NC750x Bad Engine Noise after Valve Adjustment

[lionssss]

Hi Folks,

I have a 2020 NC750x with 18k miles on it. I did the oil 4k miles ago, changed the spark plugs 1k miles ago and did the valves 500 miles ago. After the Valve Adjustment the bike was running fine, didn't seem like anything was different from before the valve adjustment. After 500-1k miles riding on the valve adjustment, I started hearing a knocking/rattling noise coming from the engine. My bike is my daily so I'm trying to diagnose and fix the issue asap, any ideas of what went wrong?

UPDATE:
Me and a more mechanically inclined friend re-did the valves and the noise still remains. He put a screwdriver up to the tabbot cover, and said that he thinks the noise is coming from the fuel injectors. These symptoms first appeared when I got home from running my tank down close to E, I actually thought I ran out of gas before I thought the valves were messed up.

 

[670cc]

Well, first, I'd think you need to identify the source of the rattling noise. It may or may not be related to the valve adjustment. I see you included a video, but it is hard (for me) to diagnose a problem remotely from a video/audio clip. Can you use a screwdriver to the ear or a mechanic's stethoscope to localize the rattle source?

If indeed the noise comes from the cylinder head, the best course of action would be to open the head cover and inspect the internals.

 

[trjerm]

I would start by double checking the valve adjustment

 

[halfSpinDoctor]

Maybe one of the lock nuts on the adjuster screws came loose? Did you use a torque wrench to check they were in spec before reassembly?

 

[Deleted member 1183]

Maybe one of the lock nuts on the adjuster screws came loose? Did you use a torque wrench to check they were in spec before reassembly?

I would agree with this, especially if the noise came on gradually after valve adjustment. For sure I would stop using the bike until dealt with.

 

[lionssss]

When I did the valve clearances, I torqued in the bolts to 14 Newton meters (followed a youtube video meticulously). That's why I'm so confused on to what went wrong. The hardest part of the job was gauging the feeler gauges, because I could slide the feeler gauge in multiple ways and get different measurements.

Hopefully I'll be able to get the bike apart today and take a look at the valves again. I'm definitely going to be worried about this happening again in the future.

@Griff @halfSpinDoctor @trjerm

 

[jeremyr62]

Don”t be worried. We have all done it. At least the NC is easy to work on. I messed up the clearances on a VF500. That was not easy to work on.

 

[670cc]

A potential problem with adjusting the NC valves is if you set the clearances while the crank is on the wrong TDC. I actually started to do this once and then caught myself and had to redo a few settings. However in your case, you reportedly didn't noticed the increased noise until well after the valve adjustment completion. If you had set the clearances wrong, and that is responsible for the noise, I'd think you might have noticed it right away.

 

[lionssss]

UPDATE:
Me and a more mechanically inclined friend re-did the valves and the noise still remains. He put a screwdriver up to the tabbot cover, and said that he thinks the noise is coming from the fuel injectors. These symptoms first appeared when I got home from running my tank down close to E, I actually thought I ran out of gas before I thought the valves were messed up.

@670cc @jeremyr62 @Griff @halfSpinDoctor

 

[jeremyr62]

You do hear of problems with fuelling when tanks are run dry because (supposedly) all the crap that ends up at the bottom of the tank gets pulled through. However there is plenty of filtration in the fuel lines so I never really believed it. Also the fuel pickup is designed to leave some fuel in the tank anyway so all that water and rust probably can't be picked up anyway. If you are sure the valves are good I'd be tempted to use the bike as normal but use some high detergent (premium) petrol through it and even add a few ml of 2 stroke oil to the petrol to help lubricate the injectors. At least see if this alters the noise.

 

[670cc]

You do hear of problems with fuelling when tanks are run dry because (supposedly) all the crap that ends up at the bottom of the tank gets pulled through. However there is plenty of filtration in the fuel lines so I never really believed it. Also the fuel pickup is designed to leave some fuel in the tank anyway so all that water and rust probably can't be picked up anyway. If you are sure the valves are good I'd be tempted to use the bike as normal but use some high detergent (premium) petrol through it and even add a few ml of 2 stroke oil to the petrol to help lubricate the injectors. At least see if this alters the noise.

The fuel pump fuel intake is always at the bottom of the tank. It always pulls “the crap that ends up at the bottom” first, regardless of the fuel level. The fuel level in the tank does not determine where the fuel pump inlet is. The only thing that could change is with the fuel level extremely low, the pump could eventually pull in debris that had been floating ON TOP of the fuel.

On the NC, there is a screen/filter on the fuel pump intake inside the tank, but the is no other fuel filter in the fuel line to the injector rail. Essentially, the NC has no user replaceable fuel filter.

Perhaps the OP did indeed pull debris into the fuel system. On more than one occasion I have run my NC fuel down to where there was less than a quart or a liter of fuel remaining with no ill effects, but the OP may have had contamination in the fuel.

UPDATE:
Me and a more mechanically inclined friend re-did the valves and the noise still remains. He put a screwdriver up to the tabbot cover, and said that he thinks the noise is coming from the fuel injectors. These symptoms first appeared when I got home from running my tank down close to E, I actually thought I ran out of gas before I thought the valves were messed up.

@670cc @jeremyr62 @Griff @halfSpinDoctor

I have changed fuel injectors on an NC (for a different reason). Due to limited access in that area, it is not a fun job.

 

[jeremyr62]

The fuel pump fuel intake is always at the bottom of the tank.

So how do you account for residual water pooling in the base of tanks and staying there? Sure the inlet is fixed and towards the bottom of the tank but it isn't going to scavenge everything. Rust and most types of debris are denser than petrol so sink to the bottom. Not that I am saying this is the problem. I don't belive the stuff that ends up on the bottom ever get into the fuel system unless you really agitate the tank.

 

[670cc]

So how do you account for residual water pooling in the base of tanks and staying there? Sure the inlet is fixed and towards the bottom of the tank but it isn't going to scavenge everything. Rust and most types of debris are denser than petrol so sink to the bottom. Not that I am saying this is the problem. I don't belive the stuff that ends up on the bottom ever get into the fuel system unless you really agitate the tank.

Agreed, but if the pump inlet is not going to scavenge everything from the bottom of the tank when it’s full, it‘s not going to scavenge everything from the bottom when the tank is near empty, either.

I realize this element is not likely to affect the OP’s problem, but I cringe when I hear or read about fuel pumps sucking up debris from the bottom only when the fuel gets very low. Picture drinking from a cup with a straw bottomed out in the cup. From the very beginning and all the way until the cup is empty, you are drinking what’s in the bottom of the cup.

 

[lootzyan]

So how do you account for residual water pooling in the base of tanks and staying there?...

If there is water in the fuel tank, it collects at the lowest point only when the vehicle is parked for some time.
While driving, due to the brutal shaking of the fuel in the tank, the water can be mixed with the fuel as well as a James Bond martini. No filter can stop it. This was quite a problem with carbureted engines. Water was collecting in the float chamber in the carburetor. I know this from my own experience when I serviced this type of vehicles a long time ago.
But for the last 30 years or so, I have not once noticed a water in fuel problem in any of my vehicles, although I am sure it is inevitable. Maybe, to some extent, modern fuel additives from the manufacturer can chemically bind the water in the fuel for easier disposal during combustion. But I didn't want to find out about it.

 

[jeremyr62]

The design of the petrol tank can influence it too. The VF500 had two low points in the tank on both sides and these would collect water and the tank would eventually perforate in those locations.

 

[670cc]

If there is water in the fuel tank, it collects at the lowest point only when the vehicle is parked for some time.
While driving, due to the brutal shaking of the fuel in the tank, the water can be mixed with the fuel as well as a James Bond martini. No filter can stop it. This was quite a problem with carbureted engines. Water was collecting in the float chamber in the carburetor. I know this from my own experience when I serviced this type of vehicles a long time ago.
But for the last 30 years or so, I have not once noticed a water in fuel problem in any of my vehicles, although I am sure it is inevitable. Maybe, to some extent, modern fuel additives from the manufacturer can chemically bind the water in the fuel for easier disposal during combustion. But I didn't want to find out about it.

I’m no chemist but I wonder if the modern fuel additive that may be dispersing water in the fuel tank might be the all too common 10% ethanol.

 

[lootzyan]

I’m no chemist but I wonder if the modern fuel additive that may be dispersing water in the fuel tank might be the all too common 10% ethanol.

Manufacturers of stabilizers boast that their products prevent the harmful effects of ethanol in fuel and also help in the chemical binding of water in fuel. What chemicals are used is a trade secret. I used it a couple of times but stopped. But I guess it wouldn't hurt to use it.

 

[itsmenc700]

I to believe that on a bike there is nothing in the bottom of the tank that wasnt mixed up from all the movement from you riding around!!
I also dont have and have not heard from any friend, relative, coworker about any problems from 10% ethanol in the gas.
We have had it in 99% of the gas here since around 1985. Yes 100% gas can be found.
Its kind of like bigfoot, either you believe it or not.

 

[670cc]

Manufacturers of stabilizers boast that their products prevent the harmful effects of ethanol in fuel and also help in the chemical binding of water in fuel. What chemicals are used is a trade secret. I used it a couple of times but stopped. But I guess it wouldn't hurt to use it.

I used to believe the hype about fuel stabilizers, then the stabilzer prices kept going up higher and higher, so for the most part I quit using them. And nothing changed. We’ve been using 10% ethanol for decades. Fuel stored 6 months still burns. Engines all still run whenever I need them.

I have only one rule. I do not leave fuel in carburetor bowls for over a month or maybe two. I drive the machine or I drain the bowl. Fuel injected engines require no attention and no additives.

 

[MZ5]

UPDATE:
Me and a more mechanically inclined friend re-did the valves and the noise still remains. He put a screwdriver up to the tabbot cover, and said that he thinks the noise is coming from the fuel injectors. These symptoms first appeared when I got home from running my tank down close to E, I actually thought I ran out of gas before I thought the valves were messed up.

The 700 only had 1 fuel injector, located up in the throttle body (nowhere near the valve cover).
Did that change for the 750?