Engine Knock

[rocksandhammers]

Does anyone have any links to videos that demonstrate what engine knocking on these bikes sounds like? I’ve never really heard engine knock before, but I’m wondering if I can hear it in my engine.

The last few weeks I’ve been hearing a loud tapping or rattling sound, usually when accelerating at low rpms like if I’m slowly accelerating through gears off a stop. At first I thought maybe something up front like the radiator grill was loose but couldn’t find anything. Then I thought maybe one of my valve clearances was off. Checked the front since that’s where it sounded like it was coming from but only 1 of the 4 valves was a little loose and not by much. Got home from riding for an hour or so today and while backing it into the garage I noticed the engine temp light was on. Never seen that light come on in over 35000 miles now. I thought maybe it was an issue with my fan not kicking on since I haven’t really heard it yet this year, but when I was looking at the troubleshooting section in the manual it mentions heavy carbon deposit on piston crowns as the first thing. Wasn’t sure what that was so I started looking into it and it seems like that can be the result of the detonations causing engine knock, so I started wondering if this was related to the sound. I haven’t checked any of the electrical going to the fan yet, or the coolant levels, but I wanted to get your guys opinion on things. I know engine knock can be serious and I don’t want to super fuck up the engine.

[WintrSol]

A quick way to test for engine knock is to use 89 or 91 octane fuel, instead of 87. If it doesn't make that sound, it was knock. Knock in these engines would be caused by increased compression or very high temperatures. Since you seem to have high temperatures, you may want to flush and replace the coolant, and make sure there is no air trapped in it. To check for air, when the bike is overnight cool, open the radiator; the coolant should be up to the neck with no air gap.

[navigator]

Two things to check also.
Make sure the headpipe bolts are tight, and no exhaust leaks at that area.

I had an issue one time with a headpipe, the noise sounded like a very loud knocking...like the engine was about to explode.
I removed the bolts from the head and swung the pipe down for a look.
The weld between the inner and outer pipes at the top of the head pipe had cracked.
Exhaust gases were being forced into that cavity with no means of escape, sounded horrible!!

[rocksandhammers]

A quick way to test for engine knock is to use 89 or 91 octane fuel, instead of 87.

Problem with that test is i’m already using 91 octane fuel. Usually what I fill up with, especially with how cheap gas has been this year. I’ll definitely check coolant levels in the morning after the bikes cooled.

Two things to check also.
Make sure the headpipe bolts are tight, and no exhaust leaks at that area.

I had an issue one time with a headpipe, the noise sounded like a very loud knocking...like the engine was about to explode.
I removed the bolts from the head and swung the pipe down for a look.
The weld between the inner and outer pipes at the top of the head pipe had cracked.
Exhaust gases were being forced into that cavity with no means of escape, sounded horrible!!

I actually had an issue a few weeks ago where one of the exhaust headers had vibrated loose while riding. Was going down the road into town, let off the gas and it was almost like one big misfire. Pulled over and found it loose and tightened with a wrench. Tightened again when I got home and the bike had coooled, but I haven’t actually taken them off and inspected them.

[WintrSol]

Why would you use 91 octane, when the engine runs better on 87? This is a low compression engine, and anything higher than 87 is not only a waste of money, a lot of it goes out the exhaust un-burned. If you do have a small leak at the header gasket, it would show up as navigator described. Maybe time to replace the gaskets?

[Herb]

Why would you use 91 octane, when the engine runs better on 87? This is a low compression engine, and anything higher than 87 is not only a waste of money, a lot of it goes out the exhaust un-burned. If you do have a small leak at the header gasket, it would show up as navigator described. Maybe time to replace the gaskets?

It can also cause carbon build up in the cylinder because not all of the fuel burns in the combustion chamber.

[WintrSol]

Why would you use 91 octane, when the engine runs better on 87? This is a low compression engine, and anything higher than 87 is not only a waste of money, a lot of it goes out the exhaust un-burned. If you do have a small leak at the header gasket, it would show up as navigator described. Maybe time to replace the gaskets?

It can also cause carbon build up in the cylinder because not all of the fuel burns in the combustion chamber.

It's a slow process, but it certainly can.

[hillsy]

Why would you use 91 octane, when the engine runs better on 87? This is a low compression engine, and anything higher than 87 is not only a waste of money, a lot of it goes out the exhaust un-burned. If you do have a small leak at the header gasket, it would show up as navigator described. Maybe time to replace the gaskets?

It can also cause carbon build up in the cylinder because not all of the fuel burns in the combustion chamber.

Higher octane fuels simply detonate at a higher temperature - they still burn at the same rate as lower octane fuel.

[Herb]

Just a few notes on the subject of octane ratings.

https://www.hemmings.com/stories/2014/0 ... 0pressures.

Higher octane burns slower and can/will contribute to carbon build-up

Running a higher octane than absolutely needed to prevent knock is not only costly but it can do damage to the engine and lower performance.

I used to be able to get 85 octane for the 1400 and it started and ran better on it than on the 87 octane.

[hillsy]

Just a few notes on the subject of octane ratings.

https://www.hemmings.com/stories/2014/0 ... 0pressures.

Higher octane burns slower and can/will contribute to carbon build-up

Running a higher octane than absolutely needed to prevent knock is not only costly but it can do damage to the engine and lower performance.

I used to be able to get 85 octane for the 1400 and it started and ran better on it than on the 87 octane.

Did you read the comments in that article? A whole bunch of people reported real life situations where their vehicles ran crappier with lower octane fuel. I guess it depends. It was a nice theory.

My LC used to ping under load on low octane - but when I ran premium it was fine. Exhaust ran less sooty on premium as well.

[rocksandhammers]

So figured out a couple of things. Opened up the radiator and sure enough the coolant was low. Like down to just a quart low. I haven’t checked coolant levels since I changed it last year but I do remember forgetting to put the bars in, so maybe that’s it? Put some bars and new coolant in so that should be good.

I did take a look at the exhaust headers. They didn’t seem particularly loose, and no cracks that I could find. There was a lot of carbonization on the rear cylinder exhaust that I didn’t notice on the other one. Could this be causing the sound I was hearing?

[hillsy]

So figured out a couple of things. Opened up the radiator and sure enough the coolant was low. Like down to just a quart low. I haven’t checked coolant levels since I changed it last year but I do remember forgetting to put the bars in, so maybe that’s it? Put some bars and new coolant in so that should be good.

I did take a look at the exhaust headers. They didn’t seem particularly loose, and no cracks that I could find. There was a lot of carbonization on the rear cylinder exhaust that I didn’t notice on the other one. Could this be causing the sound I was hearing?

If your exhaust headers are leaking at the head you should be able to hear this at idle. If you are a smoker you can gently blow some smoke at the joins and you will see any leaks (that's kinda the only time I valued my friend's smoking habits...lol...)

[rocksandhammers]

Yeah. I don’t really hear it at idle. The only time I really notice it is slowly accelerating. Don’t really notice it at highway speeds either but that may just be because if the wind.

[hillsy]

Yeah. I don’t really hear it at idle. The only time I really notice it is slowly accelerating. Don’t really notice it at highway speeds either but that may just be because if the wind.

So can you hear it if you are stationary and revving the bike? Or moving with the clutch in (coasting) and then revving?

Might be something in the drive-train if that's the case.

[rocksandhammers]

I don't know if it does it while stationary. I haven't really tried it yet but I will here soon. It doesn't happen with the clutch in though. Usually it's right after I drop the clutch and I'm picking up speed.

[rocksandhammers]

So I can hear it when the bike is stationary. I could hear it at idle slightly. Started listening around with a makeshift stethoscope (I.e. a screwdriver... haha). It’s definitely something with the front cylinder. If I hadn’t just checked the valve clearances I’d swear it sounds like one is loose or too high or something.

[rocksandhammers]

So I did a fair bit of riding today (~200 miles) and I have done ideas about the sound I’ve been hearing. The sound is definitely coming from somewhere in the vicinity of the front, either from the front piston or from just near the clutch (don’t think it’s the clutch itself, haven’t noticed any performance issues). I don’t really feel it much at highway speeds, but the engine may be vibrating more. Not sure. I may just be misremembering how smooth it ran before this year, but there was definitely an almost uncomfortable amount of vibration going up to my hands. I think I can hear it at idle, but just barely. It seems to get worse as the bike warms up. I mostly notice it when cruising around town at 20-30 mph. seems to get worse as I gradually open up the throttle then go away as the rpms increase. Don’t hear it at all when I pull the clutch. Even when I release the clutch lever and I don’t hear it until I start to lay on the throttle. I still am real unsure of the culprit, partly because I’ve never had to tear into an engine before (besides a lawn mower years ago), and I’m still inexperienced enough that I don’t have a frame of reference to really know how to describe and identify the sound. It’s like a loud rattle.

My main suspects:

The front piston/cylinder:
-The sound seems located to this area. As I’ve posted previously my compression readings were low a couple weeks ago, and there was a ton of carbon build up in the rear exhaust and the troubleshooting in the manual mentions foiled combustion chambers as a cause of engine noise. Most likely culprit?

Timing chain:
Perhaps the timing chain is stretched or something causing it to slap around inside the engine? Looking at a diagram of the inside of the engine it seems like the location of where the sound is originating.

Crankshaft:
The sound could possibly be some worn bearings. This seems the least likely to me, but I have no idea and seemed within the realm of possibility.


What do you guys think? My big question is, is there any way to test any of these without tearing the engine out and pulling it apart? I’m getting myself psyched up for the idea of doing an engine rebuild. Never done one and it would feel like a right of passage, but it would be a real bummer since this is my only set of two wheels and likely will be for a while so it will be an early end to the riding season. And my garage isn’t the biggest.

I can try to record it and have you guys listen to it but I’m not sure if my phone will be able to pick it up real well. If I do get a good recording what would be the best way to get it on here for people to listen to?

[hillsy]

It's possible one of the tappets / valve tips has mushroomed and the clearance is actually too large. It's deceptive because you slide the feeler gauge in and it seems right but the feeler doesn't bend and allow for the extra clearance

I would have another look at these - you should be able to move the rocker by hand and if there is a too large a gap this should be evident.

If it's not that then check the cam caps / end float while you are in there (if you can).

Other wise - get a louder exhaust...lol..

[hillsy]

Sorry - I posted the above before I read your newest post. Still worth checking the tappets again as it's pretty easy to do.

[rocksandhammers]

Yeah. That was going to be my first step since it’s the easiest. I never checked the rear (partly because I didn’t want to dick with removing the rear carb manifold) since the sound was coming from the front.