Who's Jerry Mac Kay/sachs porting specs

[Gavin Housh]

Does anyone recognize this name? Found three pages of porting specs in an old Penton dealer shop manual circa 1973. Letter head on all pages reads "from the desk of Jerry Mac Kay" with smily face in upper left hand corner. Porting specs for 125 sachs motor includes cylinder head modifcations, piston rewoking, and port timing specifications. The information contained in these pages is not perfectly clear. It looks as if someone wrote them down in a hurry, understanding themselves what needed to be done. When I read this everything is not exactly clear. I'll start with the cylinder head. .040in. from head .060in. max 14 degree tapper/angle on squish band. Next the piston. 2.5mm off piston skirt (back or intake side I beleive). .028in. hole? (I don't know what this applies to). .080in. off piston? (does this mean take .080in. off the dome of the piston? Why would you do this, and if you did wouldn't the top of the piston end up flat?). Now the port specs. Widen exhaust port 2mm each side, total port width 36mm. Riase exhaust port 2mm. Do not exceed 1.100 in. from top of port to top of cylinder liner.(Don't just take off 2mm, check before you start. Some later models start out higher!) Do not widen intake! Intake 28mm.(I think this means bore out sigot that the carb clamps onto, because it later says to use a 28mm bing carb) Stock transfers. Transfers cutaway to base level.(I take this to mean leave the tranfers up in the cylinder in stock configuration, but as far as cutting away the transfer to base level I don't know. It must have something to do with the bottom of the port and the base of the cylinder). Then it goes on to say . Bost port lower than regular. People that I've talked to about this motor say there isn't enough room for a bost port with a double ring piston. I've never seen a single ring piston, I've heard that they used to sell them. Does anybody know anything about bost ports in these motors? Then it has info for timing, carb, and plug. Set timing at 2.8mm BTDC, 28mm Bing carb, and 260T1 Bosch. The bikes came with 27.5mm carbs. Some people used to bore them out to a larger size.Then it gives information on cutting off the back of the pipe. I know some of you are building your bikes for show and cutting the end of the pipe off would be absurd. Those who wish to increase HP will want to cut it off. To cut take hack saw and cut 1 1/4in. behind(closer if your carfull but you might want to make a couple of cuts to see how close to the second layer of metal you are.)the last weld on center section of pipe. This will remove the cover off the back of the pipe exposing the last tappered cone of the pipe and the stinger. When cutting with the saw just cut untill you go through the first layer of metal. Then rotate the pipe and start again just untill you start to braek through. Rotate and start again. Keep doing this untill you've cut all the way around. It takes time and you have to be carefull, but in the end it's worth it.After your done here you'll want to peen the sharp edge down with a hammer in the area were your pants are going to rub. I welded a small beed on mine to make shure my pants don't rip. Now measure from the begining of the stinger to 7in. and cut the rest of the stinger  off. A small silencer will need to be fitted to the end so as not to upset anyone. I found an old J&R .875in. it fits right on with a hose clamp and it's repackable. I tried to show this to Carle Cranke last year but missed him.It would be great if we could get someone like Carl to go over this stuff and put togeather porting specs like the ones puplished in the POG newsletter for the 250 motor.I'm shure some of you will find this info intresting and I hope you'll help to fill in some of the blanks. thanks Gavin

 

[400gs6]

I love to read a post like this. I is great to find out all the trick set-up`s of the day,a friend of mine lent me his collection of "Keeping track" the old Penton newsletter and it also is full of tricks of the day,Sachs gearbox adjustments, carb tricks etc. And there are some great old pics. of the top guys of the era, Paul Danik there is a whole page pic. of you on a 125. When I figure out how to use my scanner I`ll try to post some info. Happy Penton restoring, Kurt

 

[DKWRACER]

If you send me a SASE and 1 dollar I will send you the article of SACHS engine secrets (porting)
Tom Brosius
209 So Yates St.
Denver, Col 80219