125 sachs porting

[Mike Lenz]

I would like to some day try and make my 125 Jackpiner competive for sportsman 125 class.  If you dont know I put a Sachs cylinder on a 73 Jackpiner to try and make a good shifting reliable vintaqe Penton 100 for the 100cc Nationals they used to have in MO.  Well it worked great and we won that race three years in a row...and then everybody quit comming and the 100cc national was no more.  So the bike just sits there, not legal for AHRMA 100 class.  I know I couldnt run it in 125 classic so Im left with sportsman.  There are some fast motor scooters in that class!

I have been looking in this site and others for porting ideas.  If I want to go all the way it sounds like the S or worm boost type port would help if I really opened up the intake and ran lets say a 32 Bing.  I understand about how and where this port went but I cant see how it could be done without the ring ends getting into it.  Were they putting the ring ends on the exhaust side?  Has anybody seen this done and want to share...or am I getting into much to top secret stuff here?  Also what about extra exhaust holes drilled along side the top edges of the exhaust.  I've seen that before.  Anyone ever tried it with a Sachs?

[Larry Perkins]

Mike,

I always give up too many secrets but if you do it then do it like the KTM 125 V port and run the 125 KTM piston with the window.  Vroom Vroom[8D]!

Larry P

[JP Morgen]

Reed valve is really the only way to make some serious horsepower. Also frees you up to use all sorts of pistons, and have more effective boost ports. By chance, I have figured out how to add two boost exhaust ports, haven't actually done it yet, but I have some dead cylinders to practise on! Might be a little different with a 100cc bore though? believe it or not the actual exhaust and transfer port timing on a Sachs cylinder is the same as a modern KTM SX 125!

[rob w]

Bought this complete 125 6B engine in 2004 at Mid-Ohio for $75.
DH reed valve with booster ports.











Bob

[joe novak]

Rob,  Nice modification job.   How about a photo of the exhaust port?   What goes in must go out....   joe

[john durrill]

Mike,
  A friend in the Netherlands built this one up several years ago and had good results with it. You wouldn't need the water pump and drive
with an air cooled cylinder but the intake did work and did very well at the races. Down side was he would get one race to a set of clutch plates. I think their are still the parts to do this in kit form available.
 







It made right at 31 hp.
For dirt you could build up a Can Am type intake tract . You could use the TNT rotary cover as a tested model to build from.

JP ,
 What reed cage would you use ? The DH and Gems that were made for the Sachs 125's are a little small.

Get a dead CT2 cylinder and weld that reed housing on the Sachs cylinder?
Or does someone make up a kit that would work now for a 32 or so mm carb ?

john d.

[rob w]

quote:Originally posted by joe novak

Rob,  Nice modification job.   How about a photo of the exhaust port?   What goes in must go out....   joe

Hey Joe, How's it goin.

Bob

[gooddirt]

Will a 100 liner press in a 125 barrel ? Any mods needed?

[OUCWBOY]

Larry,
It will work with some modifications, as the sleeve ports on the 100 vs the 125 will have a slight bit of difference in angle and position.

Donny Smith
Paragould, AR

[JP Morgen]

To be technically legal, I usually use vintage period Yamaha reed cages, sometimes updating with carbon reed petals, although a modern 80/85cc block would also work good. I never use the Yamaha rubber carb manifold because they all have a tight kink in them, poor flow. The problem with good horsepower on the Sachs motor is the clutch will slip, then I have squeezed in another plate, or added three more springs, of course then hard to pull and sometimes drags. JP

[joe novak]

Thank you, Rob.  Beautiful exhaust area!   It is hard to remember how "rectangular" the opening once was....                          Joe  p.s. We just received 3-4" of beautiful snowfall.  Really!   Soccer practice was cancelled last evening for our daughter, and I will cancel practice for our son this evening.   Balls don't roll well in the thick snow.

[SouthRider]

What is this "snow" you are referring to?

It will hit 80 here tomorrow..... and spring is almost over....

[jeff greenberg]

Suppose to hit 97 here tomorrow!!  Boy, I wish I had some of this sweet porting back in the day. If memory serves, I think all I had on my GS, 125 was a milled head, a little port work by my pal Jeff Piasecki. May have taken a little bit off of one on the expansion chamber cones. thats it.
JG
Scottsdale,AZ

[Mike Lenz]

Wow, thanks for all the ideas.  John, very cool but way over my head.  I know JP builds some FAST motors, maybe I will go that route.  Larry, that was my first thought also. But after looking I dont see how you could use a KTM style boost port because the piston window will be open in the intake tract, with the Sachs oval intake port, when the transfers are open.  The worm boost port I mentioned was the same concept except it was two channels that ran up each side of the cylinder from the bottom side edge of the liner, and opened when or just before the transfers opened on the rear side of the piston. This acted just the same as the KTM set up.  But how to squeeze a quarter inch channel into the side of the cylinder and up behind the piston without getting into the ring end gaps, as they are stock anyway, is my dilemma. This would be the easiest route on my already ported cylinder I have to try and gain some extra air flow.
Again thanks for your input.

[firstturn]

Ok Big Mike...how did the 100 cylinder I sent you work?  Let me know.  I will look around and see what I have as far as a 125 Trick cylinder.

Ron Carbaugh