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Old 29th December 2015
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aswracing aswracing is offline
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Originally Posted by 69xlch5213 View Post
Thank you ASW: Was able to get a great deal on a new 883 5 speed so I was doing some break in miles to check for assembly problems from the factory and to see if it was basically sound when I look down after parking the bike and there is maybe an ounce of engine oil on the gear case. Called the Dealer as I figured the motor was about to blow and says *they all do that, very common*. This was at 500-1000 miles.
IMO the real problem is that the oil breather bolts are lower than the highest points oil reaches in the engine- this is just asking for trouble. So I remove the rocker boxes and inspect. Lots of casting flash- clean this up- reassemble- and it does it again though not so bad. Drips *less* but does put a lot of oil on the air-cleaner element. Since I was planning a performance build to 1200 with real good stuff I worked out a permanent fix.
Dyno tests are very good data collectors but they are very brief so I do not expect that you will get a crankcase overpressure in a short period of time but they seem to build pressure in continuous running at speed on open roads. In stop and go the pressure may return to normal. I think this because I blew a rocker cover gasket out on the highway on my Buell. I believe this had to be from internal pressure. I will not be riding around looking for oil pressure or crankcase pressure leaks and I full accept the HP results you have from the Dyno and thanks for posting them.
A pro HD racer told me there was no HP diff between single fire ignition and the old dual fire system and I believe that was correct also from the dyno but the engines run more smoothly on the road with SF in my view, idle batter and quit less. I think that crankcase overpressure/ air spring effects are cumulative but most races are very short so it is not an issue.
Thanks to Dudley Perkins HD for quickly replacing the rocker box gaskets.
So maybe I overdo things ;-). This is why I like using the top R box for future venting as oil liquids cannot rise that high and that will solve the biggest part of the problem. On the 5 speed solid mount engines I like to cut the excess metal from the cam case cover to get better access to the oil pump and it is easy to tap into the side of the case to the left of the rear exhaust cam. Then with plugged breather bolts, better replaced, your high flow air cleaner element no longer looks like one from an old truck.
ASW has me thinking that we need a volunteer to plug the venting and install a pressure gauge at a convenient place and see how high that goes after 2 hours at 85 mph.
You have some really different theories, and that's fine, and I sure like to think I keep an open mind and can still learn things. I think it would be terrific if you could gather some data to support your views and I'm certainly open to having my mind changed.

Let me just repost something I originally posted in early April 2002. You might find this interesting reading. It was a long time ago, sure, but as far as I know, the laws of physics remain the same

This page is to share some dyno testing of using the timing plug location for an additional crankcase vent.

First, a little background. In the stock configuration, the crankcase vents through a pair of "umbrella" valves, which are essentially check valves. There is no air inlet into the motor. As I understand it, the idea is that as the pistons come down the first time and the crankcase air is expelled, the air is forced out through the umbrella valves. But when the pistons go back up, the umbrella valves block the inflow of air, causing a slight vacuum in the crankcase. The next time the pistons come down, crankcase pressure will return to atmospheric. If no air is allowed into the motor, the crankcase will cycle between a vacuum (pistons up) and atmospheric (pistons down).

However, some air is actually allowed to enter, primarily in the form of blow-by that escapes the combustion chamber past the rings. Therefore, in the stock design, there is a small net outflow. The amount will vary with the condition of the motor.

Properly functioning umbrella valves therefore serve the purpose of significantly reducing the breather capacity requirement while also minimizing crankcase pressure. Excessive airflow & oil discharge through the breathers can be caused by malfunctioning umbrella valves that are allowing air into the motor.

For this test, an additional vent was added at the timing plug hole. No check valve was installed on this vent. Therefore, the crankcase is being allowed to pull in air as the pistons go up. This is fundamentally changes the engine's venting design.

Some people feel that allowing the engine to both inhale and exhale in this manner reduces crankcase pressure. Several people cite a "seat of the pants" improvement in performance. The purpose of this test was to determine if there actually is a performance improvement from this change to the venting system.

This is the fitting arrangement that was used. The first fitting is a 3/8" flare to 1/4" fpt fitting. The thread on the 3/8 flare side matches the thread in the timing plug hole. Attached to that fitting is a 1/4" mpt to 3/8" hose barb fitting. Two feet of 3/8" i.d. hose was attached here.

Here's a picture of the fitting and hose as installed on the bike.

And here's a picture of the bike on the dyno, a near stock 1999 M2.

Okay, on to the results. Lots and lots of dyno pulls were performed in each configuration, and the configuration was switched back and forth a few times. Dyno results are not 100% repeatable, and as such, I'll present a range of results for each configuration, as well as a comparison of the best pulls.

These are the 10 best pulls from the stock configuration.

These are the 10 best pulls from the timing plug vent configuration.

This is the best stock pull and the best timing plug vent pull. As you can see, the difference is within the repeatability of the measurement. If a person *had* to declare a winner, the results with the stock setup would seem to have a little edge, both in the "best" results and just looking at the average of the 10 best results. But I'd be careful doing that, you could be looking at normal variation.

Observations: I was surprised at how little air movement there was at the end of the hose. When a motor is started with nothing screwed into the timing plug, there's a massive inhalation and exhalation evident. But apparently, necking it down to a 3/8" hole and connecting 2 feet of hose adds a pretty significant restriction. Air flow was nowhere near what I expected. Unfortunately, getting a 7/16" or 1/2" hose into that area would be problematic, space is tight. Plus, a fitting with the correct thread and a 7/16" or 1/2" hole may not be available.

Another surprise was just how easy it was to plug the hose with my finger, and how it felt when I did. The pressure was not great.
In addition to the above, I also did a bunch of testing of the aftermarket breather check valves from Spyke and Hayden, and even did some experiments with vacuum pumps and the like. Did some magazine articles here and there at the time. The motor was remarkably insensitive to anything I did with the breathers. Like I said, the only thing I could get to show up on the dyno sheet at all was the removing of the blow-by from the intake tract.

I also did a bunch of single fire testing, but that's another subject.
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Last edited by aswracing; 29th December 2015 at 23:53..
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