72 Six Days 125b Motocross Gearing

[Ron]

Hi Guys,
I've been reading the archives on gearing and it seems the 13T X 60T final drive is the hot set-up on these bikes.
I recently got my bike finished and have had a couple of opportunities to ride it.
I'm currently running 14T X 57T and although 1st is annoyingly low, 2nd is to high coming off the really tight turns.
It seems like 13T X 60T (forget 1st gear) should work out well.
My question is, with the current set-up the chain just kisses the top of the swing arm.
Can anyone running the 13T X 60T set-up tell me if there are any chain issues?
Any help will be appreciated.
Thanks, RonW

[jay cohen]

Ron, No problems at all with the 60T x 13 combo. That's exactly what I have on mine and it works nicely.

[Paul Danik]

Ron,

    You should not have any swingarm issues unless you have installed longer shocks which may cause the chain to touch the swingarm a bit more than normal.  I have seen a few guys install a wear pad to keep the chain from dragging on the swingarm if needed.

     If I were in your shoes I might try the 13 on the front along with the 57 that you already have bolted up and see what you think, or even try the 14 with a 60 rear, depending on what sprockets you have on hand. If you plan on trail riding as well as racing you may be looking for a suitable gearing that will work well for both uses.
     
     The 13 X 60 gearing is a great setup for MX and second gear starts, but you may not like it for trail riding or it may not suit the track that you ride, or your riding style. A little testing will give you the answer.

   Good luck, and please keep us informed on what gearing works out best for you.

Paul

I see that Jay was answering while I was writing.

[Ron]

Jay & Paul,
Thanks for your input.
I think I will try the 14 x 57 combo where I ride first. While I probably won't change to the 60T rear sprocket at the track, I will try the 13 x 60 combo and let you guys know.
I did have Works Performance build my shocks at 14-1/2" eye to eye, I wanted it to turn a little quicker.
BTW, at 6'-1, 220 lbs I'm amazed how well the shocks work with only 4" of travel. This is the first 7" front X 4" rear, vintage bike I've ridden in 30 years.
I'm also running a set of heavy fork springs from AMS, the jury is still out on them.
I put fresh 10w oil at the same time as the springs and the forks feel a little stiff in the slow chatter bumps, although no bottoming issues.
I'm going to try 7w and maybe 5w and I let you guys know how they work.
I've had great time telling the young guys at the track the "Penton Story", the bike gets alot of attention.
I've even made a few of them follow me around track (until we get to the front straight) and several guys have stopped by saying, "that sure brings back some memories". Having a blast.
Thanks again, RonW

[Gavin Housh]

Ron, I run a 13-61 on my 72 with 13.5in shock in the forward most shock mount hole. I do have some chain rub with this set up. Go to your local plastic supplier and buy some Delrin or Nylon plastic. It comes in different thickness so you may want to laminate some togeather or get some straight 1/2in thick and shave it to your preference on a table saw(carbide tipped works good). Mine is about 3/8in thich and then I relieved the back some to fit the curve of the steel tube it mounts on. I used silicone glue to hold it to the swing arm and one or two zip ties in the right spot to keep it from being pulled off by the chain. I also made a small rub pad out of lignum vide wood for the rear brake arm that passes under the chain. I would like to try running a 15-70 combination and this will need a custom rear sprocket like the 61 I have now. To do this I will scrap the rear hub because of lack of room for both chain and brake arm. The rear wheel on these bikes is very heavy and I will try to adapt the KTM conical hub (saved off excess metal for lightness) or one off a Pursang. Good luck, Gavin.

[Paul Danik]

Ron,

   I believe you probably have a set of 32mm forks on your 72 Six Days, you can easily tell by the fact that the 32 mm forks have  threaded mounting holes for a fork brace near the top of the fork bottoms. A set of 35mm forks will make a lot of difference and they will bolt right on, including the triple clamps. If you get a chance to ride someones bike with the 35mm forks you will see quite an improvement in the ride, they will also lift the front end up just a tad which is handy in the mud and ruts.  Penton went to the 35mm forks on the 100/125 in 1974.

   I know that once you get your gearing figured out you will want to have another project:)

Paul

[Ron]

Thanks Paul and Gavin,
I didn't realize the 35mm's would be that easy to install, I'll start keeping an eye on ebay.
Gavin, thanks for the swingarm protector info. I think I better make something for it, these swingarms aren't just laying around every where.
Thanks again Guy's,
RonW

[conrad2]

Ron, I listened to Paul Danik (wisely) and changed to 35 mm's on my 72 Six Days. It made quite a bit of difference in both handling and ride height... along with 14" Works shocks on the rear.
It was easy to do. However I had some minor issues with changing fender mountings and axle length.
I also listend to Paul about sprocket set up too. I run 14 X 54. But remember the rear tire size (diameter) will change the gearing a bit too as I found out by changing a 3.50 rear to a 4.00.
Good luck, enjoy and ride safe.
Conrad

Conrad Pfeifer
1972 Penton Six Days

[chuck]

Ron,

I recently went to 13 x 60 from 13 x 57 to try and eliminate having to use 1st gear. I raced once since the change but it was in the mud so not sure what it will be like when its dry. Hopefully I will be able to try it out at Devils Ridge National in two weeks.

I'm still running 32mm and I bottom all the time. I have new springs and have run 10, 15 and 20wt. I'm 5'11" 175 1bs. Like you, my next move is to try 35mm.

Good luck,

Chuck

[chuck]

Ron,

I also runa 4.00 rear tire. I'm thinking about going to 3.50. Anyone have any thougts on that.

thanks,

chuck

[jay cohen]

Chuck, If you go to the search there was a mile long thread on tire sizes.  I don't want to start the discussion/argument again but I will say that when I took my wheel in for my Six Days to get a tire, my favorite mechanic said to definitely go with a 3.50.  I think the 3.50 fits perfectly and the bike runs great with it.

[Ron]

Hi Guys,
First chance I've had to get back to the computer. Well, my gear testing came to a sreeching halt last weekend.
I had switched to a 13T and was going to test it with the 57T first.
When I put the chain back on I had to pull the wheel back to adjust the chain.
Long story short, I forgot to put the masterlink back together and you guessed it, threw the chain and knocked a hole in the center case.
I'm not nearly as upset (after all it was my own fault) as you might expect.
The motor had already had the case welded from someone else throwing a chain. In fact the weld prevented me from using the case protector.
I'm also not satisfied the trans is properly shimmed.
I bought the motor on Evil Bay, put in a fresh piston and a PVL and tried to ride it.
Wishing all the while I had a good reason to take it apart and do it right.
Now I've got one. I already have a spare set of cases and I just got all the new bearings together.
I'll get the new case ready and tear into it.
Wish me luck, RonW