When I went racing at CE, the front Forks were horrible. I'm trying to get this bike ready for the Jan 10th Race and I rather solve the Fork issue than the Shifting issue. The back end has a set of Boge-mulholands and they were great.
This is what I did before the race, Changed fork seals, cleaned out the caps and put a new little spring and ball in each. Filled each tube with 150 cc of maxum 5 weight oil. The manual says 135cc, but, I read somewhere that a little more oil will stiffen things up.
Off of the jumps the front end would hit so hard I thought the bike would break in 2. I am 60lbs heavier now, but, nobody could tell me if the forks were bottoming out. It almost felt like they were locking up in mid-stroke. Thankfully the rear shocks worked fantastic.
Note: My wife used the bike as a shelf for 15 + years. She threw the original seat away, cause, She couldn't store her Lead, 1 ft sq blocks, level on top of it. So maybe the springs are shot.
G
72 six-day
Your springs could be sacked out. If you are over 200lbs the 35 mm forks would work out better for you. LG
Hello, What I suggest is that you work at the front forks in a methodical manner. What I would do first is to place a zip-tie snuggly around a fork tube nearest the leg. As you ride, the zip-tie will slide up the fork tube indicating how much fork travel is being used. I believe the 32 mm Cerianni forks have 6" of travel. Be sure that you tighten the front axle the correct way. I believe the axle nut needs to be tightened first, then the fork leg clamp closest to the nut. Next, the other fork leg needs to be centered over the axle. I do this visually, first, then with locking the front brake, compress the forks as far as I can (I just push hard on the handlebars). I would remove the fork caps and springs (leave the tubes right in the triple clamps). Be sure that the springs are not broken. Check to be sure the legs slides easily to full compression without binding. I know you did not make this mistake, but I have heard of people filling the forks to the top with oil, then wondering why the ride is so harsh. Fluids tend to be incompressible. 5 wt. fork oil sounds light to me. Did you say you were about 190# with riding gear? Keep us informed with your progress with the forks and suspension. joe
150cc will not help as it will just blow the oil out the vent. You would have to plug the vent to make more oil help.
135cc will be fine. I use 7.5wt and it works great. I found 5wt way too soft. 10wt works good if you weigh over 200lbs.
Dwight[8D]
I'm right around 195 lbs with gear Those are a couple of good Ideas. You know, I was in a hurry the night before changing the front tire and maybee I didn't tighten the front axle correctly. I also like the one about the zip tie and checking travel. I'm gonna check it out on Tuesday.
I went to the bike show today in Long Beach and Race Tech can rebuild mine for around a Million Dollars. I was sold, my wife said no.
Thanks for the Ideas.
G
72 six-day
Changing the Oil weight to 7.5 sounds like another thing I will do Tuesday. I hate to do it, But I was thinking of adding a little spacer too to stiffen up the springs a tad. I can live with the overshifting into 2nd, but the fork has got to get better.
G
72 six-day
You need 20-30wt fork oil in my opinion.
Larry P
I agree with Larry. 5 wt. is way to thin. I think 20 wt. would be better. Thinner oil will help if your springs are weak. Not a bad idea to add a shim on top if the springs sag. Do the springs need to be lightly compressed when you install the fork caps, or do they sag into the fork tubes? joe
You can put the caps on with out pushing on the springs at all they sit about 1 inch below the top of the fork.
G
72 six-day
I ordered the Penton repair handbook from Al B. this morning and suggested trying the 20 to 30 weight oil, checking wheel alignment and adding a little peice of spring to take up sag. Thats what i will do tommorrow.
G
72 six-day
I have always heard that if you add a piece of spring it actually softens up the overall spring rate. I live in Anaheim Hills and have a '72 with 32mm forks if you want to compare your forks to another set.
Quotequote:Originally posted by garrettccovington
I ordered the Penton repair handbook from Al B. this morning and suggested trying the 20 to 30 weight oil, checking wheel alignment and adding a little peice of spring to take up sag. Thats what i will do tommorrow.
G
72 six-day
Adding spring will soften the rate, all other things being equal a longer spring is softer. If you want to preload the spring cut some PVC pipe the length you want. I set up my Berkshire's fork with some preload spacers (about 3/4 inch long I think, its been a while) and I use ATF which is somewhere around 7.5W at a relatively high level, I think I set it at 5" from the top springs out and collapsed. This gives good static sag (bare minimum) and the high oil level with relatively thin oil gives good small bump performance and good bottoming resistance too. I only weigh 140lbs though so a more "normal" size person might need heavier weight oil.
Brian
'72 Berkshire
Garrett, if I remember, there was a topic on oil height many months ago, maybe a couple years ago. I typically measure my the height the same way Brian does. Springs out and the forks completely compressed. I then measure from the top of the tube to the oil height.(Make sure the forks are vertical.) That way you are sure both legs have equal height, and can adjust up or down from there. I am not sure what the height would be for your forks since I don't have the same type of forks. I also use a pre-load on my springs using PVC. Check the search feature and see if you can locate the height that most of these guys recommend, Brian may be correct.
Lloyd
I did a search on the topic before CE and that is where I got the 150cc and 5 weight oil. Looks like tommorrow I will have a full day of testing in front of me. PVC tubing, different weights of oil and spring additions. Good thing about tommorrow, All the whoops, dust and deep sand should be gone. Thats if it rained in Barstow today. I'm in Chino Hills today and it is pooring.
Thanks for the invite Socalmx, but, I think this is just going to take some testing.
G
72 six-day
ERROR ABOVE. What I meant to say is that THICKER oil will help if your fork springs are weak (not thinner). I would say your springs are sagging about 1", and you need to take up that space. I base this on four sets of Cerianni forks sitting in front of me: steel tank 35's, 32's, 35's, and ribbed 35's. I like Brian and Lloyd's suggestion of using PVC spacers. It seems to be unanimous that you need to slow down the fork action by going to a thicker oil. I agree with Al and Larry; you need to switch to at least 20 wt. to make the difference you want.
Garrett, remember, if you do any preloading of the spring, make sure you have enough space in the spring to do the preloading, or the spring will bind. You need to calculate how much the spring can actually compress minus the actual fork travel. You can get an estimate by counting the number of rings on the spring and multiply it by the average space between the coils, or you can actually put the spring on a rod and physically compress it to its maximum. If the maximum the spring can compress is 7 inches, and you have 6 inches of travel, you can use approximately 1 inch of pre-load,(I always give in a little margin for error) but you may not need that much. Also, if the springs have sagged, the distance from the top of the spring to the fork cap is really not pre-loading, it is only taking up the sag.
Lloyd
I was just going to wing it. Now I can actually use some thought behind my spacer Thickness. Thats pretty cool, Thanks
G
72 six-day
garret,
I used the 32 mm forks for several years back when in enduros. I think they came with 20 Wt . We used ATF which was recommended and is about 20 WT. Worked for me weighing in at about 175 Lbs boots and all.
We talked with the vintage engineer at Works Performance 2 years ago on how to reduce the spring rate in the 35 mm forks for my Sachs engine 73 Penton.
He went over how we could reduce the rate of the standard 25 Lb springs to 21LBs by adding the right weight spring on top of the existing springs.
There is a formula you can use to get exactly the right rate ( either stiffer or softer ) with in limits.
Use the same formula as we do in calculating parallel resistors.
(http://farm3.static.flickr.com/2578/4166930817_6f5eb0ffee_o.jpg)
where R= total spring rate and R1 = the stock full length spring and R 2 = the added short spring.
Oddly enough a adding a stronger spring on top will give you a softer overall spring rate.
A softer spring will increase the over all spring rate ( with in limits ).
It made sense when i thought about it because, we had an NOS set of short springs from Penton , for the 35 mm's and they were definitely softer than the standard full length stock fork spring. The spring kit was to beef up the stock springs for jumps and things.
You would still need to make sure the overall length of both springs will not bind under full compression. And maybe someone has a good set of stock springs they could measure so you would know if yours are sacked out or not.
You can double check on the formula by talking with Sandy. I think he is the only guy at Works that sets up shocks for vintage applications.
Hope this is some help.
john d.
All I did was put in enough spacer so that there was slight preload on the spring so you have to push down to get the cap threaded back on. I didnt need much, it might have even been only 1/2 inch and not 3/4, but it was not enough to cause the spring to coil bind I know that for sure.
Brian
'72 Berkshire
My Penton "Built for Champions" little 2 page prochure says the bike has 6.3 inches of travel.
I saw in another posting how to calculate spring rate so I need to do that.. For Future ref.
I need to measure my current spring length. for future ref.
While the springs are out...
I'll mark 6.3 inches on with a zip tie 6.3 inch's place the forks in the "bottomed Out" position.
Measure the internal distance between bottom spring stop and top of forks minus the fork cap thickness.
I'll calculate total spring compression length.
Subtract that from my internal distance and this should give me the distance availabe for spacer or spring. and go from there.
My original Penton handbook is missing the fork pages and I ordered a new one from Al B this morning. I'm kinda in luck (maybe) there is a junk yard in Barstow that has a couple of old CR80 mini bikes frames with forks that maybe i can use those springs to make my spacers. I don't really understand how a weeker spring will increase overall spring rate. But I don't have to. All I have to do is try it.
Good stuff Definitly the best posting about Forks and springs I've seen.
72 six-day
G,
I did a search on the message board , looking for some past posts by Tom B. He ran a 125 Six-Day in AHRMA for a year or 2 and had posted some of the things he did on his bike. I know there was one on spring mods he had done but did not find it. He ran the 32 mm forks.
I was lucky enough to watch him race at Gatorback in 2005.
(http://farm3.static.flickr.com/2577/4168142890_9e22440677_b.jpg)
(http://farm3.static.flickr.com/2513/4167381301_047b235f85.jpg)
I think he rode the little Six -Day smoother and faster than anyone I have ever seen.
It would be worth sending him a note and see what he recommends.
Below is one post.
bentrims
Advanced Member
USA
378 Posts
Posted - 03/23/2005 : 9:55:27 PM Show Profile Email Poster Reply with Quote
Mick,
ATF is time tested in my set-ups, and believe me my forks get abused. Last week my 32mm forks ran at 5 1/4 inches of oil (ATF) from the top with the springs out and the tubes fully compressed. I run helper springs to slightly stiffen up the preload. When you only have 6" of travel you best not lose any travel at resting.
I figure as in the E F Hutton commercials of the 70's...when Doug Wilford gives advice...I listen. Dane advice was mixed in also on my forks.
Dont tell the master I use ATF in my tranny too.
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bentrims
Advanced Member
USA
378 Posts
Posted - 03/23/2005 : 10:00:28 PM Show Profile Email Poster Reply with Quote
PS...ATF only comes in one weight to the best of my knowledge. It does have different (Types)additives in it that manufacturers coin to try to manipulate their market share. For our purposes it all does the same thing regardless the type you buy.
Tom B
John, Great Pics! as a matter of fact I think I found that search when I was replacing the fork seals , I put in ATF, 5 1/4 from the top and it seemed to me to be way, way to much fluid, well over 135cc's. I don't know, I just wasn't feeling the love from the ATF and promptly drained it all out. I guess I'm superstitous and i don't want to open up the ATF/OIL debat. Then on another post I found try 5 wght and 150cc. The bike felt good in the desert, where there is very little jumps and it cornered perfect. But on the track, on down hill jumps it was wrong. I have a couple of weeks before the next race so I think I am going to try abunch of different stuff. I want to use all the formulas provided. If all else fails at least I will know what info to go to Race Race tech with.
G
72 six-day
Garrett, it doesnt matter what CC is supposed to go in a fork, the proper way (regardless of what the manual says) is to measure from the top, springs out fork collapsed. I do the same thing to a '72 CMF Penton and an '84 KTM. Unless you completely disassemble and clean the fork, that is the only way to get your oil level consistent. 5" from the top is about as high as you can go, but the less air you have in there, the more progressive the action.
Brian
'72 Berkshire
This is what I measured today
Total stroke of Fork 6 inches
Total length of spring 20.375 inches
Spring Dia. .985
Spring wire Dia. .160
(Note: the spring is progressivly wound.)
Length of spring completly colapsed 12.187
(note: 5/8 rod inside spring with nut and washer on both ends tighted until no more gaps, this caused my spring to lose 1/4 inch in overall length when removed. I streached the spring until I got back to 20.375)
Spring Rate ? Haven't found a scale yet. I'm gonna call progressive.
Depth of fork leg (Where bottom os spring sets to top of fork) 20.687 inches
Cap thicknes .750 inches
Thickess spacer or spring can be is 1.75 inches. However this thick of spacer will go past the yeild point of spring and bend it
20.687 Depth
- 6.00 Stroke
-12.687 Colapsed spring length
- .750 cap
------------
1.75 room for spacer or spring
Sag of bike by itself 9/16 inch
Sag of bike with me on it 2 inches
Next step call progressive or race tech Off to the junk yard to find springs get thicker oil, get pvc pipe. go riding.
G
72 six-day
The oil level increases or decreases the air space trapped in the fork leg between the oil level and the top of the fork.
Decreasing the space (higher level = more oil) causes a faster rise in the air pressure as it is compressed and therfore increases resistance to botomming.
Raising the oil level will effect bottoming resistance and will not influence the forks effect on smaller bumps.
Exactly, which is why I run ATF at a very high level. The ATF gives plush action on braking bumps and small stuff, and the high level makes it as resistant to bottoming as possible. From my experience thats about as good as you can make 6" of fork travel work but like I said, I'm small at 140lbs so what works for me will not necessarily work for someone else.
Brian
'72 Berkshire
OK, Didn't get to test the bike today. However, I did add a 1/2 inch spacer to the springs.
Tested to see if the forks were binding in the travel. They were good. I did notice a little back and forth movement at the bottom, with the legs fully extended though????
Called Progressive and they recomended spring # 11-1111 a 35-50 lb. spring that is 20 3/4 inches long. They also recommended 1/2 PVC spacer and 20 weight oil.
Didn't go to the junk yard.
Added 20 weight oil.
I didn't read the last 2 posts from Ron or Brian before I added the oil. So I added 135 cc again. It ended up measuring 5.25 from the bottom of the fork leg. It was 9.125 from the top. ATF and 5.25 from the top next test.
Now the bike measures
Static sag 0 inches
Sag with me sitting on bike 1/4 inch.
I'm want to test it tommorrow. I even have a vacation day put in for tomorrow, but, I just hate missing work. we'll see.
G
72 six-day
Garrett, check with Bruce's Suspension. The owner (Bruce) can get springs made to fit your bike. He and his family owned the Penton dealership that sold me my 73 Jackpiner.
http://www.brucessuspension.com/
Lew Mayer
THANK YOU to all those who responded with their knowledge of front suspension set-up. There certainly are different ideas of how to set them up, and I'm sure each rider has his or her own preference for their riding style and track conditions. I have read and learned a lot of valuable information about fork set-up for different conditions. Thank you again to all those who shared their knowledge. "Knowledge is Power" joe
Ok, I'm going out testing right now. Its 34 degrees out. with a high of 48. Its the Desert,,, its a dry cold. So is my freezer, but I don't like to stick my head in that either.
I'm gonna try find some table tops like CE, Thats kinda hard to do without going into the middle of nowhere. I don't like riding alone and I plan on going to Outlet Center Drive. There is a good drop away and its close to alot of people in case something happens
G
72 six-day
Be sure to stop at In and Out for lunch. Good luck with your test.
Quotequote:Originally posted by garrettccovington
Ok, I'm going out testing right now. Its 34 degrees out. with a high of 48. Its the Desert,,, its a dry cold. So is my freezer, but I don't like to stick my head in that either.
I'm gonna try find some table tops like CE, Thats kinda hard to do without going into the middle of nowhere. I don't like riding alone and I plan on going to Outlet Center Drive. There is a good drop away and its close to alot of people in case something happens
G
72 six-day
I'm Back, I'm around 200lbs with full gear, thermals, jacket, sweater, blah, blah. Traction was perfect and I still can't beleive how fast that little bike hauls my lard butt around. I decided to leave the 20 weight and 1/2 spacer in it. I say its a little stiff, but it seems to match the rear end pretty good. They both are a little stiff over the small stuff. I'm gonna call it a day and wait and see what happens at the next race.
Static sag and with me on the bike the sag still measures the same.
Now I need to work on the overshift and I should get the tools today.
G
72 six-day