How fast will she run ?

[Paul Danik]

Greetings,

   A recent discussion brought up the question as to just how fast will a 125cc 6B Sachs powered CMF Penton run with 14 X 54 gearing? Not really looking for sustained speed, just a peak speed that could be attained if you twisted the Sachs for all she was worth for a brief period. Care to make a guess?

  This issue just might need to be settled once and for all on The Flats ! To clarify, The Flats referred to are not the Great Bonneville Salt Flats, but the Pretty Good Mars Pepper Flats...

   All kidding aside, whadda think she will do? How many RPM do you think is a safe bet? If you know the max RPM can any of you scholarly math experts figure out what she outta run mathematically ?

Paul Danik
Timing Officer at The Pretty Good Mars Pepper Flats

[ssquickel]

My guess ill be 60  mph at 8500 rpm

[LeeBuff]

I don't know what a Penton Sachs 125/6B with 14-54 gearing will do. But what I do know the Penton Cafe Racer Sachs 125/6D with 14-48 gearing will top out at 92 MPH. I have no idea what the RPMs were but it was screaming!!  That said it has a ported D cylinder with a K&N filtered 32mm Bing Carb. and a CMF Hipoint down pipe without the baffle.

Lee Buffenmyer

[firstturn]

My 1973 1/2 100 Penton would run 72 MPH stock as clocked by my friendly Police.  I do not remember what the sprockets was as Penton had sent me a supply of sprockets.  It was stock and I was shocked when we made the second run at same speed.

Ron Carbaugh

[Don Roth]

Laying down on the bars ala Hopkins my 72 bounced off 70+ one nice day along the river, wasn't much left in the right hand.

[wfopete]

Gather your numbers, add a rider and plug them in here:

http://www.dansmc.com/mc_software1.htm

.

Pete Petrick
175 Jackpiner
Slow but Good

[Paul Danik]

Don,

  Do you know the gearing ? 14 x 60  14  x  57  14 x 54  or ?
Stock gearing out of the box is 14 x 60.  Were you heading up stream or down....  Just had to ask......  

Paul

[Don Roth]

Paul,
Stock gearing, tried the 54 rear and actually slowed the bike down,
was chasing a trout, so I guess downstream.
-don

[Tom Penton]

1971 ISDT, Isle of Man. Final Special Test on TT short course that included the last couple of turns and long final straight of the TT with start/finish line 3/4 way down. The straight saw a slight rise out of the tight final corner for 1/4 mile, followed by a long slight downgrade past the finish line. I had gotten a factory bike from KTM, hopped up quite to the MAX (I had paid for it the prior 6 days with a light switch power band!) and it was now just broken in, running better than as at the start. (relative dry event, kept clean air to the engine). I put on a sprocket a KTM mechanic tossed to me, barely large enough to fit the hub.  I rode the whole special test with a British Trophy Team member on a BSA Cheney, a 350cc I believe.  I'd keep ahead of him in the corners, but he would pass me out of that last corner up the rise of the final stretch, but I'd draft and let him pull me up the rise, then I'd gain speed at the leveling out, and slingshot past him at the finish line. Mr Trunkenpulz and all were there cheering me on!  I was tached out.  I can't say how fast, wish there were radar guns then, but figure about as fast as one of our 125 dirtbikes would go!    Tom

Tom Penton

[Rick Bennett]

Great story Tom. You should write more about events like this. Paul Danik has talked about writing down some day the whole process of how he got to the Six Days. For us guys that were out of the loop but riding Pentons back then this history makes for good reading.
This whole speed topic has been brought about by the fact that I am planning on taking a 2500 mile trip and thinking about riding a Penton Six Days in May. I need to ride it 700 miles to Chattanooga, TN and back to get to the "Vintage 1000". A 1000 mile in 5 days on "as much dirt as possible" dual sport ride put on by Speed Deluxe. Larry Maiers, Paul Danik and I have been discussing what this might take to accomplish on a Penton 125. Wondering about poor gas and carrying tools, parts, oil and camping gear.

[242]

I recall a story about a KTM rider who put road tires on his KTM 250 in Ohio maybe KTM Lorain, and road it to Texas. Changed to dirt tires, raced it, then put road tires back on, and road back to Ohio. I'm looking for the story but have yet to find it. Maybe some one else can remember this? Dave   This would be around 1980

[Rain Man]

Probably would go a might faster with some of that JP race fuel and a kid on Red Bull!


Raymond
 Down East Pentons

[Pat Oshaughnessy]

Thanks Tom for the great story! I love that! My 73 125cc Penton felt like about 70mph with stock gearing. Fast enough to pass a 450 Husky on a smooth? dirt logging road in the 1974 Sonara Enduro[]

[Paul Danik]

Greetings,

   Whenever anyone would ever ask me for advice in setting up a 125cc Penton for enduros there was always one item that would generate some extended conversation, that item was my recommendation to run 14 x 54 gearing. That is also my recommendation to Rick Bennett for his Vintage 1000 machine and was the reason behind the question of "How fast will she run".

   My logic for running that gearing is very simple, and this isn't  just an idea that looks good on paper as it works ! Will it work for you?? First you need to let the concept sink in and then if you give it a try you will realize what is occurring, and why, as the characteristics of your power delivery will change dramatically compared to a 14 x 60 geared machine and even a 14 x 57 geared machine.

   The Sachs engine has a certain range of strong power, and when you run the 14 x 54 gearing you will have a wider range of ground speed in each gear in the power band which has several benefits, including a top speed wide open in 6th. gear approaching 90 mile per hour. Most times when I mention the top speed it raises a few eyebrows, that is why I asked this question and Lee Buffenmyer's answer of 92 mile per hour with 14 x 48 gearing is what I was looking for. I would hit those speeds on road sections of National Enduros when the need to make up time when coming out of a tight woods section late would make the need to get back on time paramount. Running the standard issue VDO the needle would climb north of 80 and I never spent much time looking at it, but it was always interesting to pass machines with much more power that were running wide open but were gear bound. But trust me, there were some big bores that would pass me when I had her pegged, they were certainly not gear bound I wonder how fast Crazy Jake's Husky would run........

   Rick won't need to run that type of top speed, but when he is running down the highway traveling at 50 - 60 mile per hour for many miles he can let the engine work at a reasonable rpm and at the same time he can run the engine up some and then let it wind down which is much better than having it wound up for extended periods of time. Having the carb properly set is paramount to making this all work, and "back in the day" we would drill out a 140 main jet to 150 to allow for plenty of fuel / oil mix when it was needed. Getting the carb spot on is a whole other topic, but trust me when running 14 x 54 gearing you need the engine to run crisp, not lean, but properly crisp and clean.

    I am sure that many of you know how a woods section might be a 2nd. gear section, or a 3rd. gear section, ect., or even when dropping into a creek and climbing out the other side and up an embankment, 1st. was the only choice. With the 14 x 54 gearing the top ground speed in each gear is higher than with the other gearing, and a higher ground speed gives you more inertia as well. So figure that you have a mile of 3rd. gear woods section and you run it hard and fast, you will be passing the guys with the other gearing who are pretty much tapped out in 3rd. but can't even think of hitting 4th.as the rpm will drop off below the good power band.

   Didn't mean to run on, but wanted to give an explanation of the question of "How fast will she run". And to me, all of the above is part of the challenge and extreme pleasure of running a small bore machine.

   Thanks to all for your replies.

Paul

PS  At the POG meeting the other night Rick said the promoter of the event expressed concern that Rick would be on a 125 Penton and the rest of the guys on his minute would most likely be on 350 Hondas and the like, and that how he liked for the guys on each minute to basicly ride together....I suggested to Rick that he let the promoter know that he will be glad to occasianilly wait for those guys....

   

   

[wfopete]

Rick, if you are in doubt on top end jetting during high speed running, remember to push that kill button once and awhile to keep the cylinder cool  

And don't rub it in to your buds when you roll in on two wheels, while they are on a trailer.

Pete Petrick
175 Jackpiner
Slow but Good