I always had a little oil out the air cleaner, especially on long rides at high speed....anybody have any input?
In late ’05 I installed a set of gear drive cams in my ’02, 103” Road Glide. When planning the job, I looked at installing the S&S crankcase vent. I didn’t have a problem with air cleaner oil carryover, even with the old style back plate; sure the air cleaner would get oily over time, but I never had oil accumulating between the pushrod tubes below the air cleaner.
I was interested in the S&S vent because it looked as though it would reduce crankcase pressure and S&S claimed a small HP gain with the product; this thing looks like a well built quality piece.
I installed the S&S crankcase vent along with the gear drive cams, and afterwards my machine immediately started dripping oil from the air cleaner. The oil would accumulate between the pushrods below the air cleaner. I thought that maybe I could collect the oil; bottle it; create a label that said “Oil of Har-Lay” and sell it to the ladies. My wife killed that idea.
I removed the cam plate assembly, inspected the cam chest area and discovered something interesting; first a little background. In the Pre-Twin Cam engines a full-circle airflow had to be established in order to effectively return oil collecting in the pushrod tubes and rocker boxes, where it accumulates after lubricating the valve train. This full-circle airflow although necessary, did not exist prior to the mid 1982 production machines. It is worth mentioning at this point that this airflow concept is not necessary or even possible in the standard Twin Cam engine.
A “breather gear” valve is used on pre Twin Cam machines to control the flow of air and oil from the crankcase (flywheel area) to the gear-case cavity (cam-chest). An oil pickup in the gear-case cavity returns oil back to the oil tank. The breather gear opens on the piston down-stroke transferring oil and air to the gear-case cavity and closes on the piston upstroke, creating a negative pressure in the crankcase which is intended to draw the returning top end oil into the crankcase.
It’s funny to think about it now, but prior to mid-1981 the rocker box/pushrod tube area was not vented to anything. The pistons go up; the breather gear closes, creating a negative pressure in the crankcase and top end return passage, but little oil flows. The un-vented rocker boxes cause the oil flow to stop just like the Coca-Cola you are trying to suck out of an upturned bottle; the pressure drawing the oil down the return passage is matched by the negative pressure in the rocker boxes.
By the middle of 1981 production, HD realized there was a big issue with oil accumulating in the push rod tubes and rocker boxes. Their fix was to connect the bottom of the pushrod tubes to the base of the cylinders with fittings and hose. The idea was to apply a negative pressure to the bottom of the pushrod tubes on the upstroke of the pistons in order to evacuate the oil. The problem with that approach was that on the upstroke of the pistons, the same negative pressure was applied at both ends, the oil return hole in the bottom of the cylinder as well at the bottom of the push rod tubes. The “fix” actually made the problem worse to a small degree.
By the middle of the 1982 production, the answer became clear; connect the pushrod tubes to the gear-case (cam-chest) with a passage through the tappet blocks. This allows the positive gear-case pressure up the pushrod tubes, over the rocker boxes and down the top end oil return hole in each cylinder and finally into the negatively pressurized crankcase area; full-circle.
The result of this change was dramatic and the oil flowed freely. This concept can be best illustrated by comparing the EVO tappet blocks to the Shovel units. The modified Shovel tappet blocks each have two small holes, approximately 1/8” to accommodate the air flow up the pushrod tubes. The EVO tappet blocks both have large air chambers built into them to accommodate the moving air/oil.
Enter Twin Cam oiling system and the S&S reed style crankcase vent. The S&S vent performs a similar function to the old H-D breather gear. On the piston down-stroke air and some oil mist are transferred from the crankcase area to the cam-chest. On the piston upstroke the reeds close, creating a negative pressure in the crankcase. I can relate to this; kind of warms the heart. Well there is one small detail, the Twin Cam top end oil drain passages no longer run into the crankcase area. Twin Cam top end oil is routed down the cylinder and into the cam-chest area. The air movement that was essential for good oil control in the EVO and earlier machines is no longer necessary in the Twin Cam engine.
The S&S vent increases the cam-chest pressure as well as the pressure differential between the cam-chest and air cleaner. This is significant because Twin Cam top end oil no longer drains into the crankcase flywheel area. The pressure differential that worked so well in the pre Twin Cam engines now works to promote air movement from the cam-chest area up through both the pushrod tubes and top end return passages, out to the air cleaner. Enough air/oil movement in this direction can exceed capacity of the air/oil separators resulting in oil carryover.
I removed the S&S crankcase vent, put my machine, now 113” back together and the old girl runs clean and dry.
djkak
Author
Topic: Switched from Syn 3 to Amsoil, oil out the Air cleaner (Read 2572 times)