NC750x Bad Engine Noise after Valve Adjustment

[lootzyan]

The 700 only had 1 fuel injector, located up in the throttle body...

My model has two injectors. Yours is probably a simplified model, little known...

 

[670cc]

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

Shown in the attached photos is the cutaway demo engine model that Honda displayed when the NC700 was first introduced. The 700 always had two fuel injectors, from day one. It looks like the injectors are just a short distance from the intake valves. There is one throttle body. The 750 used this same configuration at it’s introduction.

 

[MZ5]

Thanks for the correction.

 

[Saturday Morning]

I second the earlier comment that the valves may not have been at TDC on the compression stroke. For anyone reading this in the future, wiggle the rocker arms by hand before doing any adjustment to verify that the rocker arm is not under tension. It should have a very small amount of play. If the rocker arm doesn't move, rotate the crank and re-align the marks on the cam sprocket with the proper index line on the cylinder.

 

[lootzyan]

...the valves may not have been at TDC on the compression stroke...

If someone makes such a mistake when adjusting the valves, the effect should be observed practically at the first attempt to start the engine after adjustment. Valve timing would be off 360 degrees. If the mistake had been made on both cylinders, I don't think it would have been possible to start the engine. If even only one cylinder had the wrong valve timing and the engine could be started, there is a high probability of valve damage (burnout). I don't know of such a case of a mistake in timing, despite the fact that I have adjusted the valves on hundreds of engines. You must know what you're doing. A mistake can be costly.

 

[670cc]

If someone makes such a mistake when adjusting the valves, the effect should be observed practically at the first attempt to start the engine after adjustment. Valve timing would be off 360 degrees. If the mistake had been made on both cylinders, I don't think it would have been possible to start the engine. If even only one cylinder had the wrong valve timing and the engine could be started, there is a high probability of valve damage (burnout). I don't know of such a case of a mistake in timing, despite the fact that I have adjusted the valves on hundreds of engines. You must know what you're doing. A mistake can be costly.

I think what is meant is that if the TDC for the given cylinder is between exhaust and intake strokes, and the valve lash is adjusted, it results in the valves being set too loose. On the wrong TDC the valves might be slightly open due to exhaust/intake overlap, so the wayward mechanic loosens the valve lash to get the proper clearance. As I said, I started doing this by mistake once. The adjust needed is not too great, but certainly more than a normal valve adjustment. I quickly realized my error and set things right. The engine might still run if adjusted on the wrong TDC, albeit poorly because the valves are not fully opening.

As for your comment, “Valve timing would be off 360 degrees”, I don't see any way a person could put the valve timing 360 degrees off without changing the relationship between the crank and cam shafts, such as by installing the cam chain incorrectly. Adjusting the valve lash does not change the valve timing, rather it can change the amount of valve opening.

I think the forum history has a case of this wrong TDC adjustment being done, particularly in the early days because Honda had an error in the early version of the 2012 service manual which could lead someone to do this misadjustment. I believe the result was a noisy and poorly running engine, but no damage done.

 

[lootzyan]

...I don't see any way a person could put the valve timing 360 degrees off without changing the relationship between the crank and cam shafts, such as installing the cam chain incorrectly.

I think the forum history has a case of this wrong TDC adjustment being done, particularly in the early days because Honda had an error in the early version of the 2012 service manual which could lead someone to do this misadjustment. I believe the result was a noisy and poorly running engine, but no damage done.

Yes, I know this case because since 2012 I have this version of the service manual (digital) with an incorrect description of the valve settings. The mistake is 360 degrees because this is the working principle of a four-stroke engine. Two revolutions of the shaft (720 deg) are required for one complete cycle.

 

[zannisvel]

Have you checked the camchain tentioner?
Also when you adjusted the valves, was the motor cold and not run for at least over night?

Does it get worse when the motor is warm or when you first start it?

 

[670cc]

Resurrected post from the dead.
Its terrible for small engines, marine generators, motorcycles.
Goggle it.

You didn’t say, but I assume you‘re referring to 10% ethanol blend gasoline. I see no point in reviving a thread about valve adjustments to turn it into an ethanol thread. People who have used 10% ethanol gasoline for nearly 4 decades with no problems are probably not going to be swayed by a “Goggle” (sic) search.

 

[INTHEWIND]

Ok, I agree, I'll delete it.
I do disagree it hasn't caused problems, ask any marine or small engine shop about corn gas.

 

[DayRider]

Hi all and thanks for an interesting thread, in fact, I found it interesting enough to wanna hear the end of it - So, has there been any conclusion yet? ... about the running problem that is?

 

[mrbios]

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

Sheee-ot, I'm gettin' old. I knew about the fuel pump circulating gas so not possible to suck up junk at the bottom (but I forgot that until I read the comments). For reference I ran out of gas once on the freeway at 190.0 miles exactly and I now have 46K miles on my 2012 NCX, original plugs and starts and runs absolutely perfect.

Also, I misadjusted the valves on my Kymco 250 scooter - used SAE units on the gauge instead of mm? I think. Heard a lot of new ticking and readjusted with mm and all was good. Sold it with 26K miles on it. Also, somehow did not do the NCX quite right @ 33K miles and redid it for peace of mind the next day.

Did OP ever find the cause of the noise? I could hear it in the video and I don't think it is the injector - sounds like valve adjuster or damaged? rocker arm.

 

[INTHEWIND]

Sheee-ot, I'm gettin' old. I knew about the fuel pump circulating gas so not possible to suck up junk at the bottom (but I forgot that until I read the comments). For reference I ran out of gas once on the freeway at 190.0 miles exactly and I now have 46K miles on my 2012 NCX, original plugs and starts and runs absolutely perfect.

Also, I misadjusted the valves on my Kymco 250 scooter - used SAE units on the gauge instead of mm? I think. Heard a lot of new ticking and readjusted with mm and all was good. Sold it with 26K miles on it. Also, somehow did not do the NCX quite right @ 33K miles and redid it for peace of mind the next day.

Did OP ever find the cause of the noise? I could hear it in the video and I don't think it is the injector - sounds like valve adjuster or damaged? rocker arm.

The Honda dealer is your friend. (hint hint)