Milled Heads

[gooddirt]

Have a what looks to be a GS ported B cylinder it was off a B motor bottom end.Iam going to  fit it to a stuffed center case lower end. The GS B cylinder also has a milled head , should I run a stock head or will there be to much compression with the the milled head and the stuffed center cases together?. Where would one find a 28mm bing  would a 30mm work or go to a MIC [ what size]?  This will be a race bike as well .Thanks any info would be great[:0]

[TGTech]

The stuffed bottom end won't hurt the compression issue, because that is the primary compression. That will help the bottom and mid range power. The modified head could cause a problem depending in how "modified" it is. The bottom line is that you don't want the cylinder pressure to be higher than about 180 lbs. The ignition timing is also tied to the compression issue. With higher compression, you don't want the timing to be any more than 2.4 mm.

Sorry I can't help you with the carburetor issue.

Dane

[socalmx]

In 1974, I took my Sachs B motor to FMF for a workover. Emmler milled .060 off the head as well as opened the ports, etc. Bike was extremely fast after that (continued to run 28mm carb) but had one minor problem. During Viewfinders Grand Prix (at long gone Indian Dunes), there were multiple water crossings. After a couple of laps, the bike lost compression and I DNF'd the race. When I got home, I pulled off the head which promptly broke into two pieces.

[dkwkid]

GS engines had the higher compression cylinder head from the factory.Along with the holes for the 6Days sealing wire. Sachs engines love compression- but in the interest of longevity you may want to store away the hot dog head and put a lower compression one on.
 Higher compression will give more torque but will also create more heat although my brother never had a heat related problem in the California desert. His 100cc Dkw motor was run wide open for extended periods in 90+ degree heat. You DO have all that heatsink finning. I would worry more about your frame cracking than compression related failures.

[socalmx]

If it is a GS cylinder, the carb spigot is bigger than the B cylinder and will accept a 30 mm spigot mount Mikuni very nicely.

[Bryson Williams]

I have several Monarks with GS motors and 2 GS PRO motors. " Stuffed case models".  The stuffed case models both have 20 th milled from the head from the factory.  

On the GS motors they also have had the heads milled 20 th.  All are very powerful 125's. My question I guess is can 60th be milled from the head the base is almost flush with 20th milled.

MY GS ported D model Monark motor also has 20 th milled from the base of the head. The spec's are available on the Vintage Monark page under the TIS section.

Dirk Williams

[socalmx]

I am relying on memory from 30 years ago but 60 thousands stuck in my mind. What I do remember is that the stock B head milled had the gasket surface about as close to flush with the finning as you could get. As my brother mentioned, the DKW 100 was very fast and reliable under desert racing conditions. The only time I got myself in trouble was when I let the bore get a bit too worn and snagged a ring. Really annoying because I had been pushing a Hodaka rider for miles. He had a ported motor because it was almost as fast as my DKW. The secret was to ride right on their tail because any Hodaka that had a ported motor could not take the heat and would fail. It finally did at around 40 miles. At that point I was leading my class and had about 10 miles left when it happened!

[john durrill]

Folks,
 sounds like you need some heads measure in CC's befor you start milling. Several NOS heads and the CC's from heads that have been milled and work. Thinner head gaskets can help bump the compression with out taking any metal off. Its easy to remove it but a lot harder to put it back on , chuckle chuckle!
If decking the head can make it too thin and prone to cracking then welding up the combustion chamber and recutting it would be a better idea or useing a 100 cc head and opening it up.
What do you think?
John D.

[firstturn]

John,
  Excellent observation....but don't be giving away all the secrets;).

Ron Carbaugh

[dkwkid]

Has anyone experimented with different combustion shapes? Tom Ruddy was the tuner for Ted Lapidakis who was the distributor for Sachs/DKW.
According to Tom Brooks Sr, Tom Ruddy created a bathtub-like shape combustion chamber and that was one of the secrets of Tom Brooks desert winning 125.
 In fact, at one of the District 37 races in which Tom won overall, his displacement was protested. So off came the head and the bore and stroke were measured(they were in spec).Tom Ruddy hid the head with a rag so nobody could see the shape.
 Unfortunatly, Tom ruddy died a few years back-he would have been an interesting guy to talk to.On a side note, I don,t think Ted Lapidakis and John Penton got along-they were selling competing models in the marketplace.