Weird engine problem got me stumped

I agree bairdco. It's got to be an air leak.
I went through this engine top to bottom for leaks and nothing I did affected it in the slightest. The main seals are the only possible potential leak not yet checked/replaced.
I'm confident the new seals will get her healthy again.
I simply wanted to be deliberate and check everything possible before tearing into the bottom end. Those damn handmade chinese woodruff keys are a real pain!

Wickedest1 said:

Theoretically shouldnt take ya more than 4-5 hours total teardown/rebuild...

Whats ur stud size? I have m6 x 1, and maybe enough m8 x 1.25 this is 12.12 hardened aerospace grade threaded rod

Both motorkits i had i used this
My 68mph e50 race ped uses the m6...

Track tested in auburn ny @ mopedmayhem in october

Let me kno and ill cut ya a set...have flanged hex nuts fer the m6 too

Get rippin brutha

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The GenV engine comes with all the hardware already upgraded to allen head cap screws.
I agree! It makes it much easier to work on and much more reliable when your engine hardware is not cheese hardened junk!

The magnet and key look fine and I tried it with a different coil and cdj box with no results.
Also tried a different head, intake manifold, carb and exhaust.
No joy.

Too late now! I have the motor out and halfway torn down for the seals already. I couldn't stand looking at the new parts and had to tear into it!
Took a break to pig out on chili! Should have it up again sometime next week (if it doesn't snow) so wish me luck!

Okay, got the seal replacement done during that debacle of a superbowl.
Everything went well, all the gears popped right off with no hassle. I decided to go ahead and split the cases just to inspect the mains and make it easy to get the old seals out.
The main bearings feel great! Nice and smooth and tight. There are no grooves on the crank from the seals so the new ones fit nicely. The old set looked okay, but the thick seal with the spring was fairly sloppy on the crank journal.
After careful inspection I discovered a visible wear mark inside where one side of the seal had a bulge from a hasty installation which led to abnormal wear and leakage.
Getting the seals installed without rolling the lip over when it slides past the step on the crank journal is CRITICAL to normal service life when doing new seals. If the lip rolls over as you mate the cases (or as you slide the seal on if you don't split the case) the seal will quickly wear off center from the distorted lip and leak.
Take the time to carefully inspect the surface of the seal after it's fully seated for distortion or bulges which are a sure sign of a rolled seal lip. You can work them out and get things right with a small stiff wire slid around inside the lip. Be careful not to gouge or tear the rubber, I usually use some thin grease to help the probe slide around easily.
I tried to get some pics of a distorted seal but my phone cam cannot resolve the detail. Besides that, I'm currently restricted to an ancient laptop and uploading pictures takes hours., so the pics of the teardown will have to wait till the main comp is fixed or replaced.
It's sitting on the counter ready and waiting for some decent motor swapping weather and a test ride!
I am now very confident the riddle has been solved, but time will tell the tale.
Stay tuned...and Thanks again to all for the helpful suggestions!

2door said:

Ahhhhh, wait a sec, maniac.
I've replaced several sets of crank seals and never had to split the case. They come out from the outside and go in the same way. Why did you install the seals with the case apart? That seems like it would make the process more difficult. And, more likely to damage a new seal.

What I've found most often is a seal, especially the left side, magneto side, that wasn't pressed into the bore squarely and the magnet rubbed it and damaged it. That will usually be evident by a black residue inside the mag cover. But not always.

I use a small curved dental pick to pull the old seal out then after lubricating the crank and seal lip with 2 stroke oil (Opti-2 , I use a socket just a hair smaller in diameter than the seal to drive the new one in. Oh, and closely inspect the crank for any roughness that could also damage the seal before installation. I make sure it is square in the bore and driven in flush with the case.
It just seems like it would be an awkward procedure to install the seals with the case apart. But what do I know?

Tom

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I decided to split the case mostly to inspect the bottom end 2 door. It also makes driving out the old mains easy peasy and I had no idea what kind of shape the seals would come out in. When they tear, it can be a pain so I wanted to do it the easy way. Your technique works when you don't want to do a total teardown. I was curious what the balanced style crank looked like since this is the first I've had.
Overall, I remain quite impressed with this engine and chalk this failure up to the spotty factory assembly.
It's an easy mistake to make even when you DON'T build 500 a day. I figured this might help those with similar seal troubles who have fewer motor rebuilds under their belts. You should do a post on digging them out without splitting the case as you have a nice clear way of explaining things.
I'm more of a documenting type rather than explaining the process. I don't really know why I do a certain thing when a motor acts up. I just kinda feel what it's doing. I often guess wrong here trying to help others, yet I rarely have any problem pinpointing the fix when I have the bike in front of me and can ride it or hear it. All my learning has been by exposure so I seldom know how to present it to others in a way they can understand. I say "you know?" a lot when I'm explaining things....and most people simply don't know.
You are good at letting them know. I always learn from your input and welcome the experience you bring!
Cross your fingers for me that The Pig will have a balanced heart again soon!

Well, as I see it, this weirdness boils down to no signs of a lean mix when there should be. I've seen engines do this before, but never without showing clear and unmistakable signs of the cause. I am really hoping I found the actual cause and not something imaginary just to make myself feel better....
I'm also thinking now the used head gasket may have had a role. I did not realize how thin it was until I had a new one next to it for comparison. I know it was not the root cause, but it surely won't help to increase compression on an already lean mix.
Maybe the re-torquing raised the compression enough that combined with a leaky seal could give this result.
I used all new gaskets everywhere (Thanks Neil!) but the case seam this time.(The case gasket was still like new)

Got the GenV re-installed today. Thrilled to find it back as smooth and powerful as ever! The seals cured the overheating with everything back to normal! LOVE this motor!
Until it snagged a ring on the transfer port and destroyed the piston.
*sighs and beats head on workbench*
Now I need a new piston, rings, and cylinder. (The cylinder chrome is fine but it gouged the transfer port lip and ruined the opening.)
I just KNEW I had far too long and too many miles without any problems...was only a matter of time till my unbelievable run of good luck with chinagirl's snapped.
Muck Furphy.

Nope. Just a snagged ring or broken land. Not sure which started the destruction. Pin and bearings are fine. It literally did almost nothing to any part but the piston. Very little damage considering how it failed. I may be able to re-use the cylinder with some touch up to the transfer lip. Just goes to show, a quick hand on the clutch can save parts!

Nope. Ain't no beer can pull tab and gum wrapper foil engine gonna get the best of ME!
IT DIES WHEN I SAY IT DIES!
Besides, this engine really does run sweet as honey. I got slightly moist every time I rode it.
Seriously. It is still the best running, smoothest engine I've owned to date.
Not giving up without a fight.
For all I know, I broke it by re-assembling it wrong.
I'm not blaming the engine until more evidence is in. You know as well as I do that some engines are finicky and hard to please...like certain Italian brands.
*ducks to avoid the beer cans thrown by everyone*