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Discussion Starter · #1 ·
Has this been posted up already?

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It has been my opinion for some time that high piston speed (high rpm highway cruise speeds) is hard on the stock piston and rings, contributes to oil consumption issues... as does cylinder distortion. Good EM interview (good info).
 

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Hmmm.

Isn't that the same thing, yet somewhat less, that several people have been saying for a number of years?
 

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I enjoyed the video and I agree that the narrower oil ring groove with fewer & smaller oil return holes (from cylinder wall thru the piston) is partially responsible for higher RPM oil consumption on many KLR650's.
But it is the Gross Over-Oiling of the cylinder walls by the un-restricted 3mm oil outlet thru the bottom rod pin to the needle bearing that needs to be Better Controlled.
I have successfully tested down to 2.06mm oil control orifice in the 6:00 oil port to the crankshaft bottom rod pin on my personal 1987 KLR650.
 

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Discussion Starter · #4 ·
I enjoyed the video and I agree that the narrower oil ring groove with fewer & smaller oil return holes (from cylinder wall thru the piston) is partially responsible for higher RPM oil consumption on many KLR650's.
But it is the Gross Over-Oiling of the cylinder walls by the un-restricted 3mm oil outlet thru the bottom rod pin to the needle bearing that needs to be Better Controlled.
I have successfully tested down to 2.06mm oil control orifice in the 6:00 oil port to the crankshaft bottom rod pin on my personal 1987 KLR650.
Yup, you have pointed out the piston deficiencies ages ago. I've been going on for years about high piston speeds, 5,500+ rpm highway cruising being hard on the piston & rings (ring flutter = higher oil consumption). No real new news in that regard, but I am glad to hear/see E-M acknowledge it. Some folks refuse to believe (are in denial) that high speed/high rpm highway cruising harms the KLR, is damaging to piston & rings.
 

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Hell, high RPM in any engine will cause faster wear and more oil usage. 5000+ RPM for a piston the size of your fist is not a happy place for it. If you do a lot of highway cruising, either slow down or switch to a 16-tooth sprocket.
 

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Moving the oil from the bottom end and cylinder walls over to the cams and transmission has also proven to be effective.
 

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Some folks refuse to believe that (..............) high speed/high rpm highway cruising harms the KLR, is damaging to piston & rings.
I would Not call it damaging to the piston & ring set.
I'd rather call it, 'Over-whelming', for cylinder-wall oil film control, with stock & standard oiling system.
 

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Discussion Starter · #8 · (Edited)
I would Not call it damaging to the piston & ring set.
I'd rather call it, 'Over-whelming', for cylinder-wall oil film control, with stock & standard oiling system.
PD, personally, I think you have a point about the piston design over oiling, and support the restriction mod... but, replacing the stock piston with a JE or Wossner "racing" piston usually eliminates the oil consumption problem. I can't help but compare the big automotive sized piston of the KLR to the pistons in Chev small blocks etc. Although the KLR has a DOHC valve train that tolerates high rpm better than a similar pushrod engine, the physics & engineering affecting the piston apply to both. Compare the 7,500 rpm redline of the KLR to a similar bore & stroke V-8 engine - 6,000 to 6,500 rpm redline would be the norm for a performance V-8, and you certainly wouldn't cruise at 5,000+ rpm with it. Personally I think the 7,500 rpm KLR redline is too high.

A few years back, curious about what I could find on the engineering side of the issue, I was surprised to find lots of piston speed related information pertaining to determining redline on performance engines, but very little on acceptable continuous "cruise" speeds. I posted this info on the KLR Only thread on advrider a few years back:

This from an aero engine overhaul facility:

Piston Motion: The Obvious and not-so-Obvious, by EPI, Inc.

... a quote from the above... "it is generally agreed that for an engine in aircraft service, 3000 fpm is a comfortable maximum MPS and experience has shown that engines having an MPS substantially exceeding that value have experienced reliability issues."

MPS = mean (average) piston speed. The KLR engine has a stroke of 83mm / .2723 Ft, and using this handy Wiseco engine calculator info: Helpful Engine Calculators - Wiseco Piston Inc. I calculated these piston speeds (in feet per minute) for these given rpms:
  • 5000 rpm = 2723 fpm;
  • 5500 rpm = 2995.3 fpm;
  • 6000 rpm = 3267.6 fpm; and,
  • 7000 rpm = 3812.2 fpm

Researching further, I found many good tech articles on-line, basically saying the same thing... as rpm and piston speed increases, eventually the kinetic forces overcome the ability of combustion pressure to keep the ring planted against the bottom of the ring groove, and "flutter" occurs, damaging the rings, degrading ring sealing. Continued operation in the rpm range where flutter is occurring, creates further ring damage, and gradually, due to reduced compression, flutter will occur at lower rpms, and oil consumption increases (a vicious cycle). This is why oil consumption (and performance!) gets worse and worse.

Is this controversial? I don't think so - there's lots of info online about the subject, and nothing particularly special about the materials and design of the KLR engine to differentiate it from automotive or aviation piston engines.
 

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I found that the 318 CID V8 Chrysler/Dodge engines were about the closest to the KLR650 bore & stroke.
And I had asked "how much engine oil would they have consumed per 1000miles, if they could have even survived continuous operation at 5000-6000 rpm?".
Would they have consumed upto 16qts per 1000 miles at those rpms? As a bad KLR single cylinder (39.663CDI x 8 = 317.30) can consume upto 1 qt per 500miles?

Aviation piston engines are usually longer stroke engines, which makes for even higher piston speeds at same rpms.
So it is a little bit of Apples to Oranges, isn't it?
 

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I found that the 318 CID V8 Chrysler/Dodge engines were about the closest to the KLR650 bore & stroke.
And I had asked "how much engine oil would they have consumed per 1000miles, if they could have even survived continuous operation at 5000-6000 rpm?".
Would they have consumed upto 16qts per 1000 miles at those rpms? As a bad KLR single cylinder (39.663CDI x 8 = 317.30) can consume upto 1 qt per 500miles?

Aviation piston engines are usually longer stroke engines, which makes for even higher piston speeds at same rpms.
So it is a little bit of Apples to Oranges, isn't it?
Longer stroke than a KLR, yes. But as far as Lycoming's go, usually oversquare, to very oversquare. Most 4-7/8" or 5-1/8" bore. In the case of an O-320, Ø5.125 x 3.875". I think rated output is only around 2700 rippums, and redline isn't much past that.

My brother is an A&P, I can ask him about oil consumption. But they also do rebuilds or at least inspections, yearly.
 

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Discussion Starter · #11 · (Edited)
" A final note on piston speed—, 2,500 fpm was considered the upper limit for piston speed not too long ago. "

That's from here (from Wiseco): Stroker Engine Science: Piston Speed, Rod Angle, and Increased Displacement Explained.

Better piston & ring materials has improved things considerably, but the stock KLR piston isn't a "racing" piston! And it's 1987 tech. Disappointing that the Gen 3 KLR uses same P/N piston as the '09 Gen 2.
 

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Most 4-7/8" or 5-1/8" bore. In the case of an O-320, Ø5.125 x 3.875"
Ok, so 3.875 inches of stroke x 25.4 = 98.425mm stroke. Like I suggested 'long-stroke', which increases the FPM of piston speed at any given rpm. But generally increases the torque output at low to medium rpms.

I think rated output is only around 2700 rippums, and redline isn't much past that.
Isn't aircraft engine maximum speed partly dictated by maximum FPM of Propeller Tip Velocity at 'X' rpm?
 

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" A final note on piston speed—, 2,500 fpm was considered the upper limit for piston speed not too long ago. "
I think that you will find many motorcycle engines designed in the 1970's with piston speeds near 4000 fpm and motorcycle engines designed in 1980's with piston speeds near 4500 fpm.
(Of course I could be remembering this incorrectly.)

KLR650 / 83mm stroke x .03937 = 3.26771 inch stroke.
3.26771" x 2 = 6.53542" x 7500 rpm = 49,015.65" per minute / 12 = 4,084.64 Feet Per Minute of piston speed at Red-line.
Isn't this correct.
 

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Discussion Starter · #14 · (Edited)
I think that you will find many motorcycle engines designed in the 1970's with piston speeds near 4000 fpm and motorcycle engines designed in 1980's with piston speeds near 4500 fpm.
(Of course I could be remembering this incorrectly.)

KLR650 / 83mm stroke x .03937 = 3.26771 inch stroke.
3.26771" x 2 = 6.53542" x 7500 rpm = 49,015.65" per minute / 12 = 4,084.64 Feet Per Minute of piston speed at Red-line.
Isn't this correct.
I just used the piston speed formula here: Helpful Engine Calculators - Wiseco Piston Inc.

Edit... I should add that I also think that cylinder distortion plays a part in the (KLR) oil consumption problem.

But, there are plenty of folks with high mileage KLRs that use little oil, and they usually are the type to keep the rpm down on the highway.

Wattman makes it pretty clear he is a believer in keeping the rpm down, and look how it's worked out for him (180,000+ miles on original piston/rings):

 
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