FJR Oil Level Myth Busting - Yamaha FJR Forum : Yamaha FJR Owners Forums
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post #1 of 23 (permalink) Old 01-12-2021, 04:50 PM Thread Starter
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FJR Oil Level Myth Busting

We've all read threads about engine oil level, in particular concerns about overfilling, and there have been some threads about oil level lights coming on. So, I have done some measurements on a set of engine cases I have here and calculations on oil volume.
My measurements are OK but volume calculations should be taken as approximate. As you read on, you'll find that less of a concern.


Sight glass checks... first of all if done by the book, "a few minutes", oil viscosity, temperature, etc. all come into play and results can be quite variable. Use a stopwatch if you want to be reasonably consistent... however, I will leave it up to you to determine where the sight glass level is if you have followed the manual, filled your oil with the 4.0 L/4.23 US Qts, and have changed the filter (with the OEM short one).


I can only offer you that I usually put in 4.2 L with a long filter change (technically an overfill by the book). I find my oil level at the top mark in the sight glass, and when cold, goes over the top of the sight glass. I would prefer all my fluids to be at their max value, just me. Observation is, when the engine is started, the oil level drops to the bottom of the sight glass, maybe below, as the engine immediately circulates the oil. YMMV, which is OK.


Others have found that when they fill with a gallon jug (3.8 L), they get an oil level light when starting/running from cold, which may go away once the oil warms up and expands... technically an underfill situation. YMMV.


The concern when there is an overfill, how much is too much and we're basically concerned about oil level so high it contacts the counterweights of the crankshaft, which can cause foaming of the oil, loss of pressure, etc. Naturally, we don't want that.


The pics I've taken are looking at the lower engine case from the sight glass/oil filter end. The first photo is with crankshaft in place, and I marked a red line where the bottom of the counterweight is. I measured this to be 36mm above the Top of the sight glass. I roughly measured the surface area of oil would be 90 square inches. Basically, 125 cu. in. of oil in that 36mm depth, 2.05 L/2.16 US qts. This would be the amount of overfill required to have any contact with the crankshaft, bike on centerstand. On the sidestand, likely half that overfill, maybe less.... but keep in mind the minute you start the engine, the oil level drops an inch.... roughly speaking. I do not know the lean angle on the centerstand, or I could estimate much closer.... the excess oil would run into the stator housing first..... so, let's not speculate too much, again, it matters little really.


A further calculation, the distance between the sight glass marks is 14mm/0.4" approx., and 90 square inches calculates out to approx. 2/3 a litre or quart, or if you like a healthy half. You can decide next time you fill with oil and see what the difference is between being at the lower mark or the top one.


So any of you concerned about overfilled by half a quart should simply relax and not get all concerned about draining out a few ounces......






Pic with crankshaft in, taken so you can see the red line I marked:






Pic taken with crankshaft removed, taken as to be in line with the sight glass as best I could. Well, you get the idea, mark is 36mm higher than top of sight glass:









This pic with engine case flipped over, in the middle is the sight glass opening, and red mark shown previously is on the outboard face of the casting, at the level of the machined boss/bored hole just south of it.



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post #2 of 23 (permalink) Old 01-12-2021, 06:42 PM
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Hey Ray, good work; it will ease some minds. Could you please reproduce your examination on a running engine at both an idle and at 7,500 RPM?
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post #3 of 23 (permalink) Old 01-12-2021, 07:13 PM Thread Starter
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The ongoing investigations in the interest of science has prevented me from reassembling that engine and firing it up..... you'll have to be patient for a while longer.....
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post #4 of 23 (permalink) Old 01-12-2021, 10:13 PM
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If anyone can do it you can, Ray.
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post #5 of 23 (permalink) Old 01-12-2021, 11:31 PM
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What is the height of that pc of 2X4 so I can get my oil level right next time I change it ...............
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post #6 of 23 (permalink) Old 01-13-2021, 01:03 AM
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Sorry to burst your bubble but the crank does not have to contact the oil to create windage problems. The airspace between the level of the oil and the crank is critical.

The open space volume needs to be large enough to accommodate the volume of suspended oil droplets slung off the crank as the oil bleeds off. A large enough space will allow the oil to properly condense and fall into the oil sump. Too little space and the oil will saturated the air space between the crank and the surface of the oil leading to windage losses, high crankcase pressure, oil in the venting system, pumping losses as the underside of a piston fights against crankcase pressure on the down stroke, and foamy oil cavitating in the oil pump gears.

High revving engine are particularly susceptible to this.

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post #7 of 23 (permalink) Old 01-13-2021, 01:28 AM
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Quote:
Originally Posted by mobilemike View Post
High revving engine are particularly susceptible to this.

Which is why racers sometimes keep their oil levels at the bottom of the high/low range.... (I'm sure I read that on the interweb somewhere).


Nice work, Ray! Another interesting post. Having a set of crankcases laying around is proving to be quite handy for you .
Designers learned a long time ago to keep spinning parts away from the oil and we've come a long way since the dipper style connecting rods on Model As etc.
For my own FJR, I'm in the "just over 4 qts and leave it" camp after an overnight drain.
This topic also reminds me of when I bought a '95 Honda ST1100 years ago. Got it home and found it a FULL 1.5 Quarts overfilled above the sight window... sheesh!!!
No telling how long it had been that way but no apparent issues or leaks but I was happy to drain it down the correct level.
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post #8 of 23 (permalink) Old 01-13-2021, 08:41 AM Thread Starter
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Well, the whole point is certainly a few ounces overfill won't hurt you.
Windage is an issue of course, and I'm sure we'd all like a look if the engine cases were made of something transparent. High lean angles in a race situation might be interesting to look at.

Wild thought, if the oil is at the top of the sight glass when cold and when you start it up, the level drops to the bottom of the sight glass, that's about 2 quarts that got pumped into all the places it needs to go.
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post #9 of 23 (permalink) Old 01-13-2021, 10:23 AM
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This is good research for those anal retentive types that count the number of drops of oil that goes into their engines at each oil change

and reassuring for those of us that dump 4 qts and 7 oz in (like the manual says) and not check it again until the next oil change lol

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post #10 of 23 (permalink) Old 01-13-2021, 11:43 AM
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Quote:
Originally Posted by the Ferret View Post
This is good research for those anal retentive types that count the number of drops of oil that goes into their engines at each oil change

and reassuring for those of us that dump 4 qts and 7 oz in (like the manual says) and not check it again until the next oil change lol
I do that too and have been criticized for measuring the oil in and being anal retentive. Meanwhile, the folks doing the criticizing dump a gallon in, start it, let it settle down and check for leaks, then dribble oil in 'til it's on the top line. I'm not seeing the difference, but as long as we're all happy, that's a win.
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