Sudden loss of compression?

I can't for the life of me see any sign of what caused the loss of compression, at least in the top end. The rings and piston look fine and needle bearings not wrecked. I guess it could have been a loss at the head gasket and it wasn't running, didn't put any carbon on so I can see it. I expect just a new gasket set and reassembly will probably get it running again. Here's pics in case anyone can see something I don't?

If your base gasket or seals blew out, you would lose most of the pressure that drives the intake charge into the combustion chamber. No air/fuel in combustion chamber to really compress. It will feel like you have no rings because the volume of intake charge is too small
Well I just ordered a gasket kit on Amazon, in hopes it works, without having to get down into crank seals. I'll probably buy a second "pre ported" engine from CMB because they have just the engine for $119 and I can use PayPal to break that up over two months of four payments. I guess if you need reliability in such a machine, you probably absolutely need a second engine so you have something while you fix breakages.

While I like the idea of ordering with a warranty, I also really can't afford a $200 hit. The ease of payments and the price makes CMB very attractive, and while he offers no warranty, I have a feeling he's a good enough guy that if I made a stink here, he'd probably fix any problems.

Anyway I guess I am probably going that route again.


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I would get a new head gasket, pop the piston off and clean it up and then it's ready to go.
I have a full engine gasket set from Amazon coming tomorrow, so that's the plan. The original head gasket got bent up in the shipping from CMB, it was in fact the only damaged part, but I figured the torque would flatten it (and it wasn't bent badly).

I suspect it might have been a head gasket leak, but since it was a sudden change, it didn't run and never made carbon marks where the leak happened, so there was no real visible evidence, but I strongly suspect that's it.

I also plan to get a "ported" engine from them for $119, and even if this engine runs again I will replace it for a bit more power and keep it for a backup for when and if the new one has issues that need repair.

I have been without a car for a long time, and my motorcycle has been down with broken intake studs. Even if I get my big bike back up, or get another, I still plan to rely on this little bike for most trips. I live in a small town where most trips I make are 2 miles or less. Just doesn't make sense to fire up a4 cylinder 650 to run to the store (unless I plan to fill saddlebags). You can't beat 60mpg around town, so I wanna have a reliable setup. Until a couple of days ago this was totally reliable.

It just sorta died, but I immediately noticed that it was rolling over way too easily with the clutch engaged. Honestly I am 99% sure it had to be a top end leak. I doubt anything that low could effect the compression that much. I mean you could literally pedal it with the clutch engaged and just roll the engine over with the bike. That was not how it was when it was running, it had plenty enough compression to stop the bike after a short bit of rolling over (assuming it didn't start which was very rare).
Wow, that was NOTHING! If you take away the base gasket scraping, it was a 15 minute job start to finish!

Runs great again. Even though I could not see the leak, I am 99% sure it was at the head gasket. You could see it got nicely crushed (why it held so long), but the new one was undamaged, and all is good.

You could notice immediately that the problem was solved cuz when I pushed the bike out of my apartment to test it, dropping the clutch immediately stopped the bike and the back wheel was almost impossible to turn without really pushing the tires down and pushing forward hard, and even then all you could get was a couple rotations of the engine before it would just skid. Before it was rolling over almost freely.

I still want a "ported" CMB wildcat, for increased power and so I'm never down more than an afternoon if possible, so I will probably still plan on that.

I sure love this hobby. I really can't afford e bikes, but this is a cheap alternative that reallot gets me around very reliably for the most part. Of course I am religious about a 32:1 mix, and now using stabilizer since I'm limited to ethanol fuel, but since I am using a splash of stabilizer, have had zero fuel issues.

Honestly you guys weren't all that much help on this one, as it's so simple, but in the past you've been, so it's always appreciated!
I did use the "chinesium" plug this time. When first I tested the NGK after this initially happened I didn't see a spark or it was weak. I think I will grab a new plug, but the China plug will do for now. I bet the old NGK still works, was probably just too bright to see (was a sunny day).

She's a beater, but damn I love the simple reliability of this silly little monstrosity!
I did use the "chinesium" plug this time. When first I tested the NGK after this initially happened I didn't see a spark or it was weak. I think I will grab a new plug, but the China plug will do for now. I bet the old NGK still works, was probably just too bright to see (was a sunny day).

She's a beater, but damn I love the simple reliability of this silly little monstrosity!
You can clean up a plug with a little wire wheel on a Dremel, or bench grinder.
Kinda disappointed now, as it seems to have lost some power. It barely got up the hill I take regularly, that it used to pull up just fine with no pedal assist. Not sure what the problem could be? Perhaps it had a small air leak before it lost compression and was running leaner than the carb was set via it's slide needle?

Also maybe the clutch needs adjusted, I have had that happen before, but usually that also means hard starting. I will check both tomorrow when I retorque the head nuts.

Makes me really want the ported wildcat. If it has just a little more power than this one did new, it will pull our local hills just fine. I can even probably keep it running up the steepest with a mild pedal assist. It came with a 41 tooth sprocket. I'm tempted to up it to a 44, standard size, maybe then it would pull hills with ease? I care more about that than top speed.
I stopped using base gaskets as they always end up leaking( atleast on most of my builds) I use ultra grey or optimum grey permatex works great. Just check squish gap should be around 1mm. Also, you can get these motors on eBay and temu for under 100. They're all the same unless it's Minarelli, just have to go through them to get casting burrs out and make sure flow is clear. Don't port unless you know timing as you can go to far very easily and motor won't fire. I would change your rings too, even if you think they look ok. Had this issue with my Minarelli and I upgraded to a Naraku piston and rings and it runs like new again.