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Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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Some nice work there And nice divide feature too.
The porting in that cylinder looks like its aimed at higher rpm. If the cylinder is too high it won't pull so well. Do you have a base gasket that will put the piston 1.0mm poking out of the cylinder? |
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I received the dummy bearings and base gaskets and got back to measuring. The addition of the dummy bearing on the fly side caused a major change in the solder compression so I'm glad I got them. I used a magnifying glass to get a better PBT reading. Feel much better about the measurements. The following are taken with a 1.5mm base gasket.
stroke 60 conrod 105 PBT + 0.80 Transfer 46.50 Exhaust 34.75 squish 1.oo The PBT has increased slightly and the squish is tighter than I had thought. Paying attention to Swiss but still fumbling in the dark. Going to pose a question. Is it possible this cylinder may be shortened 1.5mm at the base and supplied with a 1.5mm gasket for 57mm stroke, leaving the unaltered cylinder for 60mm stroke? How might those changes impact things? |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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With the 1.5mm base this does work out ok but not so good. Will lack top end but mid range will be nice.
Really needs a 1.0mm base gasket. This will make the squish 0.5mm, which is too tight, even for me. Any remote chance there is a head gasket with that kit? Assuming there is no head gasket option, 1.2mm base gasket (a 1.0 and a 0.2 together) will be better and give a 0.7mm squish. Will go really well. Can you just measure the ports with the vernier again, to be sure? inside the port to the top of the bore (on a stepped cylinder). If these measurements get any longer we are in trouble. |
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I will measure all of the ports again and again.
We have the 1.0 base gasket, 0.8, 0.5 & 0.25 Will this head gasket work? Is 64 the internal dimension? The recess in the cylinder will accept something up to 73mm OD bore is less than 64. The depth is more than 1mm. https://www.sip-scootershop.com/en/products/gasket+cylinder+head+th+05mm+_90782500 |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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If SIP supply a part to fix it, then we're on the right track. That gasket is the one you need. Your bore is 63mm but that gasket is 64mm. Don't want the gasket touching the piston, similar issues as the head touching the piston. Not good.
If you get one of those 0.5mm gaskets, then the base can be 1.0mm. Delivery might be a while. Its only thin ally. Could try to make one? |
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I have taken the cylinder in to ScooterSpeed to have a second set of eyes & tools measure. This is what I've come back with.
Exhaust 34.62mm Transfer 45.76mm Boost 46.57mm Cyl deck step 1.67mm good in knowing a head gasket should fit in there comfortably. |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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Going to need a fat head gasket.
If the Scooterspeed measurements are correct. And they are a long way from yours. This means the cylinder was well set up on a 57mm crank. The 60mm doesn't work so well in this cylinder. As it is, without port grinding, the cylinder will need to be as low as it can get without the rings popping out the cylinder. How low will it go? |
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Does anything seem fishy on the new dimensions?
1st 2nd Ex 34.75 34.62 trns 46.50 45.76 Bst 46.60 46.57 |
Molto Verboso
One or two fun scoots....nothing too precious
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What exact model is the kit? A friend bought the Pinasco Magny Cours as a 187cc kit for his 125 t.s. When it arrived, a 1.5mm base packer was included. We concluded that the 187 kit is really just the 177 kit with a 1.5mm lift to account for the 60mm stroke. When we measured the timings with the base packer, they seemed quite high, but as it turned out, he really likes the power delivery. He runs it with a 24/24 and SIP XL and it has a stock P2 gearbox (65/23).
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Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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hibbert wrote: Does anything seem fishy on the new dimensions? 1st 2nd Ex 34.75 34.62 trns 46.50 45.76 Bst 46.60 46.57 |
bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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swa45 wrote: What exact model is the kit? A friend bought the Pinasco Magny Cours as a 187cc kit for his 125 t.s. When it arrived, a 1.5mm base packer was included. We concluded that the 187 kit is really just the 177 kit with a 1.5mm lift to account for the 60mm stroke. When we measured the timings with the base packer, they seemed quite high, but as it turned out, he really likes the power delivery. He runs it with a 24/24 and SIP XL and it has a stock P2 gearbox (65/23). This kit I have is sold as the new Pinasco alum for 2 port and 57 stroke. ⚠️ Last edited by hibbert on UTC; edited 1 time
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new tools new dimensions
The recess in the cylinder is measuring 1.35mm with feeler gauges fitting under the micrometer flange. I am subtracting 1.35mm from the measured depth of the ports. The depth micrometer made things easier to measure. Exhaust 36.90 - 1.35 = 35.55mm Transfer 48.10 - 1.35 = 46.75mm |
bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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hibbert wrote: I'm still wondering if Pinasco removes 1.5mm from the cylinder for the 57 stroke? I mean it sure does appear so. This kit I have is sold as the new Pinasco alum for 2 port and 57 stroke. |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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I think enough with the measuring. This looks like its it.
With the 1.5mm packer on the base, the blowdown comes out at 24.3, which is low but with a good exhaust and less expectation of high rpm (and as swa45's mates does) it will go fine. As this is rotary inlet, to get slightly more max power, the cylinder could drop a little with a 1.0mm base packer and 0.5mm head gasket. This will be more powerful and probably faster overall. |
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this sounds swell for now we have the base gaskets and head gaskets ready for build.
When you say a good exhaust what does that mean? Was hoping for an expansion box over a full chamber. Can we improve the inlet duration? |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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No expense spared, I see. Those air filters/boxes are not cheap. 26 or 24 carb? Big box exhausts are no compromise, some are nearly as good as expansions.
Inlet can be opened but depends on what crank you are using and how it measures. Can do this on the degree wheel. Is close enough. Which base gaskets you fitting? Target rpm range changes between the two (1.0mm or 1.5mm). That's quite some box of hammers. I guess you used to have Lambrettas |
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Some of it can be expensive but only once. The Pinasco Air Cover is so much bigger than one I made and in the long run probably cheaper but it is plastic. Figured the air is free but the fuel isn't so sticking with a 24mm carburetor for now.
Put the degree disc back on and this is measured for the inlet Io 112° BTDC Ic 45° ATDC Does this mean total open 157°? Can I ask what would be the optimum Inlet close degree? Finally entering data correctly on the calculator pages? with a 1.0mm base gasket Exhuast 170.42 Transfer 121.11 Blowdown 24.65 with a 1.5mm base gasket Exhaust 172.38 Transfer 123.65 Blowdown 24.36 Admittedly I do not know what this means or what I should be aiming for. Was worried the ring may be close to the deck so I measured the ring groove it's 2.58mm below the crown so this should remain below the cylinder deck. |
bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Thanks SoCal not sure hopefully an expansion box I have a BGM that's been fun but remember reading there might be better options. There are too many to choose from
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Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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1.0mm base gasket it is then. This is the best of the two. Not enough blowdown for higher.
157 degree inlet sounds about normal. Sime66 posted data about that. For a touring setup you could go another 15 degrees at each end. Max. 187 total. This is very dangerous for a novice. One slip and you're buying a reed block. |
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what does blowdown mean?
If the Ic is 45° how could that positively extend by cutting the crankshaft? |
Molto Verboso
One or two fun scoots....nothing too precious
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To get the inlet to closer later e.g. 55-60 degrees after TDC, you can either cut the crank further or take material off the front end of the inlet port in the casing with a Dremel. Like Jack said, if you get it wrong, you could render the rotary pad useless. I tend to buy cranks thare cut for the desired close, then work on the back of the inlet to achieve an earlier opening. There is usually more meat at the back, at least on a PX motor.
For example, I've used a Mazz crank that closes the inlet at 75 degrees ATDC for a revvy motor and a Jasil that closes at 60 for a touring setup. I aim for 120 degrees BTDC for the open. |
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Thanks for looking things over swa45 and Jack221. Seems like there isn't much meat on the case rotary pad before running into the carb studs. More space at Io than Ic. When I got the 60mm crankshaft first thing I noticed was the BAJAJ crankshaft had more CUT than the Mazzucchelli.
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Molto Verboso
One or two fun scoots....nothing too precious
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Here's a definition of blowdown:
"What really matters is the degrees between exhaust opening and transfers opening. This is called "blowdown" degrees. If the exhaust port opens at 90 degrees ATDC, and the transfers open at 115 degrees ATDC, then the blowdown is 115-90=25 degrees" See this link for more context: https://martysgarage.info/reference/two-stroke-port-duration/ |
bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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hibbert wrote: Thanks SoCal not sure hopefully an expansion box I have a BGM that's been fun but remember reading there might be better options. There are too many to choose from |
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thanks for the link swa45!
Good point on the exhaust SoCal. What is good? Seems like the SIP Road 2 is popular. Didn't the Polini have good stats? Was kinda diggin the shape of the polini. I am so confuse. from Marty 'But there are factors which let you vary from these settings. Less duration favors low rpm power whereas more duration favors high rpm power.' is that about inlet duration? |
Molto Verboso
One or two fun scoots....nothing too precious
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I have a SIP Road 2 on a DR177 and it seems like a good pairing. However, the Polini is often described as a later generation of box pipe, and in fact SIP is readying a Road 3 to try and leapfrog the pack again. I put a Polini box on my P225 recently and it sounds wonderful and performs better than it did with a BGM BigBox. The aesthetics are also well suited to the older Vespa style (like your Bajaj), as it's wider, rather than deeper/taller, to provide the extra capacity.
My amateur understanding is that longer duration is probably referring to transfer duration. A torquey touring cylinder might have TD=118-122, whilst a revvier kit might be TD=124-128. Inlet duration is also relevant, as this determines how much fuel/air mix can get in during the cycle. On a rotary, you might go 180-185 degrees for either setup, but the inlet opening earlier for a touring tune, or closing later for a higher revver. Of course some go as high as 200 total duration (maybe even beyond) for racier motors. |
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thank you for sharing all that.
I have marked the crank at 55° ATDC which would extend the duration to 167°~ The mark shows about 10mm to remove from crankshaft. The info from Pinasco says 20 that would put it at maybe 180°? Will that be increase torque? Is any balancing required after this type of crank modification? |
Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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If you atart this you're going to need to cut the casing. 180 to 190 total is a good number. It's really easy to mess up.
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What should be the minimal pad length in mm? Have 10mm on the Io. Seems almost not worth it because of potential break through but as I gather you get more torque at the opening?
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Here is the inlet port flexing a ruler in the best I can. The lack of pad and potential to break through to the carburetor stud is somewhat focusing my attention on the crankshaft duration instead. If 20mm is removed from crankshaft could be around 175/180°? I could use some reassurance.
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Jet Eye Master
PX221 MHR, O tuned PX200, PX181 Quattrini and some motorbikes
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This is why you shouldn't be doing the inlet. The carb hole stays the same size and only the inside is opened up. The pad can be opened to 1.0mm from the edge or sides. Need to be sure the sides actually have 1.0mm of overlap with the crank as they all fit individually.
Opening that port would double the size. Not going to be slower. It is in good condition though and mistakes would be even more painful. |
Molto Verboso
One or two fun scoots....nothing too precious
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At the very least I would take it back to the 50mm mark on your picture with the ruler. As Jack said, slope and blend it up to the carb box hole. The carb box can be modded to blend into the inlet. Some people even work on the bottom of the carb (called ovaling) to get an extra few mm and for additional blending to smooth the flow through the entire intake. I'm not suggested that you attempt that, but just FYI.
Your inlet _could_ be widened a little, but as Jack said, a mistake will be painful. I personally would not cut the crank, but it's your show!! I tend to buy cranks ready cut and spend my time on the inlet with a Dremel and a careful hand. |
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making some progress measured and confirmed duration Io. 115° BTDC Ic. 55° ATDC adding up to 170°
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Ossessionato
79 P200E (Ruby), 62 Allstate (B-62)
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