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Discussion Starter #1
My 2017 Z with 1500 miles has developed a crankcase gasket leak on the top of the engine. Not terrible (yet) but definitely noticeable after a good ride with an engine workout. I clean it off and check after every ride and it’s definitely leaking, less so putzing around town. Bike has the 143cc TB top end, cold air intake, Graves pipe. These mods have been running fine the last 1000 miles. Tried loosening and retightening the 2 upper case screws and motor mounts. No luck.

Anyone have experience with a leak like this, stock or modified? The cases have not been split on this bike.

Hadn’t planned to split the cases, but it’s looking like a necessary winter project. Guess if nothing else it will be a good excuse for a stroker crank...

JW
 

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Seeing lots with slow oil leaks in front at the notch in the case, But haven't seen any where you showing.
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Guessing you defiantly ruled out it's not coming from the vent hose and running down and showing up there
Not much of a spring clamp on it.
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Seeing lots with slow oil leaks in front at the notch in the case,
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Ya, pic was for front leak most seem to have
I have light mist leak there on mine all the time as well
 

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Discussion Starter #7
It looks like it is the case between the two engine mounts, is this correct? Not the area circled in the picture above. Looking at the casting it shouldn't even have oil in it right in that area (blocked off by a web on both sides).
The crankcase pix were very helpful. Here’s my arrow added to show where I’ve isolated it to. Anybody experienced a low-mileage leak in this area?

JW
 

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I would check the torque on those two bolts and see either is loose. After that you either live with it until it gets worse, or tear the cases apart and check for warping. I would use Hylomar in that area to try to seal off any non-flat areas, either that or find a shop that can fly cut or surface grind the cases (but only a little or things will get wrecked). I'd be willing to guess that 0.010 inches is the maximum that could be removed, and it could be less than that wich doesn't give a lot of room to fix things.
 

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The crankcase pix were very helpful. Here’s my arrow added to show where I’ve isolated it to. Anybody experienced a low-mileage leak in this area?

JW
I've seen various crankcase leaks over the years on all brands of bikes and if they are located on the top of the cases you can often just get by with applying a little extra case sealant right over the leaking sealant. There is no fear of a large leak up there, it's just oil mist seeping through, often due to a small gap in the factory applied sealant. So don't get all worked up about machining your cases just yet because once it's sealed you can usually wait until winter to split the cases and find the actual cause. And then add your stroker crank.
 

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Discussion Starter #10
I've seen various crankcase leaks over the years on all brands of bikes and if they are located on the top of the cases you can often just get by with applying a little extra case sealant right over the leaking sealant. There is no fear of a large leak up there, it's just oil mist seeping through, often due to a small gap in the factory applied sealant. So don't get all worked up about machining your cases just yet because once it's sealed you can usually wait until winter to split the cases and find the actual cause. And then add your stroker crank.
That’s my plan! Winter project it is...

JW
 
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