Head mods - Spree
Spree head differences
The head design changed in '86 for the Spree. See photo: Left is '84-85 design, right is '86-87 design.
Note that the later design has a raised boss for the spark plug, a wider squish zone that is evenly domed, and a much thicker material section at the back of the head.
There are also piston differences. The '84-85 pistons are dished, whereas the '86-87 pistons (and all service parts for '84-87) are domed slightly. Since they are service-interchangeable, the head appears to be interchangeable as well. However, if you start shaving heads this will be something to watch.
The '86-87 piston and head would appear to be the better performing combo. The head design, being evenly domed, should allow more material removal to increase compression. The earlier '84-85 design is flatter and actually has reliefs towards the circumference. These would, in my mind, negatively affect the combustion flame growth. As many members have noted, the '86 and '87 Spree are faster "out of the box," with top speeds around 35 MPH. The '84-85 models rarely seem to climb out of the 30 MPH range.
Some users have posted that the domed piston with the 84/85 head is the best performing combo, as it give you higher compression. Guys with 86/87 scooters report improved performance by swapping to the earlier 84/85 head. These scooters have the domed piston stock.
Watch your piston to head clearance on any modification like this.
The way to check clearance is to tape 4 pieces of electrical solder in a cross pattern on the top of the piston and reassemble the head with gasket to spec torque. Rotate the piston around once to squish the solder, and disassemble it. Use a caliper to measure the solder thickness. .0020" is sufficient clearance, as you can run the Spree with no head gasket and not have interference problems. .0010" is as close as I would ever run, currently mine's around .0020 at the closest.
Modification for big bore
This can be done by a machine shop or with a dremel and a steady hand.
The stock head for the spree is too small for the BBK. I used the NEW 44mm head gasket to mark the difference that needed to be taken away.
Here is the dremeled head that now fits the new bigger 44mm kit.
O ring seal mod
Some members have cut a groove for an O ring seal. Advantage for a stock head is increased compression via no head gasket. A good idea would be to check piston/head clearance per the above topic. Also, it facilitates reuse of the seal after dis assembly. Full detail for groove dimensions and o ring are not present. It is said this is a 51mm Viton ring.
Lowering for increased compression
Cut Spree head to raise the compression for better performance. Here are some pictures.
Here is a stock head. Note the small step at the edge of the combustion chamber. This step is about .020". This is the reccomended maximum cut.
Chucked it up in the lathe, centered and squared it. This can also be done on a mill.
Time to cut.
Layed some 320 grit wet and dry on the drill press table. This is used to remove the tool marks and make sure that is completly flat.
Note the little step is now gone. If you want to cut more off you need to watch for piston interferance.
Stamped the amount cut off to prevent future confusion.
Author: noiseguy, Trafficjamz, turtle13, keithw