32mm fork problems 125cc 6-day

[Lloyd Boland]

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

[garrettccovington]

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

[john durrill]

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.

 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.
 

[brian kirby]

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

[garrettccovington]

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

[john durrill]

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.





 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

[garrettccovington]

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

[brian kirby]

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

[garrettccovington]

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

[Ron]

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.

[brian kirby]

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

[garrettccovington]

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

[Lew Mayer]

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

[joe novak]

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

[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