what would cause my hd evo engine to build excessive crankcase pressure
"All Harleys leak."
I hear this often. Information technology'south unremarkably followed by someone spitting, hitching up their drawers, and looking smugly at their ain (non-Harley) motorcycle. Unless information technology's someone I really like, I usually just say, "Yup, they sure exercise." If someone thinks Harley products are poorly made leaking pieces of shit, I'grand not going to try to convince 'em they ain't. I don't ain a dealership and I don't demand to sell bikes. For those whose opinions I value, though, I mostly take a minute to agree with them so bespeak out why they leak.
There's some truth in the sometime adage, "I get worried when it stops leaking — then I'thousand out of oil!"
Not all leaks are skillful, simply many are not but adequate, but even intentional. Many people are non aware that there's a fair amount of drippy-ness planned into a properly functioning Harley-Davidson.
Let's rewind to before days. Until 1936 (for the overhead-valve bikes) and 1937 (for the side-valves), Harley engines did not have provisions to circulate the oil through the engine more than one time. This mode of lubrication organization is known today as "full loss." Oil fabricated its way through the engine and then was ejected onto the roadway. This was not exclusive to H-D. It was mutual for stationary and agronomical engines at the fourth dimension to miscarry oil direct onto the ground. This arrangement became impractical as engines avant-garde, but for the time, it was adequate practice. In fact, modern two-strokes are still total-loss with regard to the lubricating oil.
Oil systems became the recirculating blazon in the 1930s. This means that a scavenging pump was added to capture the oil after information technology completed its excursion through the engine, returning information technology to the oil tank. Despite the fact the oil recirculated, quite a fleck yet hit the ground, mostly by design. Engines need to "breathe" in order to equalize crankcase pressure with atmospheric pressure level. (If you don't understand this, hold tight — we're going to talk over information technology in but a bit.) Harley engineers knew this, and understood that there must exist at least ane point at which pressure level could exit the arrangement. Rather than try to fight a losing battle and fight the necessary leak, they did just the opposite — they immune users to increase the severity of the leak. Here'south why.
From the kickoff days of the recirculating oil system, a small spiral controlled the catamenia of boosted oil routed to the breather tube. (For example, on Large Twins, the screw was located on the cam cover.) Depending on the twelvemonth, either shims or a locknut were used to change the top of the screw, decision-making the flow of oil direct to the main chain. This organization allowed for a dry clutch, but permitted the primary drive chain to take a steady flow of oil being supplied to it. The tin-type primaries (chain cases) had a hole at the bottom to expel oil that had lubricated the concatenation and was flung around, to prevent information technology from building up. This pattern ran all the way through the Panhead years (late 1940s to mid 1960s).
Well lubricated roller chains generally offer very long service life, so at the expense of a few pennies' worth of oil, the bulldoze chains had long, healthy careers. The kiss of death for a primary chain is to run dry. The oldtimers who are withal with us volition tell you that a bicycle was properly adjusted if information technology left a spot the size of a 50-cent piece when parked overnight. (I personally run mine a piddling juicier than that. Oil's cheap. Principal chains are not.) To take this a footstep further, Shovelheads really had two chain oilers — i for the primary chain, also as an additional one for the final bulldoze chain. The primary oiling inverse a fleck. The scavenge pump was now continued to the primary. This had the desirable do good of keeping the principal from dripping onto the ground, merely the undesirable benefit of sending oil impregnated with friction fabric (clutch fibers) back into the engine.
I promised I'd get to crankcase force per unit area, and at present we will. If yous can imagine the big pistons moving upward and down in a Harley, squeezing air and fuel at around 100 psi, recollect about the force per unit area on the other side of the piston rings. It rises and drops dramatically, and blowby - frazzle gases which have blown by the rings - also serve to pressurize the expanse. The breather system helps to equalize the pressure level between the atmosphere and the interior of the engine. It besides exploits the regular vacuum that occurs to help return oil to the oil bag. Harleys tend to have greater pressure differentials than other bikes because they have exceptionally large pistons, and there aren't likewise many of them. (On smaller displacement multi-cylinder bikes, animate issues aren't nearly equally prevalent.)
Every bit nosotros discussed earlier, Knuckles and Pans vented to that chain area. Similar the total-loss oiling system, this was in keeping with the applied science of the times. Automobiles used a similar organization, chosen the road draft tube. Effectively, it was an open piping that ran from the engine down to the road surface, performing much the same role without the pleasant byproduct of automatically performing a necessary lubrication task. Harley was actually ahead of the blueprint curve with their oilers.
In the Shovelhead era, environmental reality set in. Releasing burnt hydrocarbons into the air contributes to smog and air pollution. The solution? The breather lines were divorced from the chain oilers. Rather than vent them to the open temper, breathers were routed to the air cleaner. From in that location, the oily mist they generated could be sucked back into the engine'due south intake tract with the incoming air-and-fuel charge. This besides had the benefit of filtering the air the crankcase breather took in as well, keeping oil cleaner.
Unburnt hydrocarbons pollute, too. The chain oilers disappeared in the the Evolution era. The main chain cases were sealed, eliminating the source of another oil leak. Rather than drip oil, the clutches were inverse to a wet design to help to cool the stator, which had been relocated to the chief. Rear bulldoze chains gave way to belts, so a rear chain oiler also became unnecessary, but the breather-routed-to-the-air-cleaner lived on.
This same system is in utilise today, which is why you lot'll see oily air cleaners on an engine that's been run hot and hard — the engine is "breathing" into the air cleaner. When the housing loads upwardly with too much oil, droplets form which volition fall downward when the bike is still or spray backwards if it'south in motion. If yous come across a Harley lilliputian oil from the air cleaner — even a modern i — that'due south what they're engineered to exercise.
Many modern bikes from other manufacturers utilise an airbox buried deep within the bike, and the filter sits horizontally, not vertically equally on a Harley. Even if the wheel does breathe heavily, the airbox contains about of the mess. Harley air cleaners, hanging off the side of the bike, are considerably more than visible than their multi-cylinder counterparts, so any airbox oil that'southward found its way out is much more than noticeable.
Ane other leak that's likewise common on nigh Harleys is the dreaded wet-sump, when oil collects in the crankcase. Harleys are dry-sump bikes, pregnant the oil is stored remotely and pumped in. All older Harleys and some new ones locate the oil in a tank that is higher than the lesser of the engine cases. Liquid oil seeks to fall, and the only thing holding it in the oil tank is a minor check ball. Dirt and grit moving through the system, wearable and tear, weak spring pressure, and imperfections in the seat can allow the check ball to let oil slip by. (For those of you who have had a carb needle not mate properly to its seat, this is a very similar state of affairs.)
If the bike sits without running for any appreciable time period, the crankcases fill with oil that slips past. Upon startup, the scavenging pump gets overwhelmed. Thus, the oil blows out the crankcase breather or air cleaner in copious amounts. Information technology's totally normal — Bill Harley and Artie Davidson designed bikes that were going to be ridden, not parked for months at a prune.
It seems ludicrous in these days of $ten-a-quart oil to waste it, but given the price of parts and specialized labor, a small quantity of oil dribbling out of a bike made a lot of sense lxx years ago. These machines were designed to be used and used difficult in a country that did not still have an interstate highway arrangement. Whether it's crankcase pressure equalization, principal or final bulldoze chain maintenance, or the scavenge pump tirelessly working to clear the lesser end of a bike that hasn't been run in a flake, one thing is certain: Harleys leak.
As they're meant to.
Source: https://www.revzilla.com/common-tread/wtatwta-why-harleys-leak
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