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Christopher_55934 wrote:
Any pictures of piston top and head?
I forgot to get them but I inspected both and I did not see anything abnormal. There is some carbon buildup from the excessive autolube before the rebuild but now that I ran some premix thru it seems to be dissolving as I could almost rub it off with a shop rag. I did not see any marks or dents from detonation/pinging or anything like that.
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A mechanics stethoscope is 7 bucks at HF or Amazon.

Tracked down a (piston hitting head) rattle on my wife's moped and a buzzing LED bulb in the kitchen the same afternoon.
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gummy8879 wrote:
Just popped off the clutch cover. I could see 1 score in the side but I don't remember if it was there before the rebuild or not.

I ran the engine for a few seconds to see if the clutch contacting the cover was the source of the noise, and the noise was still there. Next I want to try running the engine for a few seconds with no clutch at all. I want to rule out everything before I have to split the case again to diagnose this issue.


Can you repeat the video only this time apply the rear brake. The tap sounds like it matches the timing of the rear wheel spinning to me.

Hec
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It's running lean.
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SoCalGuy wrote:
It's running lean.
Ladies and gentlemen that ties it up! Two votes for "too lean" and two votes for "too rich" on my current jetting!

Seems like I've found Schrodinger's jet stack, considering people have both told me that it should be fouling at WOT and that it should be so hot my piston should look like swiss cheese.

In all seriousness though, carb setting is something I ruled out almost immediately. On this jetting my CHT only creeps above 300F under extended top gear running at 55+mph, and when I slow down it quickly cools back under 270F.

AC140, BE5, 130MJ
52/140, 2.5 turns rich

The sound is RPM dependent ONLY, and happens regardless of the carb settings. It begins immediately on cold start and does not change as the engine warms up. Choke in or out does not matter. It did not do this before the rebuild and I did not touch the carb during that time. How could identical jetting before and after suddenly cause this racket?
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What's the timing? And how did you set it?
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SoCalGuy wrote:
What's the timing? And how did you set it?
18 degrees advanced, just like the kit specified. I set it by finding TDC with a sparkplug thread stopper, marking on the case, and using a timing light. I had to dremel out the stator plate a little to get it set.
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How did you determine the 18° mark on the case?
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SoCalGuy wrote:
How did you determine the 18° mark on the case?
1deg = ~1.5mm on the case ridge. Find TDC by rotating the flywheel until the piston hits the stopper both ways. Exactly halfway between those 2 points is TDC. Mark that on case, then 18*1.5 = 27, so 27mm counterclockwise from TDC is 18° advanced. I followed FMP's guide.

To make sure that the noise was not detonation/ignition pinging, I retarded it as far as the grooves I cut in the stator would let me, to no avail. I am using 93 octane and I always have since I installed this 177 kit about a year ago.
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I'll mention what most are thinking. It's unusual to have to Dremel the stator to get 18 degrees. Definitely worth a double check, using a degree wheel or degree instrument.
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If timing was the source of this noise I would have heard it ages ago. I would also see evidence of knock on the piston and head, and I do not see either after almost 2 tanks of gas. I will re-do the timing process after I have figured out the source of this noise.

If dremeling the stator is unusual and I did it wrong, then the ignition should currently be too retarded, right? That doesn't result in knock.
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gummy8879 wrote:
If timing was the source of this noise I would have heard it ages ago. I would also see evidence of knock on the piston and head, and I do not see either after almost 2 tanks of gas. I will re-do the timing process after I have figured out the source of this noise.

If dremeling the stator is unusual and I did it wrong, then the ignition should currently be too retarded, right? That doesn't result in knock.
This won't be the rattle noise. But will be a future problem, if way out (in either direction).
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The rattle sounds to me like the gearbox. Are you running straight cut primaries by any chance?
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Jack221 wrote:
This won't be the rattle noise. But will be a future problem, if way out (in either direction).
I agree. It's a metal on metal mechanical noise.

I get that you don't hear it when spinning the engine by hand. Which is strange.

Any way you could spin it faster without combustion…like with a drill? What about taking a slomo video if your phone does that?

Just spitballing here. Just hate to have you split the cases without having something you could put your peanut buttery finger on once you open it up.
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SoCalGuy wrote:
The rattle sounds to me like the gearbox. Are you running straight cut primaries by any chance?
He is. He has installed the 23/64 Malossi Up Gear kit. It has straight cut gears. That's why I wanted him to repeat his video of it running but while applying the brake.. I wanted to drive train to stop rotating as much as possible.

Hec
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Yep, straight cuts are definitely noisier than helical.

Not sure applying the brake is going to tell much. The primary rotates whether the axle is spinning or not. Maybe run it without the clutch.

And yes, too retarded ignition can cause a low rhythmic thud at idle because spark is happening after the down stroke.
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Hmmm… No direct experience with this, but there is always the potential for the new fast stuff to not play nicely with the old team.
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Hec In Omaha wrote:
He is. He has installed the 23/64 Malossi Up Gear kit. It has straight cut gears. That's why I wanted him to repeat his video of it running but while applying the brake.. I wanted to drive train to stop rotating as much as possible.

Hec
SoCalGuy wrote:
Not sure applying the brake is going to tell much. The primary rotates whether the axle is spinning or not. Maybe run it without the clutch.
Yes I planned to run it with the clutch completely removed but got sidetracked with some college stuff. Will do that sometime this week.

If the noise is still there then I think we will have narrowed it down to part of the crank halves contacting the case for some reason. The top end possibility is still there but I think that is unlikely to be the issue.
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Can you hear the noise when in gear, holding the clutch?
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Jack221 wrote:
Can you hear the noise when in gear, holding the clutch?
Yes, the noise is solely RPM dependent and occurs in neutral, in gear, clutch in or out. But the clutch basket is always spinning with the crank; hence why I tested the clutch cover theory and will soon be testing the engine with the clutch completely out.
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I think someone mentioned this before, but it sounds like primary rivets scrapping.

you might not hear it when kicking the motor or starting the bike.

But both noises would go away when you pull the clutch lever.
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108 wrote:
I think someone mentioned this before, but it sounds like primary rivets scrapping.

you might not hear it when kicking the motor or starting the bike.

But both noises would go away when you pull the clutch lever.
I just ran the engine with the clutch completely removed and the sound was still there. Either the crank halves are contacting something inside the case, the top end has spontaneously developed the noise, or the carbon reed is just this loud.
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gummy8879 wrote:
I just ran the engine with the clutch completely removed and the sound was still there. Either the crank halves are contacting something inside the case, the top end has spontaneously developed the noise, or the carbon reed is just this loud.
Yeah I saw the video. You can hear it pretty clearly.

I don't think it's because you're using straight cut teeth. Because I've had the malossi gears on my PX before.

Pulling the clutch lever will disconnect the power to the gearbox and the output shaft.

So you'll at least know if the noise is in the top or bottom half of the engine.

Another guess is the cruciform scrapping against 1st or 2nd gear when you're in neutral.

Noise would go away if you put it in gear.
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108 wrote:
Yeah I saw the video. You can hear it pretty clearly.

I don't think it's because you're using straight cut teeth. Because I've had the malossi gears on my PX before.

Pulling the clutch lever will disconnect the power to the gearbox and the output shaft.

So you'll at least know if the noise is in the top or bottom half of the engine.

Another guess is the cruciform scrapping against 1st or 2nd gear when you're in neutral.

Noise would go away if you put it in gear.
Oh I mean just today. I completely removed the clutch so there was nothing on that side of the flywheel. The gearbox/primary was no longer connected to anything. I spun the primary by hand to feel any resistance/scraping and I did not feel anything. I checked the rivets to ensure they were not contacting too.

The only things connected to the crankshaft at the moment are the piston and the flywheel.
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Yeah good idea.

At least you know it's in the top half.

Weird though, wonder what it is…

Flywheel scrapping on the starter motor cog mechanism? I've had that before. Where the small cog doesn't retract properly after the motor has started.
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108 wrote:
Yeah good idea.

At least you know it's in the top half.

Weird though, wonder what it is…

Flywheel scrapping on the starter motor cog mechanism? I've had that before. Where the small cog doesn't retract properly after the motor has started.
I know that sound. That's a different sound than this one. Louder & more obvious, too.
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chandlerman wrote:
I know that sound. That's a different sound than this one. Louder & more obvious, too.
Yeah you'd be able to find it easier.

Then I'm wondering if it the conrod hitting on the cases?
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108 wrote:
Yeah you'd be able to find it easier.

Then I'm wondering if it the conrod hitting on the cases?
If the conrod is hitting the cases, do I just shave a bit off of the case to clearance? I was planning on doing some port matching whenever I got the Stelvio kit and some burrs for my dremel. Strange that this would happen on a stock length mazzu crank though.

Also, I checked the starter gear and confirmed that that's not the issue. I have kickstarted the scoot too and the noise is still there.
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gummy8879 wrote:
If the conrod is hitting the cases, do I just shave a bit off of the case to clearance? I was planning on doing some port matching whenever I got the Stelvio kit and some burrs for my dremel. Strange that this would happen on a stock length mazzu crank though.

Also, I checked the starter gear and confirmed that that's not the issue. I have kickstarted the scoot too and the noise is still there.
Yeah strange for sure.

You could test it before closing the cases, which is something I normally test for with new components.

Crank, piston and cylinder studs installed, slide the cylinder on the studs without the flywheel side of the crankcase and turn the crank. See if there's any interference and fouling. You'll be able to see straight into the bore. Then address those as you build out.
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Is the oil pump shaft drive gear still installed behind the clutch? If so, is there a chance the cylinder stud (upper). Is screwed in too far and contacting the gear? If the drive gear is still in,you can inspect this with the clutch out. That gear has special washers on either side of it. If they are missing the gear will walk on the shaft it spins on. Maybe it's moving enough to contact the end of the cylinder stud?

Hec
Possible culprit?
Possible culprit?
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Hec In Omaha wrote:
Is the oil pump shaft drive gear still installed behind the clutch? If so, is there a chance the cylinder stud (upper). Is screwed in too far and contacting the gear? If the drive gear is still in,you can inspect this with the clutch out. That gear has special washers on either side of it. If they are missing the gear will walk on the shaft it spins on. Maybe it's moving enough to contact the end of the cylinder stud?

Hec
Every component of the oiling system has been removed. The only remnant is the cog that goes on the crank's clutchside that acts as a spacer for the clutch. I have plugged the reed block to close off the shaft hole.

The studs are threaded in so there is 41mm of thread above the cylinder (with no head).
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So if I understand correctly, you have run the engine in such a way that the only moving parts are the crank and piston.

I'm not sure if you're at the point of splitting the cases, but I'm out of ideas.

Only thing that comes to mind is something I read about the vmc kit requiring a 60mm crank with a 105mm conrod, but that may be for a different/earlier version. Besides, you were running the kit with a stock Stella crank with no issues.

Hopefully, upon splitting the cases you would find some tell tale sign of metal to metal contact that you could clearance or adjust for. It would really suck if nothing turned up.

Also thinking about the hesitation you were having at low throttle. A difficult part of the range to jet and seems especially so with the Stella reed. I have been fighting with the same issue for awhile now as did the previous owner of the scooter. At this point, I will jet it as best I can and just live with it.
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orwell84 wrote:
So if I understand correctly, you have run the engine in such a way that the only moving parts are the crank and piston.

I'm not sure if you're at the point of splitting the cases, but I'm out of ideas.

Only thing that comes to mind is something I read about the vmc kit requiring a 60mm crank with a 105mm conrod, but that may be for a different/earlier version. Besides, you were running the kit with a stock Stella crank with no issues.

Hopefully, upon splitting the cases you would find some tell tale sign of metal to metal contact that you could clearance or adjust for. It would really suck if nothing turned up.

Also thinking about the hesitation you were having at low throttle. A difficult part of the range to jet and seems especially so with the Stella reed. I have been fighting with the same issue for awhile now as did the previous owner of the scooter. At this point, I will jet it as best I can and just live with it.
The VMC Crono kit is the one designed for use with a 60mm crank (187cc). The cylinder is taller so you dont need to use a 1.5mm spacer like most 177 kits. It's an aluminum cyl kit that seems pretty high quality and if I ever go 60mm I'll probably end up getting one.

What confuses me the most is that if the crankshaft is contacting the case or something, why does it only happen at idle RPM? I can turn the crank with the top end off by hand and not feel any resistance or anything out of the ordinary.

--

Also, I think I have figured out that hesitation issue. Switching from a BE3 to a BE5 mixer tube seems to have fixed it.
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