Mon Nov 15, 2021 4:39 pm

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
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Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 4244
Location: Nashville
Mon Nov 15, 2021 4:39 pm linkquote
I used a degree when when I marked and cut the intake on my Sprint. It's definitely the best way to measure intake timings in my VERY limited experience. Realtime eyeball feedback on whether or not the measurements make sense.
Mon Nov 15, 2021 10:20 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
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Location: california
 
Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Posts: 2639
Location: california
Mon Nov 15, 2021 10:20 pm linkquote
Wish I could blame the buzwangle.
Unfortunately - its basically just a digital degree wheel...
One thing ya'll may not fully be appreciating.
This is a full circle crank.
There is no edge of a cut out to rub.
There is no cut out to allow a tool in to mark the pad.
Its just a big flat 62mm circle blocking the view of the inlet area pretty well completely.
You have to see a 62mm crank with -5 cut in it to appreciate just how tight that area is...

As for my struggle to digest the means to calc everything.
Well... I drive a 20+ HP scooter with a leaner sidecar.
WTF were you expecting?

Jack - hadn't seen your post until just now.
Tks.
See proposed drawing.
185 it is.
Tough to maintain a symmetrical arc vs a flat...
Will do what I can.
Don't mention the war.

[i]Edit: how about a small flat in the center at 185 before arcing down




Blued. Scribed. Ready to cut.
Hmmmm. A wider webbed crank would be interesting with my double wide pad.

Tue Nov 16, 2021 2:55 am

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
Location: London UK
 
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Location: London UK
Tue Nov 16, 2021 2:55 am linkquote
Scribed line on the pad still looks like a big inlet. Thats if it is going to the line edge. Make the hole square with slightly rounded corners.

With the exhaust port be sure the centre open to edge open is within 4mm. This will give it enough flexibility.
If we were going for max power/low torque, many things would be different but save that for the Malossi. 62mm on a reed MHR will be around 30bhp but as always you can't just bolt all the bits together and expect miracles.
Tue Nov 16, 2021 9:44 am

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Tue Nov 16, 2021 9:44 am linkquote
Quote:
With the exhaust port be sure the centre open to edge open is within 4mm. This will give it enough flexibility.
Do you mean center to edge of JUST the center port or do you mean the total arc including the aux ports as shown below?
(or did you mean something completely different...)



Tue Nov 16, 2021 5:46 pm

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 8109
Location: Victoria, Australia
 
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 8109
Location: Victoria, Australia
Tue Nov 16, 2021 5:46 pm linkquote
charlieman22 wrote:
One thing ya'll may not fully be appreciating.
This is a full circle crank.
Its just a big flat 62mm circle blocking the view of the inlet area pretty well completely.
I'm following this at a distance because I was sick the day they taught us maths at school...
Are you using the full circle as a stand-in until the new crank arrives?
Tue Nov 16, 2021 5:48 pm

Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
Joined: 20 Jul 2018
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Ossessionato
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Tue Nov 16, 2021 5:48 pm linkquote
I thought full circle only usable with reed valves. You are working with rotary cases. You planning on opening up and converting it to reeds?
Tue Nov 16, 2021 7:33 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Tue Nov 16, 2021 7:33 pm linkquote
Apparently I don't know what a full circle crank is.
I assumed - since it was a full circle - it was called a full circle crank.
See pictures below.
I don't know exactly what I would rub (shhhh. don't say it) if I did a rubbing.
I suppose I would get a couple circles where the weights are.

Since we are here - I do have a question for the crowd tho.
How do you precisely mark where TDC on the crank is physically?
I mean - I can eye it up and make a mark - but that has some degrees of variation in it.
Do y'all have a trick for making a mark on the crank absolutely on center of the big end pin?

Inlet has been roughed in.
Compared to old one - it is, well, big.
There is still about .25mm all the way around that will be done by hand - and a few chips that will need to be filled to make it smooth.


I guess this isn't a full circle crank - but you get the gist.


B side


Roughed in - getting close to actual size. Chips will be filled.


Not bad for homemade. Will clean up edges and grab the last little bit of opening real estate still available.

Tue Nov 16, 2021 9:38 pm

Ossessionato
79 P200E (Ruby), 62 Allstate (B-62), 2008 Stella (Olive)
Joined: 11 Jan 2006
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Location: Florence, OR
 
Ossessionato
79 P200E (Ruby), 62 Allstate (B-62), 2008 Stella (Olive)
Joined: 11 Jan 2006
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Tue Nov 16, 2021 9:38 pm linkquote
gotta say - the last three pages - every time I start delving into what is being said I hear the adults in a Peanuts movie "Muah muah muah muah muah muah"

So I try again, and again, and yet again... Same results... Peanuts adults.

Keep up the good work - someday I may grow up enough to understand what is being written...
Tue Nov 16, 2021 10:02 pm

Banned
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Banned
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Tue Nov 16, 2021 10:02 pm linkquote
pictured is a full circle crank = no cutaway at all to act as a rotary valve because it's intended to be used with a reed intake. i'd save that for your second engine where you intend to use a reed.

If you have to use this crank, you can cut the timing wherever you need it to be. Now that you have cut the pad, you can scribe the crank for the open and close position and cut out the space in between. That's a lot of cutting in steel and not at all fun.
Tue Nov 16, 2021 10:24 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Tue Nov 16, 2021 10:24 pm linkquote
Quote:
gotta say - the last three pages - every time I start delving into what is being said I hear the adults in a Peanuts movie "Muah muah muah muah muah muah"
Hahaha.
Sorry everyone had to witness that.
Getting there isn't always pretty with me.
On the other hand - no one has ever accused me of lacking determination.
¯\_(ツ)_/¯
Quote:
pictured is a full circle crank
That's what she said!
And I agreed until I was ordering a beer and the bartender turned around and it was Ginch - wearing one of those old timey vests and polishing a crank in his hands as he asked me what I wanted.

My crank is a new fangled type - made for rotary.
Image below.
Designed to minimize turbulence and spin smoothly I think.
If you listen carefully - you can actually hear it making that BaWAAAAAA! sound right there on my bench

The money shot will be when I put the crank in the motor - and we get a look at that opening aligned with the crank's web.
But now you can see why trying to reach in and scribe the pad was tough.


(Jack - go a few posts back and check the 4mm sketch I put up to confirm I understood).



Tue Nov 16, 2021 10:27 pm

Ossessionato
1979 P150X, 1983 P200E, 1988 T5, 1995 PX200E, 2011 Yamaha Fazer 600 S2
Joined: 02 Aug 2015
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Location: Veria, Greece
 
Ossessionato
1979 P150X, 1983 P200E, 1988 T5, 1995 PX200E, 2011 Yamaha Fazer 600 S2
Joined: 02 Aug 2015
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Location: Veria, Greece
Tue Nov 16, 2021 10:27 pm linkquote
That's a rotary crank, not for reeds. New SIP's crank are like this. They have the cut outs for duration…



Tue Nov 16, 2021 10:30 pm

Banned
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Banned
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Tue Nov 16, 2021 10:30 pm linkquote
Oh good! I was in a bit of a panic for you based on the perspective of initial picture.
Tue Nov 16, 2021 10:51 pm

Addicted
Too Many piles of Junk that need too much work and too much money
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Addicted
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Tue Nov 16, 2021 10:51 pm linkquote
what you have is sometimes called a 'KNIFE-EDGE' crank.

As it seems you discovered, this design for the cutaway presents a difficult problem for measuring and marking; compared to the traditional cut-away style crank...
Tue Nov 16, 2021 11:08 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Tue Nov 16, 2021 11:08 pm linkquote
Quote:
Oh good! I was in a bit of a panic for you based on the perspective of initial picture.
haha - Flattered you considered my willingness to cut it...
Quote:
what you have is sometimes called a 'KNIFE-EDGE' crank.
We have a name!
Quote:
As it seems you discovered, this design for the cutaway presents a difficult problem for measuring and marking
No problem - I'll just calculate it using my maths... ( 🙂 )
Tue Nov 16, 2021 11:31 pm

Addicted
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Tue Nov 16, 2021 11:31 pm linkquote
charlieman22 wrote:
haha - Flattered you considered my willingness to cut it...


We have a name!

No problem - I'll just calculate it using my maths... ( 🙂 )
You got this!
Wed Nov 17, 2021 2:20 am

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 3050
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Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Wed Nov 17, 2021 2:20 am linkquote
The crank chosen does affect the transfer pressure. General consensus says more pressure gives more high rpm power. Too many factors for any definitive rules but changing the pressure does change the torque delivery.

4mm interpretation correct. Go as wide as you can , keeping well clear of the gudgeon pin. Going flat on the centre of the centre port will make the 185 more prominent. Not sure this is a good idea for the "running in set up". See how it goes first.
Wed Nov 17, 2021 6:12 am

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
Joined: 26 Sep 2013
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Location: So Cal
 
bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Wed Nov 17, 2021 6:12 am linkquote
Quote:
See how it goes first.
My favorite line of Jack's.

You know the saying "Measure twice, cut once?"

In CM's case it's "Measure twice, measure twice more, hmmm... what the? ... measure again ... wait a sec, what was I measuring?"

Just kidding man, nice work! That engine's gonna roar.
Wed Nov 17, 2021 6:13 am

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Wed Nov 17, 2021 6:13 am linkquote
you can transfer the crank open/close point to the other web with a square and a sharpie. That mark can then be transferred to the face of the case, and from there to the face of the pad.

That at least gives you a visual double check.
Wed Nov 17, 2021 5:26 pm

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 8109
Location: Victoria, Australia
 
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 8109
Location: Victoria, Australia
Wed Nov 17, 2021 5:26 pm linkquote
Well I'm glad we cleared that up!

Wed Nov 17, 2021 5:40 pm

Addicted
1958 Allstate 177VMC, 2005 70cc Yamaha Vino
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Addicted
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Wed Nov 17, 2021 5:40 pm linkquote
qascooter wrote:
gotta say - the last three pages - every time I start delving into what is being said I hear the adults in a Peanuts movie "Muah muah muah muah muah muah"

So I try again, and again, and yet again... Same results... Peanuts adults.

Keep up the good work - someday I may grow up enough to understand what is being written...
Same. I understand next to nothing going on here, but sure hope by then end I'll have some sort of an idea.
Wed Nov 17, 2021 6:37 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
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Ossessionato
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Wed Nov 17, 2021 6:37 pm linkquote
Quote:
Well I'm glad we cleared that up!
Uh huh.
Quote:
Same. I understand next to nothing going on here, but sure hope by then end I'll have some sort of an idea.
Three pages of my our lives we will never get back.
Below consolidated into 3 points.
Quote:
For future CM22. Here is what you have to remember.
1. The second number of the duration, the /XX or /60 in 118/60 for example, can be calculated using E+F-A.
1B. A is an ANGLE. Mark the center of the crank pin, put at TDC. That's zero. Rotate to where the edge of the hole on the inlet pad is (not where the crank closes the inlet). That angle is your "A". E and F are on the crank.
2. The first number in your timing, example 118/ can be calculated by:
A. knowing your desired duration, and subtracting #1 form it
B. Using 360-transfer duration/2, if you want to open the inlet when your transfer opens.
Think its as simple as that.
3. The two numbers added together = your duration: example 118/60 = 178 duration.
See prior page image for what E F and A represent...
Its that simple!
🙂

Now - back to the grinding.
Cant believe no one even mentioned the sewer hole I have cut in the top of the cases.
The only reason that was possible was that I welded on the inside of the cases so I could grind in to them.
Few pictures below - including today's trenching of the transfer ports.
I've always hated that term - but the Crono transfers in the skirt are enormous - and it kinda felt like I was doing some trenching!


All that welding left and right of the transfer port was just build up so I could get aggressive with my transfer port size and create more case volume.


Clutch side "trenched" to match the Crono transfers.


Gratuitous repost of the inlet. Hmmm. with a little welding and machining, couldn't it be 2 or 3 mm wider? 🙂

Thu Nov 18, 2021 4:03 am

Hooked
Bodgerific 150 Super, PX200(ish...), US 50 Special in progress
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Posts: 442
Location: Melbourne, Way Downunder
 
Hooked
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Thu Nov 18, 2021 4:03 am linkquote
I tended to be bored a lot a school, and sit at the back and read. I did try to at least listen though, in case there was an exam, or my interest got piqued.

So, to sum up the last 9 chapters...

The following are adjustable on a rotary 2 stroke.

1. The amount of fuel and air you can cram in. Initial adjustment factor (given a fixed maximum carb size) is the size and shape of the hole from the bottom of the carb to the inlet port at the crank (via the hole in the outside of the case). Width of this port at the crank will also affect this volume.

2. The length of the inlet hole. (See 3.)

3. The amount of material cut from the portion of the crank which, by its absence allows the air/fuel inlet port to open, and by it's presence seals it closed. The timing of these closing and openings are determined by the position of the "cuts" to the crank, and when they cross over opening and closing edges of the intake port. Note that their position relative to the pin on which the piston connecting rod rotates is fixed, and this will affect their timing relative to point 4. Theoretically, the port can be made to open (or close) earlier or later, and/or shortened or lengthened.

4. The timing of the opening of the intake and exhaust ports on the piston is controlled by their position relative to TDC of the piston. The characteristics of the engine (ie. if it has torque, revs, or a mix of both) is determined by the relationship of the opening and closing of the intakes and exhaust, and this is further affected by the timing of the inlet port opening and closings.

5. Further factors include case volume, squish, ports size and shape, ignition timing, THE EXHAUST(ie, the amount of air you can get out, and how much more air that will suck in as a consequence, but that would need a new post), dogma, buttdyno, other stuff.

6. Opinions vary.


Hopefully, I'll pass the exam, and we can move on.
Thu Nov 18, 2021 7:29 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Thu Nov 18, 2021 7:29 pm linkquote
Finished up porting cases.
Commensurate picture below.
Drilled and tapped custom hole for what will be a new intake manifold
Clutch side of cases are ready for clean up and build.
Fly side are close.

So if you are just watching re-runs, let's talk about pad girth ladies, shall we?
As I've referenced - the German crowd are getting about 25-30 with the Crono - same as MHR - but those are all with reeds.

The few that have kept it rotary, have struggled to get must past 20HP.
With that said - they've all used the narrower "small block" crank - narrower web width.
As I've documented... I have the wider crank in - allowing the inlet to also be wider.
But I have a lot of unused pad still.

To utilize this - the crank web would have to be offset from center.
I would also need to add weld material and machine it off - but hey - let's not let the details get in the way.
with every mm off center the crank was positioned - I could get another mm of pad opening.
I.e. shift the crank 2mm - pick up 2mm of pad opening over its length.

Now those 25-30HP reed motors over on the German Scooter Forum are admittedly using bigger carbs - 30-35mm.
But what I wanna hear about is what the cognoscenti thinks would happen with some rod offset from center to achieve an additional 20% width of inlet.


This pic was shot after rough in - not optimized yet.
But you can still see a lot of pad available.


Little bit of clean up on the boost port still needed... Transfers are pretty well ready.

Fri Nov 19, 2021 7:58 am

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Fri Nov 19, 2021 7:58 am linkquote
Related: can the crowd confirm how much overlap of pad to crank web width I need for min. good sealing on the sides? 1mm? 1.2mm?
Tks
Fri Nov 19, 2021 8:13 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 4244
Location: Nashville
 
Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
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Posts: 4244
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Fri Nov 19, 2021 8:13 am linkquote
charlieman22 wrote:
Related: can the crowd confirm how much overlap of pad to crank web width I need for min. good sealing on the sides? 1mm? 1.2mm?
Tks
I'm pretty sure 1.2 is sfe, but I'm still rooting for you to come to the Reed Dark Side on this beast, so my guidance may not be for a Minimum Safe Distance...
Fri Nov 19, 2021 8:27 am

Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
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Ossessionato
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Fri Nov 19, 2021 8:27 am linkquote
Got your other engine together? Mark the crank at the lip and then pull the crank to see how much overlap.
Fri Nov 19, 2021 8:34 am

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Fri Nov 19, 2021 8:34 am linkquote
Quote:
Mark the crank at the lip and then pull the crank to see how much overlap.
It's more about what the minimum overlap SHOULD me for a tuned motor.
Quote:
I'm pretty sure 1.2 is sfe, but I'm still rooting for you to come to the Reed Dark Side on this beast, so my guidance may not be for a Minimum Safe Distance...
Ha! but not gonna happen - at least not before I test out an optimized rotary.

I've seen the dyno's.
I get that reeds are 5HP more.
However - that is with a set paradigm on allowable surface area created by length and width of inlet.

There are limiting factors on those variables.
No overlap of inlet and transfers means my inlet can't open before 119°.
I've been told that closing by no later than 60° is also prudent (70° on the pad).
So length is fixed.
Normally - min. allowable overlap of crank and inlet pad at side edges determines max width of inlet hole.
However - I am kicking the tires on the width question.

My prior question on offsetting crank by an additional 2mm stands - as this would allow another ~20% width of inlet - beyond what anyone else has done as far as I know.

No taker's so far...
But the mind ponders as I prepare the other details on the cases; the welder and lathe just chirping behind my back saying - "feed me now".



Fri Nov 19, 2021 8:40 am

Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
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Fri Nov 19, 2021 8:40 am linkquote
as FMP says.. if someone tells you to widen the rotary pad.. ignore it. No reason to risk it. You will gain more elsewhere.

Granted.. I'm just taking his word for it.

And lengthen it as much as you need for the timing you are targeting!
Fri Nov 19, 2021 8:42 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
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Lucky
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Fri Nov 19, 2021 8:42 am linkquote
charlieman22 wrote:
My prior question on offsetting crank by an additional 2mm stands - as this would allow another ~20% width of inlet - beyond what anyone else has done as far as I know.

No taker's so far...
But the mind ponders as I prepare the other details on the cases; the welder and lathe just chirping behind my back saying - "feed me now".
I think this is a perfect time to adopt the "fuck around and find out" method of tuning, then

Seriously, unless the offset created twist or a relevant level of lateral pressure on the crank, I don't see any reason it wouldn't work--and even then, you could throw a couple spot welds on the crank pin to reduce the risk of the pin getting worked loose.
Fri Nov 19, 2021 8:44 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
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Lucky
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Fri Nov 19, 2021 8:44 am linkquote
Second thought...are you only considering laterally shifting the crank to avoid having to re-replace the rotary pad?
Fri Nov 19, 2021 8:51 am

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Fri Nov 19, 2021 8:51 am linkquote
Quote:
as FMP says.. if someone tells you to widen the rotary pad.. ignore it. No reason to risk it. You will gain more elsewhere.

Granted.. I'm just taking his word for it.

And lengthen it as much as you need for the timing you are targeting!
It's all about the balance of the components.
Carb/inlet/CC's/Port timing/Exhaust...

FMP is also working within the confines of the normal width pad.
I am looking at a "bespoke" inlet pad that has significantly more width than stock.

What is clear: volume that the inlet can allow has a meaningful effect - example reeds vs rotary. And at WOT - where you are at peak power - reeds are just letting more fuel pass.
Quote:
I think this is a perfect time to adopt the "fuck around and find out" method of tuning, then
Old crank (worn out big end) is on the bench.
May experiment with some welding and grinding to see if I could hold a tight enough tolerance to customize the crank web thickness on that one as a Fri afternoon experiment.
Fri Nov 19, 2021 8:57 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
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Lucky
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Fri Nov 19, 2021 8:57 am linkquote
swiss1939 wrote:
as FMP says.. if someone tells you to widen the rotary pad.. ignore it. No reason to risk it. You will gain more elsewhere.
While FMP is, in general, not wrong...this is not the general tuning case we're talking about here.

I'm genuinely curious to see what sort of output CM2 gets, and how well the 20% increase in intake area translates to power out.

Even better would be to build it and (GSF)dyno as-is, then tear it down, make the change, and re-dyno, because...science!

Also, because the build is already exotic enough that I don't think there's a good baseline out in the community to compare it against, but then, it's easy for me to volunteer CM2 to do work.
Fri Nov 19, 2021 9:06 am

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
Joined: 26 Sep 2013
Posts: 6215
Location: So Cal
Fri Nov 19, 2021 9:06 am linkquote
You're playing with fire when you widen it. Risk of leakage and not a big payoff, from what I've been told. The tiny extra sip of mix it would provide won't be missed on that engine.
Fri Nov 19, 2021 9:29 am

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Fri Nov 19, 2021 9:29 am linkquote
not understanding "shifting the crank"

Is it because the lip of that fancy smooth flowing crank of yours is too thick? If so, grind it off in the open area.

Piaggio added the lip to the crank on the smallframe and Rally/P200 to get extra intake pad width.


quick cross section to help the conversation

Fri Nov 19, 2021 3:06 pm

Addicted
Too Many piles of Junk that need too much work and too much money
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Fri Nov 19, 2021 3:06 pm linkquote
SoCalGuy wrote:
You're playing with fire when you widen it. Risk of leakage and not a big payoff, from what I've been told. The tiny extra sip of mix it would provide won't be missed on that engine.
I agree with this on a stock pad. Widening is risky, and can potentially ruin the intake function all together. Lengthening the intake is exponentially better than widening.

That being said, you are dealing with full on custom monster frankenstein beast mode beast - so 'stock' directives don't really apply here. Rule of thumb, 1.0mm minimum overlap to get a good seal. Any narrower is risky IMHO
Fri Nov 19, 2021 6:34 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
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Ossessionato
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Fri Nov 19, 2021 6:34 pm linkquote
So sometimes a pic is worth a 1000 words.
I was talking' theory - but perhaps I hurried the lead.

The concept:
1. Add weld material to the outside of the crank. OCT - think of that lip you were talking about being 2x as wide.
2. That shifts the crank toward center by 2mm - but the crank's pad is now 19mm instead of 17.
3. Cut the inlet to 17mm wide opening.

The idea here is - what if you make the CRANK wider - then you can widen the inlet a commensurate amount. No need to have long timings - cause you have a PHAT inlet hole.
Keep moderate inlet duration - pump as much fuel as a reed set up.

So... I had this old crank, and an indexing head with chuck that I could put it in, and a drill... Just to see if I could weld a bead on the edge of the crank all the way around. I mean - how hard could that be?

Hahaha - let's just say that I didnt have my settings right out of the gate - and that crank took a beating - but if you look at the back half - it kinda worked!

Now - could I machine that?
Would I trash my crank if I tried it?
I dunno - but it wasn't that far off successful.

So OCT - I would be moving my crank off center by 2 or 3mm so that I could have a wider crank pad - and thus - cut a wider hole in the inlet - but not sacrifice any overlap of inlet and transfer timing. Looking for some feedback on that.


The set up (minus the clamp I put on the drill's trigger to run it and make the head turn)


TIG torch is spaced just off the crank - like a record player before the needle touches down


Houston - we have a problem. This got a 'lil hot. Oops. Guess I should have practiced with less heat...


Once I got the hang of it - had some pretty good results. The idea would be to machine this into the lip shape that is on the modern cranks - only twice as deep. What could possibly go wrong?


Here is what it would look like in x section using OCT's diagram

Fri Nov 19, 2021 8:04 pm

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Fri Nov 19, 2021 8:04 pm linkquote
ok, so if you are adding a wider lip, the crank does not need to move at all, just machine a groove into the case. It will be weakening the case around the bearing but I like the idea.

To do it right you will need to press the crank apart and do the machining between centers.

All that said, I'm totally confused about what components you are actually using.

Edit:

I'm not sure that more width is really needed as the area of the port in most cases is already above that of the carb. been playing with ideas for "ideal intake shape" given the oddness of the vespa intake. here is my current favorite.


note that the length of the port is shorter than on many bikes, but the area is still slightly above that of the carb.

Fri Nov 19, 2021 9:58 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
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Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Fri Nov 19, 2021 9:58 pm linkquote
Won't be slower. As long as the conrod is still fairly central in the piston and the crank can be re-balanced for the extra weight (exactly where its not needed), all will be fine.

Unlikely to be beating the solo German riders on reeds without lengthening the pad. You would think that width would compensate for length but it doesn't. The problem is duration and not area. Bigger carb would help. 35mm could run on that pad.
Fri Nov 19, 2021 10:09 pm

Ossessionato
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Ossessionato
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Location: california
Fri Nov 19, 2021 10:09 pm linkquote
Patric - that is super interesting.
Looks like a vacuum cleaner head.
Makes perfect sense.
My "sewer hole" attempt is like a compressed version - now questioning if I could have had a smoother transition as you have shown...

Interesting comment on the inlet as well.
If my inlet is larger surface than my carb - the inlet shouldn't be the constraint.
So what do you make of the reed's making so much more power - all other things being equal?
Seems like the available charge is larger?
Quicker?
What is the magic if not size of inlet?
Question for anyone that has an insight.
Fri Nov 19, 2021 10:46 pm

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Fri Nov 19, 2021 10:46 pm linkquote
I think this is the closest model engmod has to the vespa intake, bit of a hack to make it work.

plugged in your timings, guessed on the rest:
Port Window Height = width of the port at the crank on the Vespa
Port Window Width = length of the port (measured horizontal) at the crank

happy to plug in your numbers in as many configurations as you like.



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