my BLUE Bajaj fitting 60mm Crankshaft
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Hooked
Honda elite
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Fri May 24, 2019 3:43 pm quote
I have cut in the 3rd transfer and filled a void with JB Weld

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Molto Verboso
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Fri May 24, 2019 7:42 pm quote
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?
Hooked
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Wed May 29, 2019 10:25 am quote
the cases are roughed in waiting on base gaskets.

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Hooked
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Thu May 30, 2019 1:47 pm quote
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?

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Molto Verboso
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Thu May 30, 2019 7:43 pm quote
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.
Hooked
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Thu May 30, 2019 10:53 pm quote
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
Molto Verboso
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Thu May 30, 2019 11:19 pm quote
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?
Hooked
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Thu Jun 06, 2019 11:20 am quote
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.

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Molto Verboso
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Thu Jun 06, 2019 7:23 pm quote
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?
Hooked
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Thu Jun 06, 2019 11:31 pm quote
Gosh darn it.
Hooked
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Fri Jun 07, 2019 12:32 am quote
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
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Fri Jun 07, 2019 1:49 am quote
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).
Molto Verboso
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Fri Jun 07, 2019 7:00 pm quote
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
1mm under on the transfers?
Ossessionato
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Fri Jun 07, 2019 8:10 pm quote
Either the transfers and boosts are at the same height ... or they aren’t
Hooked
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Sat Jun 08, 2019 10:22 am quote
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).
Thank you swa45 I would sure like to take a look at the Magny Cours. From what I can tell looking at the Pinasco Catalog the 60 stroke kit comes with the center plug head. This is all I can tell and like you mention also comes with a 1.5mm base gasket and the spare part number is the same gasket listed for the 57 stroke kits. But 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.

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Last edited by hibbert on Sat Jun 08, 2019 10:25 am; edited 1 time in total
Hooked
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Sat Jun 08, 2019 10:22 am quote
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

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Ossessionato
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Sat Jun 08, 2019 10:48 am quote
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.
When I helped modkuo install his Pinasco aluminum 2 port (with a standard crank) I asked Rob Hodge the same question about the 1.5 spacer. He said he was “pretty sure Pinasco turned down the base of the cylinder”. So there you go.
Molto Verboso
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Sat Jun 08, 2019 6:53 pm quote
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.
Hooked
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Sun Jun 09, 2019 6:56 am quote
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?

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Molto Verboso
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Sun Jun 09, 2019 7:35 pm quote
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
Hooked
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Tue Jun 18, 2019 12:31 pm quote
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.

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Ossessionato
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Tue Jun 18, 2019 2:05 pm quote
What exhaust are you planning to use? Sorry if it’s already been mentioned in the thread.
Hooked
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Tue Jun 18, 2019 4:42 pm quote
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
Molto Verboso
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Tue Jun 18, 2019 9:32 pm quote
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.
Hooked
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Tue Jun 18, 2019 11:04 pm quote
what does blowdown mean?

If the Ic is 45° how could that positively extend by cutting the crankshaft?
Molto Verboso
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Tue Jun 18, 2019 11:46 pm quote
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.
Hooked
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Wed Jun 19, 2019 12:07 am quote
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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Last edited by hibbert on Wed Jun 19, 2019 12:38 am; edited 1 time in total
Hooked
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Wed Jun 19, 2019 12:33 am quote
what is blowdown
Molto Verboso
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Wed Jun 19, 2019 1:08 am quote
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/
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Wed Jun 19, 2019 8:03 am quote
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
The reason I asked is that you might want to take the characteristics of the exhaust you’ll be using into consideration before settling on port timings.
Hooked
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Thu Jun 20, 2019 6:20 pm quote
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
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Thu Jun 20, 2019 11:25 pm quote
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.
Hooked
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Sun Jun 23, 2019 10:47 am quote
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?

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Molto Verboso
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Sun Jun 23, 2019 9:39 pm quote
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.
Hooked
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Sun Jun 23, 2019 11:11 pm quote
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?
Hooked
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Mon Jun 24, 2019 12:54 pm quote
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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Molto Verboso
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Mon Jun 24, 2019 10:59 pm quote
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
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Tue Jun 25, 2019 12:07 am quote
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.
Hooked
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Sat Jun 29, 2019 9:28 am quote
making some progress measured and confirmed duration Io. 115° BTDC Ic. 55° ATDC adding up to 170°

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Molto Verboso
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Sat Jun 29, 2019 10:06 am quote
Very nice Hibbert - very nice!
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