CT70 Heavy Fork Springs

Gary

Gary

Well-Known Member
Never owning a mini with actual hydraulic forks how similar were/are they to the bigger bikes of the day? I put DG air caps on my CR 250 back in the day. They replaced the springs completely. They seemed to do the job then when there was no other options. Any thoughts?
 
6

69ST

Well-Known Member
IMO, suspension technology was primitive in that era; we are talking about designs that are nearing the half-century mark. That said, tall-tire machines were okay. The early hydraulic forks were a big improvement over springers & pogo sticks. Properly setup & tuned, CT70 K1-79 forks are surprisingly good...vastly superior to K0 pogo sticks.

For the dedicated K0 enthusiast who still wants something better, there are hydraulic cartridges that retain the outwardly stock appearance.
 
6

69ST

Well-Known Member
ArcticMinibike said:
The heavy BBR spring set I bought for my kid's KLX110L came with instructions to do the exact same thing, depending on the weight of the rider. In their example, riders up to 170 would use one heavy spring and one stock spring. 170 and over, use both heavy springs. My only concern with that is putting an uneven twisting load on the forks, seals, guides, etc., but it sounds like plenty of people do it.
Click to expand...

In scientific terms, you're on-the-mark...unequal vectors will create a lateral torque load that wouldn't exist if both sides had the same springs. That said, the amount of torque should be relatively minimal. K1-style fork legs have wide axle flanges to spread the load. Just keep the axle properly torqued and you should be fine.
 
kirrbby

kirrbby

Well-Known Member
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C

CT70_Scotts

Member
Thanks! That's my plan I have a friend's K1 getting one spring and mine is getting the other. Probably go to 15 or 20wt fork oil too!
 
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C

CT70_Scotts

Member
Ok so I did the legs one at a time today. I used Specta 15w to flush and check the level 3" fully compressed was about 3.7 oz.
I did switch over to 20wt and brought it to about 1.5" from the top. Now it takes force to bottom out but does not make it impossible to bottom out with me pushing on.

I currently have both legs filled at the same height at 1.5" with one with 15wt and one with 20wt. I really can barely tell the difference, to me the critical thing is to fill it full enough to eliminate the bottoming out.

I will install the newly purchased HD spring on one side and try it out.

To me this is the best method to do this is off the bike one leg at a time.
 
C

CT70_Scotts

Member
So I did the install of the HD spring on the left side and a conventional on the right what a difference! It's a bit of a challenge to set the leg up high enough to start the top bolt as you have to overcome the spring pressure alittle. With a set of Beatrice cycle BCI rear shocks this is the best riding CT70 I have ever road. Btw I weigh 180lbs. I just did a short drive combined driveway and paved Michigan road. No rattles or strange noises. I did notice that the stock spring I can move around the chrome lower tube and the lower painted tube when on the stand. I expected this and tried to stretch the stock spring before reassembling. But once off the stand the bike alone is carrying enough weight to load that spring. Can't wait to do this to my own red K1! As this is my friends bike that I am fixing up for her.
20180322_165518.jpg
 
RMHRC

RMHRC

Member
racerx said:
AFAIK, the heavy-duty springs are actually spec'd for a non-US model. IOW, factory-spec for another bike, they happen to be stronger than CT70 K1-`79 springs.

As for determining optimal fill level, it's at least partially trial & error. The old-school method is starting with the recommended 3.5oz, reinstalling the fork cap, then attempting to compress the fork leg. The process is repeated, adding 5-10cc of oil at a time, until you feel the fork action begin to get stiffer near the bottoming-out point. From there, it's a hair-trigger proposition; that amount of oil can put you over the edge...the fork will hydrolock before it can mechanically bottom-out. Removing the excess, with precision, is a hassle. However, once you have the quantity dialed-in to your preference, it's easy enough to repeat on the second side.

The shortcut method...start with 3.5oz (dry fill, as in in post-rebuild), compress the fork leg completely then fill to within ~3" of the top. That will get you very close. Note the level or/and oil quantity and you never have to repeat the trial & error process. Note that dry fill quantity can vary, anywhere from 3.7oz to ~4.2oz.
Click to expand...

So are the forks on the bike when doing the oil fill?

or off the bike ?
 
OLD CT

OLD CT

Well-Known Member
You can fill the forks either way, but you do want to put the front end up in the air on a stand if the forks are on the bike, then fill and cap up the forks before you put the front wheel on the ground.
 
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