Porting specs for the 100 cc Sachs

[john durrill]

Dane , Doug , Ron C., Jack
 Could one of you folks give us some input on the exhaust port width recommended by Carl in the old tec. sheet he sent out on Mx mods for the 100/125.
  The 100 is a 48 mm bore and the 125 is 54. Is the width shown in the dotted lines the width for both engines or just the 125?
Here is a short cut to the article for reference.

http://www.flickr.com/photos/12809785@N06/sets/72157603633128912/

 Thanks folks. Its easy to take metal away but not so easy to put it back[]

John D.

[Larry Perkins]

John,

I know you did not ask it of me but when did that ever stop me from piping in?  The porting changes are for both.  Compare sometime the stock ports of a 100 and a 125.  You will be surprised.  The only real difference in Carl's mods were in the squish band area after head milling if I remember correctly.  Also in carb and pipe of course.  But you know about the pipe.  Do these mods, put it all in a non hi-breather 72 chassis, add a Hipoint aluminum tank, an aluminum seat base, Koni shocks, internal rotor ignition, have J.P. Morgan drop mod the gears, hand stuff the crank, hold her open, and she will wail.  They work with this setup especially good indoors in a big dome.[8D]

Larry P

[Marc Biro]

I might ad that the original Results and Dyno test for these modifictions were compliments of Mettco

marc biro

[john durrill]

Larry ,
 Myself being not much smarter than a fence post thank you kindly for the help Chuckle chuckle![:I] I Rode a 72 100 6A for several years and never had to do anything but put a set of rings in it. I never paid much attention to the porting ( it had enough power for me) so i can not help here. Mark I saw the note Carle left in place on the Dyno chart .
 Double checking on the width just look like a good idea. I usually wait till i have cut the darn thing and then think about things like this[:I].
 Larry , Mark , Dane , Doug , Ron , Jack If you folks can pass any info on the the group building 100's for this class please do. Larry like how you did the hand stuffing on the crank. Mark and Larry, the tranny mod. Where to send it and how you liked it. It will help a lot guys. Pooling our knowledge as a group is a lot better than each of us having to learn the hard way what has worked and what does not [xx(].
 thanks guys,
 John D.

[Ernie Phillips]

John, Good idea to collect all that tuning info.  My son and I are building a 6B Berkshire for him to race.  It will be STOCK except for 28mm Mikuni and PVL ... and maybe a downpipe for "looks."  He is still learing how to ride and needs to focus on improving his riding skills first, thus a good handling and relialbe bike is needed.  We did too much "horse breeding at the race track" last year.  This is the year of reliability for us (at least that is our goal -- no DNFs)  Plus at only 150 pounds, he should be competitive against a 200 pounder riding a pipey Super Rodent.  If by chance there is a 150 pound rider on a RAT, then we will need the porting info.  Horsepower, Handling, Reliability - in stock form Pentons have two ... do we need all three?  When the flag drops, we will know.  Thanks,

Ernie P.
Chattanooga, TN

[Larry Perkins]

John,

Whatever!  In my book you are incredibly smart.  There must be some bright fenceposts where you live.  Anyone that followed the progress story of your KTM/Sachs 175 would agree.  I wish I had half the engineer's brain that you do.

For the stuffing use the 6B cases as the crank is smaller and the crank area is smaller so presumbably more crank pressure to begin with.  If memory serves the crank wheels were drilled at the machine shop while the crank was apart for a special Sachs rod that was used on mine.  Then these holes were stuffed with cork and epoxied over.  Someone that really knew what they were doing balance the whole deal first of course.  This combo made for lighter crank and more crank pressure. Revability and torque combo.

J.P. is out in California.  Mark can probably supply some contact info.  If not I can dig it up.  How does it work.  My opinion is you will wonder why Sachs did not figure this out and do it.  John might never have switched to the KTM motors on the little bikes.

Something that helps bring back some low ponies and will let you run a bigger carb for more topend is a reed which should be legal in this class as some of the other bikes came with one.  Have not tried this but always knew it would counteract some of the lag down low with a really big carb.

The pipe is a real critical addition for the 100.  The 125 pipe will work but the 100 really needed the snubby that Carl maps out in this Tech Bulletin.  John, you can shed some light for the others on where to get the cones built today.

Another real important factor to make this package wail is gearing.  Gear it so low that it is easy to start in second so that first is not necessary.  The worst shift for the Sachs in Moto is from first to second.  The top speed the 6 speed provides is not necessary on most MX tracks anyway.  Makes the whole box closer ratio also.  I can check mine but I believe it is 13-60.  Don't use a 4" back tire go with a 3.50 also.  It is hard to find a good rubber one today, however.  I see Hipoint Metzlers around from time to time but now with the 100 class they will go away fairly quickly as 4.00 and 4.50 did.  

If I was battling on the 100 this year I probably would not remember as much.  But the desert is the battleground for now.  Hope this all helps some Pentons win!  If I can help anyway else let me know.

Larry P

[john durrill]

Larry,
 Thank you ,
 That was a lot of information. Air Cone did the cones for your pipe. They were expensive we thought at the time ( $ 78 ) but it looks like they are no longer in business.
   Ron C , Paul, Doug anyone else that knows a local sheet metal shop, can you folks find a sheet metal shop that would make up the parts shown in the diagrams on the link posted ? I can post the tec sheets on here if someone can show me how.
  You may have had a 175 rod kit installed from what you say Larry. That would give you 2 mm more width in the big end bearing i think.
 I have a tec sheet for a Zundapp reed kit install. Zundapp used the same materials  in their cylinder ( It may have used a chrome bore though ) and pistons same bore and stroke as the Sachs. So it should work on a Sachs engine. I can post those if anyone would like. Speedy has some experience with that motor and could be some help with that modification .
  Ron C and Dane Marble Might be able to help some on a reed kit install also. I dont know though they may have had one of those ( we will only give up that info when you pry if from our cold dead hands ) signs posted on their rear bummpers at the RR last year.
 I did several reed kits on the 93 rodent and Ace 100 Hodakas and will share any thing i learned from them with you folks.
 Ernie, Stock is better if  it will do the job. Stock that engine lasts a very long time. When we modify an engine its like placing a grenade on the cylinder head. First start the pin gets pulled. The time on the delay fuse for detonation is set by how well we did the job and how far we went above the design envelop on that engine.[:I]  
 Mikuni,  it looks like ,has stopped production on the 28 mm carb so......... You either have to find an old one , bore out a new 26 ( that should leave 1 mm on each side of the bore to seal the slide  or use a 28 or 27mm Bing.
 I think you can still get 28's new from Bing.
 I think the Bings flow more air for there size than the Mikunis  from the few i have worked with. Someone with a flow bench or dyno would have to do the comparison on the same engine and pipe to be certain though .
  The old Iron barrel Hodakas have a special place in my heart. We started our small dealership with them. To me they are a true classic design . I watched a bunch or folks get there start in the dirt on them. There are many more 100 cc Hodaka owners out there than Sachs  guys. I know they have been chomping at the bit to have a class they can ride in for years. We only have a few 100 Birkie men but i think they have the same desires . The Rodents will bring their A team and their A game chuckle chuckle!!!!!!  I think that Hodaka has passed the small block chevy in things available to modify that design to work in every thing from Road Racing to Trials. So be ready:) !!!!
 My first Penton was a 72 CMF 6A Bosch Mag Berkie . Of all the 100's i have had it was my favorite. They were a wonder to me. The wife did a little riding with us back then. She rode one enduro only just to see what they were like. She rode the Berkie and placed 2nd in the Powder Puff class. To me thats prof of just how good that bike was.
 I hope the class become a Fixture in ARMHA. It lets the young set become involved in vintage bikes and that is the future of the sport we love.
 Sorry for the long post Folks. Until we get this cast removed from my left arm I have way too much free time [8D]
 John D.

 

[tooclose racing]

Those porting specs are just so cool. They're like the Dead Sea Scrolls or something.  And someone already anticipated my own question regarding stuffed cranks.  

I'm going to do some motocrossing with my first Six Day (a 72 CMF) this year....and I am just loving some of these threads.  I'll keep it simple for year #1 (bigger Mikuni and some 35mm forks!), but I'll keep those specs nearby...

Great stuff, gentlemen...have fun with those 100's!

[john durrill]

Bob ,
 28 mm is as big as you can go in carb size as the rules stand. The stock 27 mm Bing probable flows more air than a 28 mm Mikuni so you would be better off useing the the Bing that came on the 100.
 Ernie It looks like the new 26 mm Mikuni's would only allow us to bore them out to 27 and a hair.  Old Mikuni 28's had 2.5 mm sealing between the slide and carb bore. 1 MM probably wont be enough to seal.
 Try and find an old Mikuni 28 if you want that carb.
        Would some of you folks check and see if a local sheet metal shop would roll the one cone and 1 straight section needed to make Carls 100 pipe? 20 gauge mild steel should work fine. Anyone that can use  an oxy acet torch can weld the parts on. It does not take special gear to do pipes.
 One thing i believe would help the 100 a lot is straight cut primary gears. Several Pog members went in and had a 5 sets made a few years ago.
  Has anyone had any track experience with them ?  Talking to Doug a few years back he mention something about the added gear lash between the helical and straights could be an issue. I may have misunderstood him. Hope he reads this and  gives us his input. If there are no problems with them on this type tranny then they are what i call FREE HP. Rule of thumb i was told years ago was about 10 % more hp on small bores like 100's.
We have 1 of the sets and am planning on using them in a 125 5A alloy. That engine will be in my bike on and off this year, we can let you know what we find out as I ride it and will post that as it happens.
 I think we have found some reed cage sources as an option if anyone wants to go that route.
 Have a great Day folks'
John D.
 

[Ernie Phillips]

John,  I got lucky and was able to acquire some 28mm Mikunis last year.  We have run them successfully on 125 6A&B this year.  On our 100 project, we will use 28 Mikuni but if we can piece together a good 27 Bing we will try that as well.  I am converting my hot 125 5A to a 6B with PVL and 30mm Bing.  There is nothing better than a properly jetted Bing.  However, once they get a little wear, they seem to get very finiky ... and if you fall over they load-up.

Are you going to bump the compression on your 100?  If so, how?  What are your target values for actual compression gage readings (kicking over with full throttle)?  Thanks,

Ernie P.
Chattanooga, TN

[john durrill]

Ernie ,
 We are building a 125 5A . Will check what it does stock once the rings are seated. I wont run more than 160 on my engines, usualy less ,150 or so. I have been a trail and enduro rider most of my dirt bike life so my thinking and changes are for that type of riding.  Reliability would be a big part of any changes we would do to our bikes.
 I dont Race like you folks do. Just the RR and trail rides are my only passions.
 Something i did not know but learned last week reading an article by Gordon Jennings is, that what we get for a reading with the throttle wide open and 5 hard kicks its actually lower than what the engine will make at max rpm the pipe is designed for. The back pressure from the pipe will raise the compression when the pipe hits its sweet spot. The article was on some dyno testing he did on Webco's 125 kit for the 100 cc Hodaka for Webco. He had to lower compression to 140 from 175 to get the jetting to work through out the pipes range. He got 2? more Hp with the lower compression.
 If i am mistaken or uninformed on a subject someone please kick holes in my ideas.
We have some of the best 100 cc folks in the USA to learn from here so if we dont know its because we did not ask them and SHAME ON US chuckle chuckle! John D.

[Jim A]

In regard to 28 mm Mikunis they show up occasionally as they were used on TM100/125 Suzukis. The ones on the TMs had a taller cap but will still fit. The 1974 TM 100 used a 26, the 1974 TM 125 used the 28. For some unknown reason the 1975 models were reversed, 28 for the 100 and 26 for the 125. The 1973 TM125 I'm not sure of, probably 28 mm also.

Jim A

[dkwkid]

Mill .060 off the head and recut the chamber angles (or find a GS head).Smooth out the base of the transfers and remove excess material where the liner mates with the cylinder. You may want to cut the intake side of the piston a bit as well to increase intake timing.You can raise the exhaust a little but I would go against widening it-you could snag a ring. When changing timing you will make it somewhat pipey with a chance of loading up so you would have to ride it accordingly

[brian kirby]

Some mid '70s Yamaha DT250s had 28mm carbs. I will look up the years and post them. They can be bought very cheap on eBay.

Brian

'72 Six Day (on loan from Ernie P.)

[Mike Lenz]

I am running a 26 Bing on my 100 "Jackpiner". Has anyone ever tried to bore out a 24 or 26 bing to 27 or 28mm? It looks to me if tried you would have to bore it off center to the bottom more.  The top of the bore is already very thin.