KTM LC4 640 Engine Noise

[LXnastynotch93]

Does this sound right to anyone? There's a distinct knocking/tapping noise and that doesn't sound right to my ear.

I apologize for the vertical recording...

http://youtu.be/Ok644ZH1cJ0

[Chippertheripper]

The lc4 is a noisy motor, but that doesn't sound right. Sounds a little like the valve lash is too loose.

[stoinkythepig]

That sounds broken...

Put a timing light on the plug wire and see if the noise is double the speed of the timing light pulses (bottom end problem) or at the same speed as the timing light pulses (top end problem).

[LXnastynotch93]

Sounds like it's making the noise at the same time as the timing light pulses

[Paul_E_D]

This bike has a common top end problem. THe roller/rocker bearings fail. That is 90 percent chance what this is. It is an easy and cheap fix if you catch it in time. Replace the whole rocker arm for like 60 bucks and be on your merry way.

[LXnastynotch93]

This bike has a common top end problem. THe roller/rocker bearings fail. That is 90 percent chance what this is. It is an easy and cheap fix if you catch it in time. Replace the whole rocker arm for like 60 bucks and be on your merry way.

Does the motor have to come out?

[Paul_E_D]

No, this thing is very easy to work on. Get the manual and remove the airbox, valve cover, find TDC and remove rocker arms by the book. You need like an 8 and 10mm socket, and a 5 or 6 mil hex key. Check the roller bearings for play. replace if you find any. It can be done in like an hour taking your time. two if you are a total newb.

[LXnastynotch93]

No, this thing is very easy to work on. Get the manual and remove the airbox, valve cover, find TDC and remove rocker arms by the book. You need like an 8 and 10mm socket, and a 5 or 6 mil hex key. Check the roller bearings for play. replace if you find any. It can be done in like an hour taking your time. two if you are a total newb.

Do you have a link to said manual? I downloaded a few but they were kind of shitty. Or am I going to have to buy one?

[Chippertheripper]

Ps: Paul, this Is an older lc4, not the 690.
I don't THINK you have to pull the motor, but I can't remember offhand if there's room to pul the whole top cover off with the motor in the frame.

[LXnastynotch93]

Ps: Paul, this Is an older lc4, not the 690.
I don't THINK you have to pull the motor, but I can't remember offhand if there's room to pul the whole top cover off with the motor in the frame.

Yeah about that, there was JB Weld used to fix a broken cylinder head bolt tab on this motor. Basically the guy before me hacked this thing together and hid all the shit he did wrong. I didn't see this until I removed to the tank to service the carb. Thus I think the motor might actually have to come out.

So at this point, I'm wondering what else might be wrong with this bike. I can either part it out, sell it for a huge loss, or fix it. I would probably be better off trying to find a new motor if I was going to fix it...

[Chippertheripper]

Pull the lump and bring it to cliffs. I promise they won't do you wrong.
If it's fixed right, it'll last as long as twinkles and cockroaches.

[LXnastynotch93]

Pull the lump and bring it to cliffs. I promise they won't do you wrong.
If it's fixed right, it'll last as long as twinkles and cockroaches.

Thanks man, I'll think about it. I was thinking about just pulling it and making it a winter project at this point.

[Chippertheripper]

That's certainly doable too. But if it's as simple as rocker arms, you're going to miss a bunch of riding on it.

[Paul_E_D]

Definitely fix it. These are dead simple motors, and used parts should be plentiful. It's mostly the same motor as my 690, but The frame is different. I sincerely doubt you have to pull it for this, but maybe...

[SVRACER01]

its toast...ill give you $500 for scrap

[LXnastynotch93]

its toast...ill give you $500 for scrap

Lol I'll sell you the motor for $500 if you want it.

[SVRACER01]

its easier to transport it in its current configuration

[LXnastynotch93]

its easier to transport it in its current configuration

The fork is off and wheels are off. I can remove the engine easily for you!

[SVRACER01]

we are getting nowhere here LOL

[LXnastynotch93]

I'm going to pull the motor out and install a new head.

Does anyone know if it would be okay to back off the cylinder base bolts and re-torque them without damaging the seal between the case and the cylinder? I want to make sure the base bolts are tight because the previous owner tightened them by hand.

[Paul_E_D]

that is fine.

[LXnastynotch93]

Found a cylinder on eBay but I'm unsure of whether I should trust the bottom end. Any way to check the health of the bottom end? Should I pull the drain plug and check for metal shavings?

[Paul_E_D]

What are you doing all this for? It's a 90% chance all you need to do is replace the rocker shaft/assembly.

But yes, it's easy to check the bottom end. Grab the rod and check for vertical and axial play. There should be vitually none. There is a little side to side play that is normal.

[Chippertheripper]

What Paul said.

But don't be surprised by some hair on the drain plug. If it's your first oil change on an lc4, buy yourself a six pack. You might be done with both at the same time.

[LXnastynotch93]

What are you doing all this for? It's a 90% chance all you need to do is replace the rocker shaft/assembly.

But yes, it's easy to check the bottom end. Grab the rod and check for vertical and axial play. There should be vitually none. There is a little side to side play that is normal.

The cylinder head currently on the bike has a tab missing where one of the bolts that holds on the camshaft cover bolts through.

The previous owner rebuilt the bottom end with a new crank, and piston. The main shaft bearing was replaced for the new roller bearing style. All these parts have around 500 miles on them.

The question is should I trust the bottom end. If I can then I'll rebuild the top end.