courtesy of Jens Lyck

Technical : The complex stuff - exciting but heavy reading, take your time.

Windage plates

Author: Pete Roper

OK, this will probably come in several installments, I'll try and answer questions as I go along but bear with me if I don't answer everything immediately.

Firstly it is important to realize that what goes on inside your engine is happening FAST. When the engine is spinning at 6000RPM the crank is whizzing round 100 times a second, the pistons are flashing up and down at the same rate and the valves are opening and closing at only half that speed. If you want to have a look at it so you can get some idea it is perfectly OK to take the rocker cover off your engine when it's warm and start it briefly, give the throttle a twist and see what the valvegear is doing. It'll spray a bit of oil out but you only need to do it for a second or two and it is quite impressive to see how fast everything is happening!

Now imagine what is happening inside the crankcase! Top engine shops have the test beds to run motors with the sump off. Oil is fed to the pump and then plumbed to the main delivery galleries and the engine can be run and the internals exposed and *frozen* with a strobe to examine the way oil is thrown off the crank and other parts of the motor. If one does this it is quite impressive to see. The crank looks like a whopping great 'Dough Hook' like you see at industrial type bakeries with great streamers of oil being thrown off and being dragged around by the crank. Now imagine what it must be like with the sump on and the oil level quite close to the crank.

The crank, any crank, is a big, irregularly shaped, piece of steel. As it spins the webs will create a big low pressure area behind themselves as they spin. Nature abhors a vacuum so the air/gas, and anything else suspended in it or close to it will try to rush into the low pressure area and try to fill it. Also, as the crank spins it will spin everything else in there too, air, oil vapor and droplets and the oil that the hurricane forces it creates will pick up from the surface of the oil in the sump.

This will have several effects. Obviously as the leading edge of the crank spins through this cloud of muck it is going to use energy pushing it out of the way and/or accelerating it up to crank speed. Likewise the low pressure area behind the trailing webs is going to be trying to slow the crank down, (Every action has an equal and opposite reaction, yes?) so it is in the interests of maximising power to make the air inside the case as thin as possible so less energy is used in this way. After all, any energy not used for this can be used to make the crank and therefore the wheels go round faster.

Secondly there is the matter of heat. Air is a really good insulator. While the oil is being whipped up into the air inside the case in droplet form or is bouncing about after being thrown off the crank it can only dump heat really by radiation. If, on the other hand it is more effectively de-aerated and returned quickly to the sump it can dump heat by conduction to the walls of the sump and thence radiate it away far more rapidly and efficiently. This gives the oil an easier time and helps ensure that parts that are cooled and lubricated by it are better protected.

Thirdly, there is the matter of crankcase pressurisation. Above the pistons, during the power stroke, there is a shirtload of pressure! Tens of atmospheres of pressure! While the piston rings do a pretty good job, especially with Nicasil bores, of keeping this pressure above the piston so it can be forced down the bore there is always going to be a bit of leakage. When this is happening 50 times a second even this little bit of leakage is going to ensure that the pressure inside the crankcase is always going to be higher than the pressure outside the crankcase which is atmospheric-ambient. There is also the pumping action of the pistons and leakage past the exhaust valve which add to the pressure to a greater or lesser extent during the cycle of the engine but effectively the pressure inside the case is always positive and this has to be relieved by being vented, eventually to atmosphere or in the case of most motors into the airbox. Why into the airbox? Because as the gas is vented from the crankcase it will carry oil as vapor and droplets which is then attempted to be separated by some system, either a collector box or in the case of the later bikes by using the frame as a plenum chamber in which it can condense out and be returned to the motor but a small amount of vapor will remain in suspension and by re-breathing it through the airbox and thence the combustion process it keeps the eco-fascists happy. The issue is how much oil is vented out with the excess pressure. The more oil there is in suspension in the air the harder it is for the condensing and return system to cope so it is in the interests of better oiling and return to minimise this.

OK, so what is a windage tray and what is it's function in a Guzzi motor?

Essentially the plates I use are simply that. A plate that separates the main part of the crankcase where all the action is from the sump where the oil is. In very high performance applications windage trays may have scrapers that actually drag oil off the crank webs as they spin, usually in the form of knife-edge weirs that run within a few thou of the webs, and fine mesh screens within the case to strain out oil droplets and encourage them to return quickly to the sump. These will be in addition to the plate itself that sits just above the level of the oil.

The plates I built were an adaptation of the plate we bought for the racer. This was made of very thin, (1mm.) aluminium and in that format it was very prone to stress fractures. For road applications this wasn't a particularly smart idea so I got them cut from 2mm stainless. Heavy as death, but they aren't gunna fracture!

Obviously there have to be holes in the plate to allow the oil to drain back to the sump. On the first run of plates I did there was an orifice in the plate above where the oil filter sits and the pressure relief valve, along with a pattern of holes away from the crank in such a position that the windage from the crank would push oil that had drained from the walls of the case of been thrown and settled on the plate would be pushed towards them. To be honest I think it can be done better, especially if there is no oil filter in the sump with the potential to foul the plate. While the oil level will only just come to the top of the filter, which with the early filters sits just below the level of the plate, it does mean that there is this expansive hole in the plate that the crank can still pick up oil from. For models with an ‘Outsider' type oil filter I see no reason to have this hole and would think that probably the better design would be to have a plate with no large hole but a series of slots around the edge and a thinner slot in the middle and it is this that I'm going to prototype and install on my SP or Convert as a testbed when I have the time, money and opportunity!

The whole purpose is to encourage the oil out of suspension in the air within the crankcase. Yes, it's flung off the crank at a fair old pace and will tnd to bounce and splatter off the crankcase walls and the plate itself, but at least it won't be splashing straight into the oil in the sump and aerating it and throwing still more of it into the air in the case. Once it has hit the walls or the plate surface tension will encourage it to stay there and simply drain back to the sump. I know this works because the problem with the racer pumping out quantities of oil when pressed hard was completely eradicated once we had a plate fitted!

Allowing the oil to drain onto the plate and thence through holes in it into the sump also helps ensure that the oil in the sump is less aerated. This is a good thing as you really don't want your oil pump trying to pump an oily foam! Not only is oily foam not a particularly good lubricant or coolant it is also a damn sight harder for the pump to pump it efficiently. Ensuring good separation and de-aeration pays other dividends as well, as previously mentioned it enables the oil to cool easier by conduction.

Another benefit which will be of particular interest to owners of ‘Broad Sump', post Sport Corsa, Centauro models is that the plate will also act as a baffle under hard acceleration. It has been found, certainly with hard-used V11's, that under hard acceleration or wheelieing it is sometimes noticeable that the oil pressure warning light will flicker. Believe me, this is BAD S#IT. The switch operates at some ridiculously low pressure and for it to come on there has to have been bugger all oil going through the pump for a while, (By ‘a while' I'm talking in terms of very short periods of time but remember, everything is happening ‘very' fast in there!) and if the switch has time to close after pressure has been lost then the mains and big ends will have been in a boundary lubrication situation for a good many revolutions! I don't care how many people tell me “Oh, my V11 does that quite often and it hasn't done it any harm.” Believe me, it's doing it harm. It may not kill it at once but it will be the ‘Death of a thousand cuts' only it won't take thousands of occurrences, probably only singles or at most tens of them. The most likely cause of this is the fact that the ‘Broad Sump' bikes have the oil pick-up at the front of the crankcase/sump. When the machine is accelerated hard or wheelied the oil will surge towards the back of the sump, away from the pick-up. If this is extreme enough then the pickup will be exposed. Exposed pick-up = no oil to pump. No oil to pump = no oil to bearings. No oil to bearings = ‘Dogga-Dogga' noise! So I think it would be fair to say that there are obvious advantages to fitting some sort of windage tray to the ‘Broad Sump' models, if only to help prevent this starvation problem. Now though, lets look at some of the issues with building a plate for this application.

Firstly let me say that I'm NOT that familiar with the internals of the new design. I've only had one broad sump off and that was on a Sport Corsa many moons ago so all I've got to go on are the pics in my V11 manual, usually because the filter can be changed without removing the sump via the stupid, hard to remove plate, the sump doesn't need to come off after the first oil change. (And I'll bet most dealers don't even remove it them, even though the service specs call for it!). However the crankcase is essentially the same as earlier models but it has a bolted on flange beneath it, screwed on internally rather than externally, and it is to this that both the sump and the plumbing for the oil cooler thermostat and the oil filter mount are bolted. Beneath this is the sump plate itself which is attatched by external screws. I guess, but I'm not sure that the reason the Broad sump was designed was that it has a lower profile than the earlier sumps and this allows the motor to be dropped a bit, lowering the machine's centre of mass. I DON'T know if the capacity of the sump is still the same but I'd guess it probably is, (give or take a few cc's!) given that it is wider but shallower. The location of the filter and plumbing and where the pressure relief valve, (Built into the thermostat/filter mount.) protrudes woill be the governing factors on the design of the plate. The plate itself will still sit, as do the plates for earlier bikes, immediately under the crankcase and above the flange/spacer. Holes will have to be made for a.) anything else that protrudes above the base line of the crankcase from the sump/flange area and b.) to allow oil to return to the sump. It is important tor remember that the oil level must sit just below the plate otherwise it is purposeless as oil above it will still be able to be picked up and flung around by windage.

If the Moto Special sump is used the whole oil cooler/thermostat and flange will be discarded (but an earlier type oil pressure relief valve has to be fitted to that sump, don't forget.) but the plate design will be dead simple as all it needs is holes or slots cutting in it to allow for oil return. While the starvation problems associated with the ‘Broad Sump' will be reduced, if not eradicated, by the MS sump the other benefits of reduced frictional losses, (Probably very small.) better cooling and the prevention of windage and surge will still be applicable. I know that Paul has a deep sump on his six speed Daytona but I'm not sure whether or not there might be ground clearance problems on a V11 due to the greater depth of the MS sump. Best idea would be to see if anyone at V11.Com already has one of these sumps and then if they have no problems start on designing a plate.

I've probably missed a whole load of stuff but I hope that is helpful and informative.