piston pin wear and Conn rod oil ports

7 replies to this topic
  • thumper_calgary

Posted March 05, 2015 - 09:58 PM


when I disassembled by 03 WR engine to do the valves everything was well in spec. However I noticed some pitting on the piston pin and I was thinking it could be starved for oil. has anyone ever tried expanding the oil ports in the top of the connecting rod? I was thinking this would give more lubrication. Now, I'm not about to take a grinder to it, I was just wondering if this is a known issue with other bikes as the rest of the engine was well in spec so I was suprised to find an issue at all. especially there.... I mic'd it and it's in spec. No play in the conn rod so I'm hoping to just repalce the pin and I thought I would just check to see if there was a known soloution. It's sort of hard to see on the phoots but the wear is happening only in the area under the left conn rod oil port. weird





Edited by thumper_calgary, March 05, 2015 - 09:59 PM.

  • mch

Posted March 06, 2015 - 09:22 PM


That doesn't look good.  If it were mine, I'd seriously consider replacing it.  If I felt like chancing it, I'd try to see if polishing the connecting rod cleaned it up. 

  • Krannie McKranface

Posted March 07, 2015 - 06:44 AM


You cannot change the oil passage design, as it will change the oil PRESSURE as well, which you surely do not want to reduce.


Clean oil, good oil, and OEM parts last a long, long time.


If you let oil deteriorate, it stops lubricating.




Your top and bottom end are shot.

  • thumper_calgary

Posted March 09, 2015 - 05:47 AM


I don't think the oil is under pressure at that point in the circuit. Is it not "splashed" up from below to lubricate the piston pin? Yes I will replace the piston pin but the top end looks fine. Ring gap, cross hatching etc looks fine. There's one mushroomed valve. How do you figure the bottom end is shot if only only side of the piston pin is worn like that? It looks like poor lubrication in one specific area to me, possibly resulting from a design issue. Can you elaborate?

Thanks for the responses!

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  • mch

Posted March 09, 2015 - 06:03 AM


I can't see reaming out that hole causing any PSI change either, but the picture of where the wrist pin goes looks like half machined surface vs half worn surface.  My concern would be that additional wear could lead to catastrophic failure.  If that were mine, I would change the rod or crank out.  Since you should change out main bearings when taking apart a bottom end, his comment that the bottom is shot makes sense.  You may just slap another wrist pin and piston in there and you may get another 200+ hours out of it, but who really knows?

  • bikedude987

Posted March 09, 2015 - 08:59 AM


the oil being in shear at that point will create it's own oil pressure, which can be a tremendous amount actually, if the speeds are high and flow is adequate. google hydrodynamic journal bearing.

  • thumper_calgary

Posted March 09, 2015 - 10:23 AM


the oil being in shear at that point will create it's own oil pressure, which can be a tremendous amount actually, if the speeds are high and flow is adequate. google hydrodynamic journal bearing.

Awesome. Thanks I will. Would it be correct to say then that the oil would not reach shear point under the port on the connecting rod? From what I can tell and what I learned from the previous owner this is the first time the engine has been torn down.

  • bikedude987

Posted March 09, 2015 - 11:22 AM


I'm not sure what you mean by shear point, but the dynamics of the oil flow and pressure are very complicated.  There is basically no force being provided by the open port, but there are boundary effect, momentum, flow direction, etc that will have an effect on what the oil is doing in and around the port.  And with splash feed, it's probably not a very consistent feed of oil, most of which is probably coming from the oil control ring feeding oil onto the pin.  With that theory, I would guess the port is actually the oil return, not the oil feed and that enlarging it would have a deleterious effect on oil pressure.  


I wish Grayracer would chime in here...


But I agree with Krannie, your rod and wrist pin at very least are trash.


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