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It's time to talk about XR's and their oil system


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After measuring the OEM relief valve spring rate (1.52lb/in for the record), and a number of other dimensions including how much the OEM spring is compressed during assembly, I ordered a number of standard springs that I figured would give me a ballpark at meeting a low enough force to allow air to purge, but still reliably close the check valve. Luckily I live very close to a number of spring manufacturers so I get them next day with standard shipping. I incrementally reduced spring force on the check valve until I could get the check valve to successfully crack open when the pump is "dry". I say dry in that it was completely cleared of oil, but an oil film remained on the internal components (same as would be during an air pocket entry during a crash). None of the springs I ordered worked without length modification unfortunately. I had to shorten the one spring incrementally until I achieved the desired force against the plunger. I have taken what this equivalent force is at the modified length, and am having the spring company make me a small batch to my specs. They should show up sometime in the next week. In the mean time, here's a video of the modified spring showing that the pump will purge air and also reliably close. Reliably is used lightly here as this is not in a running engine. Once I get the engine back together, I'll be testing this, along with a custom sight glass I am working on that will replace one of the banjo bolts to give visual indication that oil flow is present. 

Here's a video showing the check valve successfully cracking open with an empty pump. Peak drill RPM is equivalent to about 2,800rpm at the crankshaft, so it's not like the bike needs to be screaming. 

Video of light duty spring opening check valve.

I re-ran my previous air pocket test from my previous post, and the valve successfully blows the air pocket out and begins pumping oil with this set up, where it did not with the OEM spring. I'll let you know how things go from here. 

Edited by rcl5011
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On 8/24/2021 at 10:39 PM, rcl5011 said:

 

I wanted to contribute to this thread, as i've recently encountered a top end failure on my XR650L. Long story short, after a 30 mile or so ride, the bike stalls at a stop light. I push it to the side of the road, and attempt to start it. Acts like the battery is dead. I have a kickstart added to the bike, so I try it. It's locked up tight. I get a truck ride home.

Early into the ride, I was messing around on some offroad trails and dumped the bike with the front end facing mostly downhill while the engine remained running at high rpm, as the throttle was being rotated open while laying in a pile of brush. I scramble back up the bike and shut it off. I get the bike unstuck, stand it up and coast to the bottom of the hill. The bike starts right back up and I go for a 20 more mile ride strictly on back road pavement (35-50mi/hr). That's when it stalls, and locks up.

The first thing I do when it's home is check the oil. The tank reservoir is full. I pull the valve cover off and discover that almost all components in there are dry (like really dry). Top end is smoked, including the center cam support. I drain the oil, and find very little in the sump. Almost everything is in the reservoir. After careful investigation, I find no restrictions in any oil delivery tube or orifice. I start thinking about the ride, and dumping the bike down the hill, and the likelihood that air that was at the top of the reservoir was then sent to the bottom of the reservoir, through the bottom screen, and into the pump, where the pump ran dry for a short period of time. I've read many things about the oiling system of these bikes and feel that I understand it fairly well compared to most people, and so I decided to test whether this momentary air pocket condition will in fact cause the problem that i've seen.

After looking at all of the other components in the engine for damage, I put the oil pump back in the bike. I prime it with oil, and add a 1/4 of a quart of oil to the reservoir. I then ran a PVC hose to the output side of the check valve. I fabricated an adapter for my drill to rotate the pump shaft on the lathe, and while rotating the pump, everything seemed completely fine. I decide to run the pump dry (let the 1/4qt of oil in the reservoir be fully pumped out). I dump an additional 1/4qt of oil into the reservoir ( I used 10W-30 for the test to be on the thin side, which should be best for purging pump in my opinion). I let the oil find its way down into the bottom of the sump and into the pump (i waited probably 30seconds). I then pull the trigger on my drill to max speed, then slower speed, then creep speed. I let the drill run for a full minute. I realize at this point I should take a video to document this. I put the drill down, and pick up my phone to take the video. This took probably an additional 30 seconds.

At this point I take this video:

XR650L Oil Pump Air Entrapment Test

I run the drill again at max speed, then slower speed. Nothing comes out of the pump. I pull the check valve spring retainer pin and hit the trigger on the drill again. Oil instantly comes out. This in my mind proves that getting an air pocket in the oil line that feeds the lube side of the pump will cause air entrapment that will not purge itself, leading to oil starvation for in my case, no less than 20 miles worth of riding at a decent engine speed. During that entire time, that air pocket never left the pump. The top end and crank ran without oil pressure that entire time.

What I would like to do next is experiment with different spring rates in this check valve to see if I can get it to reliably close with a lower spring rate, but possibly allow air entrapment to escape. This situation can happen to anyone, and there's no indication that it occurs. In my case, I ruined a very new engine that I rebuilt painstakingly, and tuned to peak efficiency no more than 1,500 miles ago. I'm dedicated to finding a solution to either eliminating the potential cause of this in the future, or being able to detect the presence of this situation. I hope this helps someone else. Has anyone failed an engine after dumping the bike in a similar manner? I think it's so common of a situation that most people would not even think twice before just starting the bike back up and riding off. Really a bummer.

 

 

PXL_20210719_020003645.jpg

Why is it so rusted?  Interesting about the downhill possibly inducing air. I wonder how steep & how long for this to happen? If it could occur during a riding session? Having level at max would help?

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If you get this spring dialed in to allow self-purging of air I'd be interested in buying one or two.I could not get mine to purge air with a drill after changing to the newer pump and gears that spin it faster, I had to use compressed air in the frame to get it primed.

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On 8/27/2021 at 1:12 PM, rcl5011 said:

After measuring the OEM relief valve spring rate (1.52lb/in for the record), and a number of other dimensions including how much the OEM spring is compressed during assembly, I ordered a number of standard springs that I figured would give me a ballpark at meeting a low enough force to allow air to purge, but still reliably close the check valve. Luckily I live very close to a number of spring manufacturers so I get them next day with standard shipping. I incrementally reduced spring force on the check valve until I could get the check valve to successfully crack open when the pump is "dry". I say dry in that it was completely cleared of oil, but an oil film remained on the internal components (same as would be during an air pocket entry during a crash). None of the springs I ordered worked without length modification unfortunately. I had to shorten the one spring incrementally until I achieved the desired force against the plunger. I have taken what this equivalent force is at the modified length, and am having the spring company make me a small batch to my specs. They should show up sometime in the next week. In the mean time, here's a video of the modified spring showing that the pump will purge air and also reliably close. Reliably is used lightly here as this is not in a running engine. Once I get the engine back together, I'll be testing this, along with a custom sight glass I am working on that will replace one of the banjo bolts to give visual indication that oil flow is present. 

Here's a video showing the check valve successfully cracking open with an empty pump. Peak drill RPM is equivalent to about 2,800rpm at the crankshaft, so it's not like the bike needs to be screaming. 

Video of light duty spring opening check valve.

I re-ran my previous air pocket test from my previous post, and the valve successfully blows the air pocket out and begins pumping oil with this set up, where it did not with the OEM spring. I'll let you know how things go from here. 

I'm wondering if you have the wrong spring installed in your pump. This on-line calculator converts force & area to liquid head of water.

Plugging in your springforce of 1.52 lb and the area of the outlet of oil pump(which I think is 8mm) results in 45ft of head of water.(In other words the pump needs to develop 19psi of discharge pressure before check valve opens.)

The head of oil in the xr is no more than 3ft, so your spring seems way heavy.

I shall go check the springs in a couple of old oil pumps I have. 

 

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Edited by greyrider
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So I pulled out the springs of two old pumps that I had lying around and they are very much identical.

For the record: OD is 6.4mm, ID is 5.4mm, wire diameter is 0.5mm, 12 coils, free length is 24mm, installed length with check valve shut is 18mm, installed length with check valve wide open 9mm. The outlet of the pump is 7mm in diameter(I used 8.5mm for my calculation).

To test the spring rate I compressed them onto a scale that can measure down to a single gram.

Compressing the spring to18mm I get 170g (0.37lb) of spring force, and at 9mm I get 430g (0.95lb) of spring force.

The point of interest is the170g, as that's the force the pump has to overcome to open the check valve.

To work out the pressure required to lift the check valve this formula works, Pressure = Force(170g) x Area(57mm² outlet of the pump).

Its alot easier to use this calculator  https://www.sensorsone.com/force-and-area-to-pressure-calculator/ , as you can select different units for inputs and outputs.

The results I get for the pressure required to lift the check valve is 4psi, or 9ft of water, so theoretically there's room to install a lighter spring as the head of oil in the XR is no more than 3ft.

Edited by greyrider
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Does temperature change spring tension? Because it could get up to 200*F-275ish? Also, overtime, can the stopper on end of spring swell & bind on the OD of the bore? Too bad the bore/passage wasn't vertical & use a ball & gravity instead of spring.

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So you are getting similar results as me for my spring rate greyrider. With .37lb over a 24mm - 18mm = 6mm (.236in) deflection, that equates to 156.6lb/in for spring rate, where I measured 152lb/in. 

Not to go math crazy here but, I get that if we have a 7mm(.276in) pump outlet diameter, and a .37lb preload on the plunger, then the pump must produce 6.2psi to crack open the check valve. Using 10W-40 oil at room temperature (https://wiki.anton-paar.com/en/engine-oil/) it comes out at .85g/cm^3 (.031lb/in^3). I measured my bike at 15in from the oil pump output to the top of the head. This comes out to be 0.5psi of head pressure from the oil. The lighter duty spring that I am having made applies ~25% of this pressure, so it's really only 1.6psi cracking pressure, which is still 3X oil head pressure from the oil column to the cylinder head, but allows for air to purge.

Oil Pressure Head Calc.jpg

 

Thinking this through in more depth though, the inlet side of the pump is being fed by an oil column that reaches above the height of the cylinder head (frame reservoir). This means that in my mind, if you pull the check valve out, there should actually be a net positive pressure keeping oil in the line running to the head, which is lower than the reservoir. Could it be that they really only needed this check valve in the older days when oil seals did not exist in these XR pumps, and they figured keeping this valve here is beneficial as added insurance now that these pumps have shaft seals? The fact that the cylinder head can still blead down due to the parallel path back to the crankshaft, still has me questioning whether this check valve really eliminates dry starts. My opinion is that over time, these engines could theoretically drain the oil feed line to the head as well as half of the the oil filter cavity by way of this parallel path to the crank. I see less and less value of this check valve the more I look into this and think about it. It causes air entrapment, which can be catastrophic. I'm still waiting on these custom springs to come in. I'll test them when they show up.

Edited by rcl5011
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Y

20 hours ago, rcl5011 said:

So you are getting similar results as me for my spring rate greyrider. With .37lb over a 24mm - 18mm = 6mm (.236in) deflection, that equates to 156.6lb/in for spring rate, where I measured 152lb/in. 

Not to go math crazy here but, I get that if we have a 7mm(.276in) pump outlet diameter, and a .37lb preload on the plunger, then the pump must produce 6.2psi to crack open the check valve. Using 10W-40 oil at room temperature (https://wiki.anton-paar.com/en/engine-oil/) it comes out at .85g/cm^3 (.031lb/in^3). I measured my bike at 15in from the oil pump output to the top of the head. This comes out to be 0.5psi of head pressure from the oil. The lighter duty spring that I am having made applies ~25% of this pressure, so it's really only 1.6psi cracking pressure, which is still 3X oil head pressure from the oil column to the cylinder head, but allows for air to purge.

Oil Pressure Head Calc.jpg

 

Thinking this through in more depth though, the inlet side of the pump is being fed by an oil column that reaches above the height of the cylinder head (frame reservoir). This means that in my mind, if you pull the check valve out, there should actually be a net positive pressure keeping oil in the line running to the head, which is lower than the reservoir. Could it be that they really only needed this check valve in the older days when oil seals did not exist in these XR pumps, and they figured keeping this valve here is beneficial as added insurance now that these pumps have shaft seals? The fact that the cylinder head can still blead down due to the parallel path back to the crankshaft, still has me questioning whether this check valve really eliminates dry starts. My opinion is that over time, these engines could theoretically drain the oil feed line to the head as well as half of the the oil filter cavity by way of this parallel path to the crank. I see less and less value of this check valve the more I look into this and think about it. It causes air entrapment, which can be catastrophic. I'm still waiting on these custom springs to come in. I'll test them when they show up.

 

Agree (but check your decimal points), calculations are great to help understand the principles and get a ballpark solution, of course there are always other variables to throw a curve ball like the heat input that bork mentioned, or how much 'preload' is required for a good seal, in the end only testing will show if it'll work. ...very interested to see what you come up with!!

You raise an interesting point regarding removing the check valve. As I see it, currently oil drains down to filter level fairly fast, via the crankshaft, and then down to oil pump outlet level via the check valve, although alot slower. The check valve is a neat fit in the housing but I would still expect oil to leak through. 

If you removed the check valve and installed a plug instead, the oil should only drain to the filter level (and also the drain plug level in the frame) but the pump should not run dry or fail to prime. You would have to be prepared to start the bike with most of the oil in the crankcase and be pedantic about checking oil level before you take off, lest it blows out the crankcase vent. I'm spoiled with the oil sight tube, one glance to check the oil level, and after the engine starts, the oil draws down letting me know the pump works ok, no need to touch the dipstick.

Here's a few photos for reference of oil levels in the frame and crankcase.

First, after a standard oil and filter change I filled the frame 1/2 litre at the time to show the level in the frame. (I usually tip 1.5 litres in the frame and start the bike, when there's anough room top up another 1/2 litre and I'm done.)

The second group of photos is when I filled an empty case with water(with food coloring)to see where the oil level would be with different amounts of oil drained back in the case. The levels would be slightly higher with all parts in place, but the interesting point here is that, 1/2 litre of oil in the crankcase, which is at the bottom of the oil check bolt and considered ok, already touches the windage plates under the crankshaft. (the suction of the scavenge pump is alot lower so I assume this would be the oil level after the engine has stopped and remaining oil has collected in the sump) Food for thought!!

 

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The lighter duty springs came in. I installed one of them into the oil pump and ran through the same tests as I had done before. With a drained oil pump (drained for days), the spring allowed the pump to self prime and pump properly. I have left this new spring in the pump and finished assembling the bike today. I ran out of time this evening to break the new cam in. Will have to do that this week. I wanted a way to verify oil is in the line running up to the head, so I sacrificed my top banjo bolt and made a sight glass adapter for it. I'll see how this works out for oil flow visibility and report back. This should also help give visibility as to oil drain back after shutoff. Here's the end result. 

Spectrum Moto Oil Sight Glass.jpg

PXL_20210906_233126394.jpg

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as an aside (this may be a repeat - sorry), a few years back i spoke to a local rider who used to assist in the Honda Baja 1000 pit. he told me that every time an XR was started, one of the factory mechanics would crack the oil feed line at the head and if there were any delays in oil flow, they would shut the bike down and flat replace the pump w/ a new one. 

another thought on the lower pressure spring concept is that it may reduce the possibility of the "stopper" sticking to its seat. not a common occurrence to be sure but i do know of two cases of that happening.

i don't recall any bevel in the pump body (i will go check a pump in a bit), but i do remember the bevel on the rotors. never gave them much thought other than maybe needed for rotor lubrication - i think w/ oil in the pump, there should be little movement of oil there. but i sure can see how air could occupy that space and cause the issue described.

up until i snapped a drive chain and broke the main case, i had been running my stock 650L motor (w/ -690 oil pump & enlarged hole from oil tank to downtube) w/o either of the oil restrictors. i can see no reason to restrict scavenge oil other than to force oil thru the trans feed line so i will take a long hard look for damage  to the trans when i tear this motor down. in the end i will probably do the banjo-off-the- main feed update. i think the existing restriction to the crank is enuff to divert the extra flow to the top end. going to do the greyrider oil manifold/piston squirter during the rebuild

just ordered a couple more -690 pumps and feed lines from Japan. the feed line for the -690 pump is now NLS as are xr400r oil coolers, 600r countershafts and who knows what else... i am thinking gearbox parts are next. the loss of ez access to the xr400 oil cooler is a bummer - it is such a nice fit and clean install. at least on my xr650r i can do a oil to water heat exchanger or build a cooler into a rad tank...

and i am definitely interested in a dozen or more of the uprated springs!

neil

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  • 4 weeks later...
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On 9/10/2021 at 1:13 AM, SoCalXR600Rmonkey said:

as an aside (this may be a repeat - sorry), a few years back i spoke to a local rider who used to assist in the Honda Baja 1000 pit. he told me that every time an XR was started, one of the factory mechanics would crack the oil feed line at the head and if there were any delays in oil flow, they would shut the bike down and flat replace the pump w/ a new one. 

another thought on the lower pressure spring concept is that it may reduce the possibility of the "stopper" sticking to its seat. not a common occurrence to be sure but i do know of two cases of that happening.

i don't recall any bevel in the pump body (i will go check a pump in a bit), but i do remember the bevel on the rotors. never gave them much thought other than maybe needed for rotor lubrication - i think w/ oil in the pump, there should be little movement of oil there. but i sure can see how air could occupy that space and cause the issue described.

up until i snapped a drive chain and broke the main case, i had been running my stock 650L motor (w/ -690 oil pump & enlarged hole from oil tank to downtube) w/o either of the oil restrictors. i can see no reason to restrict scavenge oil other than to force oil thru the trans feed line so i will take a long hard look for damage  to the trans when i tear this motor down. in the end i will probably do the banjo-off-the- main feed update. i think the existing restriction to the crank is enuff to divert the extra flow to the top end. going to do the greyrider oil manifold/piston squirter during the rebuild

just ordered a couple more -690 pumps and feed lines from Japan. the feed line for the -690 pump is now NLS as are xr400r oil coolers, 600r countershafts and who knows what else... i am thinking gearbox parts are next. the loss of ez access to the xr400 oil cooler is a bummer - it is such a nice fit and clean install. at least on my xr650r i can do a oil to water heat exchanger or build a cooler into a rad tank...

and i am definitely interested in a dozen or more of the uprated springs!

neil

Would it be possible to modify a different oil pipe since the 690 one is no longer available? 

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