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Having had rough starting, poor idling issues I double checked the valve clearances. Done. Double checked for air leaks. None. So decided to tear the engine apart and hoped to SEE the issue. Not really - to this inexperienced eye. But I'll ask - are the piston and cylinder ok?
Forum member supplied image with no explanatory text
Side one
Side one
Side two (flipped the cylinder around for the pic)
Side two (flipped the cylinder around for the pic)
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Are the dots in the cylinder cosmetic or can you feel them?
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How about the cylinder head, looks like debris was in the cylinder and caused damage to the piston?
Cylinder and piston do not look good.
The arrow on the piston is pointing toward a particularly bad spot.
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That piston face looks pretty beat up around the edges.
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Motovista wrote:
Are the dots in the cylinder cosmetic or can you feel them?
Cosmetic. Walls are smooth.
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Lottolearn wrote:
How about the cylinder head, looks like debris was in the cylinder and caused damage to the piston?
Cylinder and piston do not look good.
The arrow on the piston is pointing toward a particularly bad spot.
Thanks for the heads up on the cylinder head. Here's a pic. Maybe a little less damage????
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jess wrote:
That piston face looks pretty beat up around the edges.
Yes, that's the issue I'm most unfamiliar with. Is it toast? Perhaps with the evidence of the cylinder head I just added?
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gitder wrote:
Yes, that's the issue I'm most unfamiliar with. Is it toast? Perhaps with the evidence of the cylinder head I just added?
I'm not an expert here, but I would think that the chips and dents would, at the very least, give rise to potential detonation.
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gitder wrote:
Thanks for the heads up on the cylinder head. Here's a pic. Maybe a little less damage????
Yeah, something got in the cylinder but the damage isn't extreme.
I'd be more concerned with the staining/etching on the cylinder.
Did you happen to do a compression test?
Now that the head is off you can spray some brake clean in the intake and exhaust ports and see if it is leaking around the valves (you can also spray a little on the valves and blow compressed air in the ports to look for bubbles) not that it's the cause of your concern but being that it's apart might as well check.
Best of luck.
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I've seen Piaggio cylinders that look worse but were smooth as well, so it's not surprising that got into a production vehicle and not your issue. It looks like something fell into the cylinder, banged it's way around, and then exited via the exhaust valve. One of the intake valves looks a little banged up. I would next check the seat on the valves. The quick and easy way is to put the head upside down on something so it's flat, then fill the combustion chamber with gas. If it leaks out, you have a valve job in your future.
If that's the case, a valve job, top end gasket set and a set of rings should make your bike work again.
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The fact that it shows a little beat up is not in itself a big issue and it would run mostly normal that way but what caused it likely tweaked a valve stem and my bet is you will find a valve bent slightly and have low cranking compression. I also recommend the brake cleaner spray in the int. and exh. ports to see if it instantly leaks out around the valve seats. You should be able to pool a small amount around the valve head on the inside and not leak thru instantly. It is bizarre as to what has went thru there to cause that damage.
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Parts may be able to be saved. I would be thinking, now that the time and effort to inspect and found some damage, I would be considering a upgrade in cc's might be the better investment of time and money.
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Motovista wrote:
I've seen Piaggio cylinders that look worse but were smooth as well, so it's not surprising that got into a production vehicle and not your issue. It looks like something fell into the cylinder, banged it's way around, and then exited via the exhaust valve. One of the intake valves looks a little banged up. I would next check the seat on the valves. The quick and easy way is to put the head upside down on something so it's flat, then fill the combustion chamber with gas. If it leaks out, you have a valve job in your future.
If that's the case, a valve job, top end gasket set and a set of rings should make your bike work again.
Appreciate this advice, as well as others mentioning the same. The test was positive - there is a leak on a single valve. As I see that I need to do a valve job, I'm having trouble finding a how to video. Not sure how to get at the clips at the top of the springs that hold the valves in place, for example.
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gitder wrote:
Appreciate this advice, as well as others mentioning the same. The test was positive - there is a leak on a single valve. As I see that I need to do a valve job, I'm having trouble finding a how to video. Not sure how to get at the clips at the top of the springs that hold the valves in place, for example.
Not really a diy project, best left to a shop that has the right equipment.
You can hand lap the valves but I would suggest getting it done properly.
The valve keepers are tapered and you would need a valve spring compressor to remove, properly.
Others ways to remove but seriously, get a proper valve job.
Have a qualified shop also check the cylinder for taper and runout.
Since it's apart do it right.
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How many miles on the motor? Do you plan to keep it a long time? If yes, I am with this guy's advice: I would be considering a upgrade in cc's might be the better investment of time and money. I plan to install the malossi hi performance piston, cylinder and head when my motor needs a rebuild. You will enjoy it much more.
Tony in Tn. 07 GTS 250 with 37k on the clock, last milage check returned 99 MPG.
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Given that the crosshatching is still in the cylinder, it's likely fine as is. Once you remove the leaky valve, you might find more damage. It's hard to guess what you are going to find, whether the valve is bent or the seat is damaged beyond repair. Most dealerships either farm this sort of work out or will replace the head assembly, so a machine shop that specializes in this sort of work is likely to be a better place to take the parts. The tools and compound to lap the valve seats are cheap and widely available, but that combined with Youtube videos doesn't mean you are going to be able to do it right if you've never seen it done.
If you compress the valve spring, you can pop the retaining clips off, but the odds are that you won't be able to get it back together without a valve spring compression tool. You can roll the valve across a table top and see if it's bent or not.
Once you get prices for the spare parts and work to be done, you might find it's cheaper and quicker to buy a used head on Ebay.
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jess wrote:
I'm not an expert here, but I would think that the chips and dents would, at the very least, give rise to potential detonation.
All those "edges" created by the hammering of debris through the cylinder do tend to create hot spots that can lead to detention.

I'd bet that whatever debris caused that damage bent a valve on the way in/out. That would cause the poor starting and idle. Take the cylinder head into a dark closet. Shine a bright light into the intake and exhaust ports. This will usually tell you if you have a bent valve. You'll see light come out around the valve seat.

Edit: I see MotoVista already diagnosed a leaky valve. So... What he said. 😂
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looks like a great time for an upgrade kit, while you have it apart.
https://www.scooterwest.com/malossi-74mm-cylinder-kit-for-gts-and-250-quasar-piaggio-motor-275cc.html

combine with the head
https://www.scooterwest.com/malossi-4-valve-cylinder-head-for-liquid-cooled-vespa-piaggio-m3813273.html

you will notice a very nice performance boost
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tonymarchman wrote:
How many miles on the motor? Do you plan to keep it a long time? If yes, I am with this guy's advice: I would be considering a upgrade in cc's might be the better investment of time and money. I plan to install the malossi hi performance piston, cylinder and head when my motor needs a rebuild. You will enjoy it much more.
Tony in Tn. 07 GTS 250 with 37k on the clock, last milage check returned 99 MPG.
And I thought 73mpg was good at 12000 miles, may my mpg get better as my 250 GTS Vespa accumulates mileage.
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Switching to a malossi cylinder kit that was discontinued five years ago might make sense to people who don't know much about scooter tuning. I didn't know they are still around, and we are the largest distributor of Malossi products in the US. But it won't make much of a difference unless you also add a force master ecu and upgrade to the Malossi head, which has been unavailable for about two years.
The current Malossi 75.5mm cylinder kit for the GTS 250 is 3113924, and it's about $370.
A new OEM Cylinder kit is about $250, but in about 90% of the world, someone would fix what's wrong with the head and valve, run the top of the piston across a piece of 1000 grit paper, slap a new set of rings on and send it.
⚠️ Last edited by Motovista on UTC; edited 1 time
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Motovista wrote:
Switching to a malossi cylinder kit that was discontinued five years ago might make sense to people who don't know much about scooter tuning. I didn't know they are still around, and we are the largest distributor of Malossi products in the US. But it won't make much of a difference unless you also add a force master ecu and upgrade to the Malossi head, which has been unavailable for about two years.
The current Malossi 75.5mm cylinder kit for the GTS 250 is 3113924, and it's about $370.
A new OEM Cylinder kit is about $250, but in about 90% of the world, someone would fix what's wrong with the head and valve, slap a new set of rings on and send it.
Oh crap I'm a 10 percenter!
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Lottolearn wrote:
Oh crap I'm a 10 percenter!
It's an American thing. We like to replace things, not fix them.
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Motovista wrote:
It's an American thing. We like to replace things, not fix them.
Possibly, I just like to do it right.
Any backyard mechanic can put something together and make it run but that doesn't mean it's right.
Throwing a set of rings in and lapping a valve might make it run.
Me, that cylinder would be measured and at a minimum honed.
I can't see just throwing a set of rings at that cylinder.
Again it will run but then again it ran before.
As far as the post on the cylinder and head. I believe the poster was just making a suggestion and being part of a conversation, didn't see the need for insults about his tuning ability. I didn't see anything that he said alluding to that.
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I am indeed an amateur, so I defer to Motovista for the in depth knowledge he brings to the table. I was totally unaware you would need to upgrade the ecu. I think this much of an upgrade would cost more than my scoot is worth.
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Lottolearn wrote:
Possibly, I just like to do it right.
Any backyard mechanic can put something together and make it run but that doesn't mean it's right.
Throwing a set of rings in and lapping a valve might make it run.
Me, that cylinder would be measured and at a minimum honed.
I can't see just throwing a set of rings at that cylinder.
Again it will run but then again it ran before.
As far as the post on the cylinder and head. I believe the poster was just making a suggestion and being part of a conversation, didn't see the need for insults about his tuning ability. I didn't see anything that he said alluding to that.
Now that's funny. Why not port and polish it while you're in there? How long have you been repairing engines?
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Motovista wrote:
Now that's funny. Why not port and polish it while you're in there? How long have you been repairing engines?
Why would I port and polish?
Not trying to make it special just repair it properly.
47 years, factory trained master tech, Volvo, MB, Hyundai, you?
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I've taken the head and cylinder to a machine shop. They confirmed the cylinder is ok, no need to hone. It will be a few days until they can get to the head to examine the valve situation and offer advice.
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gitder wrote:
I've taken the head and cylinder to a machine shop. They confirmed the cylinder is ok, no need to hone. It will be a few days until they can get to the head to examine the valve situation and offer advice.
Good deal and piece of mind.
I would still, at a minimum, deglaze that cylinder. It literally takes a few seconds. It will knock off the shine and bring back the cross hatching to hold oil and lubricate. Your engine, certainly, your choice.
If you are changing the rings it's a no brainer.
⬆️    About 1 month elapsed    ⬇️
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At the re-assembly point, got new valves and piston installed. But I'm trying to figure out how to ensure TDC during re-assembly. The Scooterwest video shows Robot making marks, but I can't find where he did this or how? Or is there another method? Maybe if the piston is at the top like in the pic?
Forum member supplied image with no explanatory text
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Forum member supplied image with no explanatory text
Forum member supplied image with no explanatory text
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The easiest is if someone tells you where the TDC marks are located. Without that put the piston at the top of the cylinder like you have in the picture. Get a fine line marker and make a line on the case, you can draw it on the green gasket, in an area that has the closest gap between the flywheel and engine case. Rotate the crankshaft CCW until the piston moves down a measurable amount, say an 1/8". Place a mark on the flywheel in line with the line you drew on the case. Now rotate the crankshaft CW until the piston drops the same amount 1/8" and put another mark on the flywheel aligned with the case mark. Now measure between the two lines you made on the flywheel, divide by two and place a mark on the flywheel between the two previous lines you added, align the middle mark with the case line and you will be at TDC.
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Sorry, I may not be much help, but isn't it basically aligning the 4V mark on the cam wheel (apologies for bad memory of actual part names), as well as the flywheel mark with the little indicator inside the opening in the flywheel cover?
Maybe it's bad eyesight but I'm not seeing the flywheel mark, and with the cover off there's no reference point.

And yes, piston at the top, but that's a given.

Hope someone who really knows what's going on happens by....
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fledermaus wrote:
Sorry, I may not be much help, but isn't it basically aligning the 4V mark on the cam wheel (apologies for bad memory of actual part names), as well as the flywheel mark with the little indicator inside the opening in the flywheel cover?
Maybe it's bad eyesight but I'm not seeing the flywheel mark, and with the cover off there's no reference point.

And yes, piston at the top, but that's a given.

Hope someone who really knows what's going on happens by....
Just so.

Piston at the top is by definition TDC. Next is getting the timing of the valves in sync with this - which is where the 4V arrow comes into play as you re-attach the cam gear while keeping the timing chain tensioned correctly before finally fitting the tensioner.
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jimc wrote:
Just so.

Piston at the top is by definition TDC. Next is getting the timing of the valves in sync with this - which is where the 4V arrow comes into play as you re-attach the cam gear while keeping the timing chain tensioned correctly before finally fitting the tensioner.
Jim, the piston being up is mostly correct but there is a transition point where you can rotate the crankshaft back and forth without visually seeing a piston movement. Depending on the stroke it can be enough to not visually notice and be off. I would recommend the MFG marks or measure. The dead center in TDC is absolute.
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gitder wrote:
At the re-assembly point, got new valves and piston installed. But I'm trying to figure out how to ensure TDC during re-assembly. The Scooterwest video shows Robot making marks, but I can't find where he did this or how? Or is there another method? Maybe if the piston is at the top like in the pic?
I think I see what you're getting at about the mark. I think Robot's marks were done to highlight the already existing marks for the camera. Weird that you don't have a mark on your flywheel.
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Got the wreck buttoned up, with requisite amount of finger crossing. Re-installed the engine and fired it up. Not. After ensuring the battery was fully charged overnight, I tried to fire up again. Exactly same response. The three attempts in the video are full cycles, i.e. the start button engaged, brief starter attempt and quick stop and nothing further. Then re-tried, same. Brief turnover (or whatever that is) then stop. And again. So three cranks, disengage, re-try the start process in succession, with each ending in a stopped engine despite holding the start button for a longer time.

So, in my limited experience is this a battery issue? Or, after installing new pistons, rings, valves is there simply too much compression to turn over the engine (only half kidding)? I can't recall ever hearing of a feeble starting attempt that won't even turn over the engine repeatedly for as long as the starter button is engaged, unless its the battery. But just throwing this out there in the event of other ideas.

https://photos.google.com/photo/AF1QipO2ulveyKrAAncXV_AfDlq1nvFdBMc6iTaA2u5Z[/quote]
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Can't see your video.
Without that guessing, timing way advanced and kicking back the piston, cam timing off (this would be bad), auto compression release not working (stuck in run position).
Verify cam timing, check compression release, remove spark plug and see if you can turn engine over by hand, do not force if it stops.
Can be battery, starter, etc but no video.
I wouldn't keep trying until you verify the above.
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Here's the video, appreciate the help. I'm thinking crossing fingers isn't a very effective mechanical skill...

https://youtube.com/shorts/YTRp5OAy4D0?feature=share
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Put a meter on your battery and see what the voltage reading is when it's cranking. Sounds like a flat battery, starter could be packing it in. I'd start with battery voltage when cranking.
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UTC quote
While you have the meter out set it to DC volts, put one lead on the battery negative and the other lead on the engine case and hit the starter button. The meter reading should be .2 VDC, if the meter is reading high you have a bad ground. You can also do the same by putting one lead on the battery positive and the other on the starter + terminal and again hit the start button, if you are showing high voltage at the meter, spec is .3 VDC, you have a problem in the wiring or relay. You can isolate at the relay by keeping one lead on the battery positive and put the other on the relay terminal from the battery, hit the start button read voltage, move the lead to the relay output terminal going to the starter, button, read voltage. If the reading was in spec to the relay but failed on the out the relay is bad.
These are voltage drop tests and one of the best ways to isolate an electrical fault (if the starter relay is marked with numbers, 30 is the input from the battery, 87 is the output going to the starter - 86 and 85 are relay coil terminals).
OP
@gitder avatar
UTC

Hooked
GTS 250...Fiddle III 200
Joined: UTC
Posts: 382
Location: Kenosha, WI
 
Hooked
@gitder avatar
GTS 250...Fiddle III 200
Joined: UTC
Posts: 382
Location: Kenosha, WI
UTC quote
Lottolearn wrote:
Put a meter on your battery and see what the voltage reading is when it's cranking. Sounds like a flat battery, starter could be packing it in. I'd start with battery voltage when cranking.
Thanks, the test showed volts varying between 9.7 and 10.1, sort of bouncing around. 9.9/10.0 was most consistent. Believe this suggests a good battery.
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