Modern Vespa

Here is my BLUE Bajaj. The engine is seized in the sense the crankshaft had rusted.

My plan is to rebuild the engine with a mild tune and start using.

I have sourced a few components so far a Pinasco aluminum cylinder and mazzucchelli 60mm crankshaft. Have some questions concerning the crankshaft. The specification for the crankshaft: 112 degrees / 10 degrees post TDC. What does the degrees mean?





Last edited by hibbert on Mon Apr 22, 2019 1:21 pm; edited 1 time in total

10° after TDC is when the rotary inlet opens. 112° is how many degrees of rotation it stays open.

Thanks SoCal!

How do you formulate the best inlet timing, is it always based on degrees or are there other variables in matching and blending of ports or a combination of both?

I'm sure there are different ways but Freakmoped used this http://ddog.at/stz/rechnen.php

https://www.youtube.com/watch?v=OXsd9vqMJhM

what is 0°

It’s a point on the circumference of a circle. Normally 0° refers to TDC.

Timing is all about when and how long different events in the combustion process take place - i.e., when the inlet opens, how long it stays open, when and how long the intake and exhaust ports stay open, when the spark occurs, etc. By altering the timing of the events you can change the characteristics of the engine ( within limits ), and make it produce peak power at different rpms, depending on what kind of riding you intend to do.

From my observation it appears the rotary valve begins to open possibly at 112° BTDC I have not used a degree wheel but in this photo you can see the crank pin is about 11:00 position the inlet is just beginning to open.

Here the crank has rotated past TDC and the rotary valve is now closed. Just eyeballing it looks like 45° past TDC. it seems the rotary valve is open longer than 112°? Still need help understanding what is what.

Pretty sure not looking to go to the extreme as freakmoped thanks rowdyc but I do want to 'optimize' what is going on.

I wish my blue Bajaj was as nice as yours! You CA folks are lucky - no rust!

someone should have told the crankshaft hahaha

See pic below.

The line thru the connecting rod is 0°.
The next line represents 10° - where inlet opens.
The third line represents 112° - where inlet closes.

Imagine the crankshaft rotating counterclockwise (since this pic is from the clutch side).

Thanks SoCal I like that picture it will be use full.

Still struggling with what is going on. When is Open and when is Closed? Is Open when the crank begins to open the rotary pad or when the leading point on the crank pad reaches the full OPEN point?

Looking at this photo what is happening? Is it Closed, opening, open? This position is 90° before top dead center, not even close to 10° and BTDC..

In that pic, it’s half closed. A few more degrees rotation clockwise (facing the flywheel) and it’ll be fully closed.

Aside from needing to measure it accurately, you're only one step from getting the inlet timing correct.

I'll try to help without making it all sound too complicated. All below refers to position in degrees of crank rotation relative to Top Dead Centre (TDC/0°), as Before, (BTDC), or After (ATDC), and is shown as xxx°/xx°, and Inlet is either opening (Io) or closing (Ic).

The crank degrees are not the degrees of Inlet timing when it's in the casings.......

…...because, as well as the degrees in the crank, you have to factor-in the degrees of opening on the pad itself, and the position of it in degrees relative to TDC.

I'm not very good at explaining stuff briefly, but I had a go recently on another thread, here (scroll to Jan 22nd):

http://modernvespa.com/forum/post2299319?highlight=#2299319

Maybe this will help:

In your crank example, you have 10° and 112°, and SCG's sketch shows what that refers to. Then using the measured degrees for the opening in the pad, before cutting, from the diagram in my sketch on the above thread, (42° degrees opening in pad, 72° BTDC), you can calculate the following:

Total opening, (Inlet duration) = 112°+42° = 154° (the total of openings in crank and pad – this also answers your previous question about it not being the crank's 112°)
Inlet opens - Io. (BTDC) = 72°+42°-10° = 104° (where, BTDC, crank opening edge aligns with pad opening edge)
Inlet closes - Ic. (ATDC) = 112°+10°-72° = 50° (where, ATDC, crank closing edge aligns with pad closing edge)
to check, it is also:
Ic. (ATDC) = 154°-104° = 50°.

So that crank and Inlet pad example you'd get 104°/50°, which you can then modify to suit by cutting (or changing) the crank, and/or cutting Inlet in pad in the casings.

Bottom of this post is an old sketch example of an old engine and crank of mine, when I was first trying to understand it, and which had similar – 109°/43°, before modification, to show the relative position of crank and pad Inlet at Io and Ic. (crank rotating clockwise from this side):

Hope that helps.

Now you need to measure (crank and pad) and calculate yours...........................

(Or eyeball it with a degree wheel, but better to be precise I think).

Thank You sime66 so much food for thought, thank you.

I have some measuring to do, can you recommend how to do it? I have a degree disc but I do not have the correct crank hub so I'm ordering one. Would having the flywheel on the crank help?

Here is a photo of the untouched rotary pad





Last edited by hibbert on Mon Apr 22, 2019 7:40 am; edited 1 time in total

Here is the measurement of the inlet about 30mm

How best to measure it; Hmm....
I had the engine in bits on the bench, and I found it easier with the crank out, but I have a scanner and AutoCAD, so I did a rubbing of casings inlet and crank, scanned them and drew and dimensioned them in AutoCAD, but I'd imagine there's many other (simpler) ways with whatever you have to hand. Degree wheel and marker? Rubbing and a protractor? Might be fiddly if you're working on half an engine in the frame though.
Flywheel wont help; you won't see what's happening, but my degree wheel fits over the threads on a crank, and can be persuaded to stay in place, (or use an old CD and a protractor with a wire pointer fixed to a casing stud), but then you're still doing it by eye, which might be OK in first instance to give you an idea. Did you mean you don't have the bearing to use the crank? - The old one would do if you rubbed it down a bit to make it loose enough to fit back in easily, or you can get dummy ones, but that would probably take time; what's the white bit in the casings in the photo; will that hold the crank and let it turn? – I'd just do rubbings if I were doing it again.
You've also got the chord dimension for the inlet (30.33mm) and can measure the diameter, so a bit of maths will give you that angle. Then you just need to mark TDC (perpendicular to cylinder face and thro' crank centreline), and measure the angle from TDC (0°) round to the inlet.
To me, I wanted it right, and it was just as easy to do it exact with the engine in bits; here a few photos I dug out – be warned, the numbers might not be the same engine as the example above, so ignore those and fill in your own:

(Excuses beforehand – I have no control over size of photos, and it's first time I've tried to annotate multiple photos, so might take a few edits........)


Used a metal square to mark the Inlet onto a paper template taped in casings

Marked TDC on template and measured angles

Did a rubbing of crank to find degrees (protractor or drawing)

Worked out existing Inlet timings and calculated cutting for my target timings.

Maybe this way (or your degree wheel) would be easier, and good enough if you can bodge a bearing?

These are all you need in the casings, and you have enough info to calculate one of them already.

so much food here not sure if I can eat any more at the moment. The white plastic is a delrin dummy bearing I made and yes it fits the crank tight. OK I have some measuring to do. Thank you sime66.

You've re-named the thread to 'fitting 60mm crankshaft' and said Pinasco aluminum cylinder (also new?), so a final observation, without wanting to give you indigestion; have you checked the Transfer and Exhaust durations with the Pinasco cylinder and 60mm crank? It all has to tie-in and work together and be giving you the type of engine you want. Just buying a couple of flash bits of kit won't necessarily give you that.
Those other important durations, and the type of engine you want to build, will dictate your target Inlet timings.
You don't have to go full-on tuning, but at least a check (measure and calc) might be wise, to consider (and/or tweak) Inlet, Transfer and Exhaust durations together.

Thanks sime66 you are good to notice the change to title. If it's too much could go back to original title.

Also glad you caught the Pinasco cylinder part because it would be great to have this working good too. This one seems so much different than one I installed a few years ago. It's difficult for me to say what kind of engine I want to prepare because I do not know how it should be. We have the Pinasco cylinder, the 60mm mazzucchelli crankshaft, a 24mm carburetor and probably a big box exhaust at the end.

Below are the measurements on the inlet port.

Pad: 127°BTDC
Io: 111°BTDC
Ic: 74°BTDC
Pad: 64°BTDC

Pinasco piston

Pinasco cylinder

Ports

Exhaust port

is this correct?

Pad: 127°
Io 111°
Ic 74°
Pad 64°


Inlet Io - Ic: 111° - 74° = 37°
Total Open: 112° + 37° = 149°
Inlet Open: 74° + 37°-10° = 101°
Inlet Close: 112° + 10° - 74° = 48°

Well done: I've just got the same results as the calcs in your last post - as long as your crank is as spec - we haven't seen it yet to check.

So you're getting inlet timing 101°/48° without mods, you can shelve that result for now; we'll need to concentrate on the other factors before deciding what to do with that.

Have you actually ordered the crank? Have you got it? Have you got a link to it (spec)?
Have you got any thick base gaskets with the cylinder? Have you got a link to cylinder (spec)?

The next part of the job is a part dry-build of half-engine, crank (dummy bearing will be OK), piston and cylinder, to do some measuring of cylinder to get Transfer and Exhaust timings with 60mm crank. you'll need a base gasket, or choice of them - preferably starting with a 1.5mm one (see vids below).

Then, with all three timings, we can go more into what type of riding you do, what you're used to riding (did you ride this one before?), what you want from engine, and whether your shiny new bits are going to help or hinder the job.

I hope, by then, some more experienced chaps, will chip in and lend some knowledge/advice. I see that Jack221 had you measuring your ports a year ago on another scooter, so you have done some of this before:

http://modernvespa.com/forum/post2241483?highlight=#2241483

What happened with that one; the thread seems to end without conclusion - perhaps it's in later threads? I learnt the little I know from Jack, so hopefully he'll help here.

FMP does a good set of videos (he's posted on this forum a few times); have a look at these to give you an idea of what you've done so far and what you'll need to be doing (if you're up for it). Have a search on YouTube and on this forum for some background - it'll make the job of going through it all quicker and simpler for us both:

I posted links, but they're converted to video frames, which don't work on Chrome; I'll try this:

(https://www.youtube.com/watch?v=aghPxomIq18)
Don't be put off by the calcs; he does charge though it, and, to start with at least, we're just checking you're not building a pig.

(https://www.youtube.com/watch?v=MvGNkw1g6C8)
This second one, covers some of what we've done in a different way to get the same result; it's good background, but no need to copy the method for the Inlet; we've done it already.

OK have some numbers

This is measured with a 1.5mm cylinder base gasket as it comes from Pinasco.

PBT: + 0.70/0.75 mm the piston is above the cylinder deck
Exhaust: 34.75 mm
Transfer: 46.50 mm
Boost: 46.60 mm
Inlet Open: 45.50 mm
Inlet Close: 10.80 mm

BDC

Your photos show a 3-port kit, does your photo posted April 19th show that your Bajaj casings are 2-port? It's a 150cc isn't it; is the Pinasco 3-port kit OK with your casings? I take it the kit is 177cc? You still haven't given any info on kit; need numbers and stuff to read, more than photos, particularly now about this question.

Whilst you find an answer to that, I'll carry on as if it wasn't the elephant in the room; so, info outstanding from my previous post:

1) Have you got a link to crank? Have you checked your previously stated 10° and 112°? Confirm also for port timing calcs: 60mm stroke, 105mm conrod?

2) Have you got a link to cylinder (spec)? Can you measure squish? Do you have head gaskets with kit too?

The measurements for your Transfer and Exhaust with -0.075mm deck, can be input into these calculators:

http://lambretta-images.com/archive/porttiming.php

http://www.race-base.com/2t-tools/steuerzeit/index.php

I get:
Td = 125.15°
Ed = 175.69°
BD = 25.27°
(Id = 101°/48°)

(Transfers high, Blowdown minimal, Inlet too short).

Transfer duration of 125° gives you peak power at 8500rpm, which I doubt is your aim, but gives rise to more info outstanding from my previous post:

3) what type of riding you do, what you're used to riding (did you ride this one before?), what you want from engine, and whether your shiny new bits are going to help or hinder the job.

At present it seems to me to be a bit of a mess with Transfers too high (are they for you?), and piston already 0.75mm above Deck (need squish to assess this); this gives rise to next:

4) Are your Transfer and Exhaust dimensions taken from the same point as your “0.75 mm the piston is above the cylinder deck”; there is a head recess in your photos – You need to be sure you've measured from same point as deck.

I expect you've noticed that your large transfers in the cylinder are much bigger than those in your casings, and I've a nasty feeling those are 2-port casings too; this leads to next question:

5) Are you prepared to be cutting your inlet and transfers in your casings to improve inlet timing and open airflow into cylinder? Have you done much of that before? I'm not sure even how well it would work, if at all, on 2-port casings.

6) It may also be (if a decent combination of base gasket/head gasket/squish/crank can be achieved) that your Exhaust port needs raising in the cylinder; is that something you're prepared for? Have done before?

7) What are the gear ratios (or tooth count on Primary, loose gears, clutch and wheel/tyre size) that you have there now with this engine?

My first impressions are that you've bought a flash kit and crank, but it's an old 150cc Bajaj (2-port?) engine that will take a lot of work to get the most out of those parts, when it seems you're not really sure if that's even what you want from it. The few times I've done mild tunes on 150cc engines I've ended up avoiding long cranks, an I'm also not sure Mazuchelli crank timings (when checked and confirmed) will help either. I've ended up sticking with 57mm and cutting a standard crank for Inlet timing.

Whatever your replies to the above questions, and whichever way you decide you want to proceed, you need input from people more experienced than me (with this kit, with LS cranks in 150 engines, with 2-port casings!?!?, with any Bajaj peculiarities.....). I don't want to be the one to get you cutting up your expensive new kit! - Or to be telling you it's the wrong kit.

Have a read here, and see if you can get some of those chaps involved in your build; they seem to have met similar timing issues and (possibly by now) made progress past them. First point to establish is if this kit and crank are going to work, in your (2-port?) engine.

Here is a Pinasco 177cc 2-port kit for information; I don't know if it is necessary, or compatible, or if 3-port kit is OK to use (note the 3rd boost channel in the cylinder because there isn't a 3rd port in the casings):

https://www.scooter-center.com/de/zylinder-pinasco-177-ccm-2-kanal-grauguss-vespa-sprint150-vlb1t-gt125-vnl2t-gl150-vla1t-super-vnb-vba-vbb-pn0842?number=PN0842

This write-up suggests, at least, some care is needed with 3-port kits on 2-port engines (whether it's a waste of money for what you might achieve with it, or even achievable, is another matter):

https://blog.scooter-center.com/en/177cc-cylinder-options-for-2-and-3-ports-sprint-engines/

More background; see here at 14 Mar 2018, Rob Hodge mentioning 2/3-port Bajaj engine/kit problems, AND the flywheel taper on the crank - I'm more convinced I'm in (for me) uncharted territory, and you need someone with Bajaj and/or 2-port engine experience:

Bajaj 150 motor question

Tpye 'Bajaj' into the search on this forum, and there's loads of threads where you might find some answers. I hope I'm wrong, but my quick passing on of a bit of basic port timing theory has got a bit trickier as the details emerge.

thanks again for your thoughtful response. Will try to fill in some of the blanks.

1. Crankshaft https://www.sip-scootershop.com/en/products/long+stroke+crankshaft+mazzu_45135600

I chose this for the 60mm and ignition simplicity

2. Cylinder https://www.sip-scootershop.com/en/products/racing+cylinder+pinasco+177+cc+_80520000

There are no head gaskets as supplied. The head is recessed slightly into cylinder deck.

3. Background; I did not drive this scooter beforehand I bought it with the engine frozen, the crank rusted. Have some experience building a 2 port GL 150 motor with possibly an older version Pinasco. In that build I had the cases welded to enlarge the 2 side transfers and cut in the 3rd port. Welding was necessary for all three ports and to seal the cylinder on the 3rd port. In doing that the cylinder/case surface was machined as well. I used a Mazzucchelli crankshaft a 64/23 straight cut primary, 24mm carb and BGM big box. Was pleased with how it turned out so I was thinking about doing a similar build minus the overdrive substitute a 60mm crank and instead of welding try to make due. One the bonuses the Bajaj case seems like it will accept a 3rd port cut in without any other case modification whereas some Vespa cases like my GL would not. My thinking was to maximize this potential and eliminate the welding and resurfacing I had done on the other build. This may of course change as things are unfolding.

The Pinasco kit came with a 1.5mm base gasket with 2 side ports. It is the one shown in Scooter Center link where it states kills 2 birds with 1 stone.

The 3rd port is different from the earlier Pinasco design, the new one is bridged.

4. Yes all measurements are taken from the same location

Yes 2 port but could easily be 3 see photo

5. Yes, if I move ahead with this set up I will match the 2 side transfers to the gasket which is not much larger than stock and cut it the 3rd port. Is it possible flow is achieved through piston porting in addition to case transfer?

What is the hole in the piston above the wrist pin, never seen that before? The hole in the piston is not shown in SIP photo set but seen in my April 24 post. The hole is on both sides of piston. Also the piston porting by the 3rd port seems more aggressive.

6. I would not do this I do not have the skill but if I had good specs could have it done.

7. Primary 67T Clutch 22T tire 3.50 x 10

BAJAJ

I'm glad it wasn't a slip-up; I was worried for a while.

So it sounds like you've got it all under control, and are sure the new parts are compatible with the casings and intended ignition, and you're aware and able to do the opening and matching of the 2-3 ports. Also aware of the potential kit/casings matching/sealing slip-ups because you tackled it before. If you were happy with the previous incarnation of this type of build (acceleration/speed/peak-power revs....), and still without an answer to the type of riding you do, I'd say you're best to stick to the same Inlet and Exhaust timings as previous as best you can, whilst keeping an eye on squish and compression ratio with this kit (guidelines in Pinasco leaflet?). When you've decided what height you want to set your barrel, and have the port timings, it seems you'll also be able to do the work to open up the inlet in the casings to increase Inlet timing to suit – Your Io (BTDC) will need to increase for sure, and there's some spare in the inlet pad to do so – hopefully without touching the crank**.
I'm surprised a 2-port Bajaj engine makes a good base for it, but it's interesting to see why you chose it; 125/150 used 3-port 'PX' engine casings are fairly readily available and cheap here, so I've never played with 2-port engines, and probably never will. I hope the Bajaj brakes are up to it! Likewise, you'll know from previous that the gearing is up to the job – you didn't give gear ratios, but doesn't matter now as you're confident.
You also have whatever guidelines came with the kit to follow or query on the forum, and you have the crank in your hands to double-check those timings if you choose to do so before committing numbers to any Inlet mods. I think you need to check it because, from the image in the link you posted yesterday, **I suspect the opening in the crank is 102°, not 112°; that the stated “112°/10° post TDC” are both measured from TDC, so the actual opening is 112°-10°, but you have it there to check, so no need to suspect when you can be sure**.

I don't think you need anything else from me, but I'll answer the piston question in your post as best I can:

Yes, there is some flow through the piston; it looks like the 3rd port especially has some magic going on – it's probably linked to why you have a 2-port base gasket supplied with a 3-port kit (“two birds with one stone”), and I don't know exactly what (nor do I need to), but I know from previous that it has the extra benefit of improving cooling of piston under crown. Likewise the other extra hole – all I'd say is see what part of the transfer it aligns with, and where in a cycle it does so, and check it's open and clear where intended to be when you've set your cylinder height. I did read this:

“Info: This cylinder is based on the PINASCO model designed for 3 transfer casings. The third transfer is closed. An additional piston window controls scavenging. “, so maybe that's it.

Good to see something less run of the mill going on; it takes me a little out of my comfort zone though, but that's what the clever chaps on here are so good at, and I'll follow with interest. Good luck with it.

sime66 do appreciate your thoughtful cautious advice. Sadly I am still under a dark cloud of confusion.

Not clear how you calculate this Td = 125.15° Ed = 175.69° Bd = 25.27 (Id = 101°/48°)

Transfers high, Blowdown minimal, Inlet too short - I don't know what this means

Went onto the Lambretta port timing calculator page. 1) How do you enter the + 0.75mm piston over the barrel deck in Box 3 Piston Crown to top of Barrel @ TDC? 2) What is height over port, Top of port to top of barrel: Box 4?

If I'm following the first step is to negotiate the cylinder, base gasket and transfer ports. Once the cylinder is finalized the rotary valve can be adjusted and compression chamber. Do not know what is good what is bad what it should be what it should not be in terms of degrees. When at 180° BTDC there seems to be a large gap between the piston and the bottom of the transfer ports. Do the transfer windows get lowered?

Waiting on the degree disc holder to measure the actual crankshaft inlet on the degree wheel however was able to measure the piston depth in rotation if these numbers have any value Io 45.50mm BTDC Ic 10.80mm ATDC

Using 1.5 and 3.0mm solder measured squish at 2.30mm. Measured on the exhaust port side of head where it's the most flat surface area in the head. There are 2 impression marks from the solder on the piston and head.

Looking forward to the next round of measures.

The head[/img]

Hi guys I'm back with a little more information and request for help.

I would like to install the 60mm crankshaft with Pinasco cylinder and optimize for a good touring rider with good torque and easy to drive. I enjoy going a little better than the speed of traffic and if needed hold it at 65mph if possible for highway travel. Is this possible please help.

I received the degree disc holding tool and measured the inlet timing in degrees. From what I see Io is 110 BTDC and Ic is 22 ATDC giving a total duration of 132. Is this correct? What should this be?

Sime66 will get back to this set up but until then a few pointers.

The solder for measuring the squish should be touching the bore or the measurement will mean nothing much.

Your inlet total duration is way more than 132 degrees. This is the duration from first opening to full closing.

Measure the port timing with the piston flush with the deck (top of the bore)

OK will do some more solder compression's. May need to get another dummy bearing to support the crank it was having some trouble with just one side in the clutch side.

Made some headway on the calculation pages and came out with slightly different results than Sime66. I modified the stroke to what was measured from deck to BDC 59.3mm.

Exhaust Duration

stroke: 59,3
Conrod: 105
Piston: +0.75
Port: 34,75
Duration: 181.86

Transfer Duration

stroke: 59,3
Conrod: 105
Piston: +0.75
Port: 46,5
Duration: 130.87

Blowdown 25.5

Happy to measure the transfers with piston at TDC but not clear on what to measure.

Still fumbling around in the dark but you're getting there.

The stroke is how far the piston moves. 59.30 + 0.75

In the calculator you added the deck height and should have subtracted it. Comes out at about 176/125. A little too revvy for what you need.
How low can you get the cylinder with the thinnest gasket? Can you get TDC to be at +1.00mm or maybe slightly more?

Can't do the squish without 2 bearings. Will be too far out to be any use.

Jack, I'm glad you're on this now, I was lacking in confidence with the 2-port Bajaj engine, LS crank and 3-port kit: I'll follow and learn. Hibbert, you're in much better hands now with Jack.

thanks fella's for helping me fumble along. My best course in school was detention. Please check back in a few weeks and sime66 please don't go, don't go away.

While waiting for base gaskets started matching the transfer ports.





Last edited by hibbert on Fri May 24, 2019 3:57 pm; edited 4 times in total