Lower End Tech Tips


Are My Compression Releases Working Properly?
The main reason for compression releases is to reduce the amount of compression during the start up of your bike. Primarily if you have altered the compression ratio and have cranking compression numbers that are higher than 180psi. 

If you are using S&S electronic compression releases and you are not sure if they are working properly here are some methods of checking them out. 

1. Note that when you are cranking the engine that both releases are opening; this can be done by looking to see of they both drop down or by putting your finger on top and feeling the drop down motion. 

2. Compression releases not sealing; to check for proper seal of the release you can do a leak down test. If the leak down percentage is high and you can here air in the exhaust it is possible that a release may not be properly sealing. If this is the situation you will need to remove both releases and verify condition. (When ever you are installing or removing compression releases it is best to remove the rocker boxes it makes the job much easier.) To verify condition, after the releases are removed look for signs of the plunger not properly sealing. Some times a poorly tuned engine will cause access carbon to build up on the release causing it to stick. The releases can be cleaned and reinstalled. If the release seems to be damaged call your S&S tech line for assistance.

3. Check the wiring; If you do not have the releases properly wired they may not work properly and you could run the risk of damaging the releases or some thing else on your bike.

4. When removing or installing our releases it is much easier to remove the rocker boxes and also the use of the S&S two piece socket will help PN 53-0045. If you choose not to use the compression releases you can install the plug into each head PN 90-4916.
How To Identify Flywheels
S&S® flywheels are manufactured in sets only. We do not sell individual right or left flywheels, nor do we recommend mixing flywheels. This is because the manufacturing techniques and/or tooling changes periodically. To prevent mixing flywheels, as well as to identify each set, the right and left flywheels are stamped with identical serial numbers (see picture below).


Serial Number Identification Information

Serial Number ID, B01810-3SLX , deciphered as follows:

(B01810) Serial Number: From this number, S&S can determine when the flywheels were made and sold, to whom they were sold, and how the flywheels were originally balanced.

(3) Stroke Code: Determines the stroke of the flywheels. In this case the stroke is 4 3/4".

(SL) Year Code: The year of the engine the flywheels were machined to fit and that the flywheels were machined to accept an S&S design sprocket shaft.

(X) Diameter Code: Diameter of the flywheels. In this case the diameter is 8 1/4".

S&S® Flywheel Identification Codes for 1936–Up Big Twins
Stroke Code Stroke Year Code Engine Year Sprocket Shaft Pinion Shaft Crankpin Type Diameter Code Flywheel Diameter
1 4 3⁄8" E 1936–'54 Stock Stock 1941–'81 None

8 1⁄2" (Stock)

4 1⁄2" L 1955–'71 Stock Stock 1941–'81 A 8 3⁄8"
3 4 3⁄4" AL

Early '81

Stock Stock 1941–'81 X 8 1⁄4"
4 5" SE 1955–Early '81 S&S Stock 1941–'81

4 1⁄4"
(Stock 80")

BL Late 1981–'99 Stock Stock 1981–'99
6 4 5⁄8" SL Late 1981–'99 S&S Stock 1981–'99
9 Special Order SF 1999–up Press In Press In Press In
12 5 1⁄4" SG S&S 4 1⁄8" Bore Press In Press In
13 3 1⁄2"
(Stock 61")
SM 1995–'99 EFI Press In S&S 1981–'99
14 3 31⁄32" (Stock 74") Y 74"/80" Indian® Stock Stock Stock
16 5 1⁄8"
17 4”
18 3 5⁄8"
19 4 1⁄8"
TA 3 7⁄8” Titan Special
TB 4.450”

Flywheel Codes:

  • Codes that pertain to the most common regular production flywheels have been listed. Many other codes for racing flywheels and special orders also exist. If you have a question about a set of S&S flywheels with codes different than those shown, contact an S&S technical assistant to properly identify what you have.
  • Flywheel ID codes that end with an “A” or an “X” designate flywheels with a smaller than stock diameter. Stock big twin flywheels measure 8 1/2”, and stock flywheels for Harley-Davidson® Sportster® models are 7 7⁄8” in diameter. Typically, “A” means 1/8” smaller, and “X” means 1/4” smaller. To verify the code, it is best to measure the flywheels.
Serial numbers can be seen through the timing hole to identify the stroke of an assembled engine. Keep in mind they will appear upside down in the hole

S&S® Flywheel Identification Codes for Harley-Davidson® Sportster® & Buell® Models
Stroke Code Stroke Year Code Engine Year Sprocket Shaft Pinion Shaft Crankpin Type Rod Bearing Type Diameter Code Flywheel Diameter
1 4 1⁄16" None 1957–'76 Stock Stock Stock Stock None 7 7⁄8" (Stock)
2 4 3⁄16" B
Early '81
Stock Stock Stock Stock A 7 3⁄4"
3 4 5⁄16" SB
Early '81
S&S Stock Stock Stock X 7 5⁄8"
4 4 7⁄16" BD 1957
Early '81
Stock Stock Stock
6 4 5⁄8" SBD 1977
Early '81
S&S Stock Stock
7 4 13⁄16" C* Late 1981–'85 Stock Stock Stock Stock
8 5" SC Late 1981–'85 S&S Stock Stock Stock
9 Special Order SCD Late 1981–'85 S&S Stock Stock
11 4 1⁄2" SCR Late 1981–'85 S&S Stock Stock 1987-Up
12 5 1⁄4" SCDR Late 1981–'85 S&S Stock 1987-Up
15 3 13⁄16” D Late 1986–’03 S&S S&S S&S S&S
16 5 1⁄8" DR Late 1986–03 S&S S&S S&S 1987-Up
17 4" PS S&S Prostock Press In Press In Press In
18 3 5⁄8" KRS 45" WR/KR Stock Stock 1957-'81 XL 1957-'81 XL
19 4 1⁄8" YS 45" Indian® Stock Stock Stock Stock

*Obsolete – S&S no longer makes this design.
Should I Use The 1993-Up Breather System Or The Earlier Crankcase Breather System?
Breathers... What kind should I use?... I just got back from the Chicago bike show. I noticed that most of the S & S powered bikes used a manifold breather (feed into the back of the air cleaner housing). My engine did not come with the manifold breather tubes. It just has standard bolts in the head to mount the air cleaner. I was going to use the crankcase vent line that is next to the oil pump. A dude at the show told me that I would get a few extra horsepower if I use a manifold type breather (I don't see how) instead of the one by the oil pump. So I guess my question is will the place I put the vent line make any change in power? Should I use both? Is one better than the other?

Now my next question. To VOES or not to VOES, that is the question. To save space (and looks) I would like not to have a VOES on my ride. Will this be a problem? I was going to use a Compufire ignition system, but I see it has a switch for 100% and 50% VOES. Will I need the VOES with it?

The manifold has nothing to do with the engine breather system. The head breather system requires 1993 and newer rocker boxes and heads. If you have these then use a 1993 and up S & S Super G and you will have all you need although it probably won't make much difference in power. My choice is to use both head and crankcase breathers.

VOES- ride the bike and if you have no detonation then you do NOT need the switch. If you want the VOES to work then you must use the switch and your intake manifold must have a vacuum port. 

Something else to keep in mind all S&S EVO style crankcases are capable of breathing out the lower end (when the 92 and earlier cam cover is used) which gives you more breathing options. You can breath out the top, bottom, or both.
Will S&S Flywheels Work In My 2003 Twin Cam®?
All S&S Twin Cam® Flywheels and OEM Harley-Davidson® Twin Cam "B" 1999–'02 style flywheels are designed for to use dual tapered roller bearings (Timken® bearings) on the sprocket shaft. They will fit directly in stock H-D 1999–'02 Twin Cam crankcases and in all S&S Twin Cam crankcases without modifications.

S&S does not produce a set of flywheels that is a direct replacement for 2003 and later Twin Cam engines. Stock 2003 and later engines use a flat roller type bearing for the sprocket shaft.

In fact, for 2003, the sprocket shaft and the pinion shaft use the same bearing part number. As many of you are aware, Harley-Davidson sells a retrofit kit (HD#24004-03) that allows earlier OEM Twin Cam flywheel assemblies that use the Timken® style bearing on the sprocket shaft to accept the flat roller style sprocket shaft bearing. This allows 1999–2002 flywheel assemblies to be used in 2003—up cases. 

S&S strongly discourages use of this kit on S&S flywheels. A flywheel that has been converted from a taper roller bearing style to a flat roller bearing style may be up to the demands of low performance use, but testing at S&S has concluded that using the present style flat roller bearing on both the sprocket side and pinion side of the flywheel produces a flywheel assembly that not have enough side loading capacity in high horsepower applications. For this reason S&S will not honor any warranty claims relating to sprocket shaft bearing failures when S&S Twin Cam flywheels are used in 2003–up cases.

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