Author Topic: STIFF FORK TRAVEL 1970 THUNDERBOLT  (Read 308 times)

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Rory57

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STIFF FORK TRAVEL 1970 THUNDERBOLT
« on: 02 July, 2017, 13:49:53 »
I have recently purchased a A65 as above. The front fork travel seems to be very hard and' locks out' every now and then.

I drained the old oil / water! out and replaced with 20w fork oil which seemed extremely hard. I have since drained this and have now filled to 200mill with 5w oil ( any less and it would clunk at maximum for extension when going over bumps) which seems softer but as occasionally seems to lock out when the forks are fully extended. I was hoping not to have to strip them down until winter comes. Any advice/suggestions would be welcome.

Editor

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Re: STIFF FORK TRAVEL 1970 THUNDERBOLT
« Reply #1 on: 02 July, 2017, 18:12:59 »
Hi Rory,
The 1970 forks were fitted with shuttle valves to provide 2 way damping. As you said you drained out an oil and water mix, its possible that the shuttle valves are gunged up with something nasty. This would cause the locking if the oil isn't squirting through in the right direct when needed. Sorry but the only way to be sure is to strip them down and give them a good clean. When done, 15w or 20w oil will be more than adequate. 5W is a bit thin in my opinion.
You'll need some readily available special tools, one to undo the fork seal holders and the other to draw the stanchions up to the top yoke on reassembly.
I would recommend you do this as its clearly a safety issue with the way they are at present.
Chris

Rory57

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Re: STIFF FORK TRAVEL 1970 THUNDERBOLT
« Reply #2 on: 02 July, 2017, 18:47:24 »
Thank you for the reply, I thought that it might be the case that I would need to strip them down. I think I got most of the congealed gunk / porridge out but as say the only thing to do is have a look.
The chap I bought it from did the Somme tour last year and 600 miles on it in a week.
Is it a 'hook' tool I require for seal holders or something more complicated?

 

Editor

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Re: STIFF FORK TRAVEL 1970 THUNDERBOLT
« Reply #3 on: 03 July, 2017, 16:25:19 »
Hi Rory,
The proper tool consists of a threaded plug that goes in the top of the fork stanchion which has some smaller dia allthread in the centre. This pokes up through the top yoke and a nut and large penny washer pulls the stanchion up against the spring until safely in the top yoke and the clamp bolt in the bottom yoke is tightened to keep it there.
Its easy to make if you have an old top nut and access to a lathe, by turning down the hexagon to slightly lesser dia than the thread and drilling and tapping a hole for the allthread in the top. If you want to make one from scratch, remember the top nut has a 28 TPI cycle thread.
Some people (me included) have got away with a large enough broom handle screwed in by hand and pulled through whilst the third hand tightens the clamp bolt, getting it close enough for the top nut to catch which will then finish the job. Depends how strong the springs are.
They are great bikes so worth getting your hands dirty! Best of luck with it!
Chris

Rory57

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Re: STIFF FORK TRAVEL 1970 THUNDERBOLT
« Reply #4 on: 03 July, 2017, 16:56:34 »
Chris

Again, many thanks for the advice.

R