Topic: 650 vomits oil with sustained high RPMs

[Nicklopic]

It seems my 650 isn’t a fan on sustained high RPMs and seems to spill oil out of the top end when riding “aggressively”
Is this an inherent thing or something more? I’m running just a breather filter off the nipple on the center rocker cover. It seems to spray/leak from there as well as the outer rocker covers and the breather. It almost seems like oil is just being sling hard at these points and getting past the seals. The top end was rebuilt about 2k miles ago, 1mm over pistons, head work and everything resealed. I do burn a little oil on decel from time to time and I did make a mistake gapping the rings where one, or one set was close to the top end of the service limit for stock sized pistons. I’m also using 10w40 Mobil1 4T.
I don’t generally beat on it often but lately I’ve been winding it out more and getting on it harder. Sustained like pulling above 7k rpm.
I’m thinking replaces the rocker cover seals again, and add an extra plate to act as a baffle for the center cover might do the trick? Maybe add a small catch can or something?

[Tracksnblades1]

My old 750F1 has the Honda type of a PVC crankcase separator.
Perhaps you could use something similar that could separate the oil and return it back to the crankcase.

Do you think it’s blow-by carry over or uncontrolled crankcase windage…?

[Nicklopic]

I want to believe it’s from splashing and oil slinging, it has done this once before the rebuild when my brother rang its neck pretending it was his cbr. Last night was just more than ever and I was on it more than ever for sustained times

[HondaMan]

Unseated piston rings and loose valve guides can both cause oil foaming, even with [fully] non-detergent oils. You might want to try breaking it in with non-synthetic oil first, as the rings will take a mighty long time to seat with synthetic oils. The symptoms you're describing sound a lot like ring blowby.

Also: what is the piston-to-bore clearance? It should be less than 0.0010" on this engine: I usually set them at 0.0008".

[Nicklopic]

I broke it in with regular dyno valvoline 10w40 and used that for about 1000 miles and 3 oil changes.
I do not know the piston clearances. The jugs and pistons were sent to Mike at JMR and the machinist he uses bored them and labeled the pistons and their respective hole for me. I didn’t ask any of the measurements. He also did my head as well.

Should I try going back to regular oil for a while and see if I can get the rings to seat better?

[Tracksnblades1]

I broke it in with regular dyno valvoline 10w40 and used that for about 1000 miles and 3 oil changes.
I do not know the piston clearances. The jugs and pistons were sent to Mike at JMR and the machinist he uses bored them and labeled the pistons and their respective hole for me. I didn’t ask any of the measurements. He also did my head as well.

Should I try going back to regular oil for a while and see if I can get the rings to seat better?

Do you know what rings you have on your 65mm pistons.
I’m sure your cylinders hone finish grit and crosshatch angle were correct.
  Chrome rings can be a witch when using really good oil..

You can make your own separator by place something in your breather line vertically and above your valve cover with a large volume area that allows the most and oil to fall out of the air stream. It will have a better chance when the air steam or sling velocity goes to near zero when it enters the larger volume area. Similar to what they’re using on modern engines without the filters in them..

Almost every 750 I’ve seen with a K&N type valve cover breather did the same. I had to experience it too for myself and immediately went back to what Honda installed on it.  Early K’s just ran it to the ground in front of the back tire.

[Nicklopic]

I don’t have any photos of the rings, they’re Cruzinimage pistons and their rings. I’m pretty sure they’re iron or something. There was no coatings on them. I found the picture of my stuff from my build thread. Cylinder 2s second ring is .022” instead of .017 like the rest were. Photo attached

I have a few idea on how I can combat it. Even just an extra plate between the rocker box and the cover to keep things from slinging right at it. I want to avoid a real catch can just because I don’t want to have to package/hide it

[HondaMan]

It seems that all of the oils you've mentioned contain detergents. By now, there's quite a bit of it spread thru the engine in the many places where the oil doesn't drain with a pull of the plug and draining the filter. My suspicion is that there's still enough detergent in there to make the foaming happen.

In the 500/550/650 crankcase there is much oil residing in the bottom when it runs (unlike the dry-sump 750's version) and the whizzing of the crank weights, rods, and tranny gears immersed in that oil whips it pretty hard. That's what makes the foam happen. From there it travels all thru the engine. It takes at least 2 oil changes without detergent (and filter both times) to remove the detergents.

Today's detergent-inclusive oils also have MUCH more detergent than the older oils of the 1970s. We used to experience weeping from the engine seals and gaskets back when that witnessed the use of detergent oils. Today the stuff just foams like dishwasher detergent in dishwater!

[Nicklopic]

What even should I be using at this point then? I’ve been trying to run quality synthetic stuff since it’s air cooled and gets toasty. I didn’t think aerating would be as big a thing

[fizzlebottom]

What even should I be using at this point then? I’ve been trying to run quality synthetic stuff since it’s air cooled and gets toasty. I didn’t think aerating would be as big a thing

Rotella T4 15w40 is what I've been running in mine for the last 12 years with no problems. Has right right JASO certification that we look for so it works for wet clutch applications.

[Tracksnblades1]

What even should I be using at this point then? I’ve been trying to run quality synthetic stuff since it’s air cooled and gets toasty. I didn’t think aerating would be as big a thing

Rotella T4 15w40 is what I've been running in mine for the last 12 years with no problems. Has right right JASO certification that we look for so it works for wet clutch applications.

https://pqia.org/shell-rotella-t4-sae-15w-40-heavy-duty-diesel-engine-oil/

Oil analysts for the Rotella Calcium and magnesium are known as detergents Barium was the older one..
Your Mobile 1 4T will have a similar calcium content…

Both are excellent oils…

[RAFster122s]

Good mineral oil, Belray EXL
Spectro is a very good oil, available in regular, blended, and full synthetic.

Testing your oil will tell you if the transmission is sheering the long chains in the oil that help it lubricate. Also generally will find out if you have metal in suspension and similar things.
If you can afford to go that route to determine the best oil change interval.

[Flyin900]

As a contrarian view have you checked the compression, or even better a leak down test to see where you're at there? You have enough miles on the motor now that it would be interesting to see if there is excessive blow by caused by ring leakage.

[Nicklopic]

I have no yet, I really should just to be certain the motor is healthy enough.
It would be nice to have the reassurance lol

[PeWe]

Have you ridden it in various speeds, accelerating, decelerating and rather high speed between with biker friends behind that can feel burnt oil if actual?

If not a smoker and oil is not disappering, no problems.

[Nicklopic]

I ride solo more often then not. I have noticed a little puff of smoke on decel from time
To time but I haven’t been able to go “yup it happens at x time and y rpm”
I’ve had a friend behind me mention he did see a Couple puffs of blue smoke here and there but it was again just sometimes he noticed

[PeWe]

If happen after decel only, valve guides with their seals can be the reason.
Deceleration followed by a little more throttle to let the smoke out. Easy to test by riding it on high rev, close throttle completely for a few sec, open throttle and see the smoke behind.

My CB750 K6 had huge oil consumption via the IN guides. (High lifting cam vs stock guides not sunken enough in head so valve keeper groove entered the seal).

No smoke visible behind. Non smoking oil ...
Maybe back then too rich needles in carbs helped to mix the oil.

Oil consumption must be seen on spark plugs.  (And oil level)
Piston crowns with a crusty black layer. Bore scope thru the plug hole might show the status.
There are cheap ones to be used with phones.

But oil thru the ventilation is the other way.
Use the long hose as Honda used from the very beginning.

Ventilation going back the foot pegs smells less then ventilation right under tank  when idling a got engine waiting for green light.