I f***ed up my big bore and now my bike is garbage.
 

Okay. I broke it. No idea what’s wrong.

https://youtube.com/shorts/18h7xqt5nm4


Doesn’t sound good.

Charles.

I don't hear anything odd but it's really hard to make any kind of diagnosis based on an audio file.

Sounds like a Goldwing on my phone!

You're an experienced mechanic. What do you think is going on?

I wish I could be more helpful CC. It sounds like exhaust notes to me. In the video it seems the noise lessens as you accelerate and the engine sounds fine. I bought a big bore kit as well but never installed because I knew it would run lean. If you're convinced the big bore kit is a lost cause then revert to the original set up. Good luck!

Can't tell from the video....
The only thing to do is take it back apart and see what you can see. At least it's still running.

Well, if I have to take it apart again it will be a lost cause, because I don't think it's possible to buy the head gasket separately from the kit.

The whole reason I did this is because my exhaust valves were sinking and I had to replace the head. I figured if I was going to replace the head I might as well go the full monty.

Charles.

Stock head gaskets are available on AliExpress:

https://www.aliexpress.com/item/4001...archweb201603_

Having said that, if it were me, I would be willing to reuse the one that you just installed with the big bore kit. They don't get torqued that tightly on a motorcycle and I doubt that they crush that much that it will make a difference. And since you have to go back to the stock piston and cylinder otherwise, you don't really have much to lose at this point.

double check the valve lash, and the cam chain tensioner possibly?

Also, GPX would have gaskets, the FSE300R is the NC250 with a bbk.

It might be the tensioner. I couldn’t find any information anywhere about how to install the front cam chain guide. Is there a recess it fits into deep down in the motor? That’s the only thing I didn’t check, the only thing I might’ve missed.

I did re-check the valves and they are spot on.

The bike seems to run and idle fine, but I’m scared to take it for a ride with making noises like that. There’s plenty of oil covering the valves after running it up to temperature.

Charles.

This video makes it easier to hear.

https://youtu.be/ij1UneHswJE

Charles.

There might be some help in Spud's thread on his rebuild;

http://chinariders.net/showthread.php?t=18895

Post #11, he lists the process and there's good photos of the tensioner.

In the section labeled 'removing the camshaft' there is a picture in Spud's thread showing a washer that positions the compression release. It mentions that if the washer is installed in the opposite position, you will get noise. Might be a good place to look.
I don't have one to compare, but a common washer used is a "Bellville" washer that provides spring tension to hold things in place. They are regularly used on flywheels to insure good contact between the crankshaft and flywheel tapers. The taper, not the key, keep things aligned, so good contact is a must. They are NOT flat, but more of a very low 'cone', with not much height. They must be installed properly to work.
It may be the washer in the image is a 'stepped' washer that provides clearance if the step is on the correct side.
Other designs with a drop in tensioner on the exhaust side use two tabs that drop into notches, leaving the lower end of the tensioner to move about as they will. IOW, drop the tensioner in, placing the tabs into the slots, yur done.
tom

I followed those instructions meticulously, and installed the washer correctly.

There's also no photos of the front guide as it fits into the bottom of the engine. No mention as to whether it fits into a slot or is supposed to be free at the bottom.

Charles

I could probably help guide you, but I would need to see pictures of the front guide. Sometimes they have a sort of 'tooth' to them that engages with the crankcase. Can you see if it's aligned by removing the flywheel?