Well we are starting to get to the bottom of the '21/'22 RSV4 oil burning issue, at least two of the gross offenders appear to be missing the valve guide seals from the factory build, another victim of COVID?

What are your thoughts Hub?

Comparison of the valves in two cylinders in the same engine after about 3000 miles:

* Last updated by: Kruz on 7/21/2023 @ 7:12 AM *

For sure a factory fuckup. I'd call the dealer and show those pictures. That means it's a blatant QC problem at the factory, or engine supplier. Unless they don't use seals, it's still bored out to much. They should have a dial indicator, springs off, then move the valve in the guide and note the deflection reading. Look in any factor shop manual you have and see the breakout number for guides. Should be close numbers, basically.

No joy at the dealer level, then it's more a factory call. Have a district rep come out view the photos. Still no joy and they wipe their hands, I think you can get them on a 50,000 mile emission blip. So technically it's an emissions problem. Don't know if that too applies to bikes? I think I read long ago it was for cars.

Factory complies, it goes down two ways. One will be your out of warranty so it's labor to then, you pay for parts. Two is a full repair for free. If anything you're out a set of exhaust crush gaskets, head gasket and guide seals.

My goto decoking is a mix of vinegar and hydrogen peroxide, dip the valves as high as the carbon build. Wait a full day, they should wipe off with a paper towel, if not, soak longer.

Good luck.

I believe the RSV4 uses the green Viton stem seals but it appears they were left out by either Guido or Marco when they were assembling these engines.

So much for quality control during Covid.

That is not my engine, the photos are of a '22 RSV4 that was burning about 2 liters of oil per 1000 miles, Piaggio denied warranty saying it is "normal" oil consumption ...lol. What planet are they from anyway?

The owner is having to fix it on his own dime.

I am doing an oil burn study on mine now, approaching 2000 miles since the 600 mile first oil change and have added 600 ml oil so far, will wrap it up in 200 more miles, top it off and see what I have.

Let's say I have to add another 200 ml to bring it up to the full mark. That would be 800 ml in 2000 miles or 400 ml per 1000 miles.

Not enough to get a warranty repair by Aprilia I'm afraid. Someone said to set the engine braking to highest level (3) to try and seat the rings, I have it on minimum (1) now.

One of the experienced Aprilia engine builders says he likes the stem seals a little on the loose side as they allow more oil to lube the valve guides and the guides last longer. So a bit of a trade off there.

* Last updated by: Kruz on 7/21/2023 @ 3:46 PM *

I call BS. With ex being 0.0035". In at 0.0012"... that's the tight side. 0.014" ex and in 0.012" are at their serviceable limits. I showed they can live and be lubed at to valve bore clearances.

That's a pretty sloppy gap [S/L] to claim warranty. Doubt it's even that close. Meaning, I'm using a high performance head like the 14's production numbers to sort of match the ape's guide clearances.

So that means blueprint is even wider or in the middle of the high and low clearances that are within spec. I called out the low spec it can still live in. No way do I want loose guides to have the oil sucked out if it on intake stroke.

Remember, vac is like E, finding the shortest path and that is sucking oil out the loose guide or intake side. Poor ring seal will push oil up the chamber to burn. So you have two bleeders depleting the oil.

Once again, Hub has it .....

Huberator, it is long understood that aggressive engine braking is useful in the early seating of rings during the break in period,why?

My thoughts on the subject are that there is high manifold vacuum during engine braking (throttle valve nearly closed) on the intake stroke so that gas pressure above the piston is low (high suction) while the pressure below the piston is subject to crankcase pressure which is above atmospheric, thus there is high differential pressure applied to the rings which forces them out against the cylinder walls and into intimate contact.

Of course my analysis could be all wrong.....

What sayest the Great Hubinator?

* Last updated by: Kruz on 7/23/2023 @ 8:33 PM *

Correct Kruz. But the crankcase is not a closed chamber like the cylinder. It remains neutral as the rings bleed down into the crankcase. The venting keeps any pressure from building. So that's still 14.7 psi at the close of the intake valve, 14.7 at the crankcase. Nature is just pulling in more air faster. Still reverts to 0 pressure on the close. Nature returns to neutral if not lightening fast. She's Marge in charge. Sucks the chrome off the bumper only Large Marge can do.

This crankcase to the intake air box is a balancing effect. Old 1950's race trick if I recall? Not an emission plug up per say. So crankcase vac having an effect, not much. So upon full lift, it still says compression stroke coming: gas or no gas.

Ring pressure still happens on lift going thru the strokes. Nature reverts back to 760mmHg every 4th stroke. Lift on break-in probably means a cooling cycle. Like turning the gas off on boiling water. No matter how you look at it, the water is cooling off the instant the BTU's stopped.

That's my take on it, Kruz. I could be out of left field on the cooling effect, but not the 1 atm. That's why book says something like, 'lose the intake pressure sensor, we set Pa 760mmHg to calc as backup.'

OK Hub, I'll buy that, my thoughts were that crankcase pressure is slightly higher than atmospheric going back to my aircraft engine days.

There, the crankcase is vented through a crankcase breather and an inlne air/oil separator and then overboard similar to watt we do on motorcycles but as I recall the engine mfg gave specific crankcase pressure limits that were slightly above atmospheric, not a lot but just a slight amount.

In any case the differential pressure across the piston rings during engine braking is watt seats the rings against the bore I hope we can agree.

* Last updated by: Kruz on 7/24/2023 @ 1:58 PM *

Yep, I'm not going senile Hub, crankcase pressure runs slightly above atmospheric but it's so small an amount it is measured in inches H2O. We used to use an airspeed indicator plumbed into the crankcase vent as it is very sensitive to even small pressure differentials.

John

https://www.csobeech.com/files/TCM-SB-M89-9.pdf

* Last updated by: Kruz on 7/24/2023 @ 3:16 PM *

No, I'm the one with the senior moments, Kruz. Watching the -0 vac on the downhill, it creates a vacuum at the cylinder chamber side. That could pull air at the crankcase on lift. But again, has to pass thru the ring end gaps.

So the slowing down of engine breaking does on lift, it's not as strong of a push-out of the rings, right? When it fires, that's the push-out to the filing down of the high spots. Top ring takes the most beating. Second ring does double duty by being a second compression ring and is an oil scraper ring. Oil control ring is the dump station.

I remember the first beater had 8 pounds [cold] off of the peak compression number in the book. Next plug change I'll see what the oil tight reads.

Right Hub, which is why I'm confused why engine braking is supposedly so effective in ring seating? The big push seems to occur on the power stroke where combustion chamber gas pressure is very high resulting in high pressure on the rings outward against the cylinder walls. I have not been able to find anything on this subject on the internet which is able to explain engine brakings role other than generic statements that engine braking is effective to seat the rings, blah blah..... with no theory to back it up.

No one can answer this either. Where is the ring under compression?
1. Floats in the middle of the groove under compression.
2. Is pushed to the top of the ring groove going down.
4. Is cocked at an angle. The angled cock is the piston skirt does not go down like a floating ring where the piston is square to the bore. But the piston clearance is a the thrust of the one skirt side, thus the cocking of the ring.

Couldn't corner an engine builder to say which.

Where I read an old automotive encyclopedia mentions floats in the groove.
Where I asked one engine builder that told me it cocks the ring.

The wonders of the normally aspirated.

He didn't explain lift, Kruz, but more I'm thinking the rubbing or wear-in-friction 'under load' and 'under lift.' Kind of my: rub both hands together fast... Which palm stayed cold? So I can see the lift to load is the blending-in of both sides as far as creating a better seal.

The thing about high spots and causing a local hotspot, it could cause a coating or glaze, where the crosshatch lines are not shaved down to seal, but are like folded over from hard loads. Where the folding over acts as an extended trough and oil rides on top of the curve or folding over.

My guess would be not the rings causing the oil loss, but the cylinder walls having a glaze and/or hot spots, for it is impossible to have 3 rings not controlling that much oil loss. Has to be the oil clinging to the wall.

Once again Hub you can talk the tech like no one else, I think you just nailed it.....

Thanks, Kruz.

.......