I Have A Rattle, Could Use Some Help! New Info #3

[Tom H]

I have a rattle hat is driving me nuts. It sorta sounds like something loose, exhaust leak, or valves out of adjustment. It also seems mainly on the left side.

What I have is a '70 Ambo with a SP/G5 round fin 1000. Went through the engine when I got it. Mains were fine as well as the rings, did change the rod bearings and timing chain and seals. I kept the manual adjust chain adjuster. It also has the crank adapter to use the Field's Alt. conversion. I'm also running Loop headers with the T heads.

The bike runs pretty darn good, could be a bit better I think. No where near the power of my EVT, but a bit more then my Eldo.

Here is the problem:
Around town at lower revs it sounds pretty good in any gear, idles great and starts easily. When I'm on the freeway in 5th gear at about 60mph all is fine. Get up to about 65mph I start to notice the rattle, barely. At 70mph it's now full on annoying. It does stay the same as speed increases. I believe I did try 4th at 60ish and thinking about the same RPM and it was there. I had it also happen in 3rd at about...Ummm...45-50mph while holding the speed.
Now here is the part that I really don't understand. I'm rolling along a flat freeway holding 70mph, Then I just barely let off the throttle, I mean like a 1/16th of the range and the noise is completely gone. Touch it back up and the noise returns. Kinda made me think of a leaking exhaust? Ping, but not high pitched, more like metal to metal.

What I have tried so far:
Made sure all the nuts and bolts were tight including the Alt. bracket, spark plugs ect.. Held the side stand with my foot while it's making the noise, no help. To make the Loops headers work, you use 2 T gaskets on each header. Thought maybe one had crushed too much and added a third, no change. I then noticed my header on the left was just touching the police side stand bracket that the header passes through. Fixed that. no change.

I'm down to a few things to try, but they all mean tearing some of the engine apart. I just want to see if anybody has any thoughts as what what it might be.  I does make me wonder why the noise so abruptly stops when I just barely, barely let off the throttle.

Thank you,
Tom

[Huzo]

So the bit where you said “I barely let off the throttle” is interesting.
Once you reduce throttle by 5% the bike will assume a slightly lower speed...Will the noise come back as you hold that new speed ?
Also if you take her back up to 70 mph, note the noise then add 5% throttle, you’ll up the speed to say 75 mph..
Will a slight reduction in throttle from that new speed remove the noise, or is it confined in this case to 70 mph ?
What happens if you take it to 70 again and change down one gear, does it disappear ?
Does it make a difference if you are at 70 up a grade versus 70 on the flat ?
It does sound like throttle setting more so than pure rpm related.
How good are your uni joints and bevel box ?

[Tom H]

Huzo,

Like I mentioned, at about 60mph all is good. 65mph the noise is starting. About 70mph the noise is there. It's hard to tell if the noise gets worse at about 75mph, because the normal noises like wind and exhaust also get louder.

You do have a good point that I didn't try for very long. When I do let the throttle off, you don't really feel the bike slow. I went from holding 70mph to , how to say this, no noticeable loss of speed, but not holding 70. The next time I have it out I will see what happens when I just barely get off the throttle like I have been doing, but hold the throttle at that point. I do suspect that it will come back as it starts to hold the speed. But if the speed is below 65mph it may go away.

Tom

[bigbikerrick]

What you describe reminds me of the rattle my eldorado was making when I needed to replace the small end bushings in the connecting rods. It would only rattle when the engine was "floating", not accelerating or decelerating, at a certain RPM. new bushings from MG cycle, and had a local machinist ream them to fit  the piston pins.It was a fairly easy fix, done with the engine in the frame.
Rick.

[Tom H]

Couple more things I wanted to mention.

Checked for anything in the headlight rattling and made sure all front fender bolts were tight.

Valves: set them at .004 and .006" before and after re-torquing the heads twice. Roper I believe said anything round fin was .004 and .006". Per book it's I believe .0085 for both, so I set them at .008" both. No change except a bit noisier at city speeds and idle. But it may run a little stronger this way.

Tom

[Huzo]

What you describe reminds me of the rattle my eldorado was making when I needed to replace the small end bushings in the connecting rods. It would only rattle when the engine was "floating", not accelerating or decelerating, at a certain RPM. new bushings from MG cycle, and had a local machinist ream them to fit  the piston pins.It was a fairly easy fix, done with the engine in the frame.
Rick.

That’s got the smell of something interesting BBK.
Could Tom’s rear drive be developing some “chatter” when between load and unload. Given that unload is just load in the opposite direction which removes lash in the drive train.
I’m a bit skeptical on this myself given that you describe the symptom as manifesting as you approach 70.
There is more load on the drive train at 70 than 65 which shoots me down, but I think you have to ascertain which parameter this rattle is a function of.
RPM
Engine load
Throttle setting (as in amount you have screwed on, not balance.)
Road speed (rpm of everything rearward of gearbox output shaft.
If you can isolate which condition brings this about, you can throw away a myriad of possible causes, I like your seat of the pants diagnostic approach so far and your description of the symptoms is refreshingly insightful IMO.
Keep us in the “loop” as it were.
This is a good one.
Once we solve your problem, you can tell me why my V85 does a little “thing” sometimes....
Seems only fair..

[Chuck in Indiana]

That's a typical sound of a rod bearing. Of course, It's hard to diagnose from 5 hours away by jet. 

[Huzo]

Just had a thought.
Your description sounds identical to pinging, but I’m thinking of pre ignition due to carbon glowing on the piston head.
Before Beetle transformed my Norge into what it now is, it used to ping like buggery under certain conditions of throttle, ambient temp, humidity, altitude etc.
Point is..
At the moment it would begin to ping, a MINUTE reduction of throttle would cure it. So much so, that going up a grade at 3,500 rpm with 40% throttle under appropriate conditions would cause a ping, but an immediate down change to 4,000 rpm and 35% throttle would stop the ping like a light switch.
The left side was worse and it sounded like a box of knives and forks loose in the cylinder at it’s worst.
Whip the left head off and clean the piston crown and valve heads, the cylinder can stay undisturbed.

[Tom H]

What you describe reminds me of the rattle my eldorado was making when I needed to replace the small end bushings in the connecting rods. It would only rattle when the engine was "floating", not accelerating or decelerating, at a certain RPM. new bushings from MG cycle, and had a local machinist ream them to fit  the piston pins.It was a fairly easy fix, done with the engine in the frame.
Rick.

Rick,

Your thought is very interesting. By "floating" I'm thinking holding speed. Again all is good until about 65mph and then at 70+ it's noisy. At 75mph I can do the same small off throttle and the noise goes away. When I put it together I did check the small ends by hand and they felt fine, could not detect any movement. But this is something for me to look at as well as any other suggestions. If for some reason everyone points to the top end, I will look at all suggestions while it's apart.

Huzo,

Drive train could be a problem if it was only at a certain speed or above. This noise can happen at lower speeds and lower gears but about the same RPM. No tach on the police bikes to verify that.

Your last post on ping. When I have had ping on my Guzzies, it always sounded like a ting, like glass braking or tapping something on glass. Yes the knives and forks could be a good analogy. It's more of a metal to metal sound.

Thanks again so far,
Tom

[Chuck in Indiana]

Your thought is very interesting. By "floating" I'm thinking holding speed. Again all is good until about 65mph and then at 70+ it's noisy. At 75mph I can do the same small off throttle and the noise goes away. When I put it together I did check the small ends by hand and they felt fine, could not detect any movement. But this is something for me to look at as well as any other suggestions. If for some reason everyone points to the top end, I will look at all suggestions while it's apart.

(ahem) rod bearing. 

[Tom H]

Even one more thing. I'm running a Loop distributor with the T gear.

The 1000 is timed at 2deg BTDC on the LH cylinder. That is where I set this bike. I have also tried 5deg BTDC and the bike seemed a bit peppier, and no what I think of as ping. But the noise was there either setting at 70mph+.

Again, thanks so far!!!
Tom

[Chuck in Indiana]

Ok, this is the last time I'm going to say it, Tom.. 

[Tom H]

(ahem) rod bearing. 

Installed new big end rod bearings when I went through it. STD came out, STD went in. Crank was clean and smooth. I would also think, but could be wrong. If it was a big end, then it would do the noise over a larger range of RPM and or throttle settings.

Chuck, I'm definitely listening to what you say. And again, if all points to pulling the upper end, I will also look at the bottom.

Thanks again!!!
Tom

[Chuck in Indiana]

Main bearings are a thump. Rod bearings are a rattle on floating throttle. Of course, it may *not* be that.. but from what you are describing, it sounds like it to me from 2000 miles away. 

[lucky phil]

Rick,

Your thought is very interesting. By "floating" I'm thinking holding speed. Again all is good until about 65mph and then at 70+ it's noisy. At 75mph I can do the same small off throttle and the noise goes away. When I put it together I did check the small ends by hand and they felt fine, could not detect any movement. But this is something for me to look at as well as any other suggestions. If for some reason everyone points to the top end, I will look at all suggestions while it's apart.

Huzo,

Drive train could be a problem if it was only at a certain speed or above. This noise can happen at lower speeds and lower gears but about the same RPM. No tach on the police bikes to verify that.

Your last post on ping. When I have had ping on my Guzzies, it always sounded like a ting, like glass braking or tapping something on glass. Yes the knives and forks could be a good analogy. It's more of a metal to metal sound.

Thanks again so far,
Tom

I know exactly what you are referring to as "floating throttle" I use that term all the time to describe what you are conveying. My thoughts are piston slap. When the piston is under the influence of combustion pressure the thrust face is loaded and when under floating throttle it's reduced to very little. When you completely off the throttle its the flywheel crank and rod doing all the rotational work. Did you measure the piston to cylinder clearance when you had it apart? I mean with a bore gauge and mike? Also did you measure the gudgoen pin to piston clearance? Was the pin a nice tight fit in the piston?
You should be able to here piston slap when cold as well but it can sometimes get overwhelmed by the other mechanical noised at idle and slow engine speeds.
So from the extreme to the simpler, How are the slides in the carbs clearance wise?

Ciao

[bigbikerrick]

Installed new big end rod bearings when I went through it. STD came out, STD went in. Crank was clean and smooth. I would also think, but could be wrong. If it was a big end, then it would do the noise over a larger range of RPM and or throttle settings.

Chuck, I'm definitely listening to what you say. And again, if all points to pulling the upper end, I will also look at the bottom.

Thanks again!!!
Tom

Chuck, what  diagnostic method do you use to differentiate between small end and big end rod bearing noise?
Rick.

[bigbikerrick]

FWIW, when I rebuilt my eldo with Gilardonis etc. I replaced the big end con rod shells with std. crank looked/measured good, just needed polishing. I didnt replace thesmall ends, as they felt nice and tight by hand with the new gilardoni pins. Well I should have known better than to try and cut corners, as I  had to go back in and replace those about a year later to eliminate that annoying little rattle...especially when cold!
Rick.

[lucky phil]

FWIW, when I rebuilt my eldo with Gilardonis etc. I replaced the big end con rod shells with std. crank looked/measured good, just needed polishing. I didnt replace thesmall ends, as they felt nice and tight by hand with the new gilardoni pins. Well I should have known better than to try and cut corners, as I  had to go back in and replace those about a year later to eliminate that annoying little rattle...especially when cold!
Rick.

Yes pin clearance in the rod can be a "feel" thing which makes it hard. I have a new set of Guzzi H beam forged rods made in Europe and they "feel" like they have a tighter clearance to the standard Carrillo H beam rods. Low and behold they do when measured. The Euro rods are 0.008" and the Carrillos are 0.0012". It's very noticeable that 4 tenths. Interestingly Carrillo run wider small end clearances to others by around 0.0005" for some reason.
It's hard to troubleshoot these sort of things when the re builder has no actual measurements from the build. What "feels" ok to one is loose and sloppy to another. A friend of mine had a Velocette Thruxton engine apart once and thought the pin to rod clearance was fine( by feel) which I doubted and sure enough it rattled it's head off when reassembled.
When you rebuild an engine you need to measure everything with the proper tools and make a record of clearances and sizes if for no other reason than when you get these sort of issues at least you can eliminate some suspects. So if you have measured the piston to cylinder clearances and they are within spec and you have this rattle for instance you at least know you can pretty much eliminate it as a cause or conversely if you know its a bit loose then you can also have a logical possible explanation.


Ciao 

[Tom H]

I don't have the proper tools or the long learned proper skills to accurately measure engine parts. I can measure things with the tools I have, but I don't trust the tools. Maybe if I measured something then took it to a skilled machinist, then he looked at my numbers, measured and agreed, I would feel better.

One thing that I had been thinking it could be is valve springs. The noise, to me, really sounds like rockers banging on the valves. I didn't want to suggest something because that could sway opinions. How do you know if you have week springs at higher RPM's?

Tom

[Huzo]

I don't have the proper tools or the long learned proper skills to accurately measure engine parts. I can measure things with the tools I have, but I don't trust the tools. Maybe if I measured something then took it to a skilled machinist, then he looked at my numbers, measured and agreed, I would feel better.

One thing that I had been thinking it could be is valve springs. The noise, to me, really sounds like rockers banging on the valves. I didn't want to suggest something because that could sway opinions. How do you know if you have week springs at higher RPM's?

Tom

Happy to stand correction, but I’d think that weak springs would delay the proper closing of the valves and that would begin to lag behind the action of the rockers, increasing lash and consequently noise.
I’ve no idea how that would translate out in the real world conditions you describe but it’s not the biggest of stretches to imagine it. I reckon a very telling symptom is the slight reduction in cylinder pressure required to cancel the rattle, really mate I’d be checking the pre ignition thing if it was mine.

[lucky phil]

I don't have the proper tools or the long learned proper skills to accurately measure engine parts. I can measure things with the tools I have, but I don't trust the tools. Maybe if I measured something then took it to a skilled machinist, then he looked at my numbers, measured and agreed, I would feel better.

One thing that I had been thinking it could be is valve springs. The noise, to me, really sounds like rockers banging on the valves. I didn't want to suggest something because that could sway opinions. How do you know if you have week springs at higher RPM's?

Tom

Pull the rocker covers and look for the broken springs. I dont think it will be but it will put your mind at ease. However while you are in there check the rocker arms are not sliding back and forth on the rocker pins. On a square fin engine the rocker arms are controlled on the pins by bronze washers and a preloaded spring. If one of those springs is missing or broken it will cause noise. I assume your engine will control the lateral movement of the rocker arms in the same manner.

Ciao

[Two Checks]

While checking the rockers pull the rocker arm shafts and look for wear on them. That may be the source. If they are worn it would cause valve clearances to change. Only takes a minute.

[kirby1923]

Better ear plugs...

:-)

[Tom H]

I was talking to a friend of mine today that has been around bikes and engines forever and a day and told him about the noise. After I brought up what has been said here, and what I thought it might be. He kinda agreed with all the above. He looked up what issues weak valve springs show. One was high RPM excessive noise and the second was loss of power at higher RPM. Kinda sounds like what I have going on. Huzo was right on the description of weak springs.

Armed with more knowledge of the springs and the suggestions. I plan to start with the springs, may see if it can be done without pulling the head. Depends on if I can find a tool to compress the spring in place. I already have the hose to pressure the cylinder. If they check out I will closely examine the small end and if needed, pull the rod to check the big end. Also if I'm in that deep I will double check the piston/cylinder clearance.

It's 105deg in my garage today. I don't think I will start today. Hopefully I can get a start tomorrow!

Thanks again,
Tom

[Huzo]

Just musing more on this..
It can’t be your valve springs, because as you describe it, the bike will rattle at 70 for example but the noise will disappear with an very slight reduction of throttle, even before the rpm reduces.
The valve train only reacts to engine rpm, it is the revs that dictate the forces on the valve gear. A noise that comes and goes at constant rpm but varying throttle (cylinder pressure), is detonation.
Imagine your engine at 4,000 rpm with 30% throttle.
Your valve train has the same loads as it does with 4,000 rpm and 40% throttle, it is the thrust on the piston that varies with throttle.
If your exhaust valve spring is weak, then you may be clapping an exhaust valve on the piston crown...! I have had it happen on a BSA B33 years ago.
Really mate, whip the head/s off...
It’s very significant that your rattle is a function of throttle setting. Chuck’s thought is worthy of consideration also, because the load on the little end bearing varies with throttle setting.

[Tom H]

Huzo, I'm pretty darn sure it's not ignition related. When I put it together I cleaned the heads and pistons. Set the timing at 2deg per the book on LH. But...a Loop dist. could throw that off??? I have also tried 5deg LH. At 70mph, as far as I can hear, the RH is normal noise with either. Seems so far to be just LH issue. As I mentioned. I have had ping issues with other bikes, this does not sound like ping to me. But then again, I could be wrong.

I will be digging in in the next few days and see what I can find. More suggestions are very welcome! I'll let all know what I find if anything. Could b more questions?????

Thanks again!
Tom

[wirespokes]

I had a 74 Volvo that made a rattly buzzing at a certain RPM. Drove me nuts for years and couldn't find the reason. Finally when I was rebuilding the engine I discovered that brace running from the intake plenum down to the block near the oil pan was missing a bolt. The upper was attached nice and solid, but the lower was just resting against the block. Most of the time it just rested there, but at 3200 RPM it would buzz like crazy.

I have an R100GSPD that would rattle around 2800 RPM - usually on decel. I looked everywhere under the tank for something that could be vibrating. Changed things around and found numerous things to optimize or fix, but the rattle stayed. Checked the wrist pins - good. While I was there I checked the right side rod bearing, but for some reason not the left. After I'd run out of all possibilities I thought - my initial idea was 'rod knock'. But it didn't sound or act like what I figured a rod knock should be. I'd never had a rod knock before. Went back in and checked the left side and sure enough - the left side rod bearing was toast.

Are you sure nothing is vibrating or rattling under the tank? Is the alternator/generator mount tight? Not broken or cracked?

[lucky phil]

Just musing more on this..
It can’t be your valve springs, because as you describe it, the bike will rattle at 70 for example but the noise will disappear with an very slight reduction of throttle, even before the rpm reduces.
The valve train only reacts to engine rpm, it is the revs that dictate the forces on the valve gear. A noise that comes and goes at constant rpm but varying throttle (cylinder pressure), is detonation.
Imagine your engine at 4,000 rpm with 30% throttle.
Your valve train has the same loads as it does with 4,000 rpm and 40% throttle, it is the thrust on the piston that varies with throttle.
If your exhaust valve spring is weak, then you may be clapping an exhaust valve on the piston crown...! I have had it happen on a BSA B33 years ago.
Really mate, whip the head/s off...
It’s very significant that your rattle is a function of throttle setting. Chuck’s thought is worthy of consideration also, because the load on the little end bearing varies with throttle setting.

Yes all well thought through but you wont get detonation on a floating throttle. A floating throttle is probably 1% or less off the stop. Chucks suggestion has merit of course but if the rod bearings are new and original size and the pin was in good shape there's a fair chance the the big end clearances are ok. Not sure about the little end though. As I mentioned in another post it's really hard to determine something like this from an unmeasured build and without actually hearing it. With a set of measurements to look at you can pretty much identify most noise origins.
My Daytona build is a case in point. I knew the throttle body shafts had wear in them from the get go but used them anyway. After I got the engine running the RH cylinder had what appeared to be vary distinct valve tap. The LH side was fine but remembering the TB shaft bush wear I grabbed the r/h TB shaft and the noise stopped immediately. It was the throttle bladed clicking away on each induction stroke due to the wear in the shaft bushes. Knowing exactly the wear situation with them led me straight to the issue.

Ciao

[Huzo]

Huzo, I'm pretty darn sure it's not ignition related. When I put it together I cleaned the heads and pistons. Set the timing at 2deg per the book on LH. But...a Loop dist. could throw that off??? I have also tried 5deg LH. At 70mph, as far as I can hear, the RH is normal noise with either. Seems so far to be just LH issue. As I mentioned. I have had ping issues with other bikes, this does not sound like ping to me. But then again, I could be wrong.

I will be digging in in the next few days and see what I can find. More suggestions are very welcome! I'll let all know what I find if anything. Could b more questions?????

Thanks again!
Tom

Ok mate.
I had a fair bit of faith in that theory but I may have to back away..

[Huzo]

Yes all well thought through but you wont get detonation on a floating throttle.

As I understood it, the rattle disappeared with a slight REDUCTION in throttle.
My assertion was that there was detonation prior to rolling back.