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A few days ago, I noticed several drops of oil under my bought new (in 2019) 2017 Honda CB-500F which has almost 10K miles. The drops were on from somewhere on the left side of the bike, under the left rear of the oil pan. I could see a drop of oil on the pan in that location, but there was no telltale oil "trail" to indicate where the leak was coming from.

Expecting the worst, I immediately thought it might be the counter shaft seal, behind the front sprocket. Not a big deal, I thought (I've been working on bikes since 1953 and was a Honda dealer mechanic 55 years ago) but then I read a thread by an owner of a high mileage CB-500 who had a leak at the countershaft seal and the most-knowledgeable Oyabun commented that this seal, unlike nearly all other makes and models practice, was fitted by the Honda factory (Thailand) from INSIDE the crankcase, not from the outside. In other words, if this seal was the cause of my leak, an engine removal would be necessary. At my advanced age, I am not competent or capable to tackle this job. I fell into a pit of gloom.

I cleaned the area with Motul "Moto Wash" which really does a job, but must be used in accordance with Motul's instructions, and again inspected for the source of the leak. Turns out there is an almost invisible crack (no sign of impact anywhere on the pan) about 15mm long and that's where the leak came from. I taped a piece of paper towel over the leak site and in a few minutes, there was indeed a dark spot in the center where oil was gathering.

I drained the oil tonight and will either seal the crack with J-B Weld) or replace the pan. I use J-B Weld a lot in my shop and have full confidence in it for this purpose.

If I go with a new pan, is it a straightforward replacement? It looks to be.

I'd understand this flaw better if there were some sign of impact on the pan, but there is none, as mentioned.

Very curious, but vastly better than a leaky counter shaft seal!

Ralph
 

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there was a thread about oil pan replacement a few months back (it's for the X, but all three R,F and X are the same in the engine department and i doubt there was any significant change between the years):
with pictures even! hope it helps :)
 

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Thank you, Yamato. That is a wonderful tutorial PAULRIDES presented and answers any and all questions I might have had. I sent Paul a PM to let him know of my pleasure with the thread and the clear photos he added.

I hope my J-B Weld repair works, but if it fails I'm out nothing. Part of my hesitation to just replace the pan is that I believe (from my Honda shop mechanic experience in the days of 305cc andSuper Hawks, Dreams and 450cc -Black Bombers) I believe that the assembly job done at the Honda factory is "as good as it gets" and that any follow-up work by even skilled mechanics is slightly less reliable than what Honda itself does, Perhaps what I am saying is that I doubt MY ability to do the job as well as factory employees.

Ralph
 

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I wouldn't stress about it that much, everyone is only human, if you take your time and do it properly there is no reason why it shouldn't be "on pair", but ... if your approach works for you, that means less work for you and more time enjoying the bike :)
 

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Update: The J-B Weld application stopped the leak, but for under $90 I sourced a new pan and two exhaust gaskets and will fit it next week. I still have no clue re what caused the all-but-invisible crack on the left side of my CB-500F's oil pan, as there is absolutely no sign of any impact anywhere on the pan.
Ralph
 
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