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Over the winter I dropped the engine out of my 09 Stella to split the cases and upgrade the crankshaft to a Mazzu economy 57mm, and replace all bearings+seals+gaskets as preventative maintenance. I also swapped out the primary for a Malossi 23/64 straight cut set, rebuilt the clutch, new cruciform + T5 4th gear, and disabled/removed the autolube system. Finally, I installed a GGR hot reed and cut out the reed block bar.

After getting everything back together and starting it for the first time last week, the engine now makes a loud metallic tapping sound that sounds a lot like piston slap. I have ridden it around 50 miles since then and the noise has not gotten any better or worse, and of course I am hesitant to ride it any further until I can fix it.

It sounds EXACTLY like the video in this thread, including the sound mostly going away in higher RPMs. https://vespa.proboards.com/thread/5709/noise-crank

Here are the possibilities I have ruled out so far:
>Autolube shaft bouncing from vibrations
>Flywheel contacting part of the case or cylinder
>Crankshaft contacting the reed stop plate
>The GGR carbon reed I got is just THIS obnoxiously loud for some reason (I guess this is still possible but I highly doubt it.)
>Piston rings installed incorrectly
>Piston slap due to poor piston/bore clearance (It did not make this noise before the rebuild and I simply took the top end off, put it on a shelf, then put it back on after the rebuild.)
>Washer/nut stuck to flywheel magnet
>Loose stator plate
>Clutch contacting part of the case or clutch cover
>Anything relating to the gearbox
>Primary rivets contacting something


But how could I get piston slap if it made no such noise right before I tore it down back in September? Does the piston to bore clearance magically get worse if the top end is sitting on a shelf for a few months? The up/down wobble is no worse than when I first installed the kit. This is how I ruled out this possibility, even though it was my original hypothesis.

The kit has ~1800 miles on it and it has never been seized. I have never reached a cylinder head temp higher than 370F (measured with a Trailtech TTO under the sparkplug), and 99% of rides it stays way below 320-330F.[/i]
⚠️ Last edited by gummy8879 on UTC; edited 5 times
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If the piston is not contacting the head or crank web, there's not much to worry about. The fast idle can make it sound worse. Does the noise change when the clutch lever is pulled and/or in gear?

330F is a high temperature for a 177. If the timing is ok, then the jetting is lean. This can make it noisy.
Many sound similar while they warm up.
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Jack221 wrote:
If the piston is not contacting the head or crank web, there's not much to worry about. The fast idle can make it sound worse. Does the noise change when the clutch lever is pulled and/or in gear?

330F is a high temperature for a 177. If the timing is ok, then the jetting is lean. This can make it noisy.
Many sound similar while they warm up.
I should clarify, it only gets that high if I ride it pretty hard, most of the time just riding around town it is under 300F.

Clutch/gear does not make a difference, only RPM affects it.
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gummy8879 wrote:
Over the winter I dropped the engine out of my 09 Stella to split the cases and upgrade the crankshaft to a Mazzu economy 57mm, and replace all bearings+seals+gaskets as preventative maintenance. I also swapped out the primary for a Malossi 23/64 straight cut set, rebuilt the clutch, new cruciform + T5 4th gear, and disabled/removed the autolube system. Finally, I installed a GGR hot reed and cut out the reed block bar.

After getting everything back together and starting it for the first time last week, the engine now makes a loud metallic tapping sound that sounds a lot like piston slap. I have ridden it around 50 miles since then and the noise has not gotten any better or worse, and of course I am hesitant to ride it any further until I can fix it.

It sounds EXACTLY like the video in this thread, including the sound mostly going away in higher RPMs. https://vespa.proboards.com/thread/5709/noise-crank

I came to the piston slap theory after ruling out these possibilities:
>Autolube shaft bouncing from vibrations
>Flywheel contacting part of the case or cylinder
>Crankshaft contacting the reed stop plate
>The GGR carbon reed I got is just THIS obnoxiously loud for some reason (I guess this is still possible but I highly doubt it.)
>Incorrect wrist pin needle bearing (Used both the original LML and the one supplied with the Mazzu crank (which is currently installed))
>Piston rings installed incorrectly

But how could I get piston slap if it made no such noise right before I tore it down back in September? Does the piston to bore clearance magically get worse if the top end is sitting on a shelf for a few months? The up/down wobble is no worse than when I first installed the kit.

The kit has ~1800 miles on it and it has never been seized. I have never reached a cylinder head temp higher than 370F (measured with a Trailtech TTO under the sparkplug), and 99% of rides it stays under 320-330F.
What carb and jetting?
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Robbie 11 wrote:
What carb and jetting?
SI 20/20 with the fuel passage drilled to 2.5mm
No filter on carb, instead running a foam pod filter in place of the bellows.

As of last week:
160 AC, E3 mixer (mostly the same as BE5), 130 MJ
52/140 idle
2.5 turns out


Before the rebuild, I was running this though:
160/BE3/122 main (125 when it was cold)
52/140
1.75 turns out
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gummy8879 wrote:
I should clarify, it only gets that high if I ride it pretty hard, most of the time just riding around town it is under 300F.

Clutch/gear does not make a difference, only RPM affects it.
On a 177, if well set up, the around town at speed limits, should be nominally 200F.
Change the air corrector urgently. Start with an AC120. This will make the temperature plummet.
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Jack221 wrote:
On a 177, if well set up, the around town at speed limits, should be nominally 200F.
Change the air corrector urgently. Start with an AC120. This will make the temperature plummet.
Just going down to the 140 AC that I have causes it to hesitate/4 stroke right before hitting the powerband pretty significantly. I made a thread trying to tackle this issue earlier this week.

Honestly I might be misremembering the temperatures a bit too because I haven't ridden it normally since September. Once I trust the engine enough to actually get me back home I'll report back on the temps with the current jetting.
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Wouldn't ride on the current jetting. It's too lean and will slowly damage the piston.

The four stroking at 1/4 isn't the fault of the air corrector. It's all the other bits.
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Jack221 wrote:
On a 177, if well set up, the around town at speed limits, should be nominally 200F.
Change the air corrector urgently. Start with an AC120. This will make the temperature plummet.
I second this, my P200 motor, DR177 motor, P221 motor and 50cc China scooter all run in the 200-225 range.

Spontaneous piston slap is interesting, I'd be worried also. Did you check crankshaft before install to make sure it's true? Maybe it's twisted a bit causing issues? Or it was doing it previously and you didn't notice and you're now sensitive to it because of refresh.

Worked as an engineering tech fixing product issues during manufacturing. During final inspection every once in awhile a "new" issue would come up. I'd get notified, start investigating issue and find out defect has been there for three days and 100,000+ parts.
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gummy8879 wrote:
I came to the piston slap theory after ruling out these possibilities:

>Incorrect wrist pin needle bearing (Used both the original LML and the one supplied with the Mazzu crank (which is currently installed))
It could be the Mazz wrist pin bearing. I did not use the Mazz Gudgeon bearing per FMP's warning. FMP has a video regarding not using them. I just put my engine together which has a Mazz 60mm stroked and cut crank(no economy crank either) and the wrist pin supplied was crap and fit loose compared to the Piaggio one I installed. Seeing his video before I assembled the engine was helpful and I was ready with an assortment of Piaggio wrist pin bearings when I installed my piston on my VMC Stelvio 177 kit. I purchased 3 different Piaggio Gudgeon bearings and found the perfect fit it was part no.90132000 (15x19x20 mm) Part No. 90131000 and 90133000 were also tried. 90131000 was a little loose and 90133000 was too tight. The Mazz bearing was the loosest. My engine is still on the stand and hopefully I have no issues.

Hec
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Jack221 wrote:
I was told by another user that my current setup should actually be on the rich side, and that going down to a 125 main should be about right. Now it's all too lean? I have tried jetting with the 140 AC before and changing idle jets, screw, mains and swapping between my BE3 and E3 atomizer and I could never get rid of that hesitation. It isn't confined to 1/4 throttle, it makes it much harder to rev up onto the pipe period.

I was on the even leaner jetting (BE3, 122) for most of that 1800 miles and both the piston and head have no visible damage from overheating. There is some carbon buildup which I believe to be from the excessively oil-rich leaky autolube system, hence why I removed it.
Christopher_55934 wrote:
Spontaneous piston slap is interesting, I'd be worried also. Did you check crankshaft before install to make sure it's true? Maybe it's twisted a bit causing issues? Or it was doing it previously and you didn't notice and you're now sensitive to it because of refresh.
I know this was a little reckless of me but I know for a fact that the LML crankshaft was very out of true and possibly twisted (as they all are), and I know I would remember a sound as loud and concerning as this one. I did not true this crank myself but while spinning it in the case half I could tell it is much better than the stock one because I couldn't see the runout with my naked eyes. I could not see any significant twisting either, but I know this is something you usually do with a truing stand.
Hec In Omaha wrote:
Where did you buy the Piaggio bearings from? I see them on SIP but their shipping to the US is a little pricey.
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gummy8879 wrote:
Where did you buy the Piaggio bearings from? I see them on SIP but their shipping to the US is a little pricey.
I got mine from SIP. You can order SIP from Scooter Mercato and save on shipping!

Scooter West has these however brand says Vespa.



https://www.scooterwest.com/wrist-pin-bearing-15mm-i-d-500541.html


https://www.scooterwest.com/wrist-pin-bearing-15mm-i-d-500542.html

https://www.scooterwest.com/wrist-pin-bearing-15mm-i-d-500543.html

https://www.scooterwest.com/wrist-pin-bearing-15mm-i-d-500544.html



Hec
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While the cylinder was sitting, did you hone it? Polish it? Polish the piston?
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gummy8879 wrote:
I was told by another user that my current setup should actually be on the rich side, and that going down to a 125 main should be about right. Now it's all too lean? I have tried jetting with the 140 AC before and changing idle jets, screw, mains and swapping between my BE3 and E3 atomizer and I could never get rid of that hesitation. It isn't confined to 1/4 throttle, it makes it much harder to rev up onto the pipe period.

I was on the even leaner jetting (BE3, 122) for most of that 1800 miles and both the piston and head have no visible damage from overheating. There is some carbon buildup which I believe to be from the excessively oil-rich leaky autolube system, hence why I removed it.
Most guys run lean, some very lean. And many for years, blaming the kit while it rattles, until it eventually blows. Many are certain the hotter it is, the faster it is.
SI carbs use the same technology as the Webber carbs on our Fords in the 70s. They are not simple carbs. You will not find maximum performance on your own.
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In that case I will order some Piaggio bearings and try them out. Really hope this is the fix, since I was hoping to save up a bit more for a VMC Stelvio top end but if I need one before June I might have to go with another Super G.
MJRally wrote:
I did nothing to the top end while it was off the engine.
Jack221 wrote:
In that case, what stack+idle do you think I should try?
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AC140/BE3 is where to start. Need a main jet so big it has continuous WOT splutter in 2nd gear. What number this is decides the next step.
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You said you had the foam filter instead of the bellows?
Maybe a good idea to go back to bellows and remove the foam filter.
You are sucking warm air into the carb…
Probably not a good starting point for trying to set-up the jetting…
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As a sanity check, pull the flywheel and make sure the magnets didn't pick up a washer or something.

Just a thought.

Hec
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Hec In Omaha wrote:
As a sanity check, pull the flywheel and make sure the magnets didn't pick up a washer or something.
Or a wrench...
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Hec In Omaha wrote:
As a sanity check, pull the flywheel and make sure the magnets didn't pick up a washer or something.

Just a thought.

Hec
Yep, just checked and theres nothing on the stator or the flywheel. Was kinda hoping there was since that would finally put this case to rest without me spending more money haha
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gummy8879 wrote:
Yep, just checked and theres nothing on the stator or the flywheel. Was kinda hoping there was since that would finally put this case to rest without me spending more money haha
Check the magnets themselves while your at it. Make sure they are not damaged or separating from the flywheel. I would also check to make sure the stator plate is secured tightly.

Good luck

Hec
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Checked the magnets and stator plate, everything is tight and I didn't see anything out of the ordinary.

I think I will pop the clutch cover off to see if the clutch is contacting something. After talking with a friend I do not think it is piston slap anymore, since there is no way a top end can spontaneously get it like that.

If there is nothing contacting the clutch inside the cover or whatever, I am pretty confident that the crankshaft I received has a conrod opening just slightly larger than the stock LML one, causing both of the wristpin bearings I have to be too loose. In that case I will buy the Piaggio ones and hopefully one will fit just right.

If that doesn't fix it then I think all my hair will fall out Crying or Very sad emoticon
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gummy8879 wrote:
I think I will pop the clutch cover off to see if the clutch is contacting something. After talking with a friend I do not think it is piston slap anymore, since there is no way a top end can spontaneously get it like that.
Did the rattle change when you warmed it up?

Rather than pulling things, try a mechanics stethoscope to get a better idea where it's rattling.
https://www.harborfreight.com/mechanics-stethoscope-63691.html
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gummy8879 wrote:
Checked the magnets and stator plate, everything is tight and I didn't see anything out of the ordinary.

I think I will pop the clutch cover off to see if the clutch is contacting something. After talking with a friend I do not think it is piston slap anymore, since there is no way a top end can spontaneously get it like that.

If there is nothing contacting the clutch inside the cover or whatever, I am pretty confident that the crankshaft I received has a conrod opening just slightly larger than the stock LML one, causing both of the wristpin bearings I have to be too loose. In that case I will buy the Piaggio ones and hopefully one will fit just right.

If that doesn't fix it then I think all my hair will fall out Crying or Very sad emoticon
I listened to that video. What ever is making the tapping is rhythmic. The tapping sound speeds up with increasing RPM and vice versa. You mentioned you installed a Mallossi 34/64 up gear kit. Is it possible there is a rivet or two, on the cush gear cover plates, that didn't get peened down enough to clear the crank bearing?
I installed the same up-gear kit and had two rivets that needed a couple of additional smacks with the hammer to flattened them out more. Upon installing the primary shaft, I noticed it wouldn't rotate 360 degrees by hand but seemed to be hitting something. I found an offending rivet which was contacting the bearing. See yellow arrow. I reversed the rotation and found another rivet that was contacting the bearing. I ended up peening all the rivets again until the primary could spin freely and all the rivets cleared. Maybe you just have a rivet that is grazing the crank bearing? You may be able to feel it by rotating the engine slowly. You may also be able to see a rivet with wear marks on it if you remove the clutch and use a small inspection mirror.

Running out of ideas.

Hec
Rivet head on opposite side was contacting crank bearing.
Rivet head on opposite side was contacting crank bearing.
Potential culprit?
Potential culprit?
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Hec In Omaha wrote:
I listened to that video. What ever is making the tapping is rhythmic. The tapping sound speeds up with increasing RPM and vice versa. You mentioned you installed a Mallossi 34/64 up gear kit. Is it possible there is a rivet or two, on the cush gear cover plates, that didn't get peened down enough to clear the crank bearing?
If this was the case, wouldn't the sound go away with the clutch pulled in or if the bike is in neutral, as the primary would not be spinning?
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And I assume you've confirmed it's not something obvious like the flywheel hitting the cover?

Can you turn it or kick it over without it running, e.g. pull the plug lead, and hear it?
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chandlerman wrote:
And I assume you've confirmed it's not something obvious like the flywheel hitting the cover?
Yep, a full list of things I've ruled out is in the original post up top.
chandlerman wrote:
Can you turn it or kick it over without it running, e.g. pull the plug lead, and hear it?
The sound only starts when the engine is running. I have held the killswitch and cranked it with the electric start and the sound isn't audible. I have also turned the crank by hand with the top end and reedblock off to see if I can feel it contacting/rubbing anything and I could not feel anything abnormal.

This is why I am heavily leaning toward the wrist pin needle bearing hypothesis, and will probably be ordering a set of Piaggio ones like Hec and FMP recommended.
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Makes sense.
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Just ordered all 4 bearing options from scooterwest. Really hoping that we've finally figured out the problem!
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gummy8879 wrote:
Just ordered all 4 bearing options from scooterwest. Really hoping that we've finally figured out the problem!
The bearings I listed from Scooter West were 15mm I.D. That's the size my engine required. Please make sure to measure your old bearing size. There are also 16mm I.D. bearings.

When you are ready to install the Piaggio wrist pin bearing, check the wrist pin and Mazz wrist pin bearing for play before disassembly. My Mazzu wrist pin bearing had quite a bit play if I tried wiggle the wrist pin and bearing inside the con rod. I checked it for shit's and giggles knowing a Piaggio bearing was going in. The Piaggio bearings didn't have the amount of play the Mazz bearing did. Take care removing and installing the C-Clips for the wrist pin too.

Post some pics!

I hope this solves your tapping problem!

Good luck!

Hec
⚠️ Last edited by Hec In Omaha on UTC; edited 1 time
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UTC quote
Hec In Omaha wrote:
The bearings I listed from Scooter West were 15mm I.D. That's the size my engine required. Please make sure to measure your old bearing size size. There are also 16mm I.D. bearings.
OP
@gummy8879 avatar
UTC

Enthusiast
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
 
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@gummy8879 avatar
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
UTC quote
Bearings came in! I ordered the ones linked in Hec's reply from scooterwest. #1 and #2 are too loose, #3 has a very minimal amount of play between the wristpin and conrod, and #4 is a little snug to get in but there is no play at all. The mazz bearing is as loose as #1. Interestingly, the LML one is slightly tighter than #3.

Just as an experiment, I tried putting the same wrist pin back into the old LML crank with the LML bearing. It's so tight I can't even press it in by hand!! I remember having to use a C clamp and a 10mm socket to get it on and off. Guess it just clicked in my head that that's not normal. Both the LML crank and bearing have "III" marks.

I was spinning the crank by hand to see if I could feel anything contacting (like Hec's other hypothesis of one of the primary gear rivets), and I could not feel anything at all. Completely smooth rotation all around.


Here are some pics of the piston and head. They looked the same when I originally tore the engine down for the crank swap. I cannot feel any of the cylinder grooves with my fingernail and they look less severe in person.

External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
⚠️ Last edited by gummy8879 on UTC; edited 1 time
OP
@gummy8879 avatar
UTC

Enthusiast
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
 
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@gummy8879 avatar
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
UTC quote
Update: Used the #4 bearing, the sound is still there. Made no difference.

I am going to look under the clutch cover next, but now that I have conclusively ruled out anything to do with the actual "engine" part of everything, I am a little more comfortable about riding it.

Maybe the the new plates I put in are striping the clutch cover?

I will be updating my previous post with some pictures of the piston and cylinder.
@srd0060 avatar
UTC

Hooked
2022 HPE 300 tech/ 91 PX 200e/97 PX 200e
Joined: UTC
Posts: 109
Location: Australia
 
Hooked
@srd0060 avatar
2022 HPE 300 tech/ 91 PX 200e/97 PX 200e
Joined: UTC
Posts: 109
Location: Australia
UTC quote
gummy8879 wrote:
Update: Used the #4 bearing, the sound is still there. Made no difference.

I am going to look under the clutch cover next, but now that I have conclusively ruled out anything to do with the actual "engine" part of everything, I am a little more comfortable about riding it.

Maybe the the new plates I put in are striping the clutch cover?

I will be updating my previous post with some pictures of the piston and cylinder.
Is the crank touching the crank case?
OP
@gummy8879 avatar
UTC

Enthusiast
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
 
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@gummy8879 avatar
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
UTC quote
srd0060 wrote:
Is the crank touching the crank case?
I spun the crank by hand with the top end off and I could not feel any resistance or contacting. It spins completely freely as it should.

Keep in mind that the sound doesn't start until the engine is running either. If I crank it over on electric start with the ignition off it sounds normal.
OP
@gummy8879 avatar
UTC

Enthusiast
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
 
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@gummy8879 avatar
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
UTC quote
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.

Forum member supplied image with no explanatory text
@mjrally avatar
UTC

Veni, Vidi, Posti
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 59 Ser 2, 65 Silver Special, 90 V5N 50, 2015 HD Road Glide Special
Joined: UTC
Posts: 5150
Location: Oceanside, CA
 
Veni, Vidi, Posti
@mjrally avatar
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 59 Ser 2, 65 Silver Special, 90 V5N 50, 2015 HD Road Glide Special
Joined: UTC
Posts: 5150
Location: Oceanside, CA
UTC quote
You've done everything but swap the top end and open up the cases now. Any way I can convince you to swap top end first?
OP
@gummy8879 avatar
UTC

Enthusiast
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
 
Enthusiast
@gummy8879 avatar
2009 Stella, 2001 Honda Helix
Joined: UTC
Posts: 85
Location: Memphis, TN
UTC quote
MJRally wrote:
You've done everything but swap the top end and open up the cases now. Any way I can convince you to swap top end first?
I suppose I could put the original LML top end back on as a test. Don't think I will be able to do much riding with it considering the 23/64 gearing, but running it in neutral should be enough considering the nature of the issue. First I am going to run the engine with the clutch completely off and see if the noise is still there.

I am still struggling to understand how or why the top end could spontaneously start making this noise after a crank swap and moving to 1 size smaller base gasket. If the top end really is the issue, then I think I will just ride it either until it craps out on me or I can afford the 177 Stelvio I've been eyeing up. I have put around 2 tanks of gas on it with this noise and it has not gotten any better or worse. I have also inspected the top end (pics a few posts above) and I cannot see anything out of the ordinary.

It would be a huge letdown if I have to leave this scoot at home for this year's smoky mountain smallbore rally, which is 1 month from now. Crying or Very sad emoticon
@orwell84 avatar
UTC

Ossessionato
Joined: UTC
Posts: 3218
Location: northern New York
 
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@orwell84 avatar
Joined: UTC
Posts: 3218
Location: northern New York
UTC quote
Hang in there. You got time…even if you have to split the cases. You'll find it.
@christopher_55934 avatar
UTC

Ossessionato
2007 Stella 225
Joined: UTC
Posts: 3547
Location: Rochester, Minnesota
 
Ossessionato
@christopher_55934 avatar
2007 Stella 225
Joined: UTC
Posts: 3547
Location: Rochester, Minnesota
UTC quote
gummy8879 wrote:
Bearings came in! I ordered the ones linked in Hec's reply from scooterwest. #1 and #2 are too loose, #3 has a very minimal amount of play between the wristpin and conrod, and #4 is a little snug to get in but there is no play at all. The mazz bearing is as loose as #1. Interestingly, the LML one is slightly tighter than #3.

Just as an experiment, I tried putting the same wrist pin back into the old LML crank with the LML bearing. It's so tight I can't even press it in by hand!! I remember having to use a C clamp and a 10mm socket to get it on and off. Guess it just clicked in my head that that's not normal. Both the LML crank and bearing have "III" marks.

I was spinning the crank by hand to see if I could feel anything contacting (like Hec's other hypothesis of one of the primary gear rivets), and I could not feel anything at all. Completely smooth rotation all around.


Here are some pics of the piston and head. They looked the same when I originally tore the engine down for the crank swap. I cannot feel any of the cylinder grooves with my fingernail and they look less severe in person.

External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text
Any pictures of piston top and head?
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