Gearing for MX

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I am in the process of setting up a Monark T-model (enduro) for the MX classic  125 class.There isn't, at least I can find, a Monark page.However I am looking for help on the Sachs 125B/6B motor which was used in Penton among others of the era,what I want to know specifically is what sprocket's Penton used on the MX models.I am relatively certain the gearing I have is too high for vintage MX.Also can anyone recommend a pipe?This thing has a ten pound can hanging  on the end of the chamber,which is heavy itself.I am not chasing a National championship just looking to have some fun,but still be somewhat competitive.Thanks Frank.Any feedback on racing this class as opposed to the real old man's class appreciated.I was an expert in the 70's and have continued flattrack,however I have gained 55 pounds and slowed down a bit.

 

[SoCal996]

I'm going with Doug Wilford's recommendation of 13 and 60, which allows a second gear start.

Brian

 

[Larry Perkins]

Gearing allowing a second gear start is not only the key to holeshotting on the Sachs motored bike but also lets you skip the spot where most of the miss shifts occur, between first and second.  I think these are all options-13:57-64 and 14:60-66.  The choice will depend on available gears on hand and track.  Mid Ohio has had some really long straights while Casey, IL has alot of twisty and up and down.  The same ratios can be accomplished basing off a 12 tooth front but it balls the chain up more increasing wear and also increasing the chance of a thrown chain and potential busted case.

 

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Thanks guys I have a gearing chart somewhere but I have always used the concept that 1 smaller on the front is worth 3 larger on the back.The 13 60 info will get me where I need to go.Any tips on  a suitable pipe or has anyone had someone build one?AHRMA has a rule on aftermarket pipes which might make it difficult to get a pipe built.If I had dimensions I could get Aircone to send me the parts and weld one up myself.Thanks Frank


 

[SoCal996]

Frank,

As I recall from conversations with Aircone, they have the old Mettco specs for 125 pipes. I was going to buy a used one from a private party, but that didn't come together. The seller said it was an Aircone Mettco spec pipe, which I belive to be the case. I had a Mettco bike in '73 and it had what appeared to be the stock pipe with the tail cut off and about 1" diameter piece welded to the back which terminates near the rear shock. This is the same setup I'm running on my AHRMA bike. Its a little on the loud side. I don't know if this type pipe is what Aircone can provide. Maybe someone on the forum ended up with the Aircone I was considering. Good luck and if you can get those specs there would probably be a fair amount of interest.
 
Brian

 

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That's a real big help on the Aircone tip.If they have the info still which I would bet they do I'll have them roll up the seperate parts and I'll weld it up.I have bought several megs for my 4 stroke racers from them this way and if you weld it yourself the price is very reasonable.Frank

 

[imported_n/a]

Brian, I have a pipe like you describe on my '72 125.  I bought it from a fellow POG member last summer.  The stinger end is a built-in "silencer" that curves a little and terminates by the top rear shock bolt.  It is loud, but works really well.  I don't know the history of it, but the front is stock, the rear is different, and the middle cone looks somewhat shortened, which was a modification that was common back then to give some more top end.

Glenn