Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > A couple of engine questions.

[DC]

I have a couple of questions to ask with regards to my 748 engine.

The first one,

Is it worth going from the standard engine breather to a new shiny bling one? Is there any benefit in doing this?

I have just taken my one of to look at. I see that it works/resembles a reed valve. I see no signs of my one being at fault but I do have rather a lot of oil residue building up on the rear of the engine cases!!! Perhaps a STM for example would cure this??

Second question,

I have a clutch seal that appears to be leaking oil from behind the clutch. If I were to put another seal in, would I have to removed the engine case in order to do this or can it be pushed in from the external side of the case? I appreciate that I will have to remove the whole clutch.

I look forward to any replys/hints from the engine tinkerers.

Ta,

DC.

[Shazaam!]

The only reasons to replace the breather unit on the crankcase ventilation system is because it's leaking or you're getting excessive oil into the airbox (or you just want to dress-up your bike.)

The stock set-up is the best. The STM reedless breather unit is used only as part of a high compression Corsa set-up to deal with additional blow-by. Here's why ...

Blow-By

Piston rings act as a seal between the high pressure created in an engine’s combustion chamber and the lower pressure in the crankcase. Blow-by occurs as the rings become worn - or fail to seal properly when new - and they allow a small fraction of combustion gases to leak into the crankcase.

The consequences is accelerated contamination of the engine oil, as well as excessive release of hydrocarbons to the atmosphere - unless a crankcase ventilation system is used to route the gases back to the engine intake to be burned.

On Ducati engines, excessive blow-by can cause unusually-large amounts of entrained engine oil to be forced through the crankcase ventilation system and into the airbox. It’s not unusual however, to occasionally see a light deposit of oil in a Ducati airbox.

A small number of Ducati 998's, maybe one percent, have been reported to build up so much crankcase pressure at high revs that excessive entrained oil is forced/sucked into the airbox through the crankcase ventilation system, resulting in excessive oil consumption.

Blow-by occurs in all engines to varying degrees as they wear, but when it becomes excessive, an engine rebuild with new piston rings is in order.


Crankcase Ventilation

Crankcase ventilation is used for three reasons:

It reduces crankcase pressures to nearly atmospheric pressure in order to avoid oil leaks from seals and gaskets.

It reduces crankcase pressures at the bottom of the pistons to provide an increase in the differential pressure across the piston compression rings, and consequently provide an increase of torque and horsepower. A larger differential pressure across the piston oil rings also aids in control of oil consumption.

It reduces pumping losses. In a running engine, the size and shape of the crankcase boundary changes with the movement of the pistons. Ventilating the crankcase reduces parasitic horsepower losses involved in compressing and moving this air volume about, so net power output is increased.

The larger the crankcase volume, the less-compressed the gases it contains become, so the lower the losses. If you vent directly to the atmosphere - through a sufficiently large vent hole - the crankcase can’t attain positive pressure, even at the highest engine rpm. Further, if you create a vacuum in a crankcase, the effect on pressures is the same as increasing the crankcase volume.

It’s interesting to note that in the automobile performance world that there have been performance gains using crankcase ventilation systems that create a vacuum in the crankcase using pumps and extractors.

Ventilation Systems

The simplest way to ventilate the crankcase is to create crankcase openings to the atmosphere large enough to permit any combustion gases that have made it past the piston rings (called blow-by) to rush out. In this case, a filter element is needed on the opening to prevent dirt from entering the engine. This system was used on engines for many years until environmental laws required a modification that prevented direct release of this effluent to the outside air.



Gary Milcheck Photo

The design result of such laws is a positive crankcase ventilation (PCV) that uses the lower-than-atmospheric pressure that normally exists in the engine intake tract to extract the crankcase gases. These are then are burned along with the normal mixture of air and fuel. This system has a one-way valve that allows outward flow only, and a oil separator that acts like a maze for any entrained oil droplets that try to leave the crankcase. This (normally) small amount of oil then drains back into the crankcase instead of entering the engine intake.

On Ducati street bikes the one-way reed valve is located at the engine case opening. During certain conditions of high engine rpm and light load, more oil is entrained so the reed valves’ small drain holes have difficulty returning the additional oil to the sump quick enough. The oil separator can fill with oil and get sucked into the intake tract. Higher compression engines or worn piston rings have more blow-by, so the likelihood of oil being puked into the airbox is greater.

Because of this, and to gain about a two horsepower increase, race bikes that live at high-rpm use a somewhat different arrangement than the street bikes. A much larger oil separator box is used to effectively increase crankcase volume that reduces pressures and pumping losses.

To allow the oil to drain back more quickly, the reed valve with its small drain holes is removed from the crankcase location.



Gary Milcheck Photo

The corsa box is connected to the crankcase with a large diameter hose and located a greater distance away from the crankcase opening, under the tail. The one-way reed valve is now located at the airbox connection of the 3/4-inch vacuum line running to the oil separator. This design reduces the chances of contaminating your intake charge with oil. It also provides a large enclosed system that safely contains the oil if an engine blows.

Except for the larger oil separator volume, the advantages of the corsa system can be implemented in the stock system by hollowing-out the reed valve to remove the constriction on drainage. Alternatively, STM valveless breather connector can be used. Then use a one-way reed valve at the airbox connection. A 748RS remote breather valve works well here.

More conversion photo can be found here:

http://public.fotki.com/garymilcheck...se_cb_install/


http://www.ducatisportingclub.com/im...&NBreather.jpg

K&N Breather Conversions

The K&N breather is sold on the premise that venting to the infinite volume of the atmosphere - instead of the vacuum in the airbox - increases horsepower. It eliminates the one-way valve so it needs an air filter to prevent dirt from entering the crankcase under a negative crankcase pressure differential (pulse) when a piston is on an upstroke. Under positive crankcase pressures, the K&N device simply vents oil droplets direct to the filter medium - and beyond when it becomes saturated.

People usually buy them because they look trick mounted on the engine case. Therein lies its main disadvantage. Its location on the engine case is directly upstream of the rear tire. Since its installation also eliminates the oil separator, the increased chance of an oil mist being released onto the rear tire makes this location an unwise choice. Avoid overfilling the oil sump and wheelies with this arrangement.

Consequently, some owners have plumbed to the K&N element located in the tail where, at least, any effluent is away from the rear tire.


Here’s what the experts say ...

The following is a earlier post by BCM Ducati:

What is different about Ducati streetbike breathers in general is that the reed valve is mounted directly in the case. The breather box location and volume are good.

The reed valve location is good for emissions but not for engine power and crankcase breathing. What happens is that under certain conditions, under high rpm and light load, the oil doesn't run back because of the reed valve and it builds up in the tube above the reed.

The simplest solution is to hollow out the reed assembly and leave it internally open but still hitched to the volume bottle. This allows the volume of the breather bottle to perform its function and usually gives a slight horsepower increase also.

Then, use either a 748RS reed valve in the airbox at the end of the breather hose, OR, use a Ford diverter valve (in-line one way) just before the airbox.


The following is a earlier post by Jon Nichols:

We firmly believe the best system is the stock system. Let me expand on this. The only part worth replacing is the breather itself, and only if it is leaking or if you want to dress-up your bike. We see many Ducati's with the K&N filter attached to the breather hose. This is simply not a satisfactory replacement or alteration to replace the stock system. The stock system is less restrictive because there is more volume making it less restrictive.

Part of the problem with this modification is that the only efficient replacement systems made were made for race circumstances. This was accomplished by increasing the tank volume into which the engine pumps. On the early bikes, 851, 888, 955 in the 851/888 chassis Ducati had a very large carbon fiber tank which was connected to the engine crankcase without any breather. The tank was mounted in the tail section of the bike. This effectively doubled the crankcase volume and was responsible for an additional 3 to 5 HP at high RPMs.

This type of system is also available for the 748/916/996 chassis. This type of system is not available for Monsters or SS models, unfortunately. Therefore, the system that allows you the largest volume to pump into is the stock system. This system pumps into the airbox and has the added benefit of a collection/separation tank between the crankcase and the airbox.


(I got carried away)

[Edited on 4-3-2005 by Shazaam!]

well I guess thats DC sorted ...

[skidlids]

Yep another excellent post from the wizard overseas

[keefer]

just got myself one of those race crank case breathers (BLING)
good post Shaz
with regard to the oil seal you will need to remove the crank case cover,
not a hard job. apart from you need to remove all the clutch assembly, (still not that hard)
I have a new seal in the garage somewhere drop me a u2u

[DC]

Thanks keefer and Shazaam,

So as I understand it............. Because I have an uprated 748 engine that has been turned into an 853, with increased engine compression. ( new pistons, barrells and rings. Run in properly.) This could be the cause why I have quite a heavy oil smear/deposit behind the engine breather and on the rear engine case? This happens every time I return from a ride where I have been flat out or have covered several hundred miles in one hit?

My concern was as you have stated shazaam, that being oil getting onto my rear tyre. That and it looks unsightly/wrong.

I suppose I could add either another hole ( between the reeds) or enlarge the one in the reed valve assembly to quicken or aid the oil returning through it and back to the engine. Modifying the breather system to one like a RS is a thought although at this moment I would rather leave this for now. I have noticed that my engine does go through a bit of engine oil, not a huge amount. Perhaps there is an amount of blow by occuring.

When the engine breather is screwed back into place. Is there any sealant that is applied to the threads. I ask this because when I examined mine, I noticed that this looked like the case. Perhaps if it is, then this could be re applied as well? Just a thought.

Again, many thanks for the information.

DC.

[DC]

keefer,

If ya dont want it............send it my way. How much do ya want for it?

Also, is there an engine gasket behind the case or is it just sealant and how much for a clutch holding tool?

Thanks mate.

DC.

[DC]

I suppose,

I could clean out the internals of the standard engine breather, So it is hollow. Keep the same arrangement as stock and then put another engine breather on the tube at the other end inside the air box where it enters?

Or am I getting totaly confused now?

DC.

[Mr_S]

Maybe a daft question, but why have a reed valve at all?