Oil Consumption

[Baldini]

....was doing during lots of sustained 100mph sections on the way home....

 

Sustained high speed on older Guzzis they'd usually chuck oil out the crankcase breather. Dunno what the breather system is on the V11 (into frame?) but if it's not leaking, not burning it & your running at high revs for longish periods my guess is it's venting it ...

I check oil same as BigJ & as Belfast notes - i like to keep it topped up.

 

KB

[big J]

Standing straight up,although you're allowed to lean at any angle you like. Just let the dipstick dangle in the hole.That's how I do it anyway. You cant beat a good dangle.

[belfastguzzi]

as Belfast notes - i like to keep (it) topped up.

 

KB

54075[/snapback]

Hey! I said sshhhh! Don't mention that Baldi likes to keep well oiled...

[belfastguzzi]

You cant beat a good dangle.

54076[/snapback]

You may enjoy it, but of course, it's wrong.

 

You're meant to screw the thing in. Manual says so somewhere, I'm sure.

[big J]

Had a check,and you are of course completely right. Screw it all the way in. I have too much oil in my engine

[Baldini]

yeh - you screw it right in...

 

belfast - you checked your email?

 

KB

[belfastguzzi]

belfast - you checked your email?

 

KB

54083[/snapback]

 

baldini - you checked your email?

 

DB

[Baldini]

baldini - you checked your email?

 

yeh

 

KB

[Martin Barrett]

I did 1700 miles in all since thursday. I checked the oil prior to setting off, and topped up so was at mid point.

The light flickered on during a hill (very steep) start after 600 miles.

Then did it again a couple of hundred miles later the next day.

And today did it twice again on a pull away, but no hill required. So i picked up a bottle of oil. I decided as I didn't wish to pour most of it over the engine cases i would wait till the light came on again before attempting to add it. I will let you know how much I've used but I had to go to work so won't be topping up till at least tomorrow

[Martin Barrett]

Some where between 0.45 and 0.5 ltr to get back to mid point.

But put a bit more in for good measure.

[belfastguzzi]

get back to mid point.

54141[/snapback]

Don't you want it up to full?

[Martin Barrett]

Don't you want it up to full?

54147[/snapback]

 

There was the talk about finding it's own level.

 

Perhaps I should fill it up and check it often, to see if it finds a level.

 

She was worked very hard trying to keep Mr Baldini entertained on the way back and a little bit harder when he took the lead.

[belfastguzzi]

She was worked very hard trying to keep Mr Baldini entertained...and a little bit harder when he took the lead.

54150[/snapback]

More revelations!!!!!!!!!!!!

[Baldini]

Martin,

 

I've heard of oil starvation damaging engines when feed sucks air under hard acceleration. I think it's best filled to max mark. Oil light shouldn't be on at all with engine running - ever.

 

KB

[pete roper]

Funny, I was doing a lot of high speed work too, I did about 600 miles in all, but set off with the oil already at least down 1/3 from the top mark. If you are doing steady speeds oil surge uncovering the pickup shouldn't be a problem, it's acceleration.

 

On the alleged "damage"; its a pressure switch, and a momentary flicker is unlikely to matter if it isn't repeated too often. There would still be plenty of oil in the bearings.

 

54029[/snapback]

 

 

Hmmm, look, the oil pressure warning switch operates at some ridiculously low pressure, like 5 PSI or some such. It's effectively useless if it comes on while you're riding. Why?

 

First lets look at how plain bearings work.

 

The important thing with them is that the two surfaces of the journal and the bearing are not supposed to touch. To prevent this they need a constant supply of oil. thats CONSTANT, not INTERMITANT. Put very simply the shaft has to *float* on a film of oil that separates the two parts. If for any reason the supply is interupted, even briefly, then metal to metal contact will occur, this is known as 'boundary lubrication'.

 

Alas it's not quite that simple. Firstly the delivered oil pressure of approximately 50PSI is nowhere near enough to prevent boundary lubrication on its own. The pressures caused by the force of the expanding gas above the piston would easily overwhelm a paltry 50PSI. As the shaft spins though it creates a rolling pressure wavefront in the oil, conveniently at the point where maximum force is being applied to the bearing. This is known as the 'Hydro-dynamic Wedge' and at this point the actual pressure within the oil is muliplied by (From memory?) roughly a factor of ten! The thing is for a decent wedge to form the clearnce in the bearing has to be very exact. This is the reason why both the journal and the bearing have to be perfectly round. Any ovality will lead to parts of the bearings rotation where the clearance may be too great to allow proper formation of the wedge and boundary lubrication will occur.

 

Given that things are happening in your motor much faster than it's easy to imagine lets do a few simple sums.

 

At 6,000 RPM the main and big end bearings are going around 100 times a second. Your big-end journal is 44mm across so it's circumfirence id 44x Pi, which is 3.142. So the circumfirence is 138.25mm (Close enough.) Multiply that by 100 and you get 13825mm, divide by 1000 and you get 13.825 which is the number of metres per second the bearing is moving relative to the journal per second. 13.825M/Sec! Now imagine being towed behind a car at 13.825 M/Sec with your arse on the tarmac! not a nice thought is it!!!!! You'd want a bit of lubrication, my guess it would be self supplied and probably brown!!!!!!!

 

OK, so we've established that we need oil to keep bearing and journal apart. We've also established that we need a constant supply of oil at pressure to form a decent wedge and we also know that the parts have to have the correct clearance and they're moving bloody quick in relation to each other.

 

The second thing that the oil does is remove heat. The stresses imposed on the oil itself create a lot of internal friction between the oil molecules, you need a constant throughput of oil to take this heat away. Even the briefest of interuptions will cause rapid overheating. The bearings themselves are made out of something with a really quite low melting point, lead-antimony or some such, (There are reasons for this I won't go into here.). It doesn't take any time at all for this to melt when oil flow is interupted and when this happens the bearing will tend to 'pick-up' quite simply it welds itself to the journal and then rips free.

 

Once that has happened you're on a short and slippery slope to bearing failure as the bearing and journal are no longer going to have the correct clearance at that point so a wedge won't be able to form. this imposes greater stresses on the remaining parts of the bearing as well as usually allowing more rapid egress of oil thus reducing the pressure and therefore the strength of the remaining wedge. It's a viscious circle and wen it's all happening at 13.825 metres per second it tends to happen pretty damn quick!!!!!!!! That's when you hear the dreaded 'Dogga-Dogga' noise!!!!!!!!!

 

Being a mechanical, spring loaded, switch the oil pressure warning light, (which we've already established doesn't come on until the pressure is way too low.) takes time to come on. OK, not much time but we've already established that it doesn't take any real time for damage to occur. Add in the fact that it only comes on when the pressure is already so low that the oil can't protect the bearings properly, especially in high speed/high load situations and then add in the fraction of a second that it takes the globe of the light to start to incandese and then add in the further fact that you may not notice it immediately, (Especially if you're accelerating hard enough to expose the pick-up!) and I think it's fairly obvious that noticing a winking oil light is a pretty shitty thing!!!!!!!!

 

Why V11's are particularly prone to this and what I'd suggest are sensible solutions are something I can rabbit on about later but only if anyone is interested

 

Pete