Building The Perfect 100cc AHRMA XC Bike

[johnbowman]

Greetings Pentonland,

Thanks to the help of some awesome fellow Poggers, I am now building a 1972 Berkshire 100cc to race in AHRMA Cross Country for the 2021 season. I have to say thanks to Larry Perkins, Gary Ellis, Steve Genter, and Al Buenher. Without these gentlemen, this build would not be happening. Also, thanks to Chicago Jerry for providing sage AHRMA rules advice.

I have read the posts around the time that AHRMA started the class. There was some really good info there on what riders planned to do. I wonder how much of that worked and what they changed. I want to hear from everyone from novices to experts. Hopefully, the guys that tricked out their bikes back in the day will chime in.

Now, on to the fun stuff! If you were building your dream Berkie to run in the AHRMA 100cc class, what would you do to your bike? For those of you who run/have run in this class, what advice do you have?

I hope that you all have a great day and hope to hear from you soon.

[Richard Colahan]

John, you've ridden enough of our eastern Cross Country races by now to know that the "trickest" bike is not a requirement.
A properly prepared 1972 Penton Berkshire 100 would absolutely be in it's element tearing through the woods!
Build it light...I remove lights, excess wiring etc... but most of all reliable.
Make sure it starts easily, and the shifting and clutch are properly adjusted. Get the jetting correct.
Fresh fork seals and oil...good shocks...swing arm and steering head bearings...proper air filter in sealed air box, good brakes.
That kinda stuff.
I'm partial to hand guards, but some get by without them.
Perhaps 2 most important items are GOOD tires and tubes...with a rim lock at least in the rear so you can run lower tire pressure w/o spinning the valve stem.
And I like to gear my 125 Husky so that I can ride the tightest woods in 2nd gear...avoiding 1st except for the absolute nastiest obstacle.

Stick to that basic racer-prep and you'll be all set...of course that's just my opinion...others may differ![8D]

Richard Colahan
1969 V1225
Upper Black Eddy PA

[johnbowman]

Richard,

Thanks. That's exactly what I'm looking for- real world experience.

I'm definitely ditching everything that isn't necessary. That includes a few extra pounds on me.

What tires would you suggest?

What gear ratio do you run?

I'm going to run a freshly rebuilt 27mm Bing. What's a good starting point on jetting for cross country racing the 100?

Is the 32mm or 35mm fork setup better? I already have both.

Details like that are the difference in how a bike performs in the woods.

[Mickey Sergeant]

Hi John
I have a fast 74 1/2 Berkie that is set up for MX. If you do the facebook thing I have a go pro that I video a lot of my races. Some are also on the Penton sight.I have a few tricks to make them go fast

[tooclose racing]

Hello John (and Richard and Mickey) - good luck with your Berkshire build. I've been racing a Jackpiner in the Vint XC race for a half dozen years or so, a Six Day before that, and also thought racing a Berkshire would be fun in 2021. But you've got a headstart on me (I just asked on FB POG group on Friday) and you may have grabbed all of the available hardware from Larry and the gang!

Great advice from Richard, he's been hanging around a fast crowd for awhile now. I run 35mm forks and 13.5 in shocks on my CMF frames (I think you can use 13.75), electronic ignition, Renthal mini-high bend bars, ascerbis rally brush guards (plastic only, relatively cheap, I have beat the crap out of several sets). NEVER use stock pegs, I think Al sells a teethed set.  Tires are personal, but I currently use a Vee Rubber Tackee on front, and Dunlop Geomax 33 on back, not sure about rear fitment for 100 (and I use heavy duty tubes, which are NOT light). Can you run a 428 chain on that bike?

Always enjoy seeing you Richard, but the pandemic really limited this NY rider's schedule and ability to travel after Reynoldsville, had to cancel remainder of National schedule and aspirations (which included Barber and Diamond Don's!). Fortunate that our NE region had some excellent racing/courses this year (5 race weekends in eight weeks was tough on body).  If you survived White Rose (today), see you at York! Looks like you've got some riding chops there Mr. Bowman, based on your Ohio and Alabama results. Have fun with the build, good luck in 2021.

[johnbowman]

Good morning gentlemen,

I had a great weekend at Hayes Farm in Ramsey, IL. Ran the 73 Jackpiner both days. I barely made the start on both races due to bike problems. The first day, it was jetting. Didn't get the bike running until 18 minutes before start. Sunday, my kick starter wouldn't engage after I got to the line. It was disheartening to watch the riders taking off while I couldn't even get my bike started. Miraculously, the kickstarter caught about a minute after the last rider had left the line. I had some serious fun chasing down a buddy from my local riding group. Both days, I managed to get it around the course and get some points. That course was the best that I've ridden so far. If you ever have a chance to make the Hayes Farm race, I highly recommend it.

I had the opportunity to meet Gary Ellis and Larry Perkins in person. Gary was dropping off some parts for the Berkie build and helped me out with a needle jet for the Piner. Thanks for the help, Gary!

Since I was so close to Larry, I was going to get some parts from him. He is doing much better now, but still struggling to get around. When I showed up to pick up the parts, I saw that he still had his Berkie. When I posted about building a Berkie, he told me that he had just sold his. The night before I was there, the buyer backed out. Short version of the story: I now am the proud owner of Larry's Berkie. Larry had already raced the bike. It is mostly ready to go. With the parts that I have already, I should be able to get it done a few weeks after this season ends.

I'll post details after the build is complete. I'm really excited about getting a Penton on the 100cc line. I've been talking with the Hodaka guys. They all have a great amount of respect for the Penton. The comments usually go something like, "Those Pentons are great bikes. When I see one of those on the line, I know that I'm going to have to ride harder." Hopefully, my Berkie will make them have to ride a little harder next year.

I hope to see all of you 100cc guys on the line some time next year!

John

[johnbowman]

quote:Originally posted by tooclose racing

Hello John (and Richard and Mickey) - good luck with your Berkshire build. I've been racing a Jackpiner in the Vint XC race for a half dozen years or so, a Six Day before that, and also thought racing a Berkshire would be fun in 2021. But you've got a headstart on me (I just asked on FB POG group on Friday) and you may have grabbed all of the available hardware from Larry and the gang!

Great advice from Richard, he's been hanging around a fast crowd for awhile now. I run 35mm forks and 13.5 in shocks on my CMF frames (I think you can use 13.75), electronic ignition, Renthal mini-high bend bars, ascerbis rally brush guards (plastic only, relatively cheap, I have beat the crap out of several sets). NEVER use stock pegs, I think Al sells a teethed set.  Tires are personal, but I currently use a Vee Rubber Tackee on front, and Dunlop Geomax 33 on back, not sure about rear fitment for 100 (and I use heavy duty tubes, which are NOT light). Can you run a 428 chain on that bike?

Always enjoy seeing you Richard, but the pandemic really limited this NY rider's schedule and ability to travel after Reynoldsville, had to cancel remainder of National schedule and aspirations (which included Barber and Diamond Don's!). Fortunate that our NE region had some excellent racing/courses this year (5 race weekends in eight weeks was tough on body).  If you survived White Rose (today), see you at York! Looks like you've got some riding chops there Mr. Bowman, based on your Ohio and Alabama results. Have fun with the build, good luck in 2021.

Bob,

If you want to get a Berkshire together for 2021, I would be happy to let go of any parts that I have acquired that I'm not using. I know how hard it is to find some of the parts.

I second the opinion on Richard. If I get to race enough with him, I might actually get better.

I would also be happy to point anyone in the right direction for help with any given area. There are so many talented people in the Penton community. We are extremely lucky.

John

[tooclose racing]

Thanks for the offer, John.  Please text me at 315-297-2892 with what you have "accumulated", I'm not a builder by nature, but we'll see, and I know someone who is (Gary).  Great luck with walking into Larry's situation and scoring a relatively intact bike.  

Just a follow-up on suspension/set-up.  I was talking to Brian Kirby and he said the challenge with his CMF Berkie was ground clearance.  That's why you go to longer shocks (which also help steering) AND I even went to stiffer (WER supplied) fork springs in my bikes with very little fork sag.