These are some pictures of a cylinder and head that I recently milled my cosmetic porcupine/checkered mods on.
It came to me as an already ported to GS Pro specs (or beyond), D cylinder.
What interested me were the grooves (booster ports ?) ground through the liner, on each side of the intake. These pockets are 1/8 deep x 3/8 wide, and 1 1/2 long, that run from a height apx equal to the top of the transfer ports, to half way down the intake.
Would someone like to expound on the function of these ? Thanks
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/porky026_zps82d99ebe.jpg)
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/porky014_zpsf3eacb6f.jpg)
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/porky020_zpsf4c27c71.jpg)
Head milled all the way down to the bottom fin.
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/porky002_zps1f74f5f8.jpg)
My end of the work.
If anyone is interested, I can make notes of the port openings and heights.
Rob:
Not sure about Sachs but normally when boosters are added i thought that they were drilled into the intake track. Looks like when they were ground someone slipped and scuffed the liner. Maybe they stopped at that point before drilling into the intake?
Ted
Hi Ted, Yes I'm familiar with the type of booster ports you're speaking of. This is my cylinder modified by DH Industries back in the day. With reed valve, and booster ports running above the intake port. (not along the sides as this other one)
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/eb1018.jpg)
(http://i52.photobucket.com/albums/g8/BobWardlow/sachs%20engine%20stuff/eb1020.jpg)
A couple photos of the "E.C. Birt" style finger ports in my 100 cylinder.
(http://i957.photobucket.com/albums/ae59/CheneySachs/BglIfewBWkKGrHqYH-D4EsNCFk1bEBLFzmoINLQ_12_zps02824406.jpg)
(http://i957.photobucket.com/albums/ae59/CheneySachs/BglI2wmkKGrHqIH-DQEsKn9klWqBLFzmCF5_12_zps9661b764.jpg)
Dale Fisher
Penton Owners Group - Memberships
Facebook - Cheney Twinshock Racing Group - Administrator
'70 Six-Day 125 - V2017
'71 Six-Day 125 (Dave Fisher's) - V5553
'72 Mudlark - W257
'73 Jackpiner - 175 21159727
'74 Berkshire 100 - 40171056
And some silly other bikes...
Rob, I had something like this done on my 125 Elsinore in 1976. It was the bike I raced in nationals. All I know is that the mods turned the bike into an absolute rocket.
Probably added 1,000 rpm and 3-4 HP. Although reliability did suffer .
Jeff
Those ports are similar to what Yamaha did on the original 5 port design, back around 68-69.
They are feed through holes high on the piston that are aligned with the extra transfer ports.
They idea was that the crankcase could feed through the holes in the piston through the extra transfer ports.
As the piston descends and compresses the crankcase, it's pushing gas into the top-end before the piston closes off the transfer ports.
In the next generation, a second set of ports feeding from the base of the cylinder like the main transfers, were used.
Then came the reeded motors that had additional ports above the intake port that are opened into the intake tract and the piston holes were moved to the intake side of the piston.
Thank you for the explanation Ron. Figures that it takes windows in the piston to function, just that I had never seen this method before. I appreciate your response.
Bob