in WD40, haven't you? I found the front mount wasn't as bad as the rear for corrosion as it's more protected where it is. When re-assembling I used copperslip grease on pins and inside of alloy mounting spacers, haven't had a pin seize in shock since.

Re:

Thanks OCP, you really helped.

First off I needed to clean up the threads in the top pivot pin.


M5 0.8tp taper & 2nd used.


Picture shows your technique with a few washers removed.


In action!


Extracted


Desired effect...