Lambretta 175 TV-SS
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Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Wed Aug 17, 2016 4:05 pm quote
This space reserved for future status updates

Current status: gathering parts
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Wed Aug 17, 2016 4:42 pm quote
My TV 175 has been in need of a rebuild for a while and I've had an engine in mind to build, but it needed a short stroke crank and finding one has been impossible, till now.

Last week I got the 54mm webs in, this week I got a yamaha RD125 rod in.

And so it begins...

IMG_1469.png

Hooked
50 N
Joined: 20 Dec 2015
Posts: 267
Location: North Aberdeenshire
Thu Aug 18, 2016 1:46 pm quote
So why do you need a 54mm stroke crank? The only thing that I can think of is that you have an old Autisa kit that was used for converting the 200 blocks down to 125. From memory this was mainly a UK thing for learner laws and fitted BSSO, or whatever the body was overseeing UK racing at that time, to fit racing purposes.
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Thu Aug 18, 2016 2:00 pm quote
I'll be switching to an IMOLA kit but due to class CC limits I need to keep the displacement at 175cc. The 54mm stroke with a 64mm bore will put me at 173.7cc.

It also lowers the mean piston speed allowing for a redline of 9900rpm.
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Fri Aug 19, 2016 5:06 pm quote
While I've never considered balancing a single cylinder engine worth spending much time on I have always been curious to know where things stand. It's not so much that it's worthless it's that beyond balancing the rotating mass one is trading vibration in one direction with that in another. There is a minimum total vibration at a 50% balance factor.

But since I have the crank apart and can take measurements, and with those measurements I can model the crank and find the balance factor, I figured I would.

Screen Shot 2016-08-19 at 17.49.38 .png
Balance Factor = 44%

Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Sat Aug 20, 2016 9:28 am quote
After doing a bunch more reading and shopping for tungsten, I've decided to leave the balance as is. While a 50% balance factor will give minimum over all vibration, leaving it less than that will keep more vibration in line with the cylinder. On a lot of motorcycles with vertical cylinders a balance factor greater than 50% is used to shift the vibration into the horizontal plane. Given the horizontal cylinder on the Lambretta the 44% balance factor will result in the same 'feel' as a 56% balance factor in a motorcycle with a vertical cylinder.

Or at least I think so...
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: 6941
Location: Victoria, Australia
Sun Jan 22, 2017 1:18 am quote
A friend and I were trying to school ourselves on balancing last week and got into some deep water... but found some very interesting material.

This person has some useful-looking calculations - http://motorbicycling.com/showthread.php?t=40568
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This guy has a spreadsheet to help work out balance, and his video where he goes into some detail. But I realised he was talking about a full circle crank so left it. May be of some use - https://www.youtube.com/watch?v=ZRmx0I3k2IY and
https://docs.google.com/spreadsheets/d/1pm37N5g90aN4o9ynep7snpW2qcLhth_EPUSNjNbIdWw/edit#gid=4
He seems to be mostly drilling holes rather than adding weight, not sure if that's possible in your situation.
+++++++++++++++++++
Also thought this was kind of helpful as well - if you wanted to know what balance factor to aim for -
Quote:
Here is my understanding of 2 stroke crankshaft balance factors...

I have used these theorys for adjusting crankshaft balance for 2 stroke racing motorcycle engines. They apply equally to r/c engines.

The best way to support the crank, is like Edward said. Being that the crank has only one side journal, there is no other practical way. His way should get you very close.

In my experience, I have had the best luck with balance factors between 58-62%. It's amazing how much difference the engine runs with different balance factors. But like most 2 stroke modifications, nothing is written in stone. It's always a trial and error game.

On the other hand, 4 stroke singles, balance well between 48-54%. Go figure!!

Here is a simple diagram for my technique that may help you guys visualize the balance process.

The formula is very simple: B/A=%

where A= approx 1/2 the rod weight + the piston + the piston pin + the piston pin clips

where B= The weight of A (Piston assy, and 1/2 rod)counteracted by the crankshaft counterbalance weight

where %=the resulting balance factor

Hope this helps!!

BK


It comes from this thread - http://www.rctech.net/forum/onroad-nitro-engine-zone/64236-crankshaft-balance-4.html

Please ignore anything that has no bearing (partially intended pun) on what you're doing, but hope it's of some interest.
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Sun Jan 22, 2017 10:25 am quote
ah, good to know there's a way to get the values when the crank is together. Thanks for posting that.
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Tue Aug 08, 2017 7:09 pm quote
Woot! My crank is going together very soon. Then the real fun can start on this project.

Considering it took me more than 10 years to find the webs, a year for the build is nothing.

20626757_914466445357742_1550549802932803450_o.jpg

Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Wed Jul 17, 2019 11:41 am quote
and, after all that it looks like I'm changing up the formula again.

Plan now is to stick with a 58mm crank and sleeve the Imola down to the stock 62mm bore.

Have been running the numbers in EngMod2T and targets are for a very wide power band with max power of 26HP at 8000rpm. The uneven stud placement and cylinder angled relative to the crank getting more out of it, so going to focus on usable power by making sure everything works together to maximum effect.

So far have the transfers and exhaust mapped out and balanced, now working on the intake.

Screen Shot 2019-07-17 at 12.37.24 .png

Ossessionato
LXV 150 Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 2763
Location: Bangkok
Wed Jul 17, 2019 3:56 pm quote
What gearbox are you using?
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Wed Jul 17, 2019 9:27 pm quote
not decided on a gearbox yet, only the topend, may go 5 speed, but want power simulations before I select the gears.
Ossessionato
LXV 150 Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 2763
Location: Bangkok
Wed Jul 17, 2019 11:22 pm quote
OK. Do you have a copy of Sticky's "Bible" ?

Apparently Li150 is the best if staying with 4 speed.

i don't have mine handy as it is in storage.
Molto Verboso
Vespa LX150 GTS250ie GTS300x2
Joined: 11 Dec 2009
Posts: 1980
Location: St. Pete, Fla
Thu Jul 18, 2019 2:01 am quote
I have no idea what you guys are saying but it sure fascinates me.
Keep talking.
Member
Joined: 17 Jul 2019
Posts: 9
Location: Santa Clara, CA
Thu Jul 18, 2019 10:15 pm quote
We need more updates.
Banned
2:6
Joined: 11 Jan 2007
Posts: 7419
Location: San Francisco
Thu Jul 25, 2019 4:52 pm quote
Got the ports input and did some balancing of the port time area.
started with the transfers, then the exhaust to get the blowdown set and a basic pipe. This is where all my prior tuning has left off, just getting the port time area in line and the intake and pipe to empirical guidelines. Result in simulation: 20hp.

realized the transfers are biased to the back wall so changed the angle on the B-ports back wall to point a bit toward the exhaust. This gave more area so lowered them to bring it back to a 26hp target. rebalanced the exhaust. Result: 21hp

worked on the exhaust header and stinger area, reducing both, and got it up to 24hp. did an rpm sweep to see how thing look overall, I'd be thrilled to see that on the finished bike! still have some optimizing to do and this is only two iterations.

Screen Shot 2019-07-25 at 15.55.21 .png

Addicted
GTS 250
Joined: 19 Oct 2009
Posts: 705
Location: london uk
Thu Aug 01, 2019 9:16 am quote
TV175
Hi this was my favourite scooter in the late 60s. and now.
Hats off to your engineering prowess. It's impressive.
You don't build Saturn rockets, or Boeings in your spare time.
I couldn't dream of working out what you are doing. Actually, I'm crossing my fingers for a Lambretta style, metal bodied Electric scooter... Only a coil of copper, and a battery and I'ts good to go. I'd still have plenty of engineering polishing crash bars and mirrors though.
TVs were designed for the sportier British market.. The 175 and 200s were the E-types for mods then.
cheers gass, GTS 250 silver machine.

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