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Post by 90GTVert on Jul 28, 2024 6:18:10 GMT -5
Not sure why the pics aren't showing for you guys. Same host as usual, so maybe just down ATM.
It smeared the thrust sides of the piston against the walls and pinched the ring. Piston is junk. Cylinder should be OK after cleanup, but not fun to see on an 18 mile cylinder after 6 seconds of WOT.
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Post by xtremrox on Jul 28, 2024 7:28:30 GMT -5
The piston is actually above the transfers at BDC. I had it stuck in my head that it was the other way around for some reason. Anyway, I normally use something like a 0.2 or 0.3mm gasket to get squish right with the past cylinder kits and just leave the transfers as they are. At this point, I've got a new head, one that's in good shape and one that is now beat up a bit from the circlip. Might as well try some stuff. I put 0.7mm worth of aluminum gaskets under the cylinder (2x 0.3mm and 1x 0.1mm) to get the transfers flush. That ruins squish, which is supposed to be 0.55-0.6mm. I had 1.08mm. The combustion chamber is recessed roughly 0.5mm. Initially I tried to leave just a tiny bit of that recess, all but cutting it out. I figured maybe it's more of a firewall for the o-ring if it's not level with the rest of the head? Didn't matter. O.66mm squish clearance. Then I cut it flat. 0.57mm minimum squish. That'll work! So I cut off 0.51mm based on the squish. I'm never 100% sure on the mini lathe because of rigidity. I had to make more cuts because I was afraid the outer section would contact the cylinder and I had made the o-ring groove more shallow. Hopefully it can seal now.   It's not put together just yet. I was considering looking for 0.7mm aluminum to make a single gasket, but I may just use 3. Not generally a fan of stacking, but I've got to seal both air/fuel and coolant and I'm thinking maybe the 3 more malleable gaskets are better with light sealant on each. It's also easier and cheaper ATM. If it's a fail, I've still got a new head and can go back to the usual squish setting gasket choice. I'm hoping maybe it will cool the piston slightly better if nothing else, but don't really think it will make much difference. With a degree wheel, I got 198 ex / 132 xfer. One thing that would be amazing is a portmap with these dilensions 1.Btdc heigth in the bore 2.width and heigth of all ports at 3 diferent points 3.distance from exhaust port top to a transfer ports top 4.width of the bridges between ports With these you can analyze the engine in very precise detail. Also port pos/dir/axial parametres are important Maybe this will be of some use? Hope it's understandable. With the port measurement map, r is radius of a circle that matches the corners and H is height of the port.    Exhaust roof : 6° Downswept Exhaust floor : 9° Downswept A transfer roof : 25° Upswept B transfer roof : 19° Upswept Large boost roof : 55° Upswept Small boost roof : 40° Upswept Wow those are some real good transfer angles there. Its ok for piston to cover a bit of transfers at bdc becouse in runing the bottom edge is covered for 99% of cycle its open for such a small range of stroke |
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Post by xtremrox on Jul 28, 2024 7:33:48 GMT -5
So 1st thing if you have been running less than 0.8 of squish that's why you keep detonating or seizing the piston too much heat. You will need to run at least 0.8. Also if you have the squish at less than 0.8 I don't see that cylinder having 198ex need to be less. This is just wrong less squish actually prevents detonation |
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Post by 90GTVert on Jul 28, 2024 7:38:38 GMT -5
Wow those are some real good transfer angles there. Its ok for piston to cover a bit of transfers at bdc becouse in runing the bottom edge is covered for 99% of cycle its open for such a small range of stroke I had the same thought, but I figured if I could get any extra piston cooling at all it would be a good thing. With 3 heads around, it just took time. Now I'm lost. Did I suddenly make it horrible by moving 0.4mm to be flush with the same squish, or does it hate the conservative timing, or does the Keihin jet not supply as much fuel as my crude flow tests show, or did port matching make some significant change... or was it just my lucky day? |
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Post by xtremrox on Jul 28, 2024 7:44:35 GMT -5
Wow those are some real good transfer angles there. Its ok for piston to cover a bit of transfers at bdc becouse in runing the bottom edge is covered for 99% of cycle its open for such a small range of stroke I had the same thought, but I figured if I could get any extra piston cooling at all it would be a good thing. With 3 heads around, it just took time. Now I'm lost. Did I suddenly make it horrible by moving 0.4mm to be flush with the same squish, or does it hate the conservative timing, or does the Keihin jet not supply as much fuel as my crude flow tests show, or did port matching make some significant change... or was it just my lucky day? there is the strange possibilty that malossi has desinged the overhang on the transfers for axial flow reasons (doubt this as the bottom edge flows so little) conservative timing can lead to problems but those show as high egt. One thing is that the fact that The ports are now 0.4mm higher so higher timing (i dont see this as an issue but over 130 transfers really just put the peak power rpms higher and higher and then the pipe wont work coorrectly) So The tuning can change radically in some cases. But the piston crown being mint but melted sides reminds me of a 125cc bike i ported that used bad oil and too little % and it just friction seized the engine |
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Post by xtremrox on Jul 28, 2024 7:46:51 GMT -5
I had the same thought, but I figured if I could get any extra piston cooling at all it would be a good thing. With 3 heads around, it just took time. Now I'm lost. Did I suddenly make it horrible by moving 0.4mm to be flush with the same squish, or does it hate the conservative timing, or does the Keihin jet not supply as much fuel as my crude flow tests show, or did port matching make some significant change... or was it just my lucky day? there is the strange possibilty that malossi has desinged the overhang on the transfers for axial flow reasons (doubt this as the bottom edge flows so little) conservative timing can lead to problems but those show as high egt. One thing is that the fact that The ports are now 0.4mm higher so higher timing (i dont see this as an issue but over 130 transfers really just put the peak power rpms higher and higher and then the pipe wont work coorrectly) So The tuning can change radically in some cases. But the piston crown being mint but melted sides reminds me of a 125cc bike i ported that used bad oil and too little % and it just friction seized the engine Actually the 198/132 is a timing set that i think can make REALLY good power it is similar to the husqvarna timing i make when porting 202/130 |
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Post by oldgeek on Jul 28, 2024 8:00:17 GMT -5
Is it possible there is a problem with cooling? Is your pump or electrical system crapping out? Air in system or low flow? Something weird is going on here. As much as I dislike the PWKs I can't see it being the cause of this.  Why is it getting so hot so fast? |
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Post by 90GTVert on Jul 28, 2024 8:33:08 GMT -5
So The tuning can change radically in some cases. But the piston crown being mint but melted sides reminds me of a 125cc bike i ported that used bad oil and too little % and it just friction seized the engine My gas is now almost 2 months old because I put it together and blow it up and put it together and blow it up; instead of actually riding anymore. I was already considering it this time, but I'll slowly feed that into the riding mowers that can run on about anything and get fresh fuel next time. I feel like it's OK because starting and power haven't been an issue and it smells OK. As far as bad oil or mix ratio; it's AMSOil Dominator Racing 2T at 32:1. Same mix since day one. If it were terrible oil, it would have to be a bad bottle or something. Is it possible there is a problem with cooling? Is your pump or electrical system crapping out? Air in system or low flow? Something weird is going on here. As much as I dislike the PWKs I can't see it being the cause of this. Why is it getting so hot so fast? It runs cool and coolant temp is measured from a port in the head so it should be seeing what the cylinder is seeing. Maxd coolant temp was 134F after it shut off. 126F at the start of the run and 130F when it died. It always gets around 140 when I'm doing acceleration runs on a hot day. Again, since day one. Also, I watched coolant temp pretty intently on the break-in ride because I was worried about issues with the o-ring seal after cutting the head. Never saw any signs of trouble and it was 120s most of the time then, no pressure or coolant in the expansion tank or anything else to say head sealing was an issue. |
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Post by Lucass2T on Jul 28, 2024 10:47:26 GMT -5
Have you tried comparing numbers with 100ish cc motocross bikes like the kawasaki kx100? That might show some clues?
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Post by 90GTVert on Jul 28, 2024 19:34:59 GMT -5
I thought maybe I'd put the AliExpress "Keihin" 34mm PWK on when it went back together because it couldn't do much worse than what I am now. Then I took it out of the box. LOL Before I say anything else, I've never owned a genuine Keihin PWK. The box looks pretty official to me. These days they even clone Sudco packaging and stickers. I did quickly google S66A0 and no 34mm PWKs came up. In fact, it doesn't look like Keihin makes a 34mm. They make a 33mm.   The outside looks OK-ish, but Sudco has an article about fake vs real and it doesn't meet those specs even from a distance. There are sharp edges and it just feels Chinese. If you've dealt with much cheap Chinese stuff, you know what I mean. Fake vs Real Carbs Passages in the bell mouth are jagged and poorly finished.  The knob for the idle speed annoys me. I like a flathead screw to turn so I can watch how many turns out it is. This feels cheap and harder to operate to me.   I started taking it apart and when I removed the jet body, that's when I said NO WAY would I use this. The nozzle or atomizer bushing literally fell out. It's a light interference fit in the Polini. This drops in and fall out. The thing could end up in the engine and that couldn't go well. If they can't get the fit here right, what are the chances that passages, jets and so on are to spec?  The floats are cheap glossy plastic, just like the amazon/AliExpress rebuild kits. Jets are too sharp and too shiny and not properly engraved as Keihin.  The needle has no marking on it, nor does the throttle valve. The throttle valve also has a jagged area on the top. 
The atomizer is an 8 hole. 
Nope. I was just looking up PWK33 carburetors and it's kind of despicable what people are doing with those. Sellers are offering fakes at high prices so they seem like they're real. I'm no pro, but they don't match up to what Sudco specifies for real for the most part. I guess if you can buy them at $25 each and sell them at $200-400 each, some people's morals can be cast aside. One bad thing about Sudco spelling out how to spot a real carb is that I assume Chinese manufacturers will just adapt with that knowledge. Not that tough for them to make the adjustments mentioned so they look good in pics. To be fair though, at least most sellers aren't charging crazy money for them. At $25, you know it's fake. |
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Post by 90GTVert on Jul 29, 2024 21:32:15 GMT -5
Here's another cheap stuff fail. Remember the Milwaukee M18 knockoff battery that I bought in June? It worked OK in the scoot for brief rides a few times. I used it in the string trimmer for the first time today and it melted the terminal area and won't charge. Might be OK for light use, but for something more constant and demanding it's worthless. I also noticed that it never cut off. It just got weak and went to 0 of 4 status lights illuminating. The genuine batteries shut off before they get that low. Allegedly this battery has voltage protection, but it doesn't seem to work.  Milwaukee stuff saves itself by communicating between the battery and a tool. I think it would either need some add-on low voltage protection wired in or a different brand/style of battery that really shut itself down at x volts to be a more trouble free setup. I don't plan to switch battery types now because they serve a dual purpose for me. I may see if there are any low volt shutoffs available and affordable. |
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tysta
Scoot Member
Posts: 79
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Post by tysta on Jul 30, 2024 1:07:40 GMT -5
So 1st thing if you have been running less than 0.8 of squish that's why you keep detonating or seizing the piston too much heat. You will need to run at least 0.8. Also if you have the squish at less than 0.8 I don't see that cylinder having 198ex need to be less. This is just wrong less squish actually prevents detonation Please elaborate this one!!!!! His problem it's not directly related with detonation but the temperature the piston is reaching causing to seize! Yes at some point he had detonation but not on this last one. |
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tysta
Scoot Member
Posts: 79
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Post by tysta on Jul 30, 2024 1:17:25 GMT -5
So The tuning can change radically in some cases. But the piston crown being mint but melted sides reminds me of a 125cc bike i ported that used bad oil and too little % and it just friction seized the engine My gas is now almost 2 months old because I put it together and blow it up and put it together and blow it up; instead of actually riding anymore. I was already considering it this time, but I'll slowly feed that into the riding mowers that can run on about anything and get fresh fuel next time. I feel like it's OK because starting and power haven't been an issue and it smells OK. As far as bad oil or mix ratio; it's AMSOil Dominator Racing 2T at 32:1. Same mix since day one. If it were terrible oil, it would have to be a bad bottle or something. Is it possible there is a problem with cooling? Is your pump or electrical system crapping out? Air in system or low flow? Something weird is going on here. As much as I dislike the PWKs I can't see it being the cause of this. Why is it getting so hot so fast? It runs cool and coolant temp is measured from a port in the head so it should be seeing what the cylinder is seeing. Maxd coolant temp was 134F after it shut off. 126F at the start of the run and 130F when it died. It always gets around 140 when I'm doing acceleration runs on a hot day. Again, since day one. Also, I watched coolant temp pretty intently on the break-in ride because I was worried about issues with the o-ring seal after cutting the head. Never saw any signs of trouble and it was 120s most of the time then, no pressure or coolant in the expansion tank or anything else to say head sealing was an issue. So I know you were running a very tight squish but that was your compression ratio?! Can you measure that please and let us know |
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tysta
Scoot Member
Posts: 79
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Post by tysta on Aug 2, 2024 16:39:04 GMT -5
I thought maybe I'd put the AliExpress "Keihin" 34mm PWK on when it went back together because it couldn't do much worse than what I am now. Then I took it out of the box. LOL Before I say anything else, I've never owned a genuine Keihin PWK. The box looks pretty official to me. These days they even clone Sudco packaging and stickers. I did quickly google S66A0 and no 34mm PWKs came up. In fact, it doesn't look like Keihin makes a 34mm. They make a 33mm. The outside looks OK-ish, but Sudco has an article about fake vs real and it doesn't meet those specs even from a distance. There are sharp edges and it just feels Chinese. If you've dealt with much cheap Chinese stuff, you know what I mean. Fake vs Real CarbsPassages in the bell mouth are jagged and poorly finished. The knob for the idle speed annoys me. I like a flathead screw to turn so I can watch how many turns out it is. This feels cheap and harder to operate to me. I started taking it apart and when I removed the jet body, that's when I said NO WAY would I use this. The nozzle or atomizer bushing literally fell out. It's a light interference fit in the Polini. This drops in and fall out. The thing could end up in the engine and that couldn't go well. If they can't get the fit here right, what are the chances that passages, jets and so on are to spec? The floats are cheap glossy plastic, just like the amazon/AliExpress rebuild kits. Jets are too sharp and too shiny and not properly engraved as Keihin. The needle has no marking on it, nor does the throttle valve. The throttle valve also has a jagged area on the top.
The atomizer is an 8 hole.
Nope. I was just looking up PWK33 carburetors and it's kind of despicable what people are doing with those. Sellers are offering fakes at high prices so they seem like they're real. I'm no pro, but they don't match up to what Sudco specifies for real for the most part. I guess if you can buy them at $25 each and sell them at $200-400 each, some people's morals can be cast aside. One bad thing about Sudco spelling out how to spot a real carb is that I assume Chinese manufacturers will just adapt with that knowledge. Not that tough for them to make the adjustments mentioned so they look good in pics. To be fair though, at least most sellers aren't charging crazy money for them. At $25, you know it's fake. Be careful with this carbs alpt of them leak air through the that junction there the jets sit. You should look in to your fuel delivery also your vent line make sure you have enough flow over time. Any pwk from 28 to 33 should work with no problems in your engine I can be wrong but I don't see it needing more than a 170 jet. You can go back to a squish of 0.7 and check your compression volume so you have a reference for the compression ratio. Even using tight squish majority of the fuel sold in our gas stations don't want to work right with compression ratios over 14,3:1 Set ignition at 16 degrees through the entire rpm range. And this is what I been saying go back a little bit and just go with the basics As long your fuel supply is OK and your carb it's not foaming you should be able to find a staring point |
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Post by zekefab on Sept 2, 2024 23:20:51 GMT -5
Iv been following this thread over the last couple years . I have a rc-1 in a zuma and learned a lot simply from this thread alone. I wanted to mention my findings on the Dellorto carb. I had the same symptoms of running out of fuel on high speed runs. I first thought I was crazy and that I was fouling the plug so something. Finally I melted a piston from too lean. I rebuilt the top end and went over the carb closely. Fuel inlet nipple at the carb was easy to move around so I took it out for investigation. The hole going through the carb to the float stop valve was very small. I should have taken a picture. I drilled it out to 5/16 as well as verify the rest of the fuel system was not restricted. Last couple days Iv been breaking it in and never once ran the bowl dry. I up jetted from 152 to 155 and it’s been ripping solid. Hit 85 on the highway and didn’t get fuel starvation. If you ever go back to the Dellorto investigate that passage. Hopefully you get this back up and running 🤘🏼🤘🏼🤘🏼🤘🏼
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