Vintage Dirt Bike Q & A

I bought a 1975 Honda trials bike that came with 1980 CR125 shocks (because they're long, which raises the rear and makes the steering head steeper). They can be charged with gas, although I don't think they are now. What does the gas charging affect? Rebound dampening? Rebound and compression? Neither?

Shocks are in good shape--no pitting, new stops, etc., but don't work very well as is on this bike. Don' tthink charging will make them better, but want to find out. Thanks.

I've got the same shocks on my 76 cr125m. Nitrogen gas charged shocks and it's supposed to effect the dampening of the shock. I took mine apart for overhaul, half way thru it now and ready to reassemble. I've been told several different things but am still alittle confussed myself on the charging. Seems it's a do it yourself type thing and you have to buy some kind of adapter kit to install gas. They are supposed to be charged to around 225 psi. I'm gonna go to my local Honda dealer to find out who or where to get these puppies charged.
Good luck, I'll check back soon to see if anyone else replies to your post.
Kenny

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Kenny Rogers

'76 CR125M Elsinore

With the help of someone on the forum, I talked to someone who was very knowledgeable about shocks, but not the specific Honda CR shocks. He said the purpose of the nitrogen was to bascially keep the oil in place so to speak (not adjust dampening). Without nitrogen, the oil could cavitate during shock action, making the shock harsh (which is what I had experienced with mine), and with no gas pressure, the oil could come out.

He said new (modern) shocks used up to 200-225 psi or more of pressure, but a vintage one like the CR was likely to be less. he suggested starting with something like 90-100. I put about 90 in, and noticed an improvement (mine are mounted on a trials bike, however, so we're not talking speed or repeated action over whoops, etc.)

The fitting to add gas is a standard one like you have on the tires.

that will be not enough. you have to put about 155psi in.
do not use an usual tirefiller, when you remove it some pressure get lost and you don´t know how much pressure is in your shock.
that´s why you need a special adapter to avoid the pressure lost.

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

I noticed there was no way to read the pressure without losing it, but I was using a nitrogen tank with a regulator I can set to max delivered pressure, so I can get close without checking with a guage.

What happens with 155 psi? I can add it, but wonder what it will do in my application.