Modern Vespa

Looking to get the headaches started and switch over to a long stroke crank for a P150 motor (Rotary/disc valve). I am overwhelmed by the options out there and minimal information I see listed on the manufacturer websites. Couple this with my lack owning a bunch of cranks and just seeing the difference. Intake duration and "finely balanced" seem to be main differences between most of the cranks on SIP's website. This will be for a hopped up motor (think charlieman's sidecar build, not peaky power but will pull like crazy), ED 178, TD 122, BD 28. These are ball park and I doubt I can get BD that high. I am aiming for a 180 intake duration, but haven't done maths yet to figure out what it should be and what my rotary pad will allow.

My Crap thought process on cranks, and why I am asking for help
For this post I narrowed down to Mazzy based cranks bc we would be here all day if I went through all 12 options on SIP website. SIP stuff is usually white label of someone else's, so I didn't see benefit in exploring them (and they didn't seem cheaper either). A xxx/6 crank translate to my intake opening at ~112° BTDC and my intake opening is currently 38° wide. I will map it again to make sure I didn't make any translation errors. I will open the intake some more if needed once I have a cylinder/crank in hand and measured actual port timings of the system. With a 138/6, this would give me a 176° Intake Duration as a starting point. And yuh, the 138° could be a liar liar pants on fire number, I read someone else's thread where it turned out to be 138° after TDC and not duration starting at 6° ATDC (think is was the BGM over a barrel thread). I ruled the base Mazzy out bc is was not "finely balanced", ruled out K2D bc saw some not positive things in some of the forums, ruled the finely balanced Mazzy out bc the Worb5 was only a few shekels more. Worb5 in theory has had human hands on it and did truly balance it to the noon position.
MAZZUCCHELLI 60mm longstroke 138/6 46000000 $166
MAZZUCCHELLI 60mm longstroke 138/6 K2D 45046000 $183
MAZZUCCHELLI 60mm longstroke 138/6 finely balanced 46005000 $206
Series Pro/Worb5 longstroke 138/6 finely balanced 46003000 $248

I am open to other cranks and would love to hear your feedback!

Questions:
1. Based on the above info, what crank do you suggest and why? (doesn't have to be a Mazzy)
2. I saw some cranks that had a negative 6 (-6) BTDC, why would one want this? For my motor this would most likely put my intake opening at almost the same time the transfer closes or even cause overlap.
3. What is the ideal published crank duration and opening position (112/6, 138/6, 138/-6, etc)?
4. Conrod of 105mm is the correct length for P150 without build some crazy custom crank, correct?
5. WTF does "finely balanced" mean and does it matter for out of the box use? If you are going to statically balance does it still matter?
6. Do you guys static balance your crank/piston/rings/pin/clips?
7. Any of you nuts ever had an assembly dynamically balanced? It is $300 but I have read of some buttery smooth results for non-vespa stuff that were higher-end builds. Link to explain difference between static and dynamic balance
8. I have heard of HotRod Al cranks over the years on this forum, but can someone enlighten me what you get and what is the cost? It sounds like his service is $300, you provide the base crank, he does magic. If this is the case the crank would cost like $500 between providing a base crank and shipping both ways.
9. What's with this full circle looking crank 45216200 SIP sells for rotary valve engines?

Sorry for the long brain dump, guess I'm just cranky.

Take a look at KingWelle:

http://www.kingwelle.com/epages/78261472.sf/de_DE/?ObjectPath=/Shops/78261472/Categories/Produkte/Kurbelwellen/Largeframe

Oh man, I have never seen this company before. All there stuff looks really really nice. I was drooling at some of their engine setups.

As for cranks, not quite sure I am ready to dump that kind of fat cash yet as well with wallow out my cases.

I have one of thier 60mm crankshafts that i run in a wide body engine. i have had it for probably 2-3 years. it's food for thought and simply another way to go.

Captcha,
Well - that is alotta questions.
Lemme fire a couple answers back at you from my experience.
Others can chime in or disagree.
That's why its a forum...

My $.02
Crank.
- Since you are going rotary - so no need to break the bank. Your on the right track.
- If your skill level is high - or if you just have some patience and an internet connection - you can probably figure out how to super finely balance what ever you buy - but you aren't going to need it if you are producing peak power at 7K-7500 RPM - so save your money.
- No one knows what "finely balanced means" - we are all still trying to figure out what exactly makes something a "class A repair".
- 180 degrees of crank timing has been great for me. 180 - 185 would be a good target.
- The negative 6 you see means they are producing additional crank timing on the other side of the rod pin. This adds additional opening time.
- Scooter Center tends to provide more information. Might be worth looking up those Maz cranks on their site to better understand.
- You will get your inlet timing through a combination of crank duration and inlet size. Have a look at my thread. I posted the Pinasco crank I bought and its timings there - and you can see pictures of how open my inlet become. The crank timings from my Pinasco crank and that amount of opening give me about 180-185 duration. I have been able to tune plenty of power and torque from it.
- You can achieve the crank timings I had by grinding back the crank. It takes a steady hand and some nerve - but you can see it on Hibert's blue Bajaj thread. I believe he used a Maz crank and made its timings pretty close to what my off the shelf Pinasco had.
- So for value - the Maz is a good option. If you can't get the timings you need - you can grind them. If you dont want to grind them - then look at other models with timings similar to what Hibert achieved or I posted - and you should have room in your inlet pad to then grind away enough to get to 180-185 timings.

Above should give you a target for crank timings you are shopping for - then you can see how has something that is in the ballpark and narrow it down to those - or buy cheap and grind.

Perhaps Jack or Ginch - who both talk crank - can weigh in on some of your other questions.
Hope this primer gets you started.
-CM

Captcha - while we wait for a few more opinions - why don't you fire up the rest of the specs you are considering.
Are you using the 150 stock cylinder - with O tuning?
Are you going with an aftermarket?
What about ignition?
Piston?
Clutch (just for fun)?

One thing Jack likes to do is get the 58mm kit but use it with a 60mm crank.
This creates more flexibility in port timings - but you have to create some custom gaskets.

I used the BGM cylinder kit - and I could recommend if you are going that route.
https://www.scooter-center.com/en/cylinder-bgm-pro-177/187-cc-vespa-px125-px150-cosa125-cosa150-gtr125-ts125-sprint-veloce-vlb1t-0150001-lml-star-125/150-stella-125/150-bgm1770n

It has a slip in head - so you can play with squish with gasket thicknesses and it is aa good a do it yourself performance kit as I think there is. Also - its transfers are quite accommodating to cases without welding.

CM22, thanks for you detailed responses. Dangit, I went full rookie and left out what I am going to throw together with the crank. P150 motor in a VBA on 8".

Be warned, I am riding the backs of you and Jack from page 44 of your sidecar thread. But I have read the whole thread. I like the direction you are aiming at for powerband.

Malossi MHR 177 (57mm) on a 60mm crank. Already lined out my spacers for bottom and (top if needed). I have a cast iron Malossi and I'm happy with the kit quality and the availability of replacement parts. I know G-speed is digging the VMC right now, but looks like a super rev monster.

P ignition with Kytronik, 1600g flywheel.

Superstrong/Ultrastrong clutch w/ 25/62 to help counter the 8" tires. Wish me better fitment luck than you had.

Pinasco 26/26 carb. Want to leave the door open for autolube, so not going standalone. By maths I in theory need a 26/26 carb, but maybe I will not be able to belch out enough exhaust and it is not needed. I have a 24/24 to fall back on if I get stuck on tuning or low end sucks.

Limiting factor: SIP Road 2. This is by design as I cannot stand anything louder.

For the crank, I will grind on it if I have to. Was planning to do a dry build to get an idea of where everything will fall, disassemble, then whip out the rotary/grinder as needed.

Welding cases is stupid, everyone knows JB weld is just as good. /s

I kid, 90% sure I am going to weld the cases. Working on finding a shop that will weld as per directions (not dump tons of heat at once, not half a$$ on gas/supplies) and then deck it. Dang Gickspeed been showing off his port job pr0n got me inspired to really open them up. Shipping kills economics for me to send it to him.

With the rotary crank duration just add everything together. You said your inlet was 38 degrees. If a crank is 138/6 add it all together with the 38 and you have 182. For an MHR on a 60, it will go best with as much as possible. 200+ is a good target. Unlikely to be achievable on old style cases but that's the target. Buy the crank with the biggest numbers that you think won't break.

Captcha - you have the ace on your specs now.

Jack - if its 138/-6 rather than 138/6 how do you add that? Is that 138+12?

You lost me on the crank math, as I thought the crank numbers were (total duration/open at X degrees ATDC). It is kind of a moot point though because it looks like I'm grinding with any crank I get if I want a giant intake duration.

200° intake duration! I got some learning to do. Will that long of duration start to kill low end power (is that even a thing, I remember reading it in one of the 2T books I think)? Why stop at 200°, why not (360°-TD°); where/why triggers diminishing returns?

Below is an example of the ballpark I will be in. These are not my actual numbers as I don't have parts yet. I was just playing with the calc and I think some numbers I stole from the sidecar MHR discussion. For this discussion, let's ignore crank numbers (ie 138/6) and focus on the final result of intake duration. You are correct about running out of rotary pad surface, but for the example let's ignore this too.

This example shows an intake duration of 180° and let's say my goal is 200°. Where do you start trimming first, BTDC or ATDC? My instinct would be to cut "A" as close to "D" as possible as this would give you more advantage because backside of piston is drawing air up. Then trim B clockwise as needed to obtain the entire 200° ID goal?

What are the advantages/disadvantages of having the transfer duration overlap with the intake duration (A is cut past point D)? For a non-racing application it seems problematic to have intake, transfers, and exhaust open at same time because you could be losing air fuel mixture out the exhaust especially at certain RPM.

Part of the fun (and pain) for me is learning the science behind the build decisions.

CM22: I meant to tell you, the hint about looking at things via scooter center has been helpful.

To get anywhere near 200 degrees on old style 150 casings, you would have to cut everything. It is generally accepted that 90 degrees is the ATDC limit for our scooters. Transfer overlap doesn't really matter so much. Anything under 10 degrees isn't going to notice at all.

With your example of 122TD, if going 90 ATDC, could get 209 degrees without even going into overlap. 11 degrees overlap and it would be 220 degrees. Give that full width on the pad and it's quite some inlet. Would make a 30mm carb actually work for a living.

CM22, if a crank is minus on the io side add that too. 138 + -6 + 38 = 170

Thanks Jack for your insight. 90° ATDC max makes sense as a max and is nothing I could achieve given the pads. Being accepting of transfer overlap makes sense as well because it would take time for the air to move all the way from the intake to the exhaust.

Now I need to go stare at parts and get my head wrapped around everything.