Time for me to address the 800lb Gorilla in the room.(Engine knock thread) REVIVED!

[mcgovern61]

I have a clutch hub nut removal tool coming so I should be able to check the scavenger pump inlet next week. My Boss and I were talking and he said we can use his vibration analyzer to "listen" to a video of the '81 knock and we will be able to determine the location by the knock RPM in relation to engine order frequencies.

He is an expert in vibration analysis on ships, engines and other moving equipment. We recently did a vibration test on one of the Statue Of Liberty ferries and while driving through the water were able to tell that a specific propeller blade frequency was causing the ships bottom plates to vibrate and cause the vibration to travel throughout the ship while traveling at a specific engine speed on one of the two main diesel engines!

He said this '81 engine should be an easy one! :smilie_happy:

 

[dan filipi]

Nice boss!
Let's hope it IS easy.

 

[mcgovern61]

If I were a betting man (and I am not!) I would say that I am going to find the scavenger pump inlet full of sand (remember the sand in the oil way back when?).

I know that the #3 inlet springs are not stellar, the oil pressure drops off, the knocking/rapping starts at 3000 rpm ish after the oil pressure drops off and the carbs were leaking so I think it is safe to assume that they were putting too much gas in the mix.

QUESTION: If the #3 intake springs are no longer within spec....what happens? (Open too soon or close too late?)

 

[dan filipi]

It seems to me the valve will stay open longer and can more easily float and rather than the follower smoothly up against the lobe and under control, it can bounce around.

 

[scdmarx]

QUESTION: If the #3 intake springs are no longer within spec....what happens? (Open too soon or close too late?)

Not close soon enough - bounce and not stay closed.

Mechanically, the spring will be compressed when the rocker opens the valve. The valves weight becomes reciprocating mass. It takes muscle to push it in the direction of travel and get it going. But when it reaches the end of it's travel in that direction, it has to come to a complete stop, then change directions and get moving again the other way.

**Think of yourself running back and forth on a basketball court. First you have to shove off and get going, then slow down and stop before you can change directions and get going back the other direction, then slow down and stop, and shove off again in the other direction.....etc. You have to get your weight mass moving and build enertia, then slow your weight mass, overcome that enertia, and stop.

The cam lobe/rocker arm pushes it in one direction, then the spring pushes it back the other direction. If the spring ain't strong enough to keep up with the valves "timed event" then the valve may not move out of the way of the piston in time to avoid a collision. (that piston will arrive at the time it's supposed to, no matter what) The valve arriving late getting back to the seat, will not be "cusioned" back into the seat as desinged because that part of the cam lobe profile has already passed, allowing the valve to slam into the seat causing it to want to "bounce" with not enough spring pressure to hold it in the seat. Now you're loseing compression from where you get your power.

Also, the valve face-to-seat contact area is where the valve transfers heat. When the valve is bouncing around there is less contact of the two parts resulting in less heat being transfered away from the valve.

 

[thewhiterhino]

QUESTION: If the #3 intake springs are no longer within spec....what happens? (Open too soon or close too late?)

Not close soon enough - bounce and not stay closed.

Mechanically, the spring will be compressed when the rocker opens the valve. The valves weight becomes reciprocating mass. It takes muscle to push it in the direction of travel and get it going. But when it reaches the end of it's travel in that direction, it has to come to a complete stop, then change directions and get moving again the other way.

**Think of yourself running back and forth on a basketball court. First you have to shove off and get going, then slow down and stop before you can change directions and get going back the other direction, then slow down and stop, and shove off again in the other direction.....etc. You have to get your weight mass moving and build enertia, then slow your weight mass, overcome that enertia, and stop.

The cam lobe/rocker arm pushes it in one direction, then the spring pushes it back the other direction. If the spring ain't strong enough to keep up with the valves "timed event" then the valve may not move out of the way of the piston in time to avoid a collision. (that piston will arrive at the time it's supposed to, no matter what) The valve arriving late getting back to the seat, will not be "cusioned" back into the seat as desinged because that part of the cam lobe profile has already passed, allowing the valve to slam into the seat causing it to want to "bounce" with not enough spring pressure to hold it in the seat. Now you're loseing compression from where you get your power.

Good description Scdmarx I agree with your description completely.. Weak springs equate to valve float at lower RPM.. :Awe: :Awe: :Awe:

 

[joedrum]

ron realy knows how to put it in words :good: :mrgreen:

 

[mcgovern61]

Good stuff!! Thanks! :thanks:

So, if the #3 intake valve is bouncing around and not closing correctly ....(say.... at 3000 rpm on up) which would be during the compression stroke? Then the amount of fuel mixed is no longer correct and some would leak back before the valve seals correctly creating a lean mixture? If I understand correctly, a lean mixture can cause hesitation when you throttle up real fast (this engine did that) and if the mixture was lean, it could fire early causing detonation?

Something that I remember from my Jardine exhaust prior to my engine swap, the right side pipes were bluing.

 

[mcgovern61]

I found this online and found it interesting:

Causes of Engine Knocks.
1. Carbon is the most frequent cause of engine knocks.
2. The spark too far advanced, will waste power and cause a knock.
3. Loose connecting rod bearings, will cause knocks.
4. Worn crank shaft main bearings cause knocks.
5. Piston slap, due to loose piston.
6. Worn or broken piston rings, will cause a light knock.
7. Piston striking the cylinder head gasket.
8. Loose camshaft bearings.
9. Valve tappets out of adjustment, or badly worn, will cause noise.

How to Distinguish Knocks.
(1) The carbon knock is a clear, hollow sound, most noticeable in climbing sharp grades, particularly when the engine is heated. It is also indicated by a sharp rap immediately on advancing the throttle.
(2) Too advanced spark will be indicated by a dull knock in the engine.
(3) The connecting rod knock sounds like the distant tapping of steel with a small hammer, and is readily distinguished when the car is allowed to run idly down grade—or upon speeding the car to twenty five miles an hour, then suddenly closing the throttle the tapping will be very distinct.
(4) The crank shaft main bearing knock can be distinguished, when the car is going uphill, as a dull thud.
(5) The loose piston knock is heard only upon suddenly opening the throttle, when the sound produced might be likened to a rattle.

 

[dan filipi]

Mine is almost like (3) except that coasting there is no noise, floating rpm and slight throttle it is loudest.

(5) might be a closer description.

It's almost like the noise is being caused by more than one thing :Awe:

Loose cam bearings eh?
We haven't looked at them yet.

 

[scdmarx]

So, if the #3 intake valve is bouncing around and not closing correctly ....(say.... at 3000 rpm on up) which would be during the compression stroke?

Ummm, yes. After the intake valve closes, the next stroke would be compression.

Then the amount of fuel mixed is no longer correct and some would leak back before the valve seals correctly creating a lean mixture?

No, not neccessarily lean, just a lesser volume. For the sake of conversation, we'll use the 14 to 1 ratio. 14 parts air to 1 part gasoline. If it makes it in there as 14:1 and some leaks out, what's left is still 14:1 just less of it.
Imagine the difference between 150 grains of gunpowder, or 50 grains of gunpowder.

If I understand correctly, a lean mixture can cause hesitation when you throttle up real fast (this engine did that) and if the mixture was lean, it could fire early causing detonation?

What you're after is a controlled burn. The spark plug ignites the mixture, as it burns across the area it expands, pushing the piston down. A lean mix will typically raise combustion chamber temps. This could in turn cause "hot spots" which could ignite the mix prematurely. The mix ignites at one end of the combustion chamber (hot spot) and starts a burn across the area, working against the piston while it's still trying to compress. Then the spark plug ignites the mix in another spot, which starts another burn. The two flame fronts collide and you hear a knock.
That said, it is harder for the spark plug to ignite a lean mixture, than it is for it to light a rich mixture.
This is because the rich mixture has more fuel molecules to bridge the gap between the electrodes. It gets even easier when it's compressed into a smaller area. In the 80's when car manufacturers were scrambling to meet EPA requirements, we started having some pretty lean running cars, with spark plug gaps as much as .060" & 080", with base ignition timing set at 16 degrees. I replaced a lot of distributor caps back then. The usual 160-180 degree thermostats suddenly changed to 195 degree thermostats and coolant temps of 210-220 became the norm.
Can you say "it's not your fathers Oldsmobile"? :hihihi:

Something that I remember from my Jardine exhaust prior to my engine swap, the right side pipes were bluing.

The pipes were turning blue from heat. This is usually associated with late ignition timing. Although carburation could contribute as well. On cars I've seen cast exhaust manifolds glowing cherry red. What's happening is the mix is still burning on the way out the exhaust. It just ain't designed to handle that kind of heat.

 

[mcgovern61]

That certainly helps me understand a lot more than the very little I understand about gasoline engines. It is the difference between a parts changer (me) and folks like you that really understand these things! :thanks:

 

[mcgovern61]

The pipes were turning blue from heat. This is usually associated with late ignition timing. Although carburation could contribute as well. On cars I've seen cast exhaust manifolds glowing cherry red. What's happening is the mix is still burning on the way out the exhaust. It just ain't designed to handle that kind of heat.

I feel like I may be asking too many questions, but what could cause late ignition timing in our engines?

My other questions is, what could cause the mix to still be burning on the way out the exhaust? Does that explain the whitish exhaust valves on the right side?

 

[danf]

Sir mine had a knock before I worked on it, you said your vacuum advance was holding vacuum, you never said if you did anything to the mechanical advance, one or the other of these parts made my knock I had go away, I think it was the mechanical advance, it's needs to be moving freely and lubed..All I know is that it's gone now, the knocking sound is no longer present..Wow.

 

[joedrum]

springs are so important to running smooth ....when out of wack the varables of out come are wide and the timing can be effected by the total amount of slop in the intire motor ...slack in chains and so on ...so theres no one outcome.....in drumming its sounds cool to sound like a motor running with couple of drop clylinders ....this is very difficult to do but once doing it its easy to maintain because the action feeds on itself ....motors do the same thing .....my 83 is running like that now with one cylinder mostly droping out....valves are probably one the most key things that causes this with gas and spark .....

 

[scdmarx]

The pipes were turning blue from heat. This is usually associated with late ignition timing. Although carburation could contribute as well. On cars I've seen cast exhaust manifolds glowing cherry red. What's happening is the mix is still burning on the way out the exhaust. It just ain't designed to handle that kind of heat.

I feel like I may be asking too many questions, but what could cause late ignition timing in our engines?

I don't think Dan has put a limit on how many questions a guy can ask.


Well, I'm wondering if on our bikes with "non adjustable" ignition timing, were the parts all stamped out the same and installed exactly in the right position on every motor on the assembly line? We'll never know if Hashimoto had a bit too much saki the night before and didn't feel so good at work the next day. Or is "pretty dern close" good'nuff? I don't know. Joedrum's theory of parts wear over the years and miles sounds good to me.

My other questions is, what could cause the mix to still be burning on the way out the exhaust?

The only thing I can think of is it started burning late. Didn't have time to finish burning in the cylinder.

I haven't been into the ignition system on either of my wings yet, so I don't have all the answers. What I'm bringing to the table is just a basic "general info" sorta carried over from the automotive industry. "This is how ya burn gas". But like littlebeaver says, the advance mechanisms need to be working for a healthy ignition system. The discoloration of your pipes could also be from the carbs. Keep in mind that a lean mixture that runs hotter will exit hotter also. (more oxygen makes a more hotter fire) For whatever reason, your pipes were discolored from more heat passing through them than the chrome job liked.

 

[mcgovern61]

We'll never know if Hashimoto had a bit too much saki the night before and didn't feel so good at work the next day. Or is "pretty dern close" good'nuff? I don't know.

:smilie_happy: :smilie_happy: :smilie_happy:

 

[danf]

Did you check your timing with a timing light yet? Once you figure it out you will smile.. :grin:

 

[mcgovern61]

Did you check your timing with a timing light yet? Once you figure it out you will smile.. :grin:

Beaver, the engine is out of the bike and on the garage floor. I swapped it out last year with an '83 engine that works like a champ!!
I have the same carbs, ignition and wires that were on this '81 engine when it was knocking. I did make adjustments to the carbs to get them to stop leaking (floats were adjusted out of whack even after a professional rebuild). Again, same wires (which were new a year ago) new plugs that ran in both engines and same coils. The vacuum advance on the '81 did hold vacuum and it did move freely so I do not think that was the cause of the knock. I did not check the timing on this '81 before it was pulled nor have I checked the timing on the '83.

 

[danf]

Did you check your timing with a timing light yet? Once you figure it out you will smile.. :grin:

Beaver, the engine is out of the bike and on the garage floor. I swapped it out last year with an '83 engine that works like a champ!!
I have the same carbs, ignition and wires that were on this '81 engine when it was knocking. I did make adjustments to the carbs to get them to stop leaking (floats were adjusted out of whack even after a professional rebuild). Again, same wires (which were new a year ago) new plugs that ran in both engines and same coils. The vacuum advance on the '81 did hold vacuum and it did move freely so I do not think that was the cause of the knock. I did not check the timing on this '81 before it was pulled nor have I checked the timing on the '83.

If it's out of the frame it's a good time to remove the pulse generator housing and clean up the mechanical advance underneath it, spray it good with brake cleaner then some wd-40 then lightly grease I used 3 in 1 oil on all moving parts the thing is you need to check and see if it's rusty or not moving freely back and forth..it's a simple process, lube and put back your vacuum advance or pulse generator housing,, good luck sir.. :grin: