A forum for owners of Yamaha TTR250 trail and enduro bikes!

The big problem I have had in the past in stripping down a shock to replace a bump stop has been holding the chromed damper rod securely enough to remove the end parts without damaging the rod. A lot of force is required and it is likely that the rod would be damaged if enough force was used to hold it in a vice.

Rather than hold things up waiting for my shock to be revived, I decided to go ahead and make up a rod clamp and try it on a spare shock.

A while back I looked at Paul Olesen's impressive DIY manuals and guides and was particularly interested in his "Shock Building Tools and Parts Guide" . However, it didn't include a tool or method to hold the damper rod so I emailed him for advice. 

This is his reply:

"In order to grip the shaft without damaging it you may need to fabricate a special clamp for the shaft. You could do this by finding a piece of aluminum which is approximately 1" square and 1-2 inches long. Drill a hole (lengthwise) through the aluminum block that is the same diameter as the shaft. Then carefully cut down the center of the block and split the block into two. Each piece can be fit around the shaft and clamped in a vice. This should provide sufficient clamping force to keep the shaft from twisting while you are working on it."

So I had a plan 

I bought a length of 1" square aluminium stock from eBay and made up the tool this morning and am delighted to confirm it works!

I cut off a short length of the aluminium bar and drilled a hole of 13mm diameter. 1mm less than the diameter of the rod to get a good fit. My hacksawing wasn't very accurate and I didn't get a 90 degree cut despite marking the bar with a set square and also my technique with pillar drill isn't great and I didn't get the hole central. Word of warning, the piece gets very hot and I burnt my fingers picking it up quite a while after doing the drilling 

 

 

Unusually in my experience, there weren't any flats on the end piece to get a wrench on so, against all my rules, I had to resort to using Mole grips to get the blighter off!

 

The reason the tool works is that it grips on a much bigger area of the rod than if it was on its own in a vice where only the two sides of the rod would be gripped.

 

 

All that is needed now is to fit the new bump stop and re-assemble 

 

With the spring compressed it is easy to re-fit the spring retainers underneath the new bump stop.

 

It's good when a plan comes together!

Brian

Shock now completely re-assembled with new bump stop and, for good measure, one of our after-market top shock kits 

 

Job done!

Brian

PS I finished the project using a good shock rather than wait for the shock I originally started working on to be repaired. I have taken 3 other "spare" shocks to The Worx in Cowley Bridge Road, Exeter for assessment as they didn't have good "actions" Had a phone call from their shock guru Ian yesterday. Two will need a complete overhaul to include new seal heads, oil and re-gassing. The other one will just be serviced and re-gassed. I will let you know what I think of the service and the prices when the work has been done 

PPS Two of the springs had chips and a bit of rust on them so have taken them to get powder coated. The shop had a very good colour match so fingers crossed they turn out OK!

Brian, do you know how they pressurise the shock? Is there a Schraeder valve that they use, or something more cunning? I've read about shock recharges with nitrogen, always wondered how much difference it would make doing it with air, after all that's 79% nitrogen, would like to understand the impact of the oxygen.

The reason i ask about the Schraeder valve is that i have shock pumps for mountain bike suspension that can easily pressurise a shock to a couple of hundred psi. Wondered if it might be worth an experiment...

I have exactly the same shock pump that GreyWolf shows in his write up, if you ever want to borrow it, just let me know. It'll do 147psi withoit breaking a sweat!