Vespa Polini 210, BGM 60mm ,Dellorto SI26 – tuning test engine – Pt. 6

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Our test engine is running, we let it warm up properly. The jetting seems to be right with idle jet 48/160, air correcter jet of 160, atomizer BE3 and main of 140. So now we will see how powerful this engine is.

First of all the gear ratio needs to be measured. We measure this at least twice to be 100% sure. The gear ratio is 3.21. This can even be typed manually into the dyno software at a later date.

When you are operarting a dyno a scientific operation is a good gesture to make sure that the results can be compared. After the first three runs we see that the power output is always nearly the same. A good sign, here is the best result:

Nice to see that the engine starts to lift the power low down in the rev range. As expected from the Polini kit. A quick road test shows that is a treat to use on the street. At slightly higher idle revs of 3.500 rpm the engine pushes -thanks to 17 Nm- heavily.

The inlet induction sound is nice too. The Polini solution works not just power wise, it reduces induction sound as well. The adaptor has a small collar built in that breaks up the acoustic wave what gives a very discret induction sound.

Back from the road testing to the dyno, we take a closer look to the head design. Next we are going to test the MMW head. The previous fitted Worb head gave a squish clearance of 1.7mm. To achieve this with the MMW head we are going to fit a 0.7mm head gasket. One quick note: Never combine normal head gasket with O-rings on heads. This doesn’t work on the road. For short testing on the dyno it can be done though. And we needed to do this to make the heads test comparable with the same squish clearance.

After some more runs we have a direct comparsion of the heads:

RED: MMW

BLUE: Worb5

The higher power output of the MMW head is caused by the slightly higher (but still road safe) compression ratio and the difference in the combustion chamber design.

The highest torque reading is still at 4700 rpm, but rises to very good 22 Nm. At 7k rpm we still have 17 hp and 17 Nm. God figures for high speed motorway use.

The 60mm MMW head we are not going to test anymore. Not because we are lazy, it is more because there is no sense in it all. We already saw that the higher compression works. the 60mm version would reduce this, so we are not to keen to loose power.

A wider power band with a little more peak power at high revs would be nice though. This really seperates good road engines from the very fast ones that are hard to catch on open roads.

Well… what could be done. Something like a luxury problem here. A good working engine with nice power output in a useable rev range and we are still thinking of how it could improved.

There it is our MBgm Vespa BIG BOX. Sounds like fun to get this on the Polini. Doesn’t it?

This should be done tomorrow!

Stay tuned!

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Vespa Polini 210, BGM 60mm ,Dellorto SI26 – tuning test engine – Pt. 5

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Only a few stepd left untill we can dyno test our new engine.

The engine will go into the Silver Fern and be tested for Rally going and daily commuting then.
While fitting the flywheel care must been taken that the slot in the flywheel cone aligns with the woodruf key.

Afterwards the flywheel nut can be tightened down to 65Nm. The washer needs to be fitted, otherwise the nut will come loose.

The rear brake drum goes on the shaft next. We only put it on loose and fix it with the nut.

As sson as the rear brake is adjusted we will tighten it down to 110Nm. Securing cage and splint must be there.

For adjusting the clutch you need a little bit play at the clutch lever. This should be around 1.5mm and 2mm.

Oil and fuel hose are connected. folgen. The air bubble at the oil hose is a very good indication to see if there is oil pumped into the carb.

But the air bubble shouldn’t be much bigger than that. Otherwise there is the risk that the oil pump runs dry. And so will do the lubrication then.

For the first firing we fill the fuel tank up with 1 litre of oil petrol mixture of 4%. This should be done to have a proper lubricated engine from the start and to compensate the oil pumps delay.

The engine starts and we let it idle for a while. Then we see that all cables are connected properly. We rund down to fourth and everything is okay. The clutch works perfect.And the oil pump operates as well.

So we are ready for the first dyno sessions. Watch this space.

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Vespa Polini 210, BGM 60mm ,Dellorto SI26 – tuning test engine – Pt. 4

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Today we found the time to have a look at the port timings of the Polini kit.

With a 1mm base gasket one look at the degree disc shows us transfer port timings of 125° and exhaust timing of 172°. This results in a blow down timing of 23.5°.

Figures that really worth to try on the dyno and figures that should result in fast road engine with torque capable of raching high revs for good speed.

We have three different cylinder head designs to test on the engine. And this will be the first mod on the dyno.

We are going to try the MMW for 57mm stroke, the MMW for 60mmstroke as well as the Worb5 head for 57mm stroke.

On a first sight at the head we have a look at the squish clearance. The MMW 57mm version is a little bit tight at our 60mm crank. The squish would be 1mm on our setup, but well worth to try it with an additional head gasket. The MMW head for 60mm stroke is designed with a recess for the longer stroke. Used with our 1mm base gasket to achieve the right port timings we have a squish clearance of 2.7mm. So we have this head as an option if we want to try the setup without the base gasket. If we don’t use the base gasket anymore the port timings are lowered, but with the effect that the blow down timing is increasing. This is because of the greater reduction of transfer timing compared to the exhaust timing.

The Worb5 head is machined for the 57mm stroke, but with more squish clearance machined into the head. So we have a very useable squish clearance of 1.7mm without additional head gasket.

The different combustion chamber designs we will test on the dyno the next days. Can’t wait!

But the carb ist still waiting for fitment. And there are some important steps on the way to take care off.

First of all you have to be careful with the use of sealer. On self-lubrication Vespas the hole marked red in the picture feeds crankshaft, barrel and flywheel side bearing wih oil. If this is blocked no oil gets in and the trouble free miles will be very limited.

The very basic design of the SI carb range is very soli. But one to watch out for is the mounting of the carb, this can easily be destroyed.

If the nuts are over tightened the carb is warped and a sticking slide is the result of it.At least the later version of the SI carb is improved in this area and the nuts can’t bend the carb so that the slide sticks.

The pictures shows this feature on the later carbs and this recess can easily be done to later SI carbs.

But even on the later version the carb nuts shouldn’t be tightened not more than 16-18Nm. And they shouldnot be fully tightened from the start. Instead tighten they evenly and in turn.

For the carb mounting there are two different version available as well.

The “old” version with studs and sleeve nuts are there untill the SI carb was used first. The new version was introduced with self lubrication P-ranges labelled EFL, Arcobaleno or Lusso.

The ida came up because this was easier to fit. Carbs without self-lubrication are fitted with a very long air adjuster screw and slide hook.

Before the carb is fitted into its box we cut a slot into the air adjuster screw this makes adjustment much easier on a later point.

Damn, we spoilt it!

That happens too often. So you have to take care that the hook hits the clip of the oil pump.

If the carb is fitted like the one pictured, it simply won’t work and you foul the slide hook.

Studs for carb fitment are not supporting good work flow and Piaggio introduced the sleeved screw. But this advantage brings a risk.

The screw next to the end of the scoots is located right above the rotary valve.

If you don’t use the right washer and spring washer the rotary valve surface will for sure be destroyed.

Tighten it down in steps of 8, 12, 16 Nm.

The Polini bellmouth is secured by only one screw. The idle adjustment screw can be used to get the location of the glory hole right. So simply adjust it that idle adjustment screw and the hole align.

For the dyno sessions we simply screw it to the carb. When all the jetting is done and we are happy with it, we glue the screw into place with threadlock.

The stator plate is adjusted to 18°. This equals to th “IT” marking at the plate.

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Get In Gear – Polini 210, bgm PRO 60mm ,Dellorto SI26 – test tuning engine – Part 3

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Carb and rotary valve inlet are prepared and ready!

Now the bare casings can be filled up with all the internals that make a good engine.

For the gear box we opted for a complete P200 gearbox with layshaft, pre-assembled and in Original Equipment Manufacturer quality. Not a good idea to cut corners here. Because it is pre-assembled only, we dismantle it, double check it and re-fit it with attention to the gear box play.

To hold it properly in place, we fit the gearbox cruciform with a drop of threadlock.

Gear wheels, securing clip and Gangräder, Seeger- und the gear box shims look like this when assembled.

The gear box needs to be shimmed properly. Otherwise problems will occure. The right tolerance is 0.05mm-0.15mm. The best way to check if everything is spot on, is to use two feeler gauges. For new shims you should go for the tighter tolerances. The surface wears much more than with shims that were already used for a few thousand kilometeres.

The easiest and best way to fit the inner track of the flywheel bearing is to use the proper tool for it.

Now we are ready to get the bearing kit fitted to the engine casings. The only proper way is to heat the casing or freeze the bearings or even better do both. If this is done fitting is a job that could be done in the Kindergarten.

To safe time we cooled the bearings down with our cooling spray.

The exception of the rule are the small needle bearings. Those should be fitted with the right tool additionally.

The flywheel side bearing should be guided with the right tool for the job.

For the B188-bearing it is a good idea to consult a good persuader to get it properly fitted into place.

When you the bearings in place, there is the time to get the oil seal set fitted.Normally fitting the oil seal shouldn’t disturb the work flow too much. Much more patience is needed to get the bearing needles of the Xmas tree in place. To give each needle a good smear wih a nice grease does help very much here. Every needle should be counted and the end result needs to be 21.

The Kickstart sprocket and Shaft are the only parts remaining at the workbench, while the engine is waiting for those.

One to watch! Don’t forget to fit the kickstart spring, holding it in place with some grease is advisable.

Now the crank is fitted and the casing halfs can be put together.

The engine casing studs are torqued down evenly.

The oil gear drive is fitted.

The drive wheel has one washer on each side. At the picture there is only the securing ring missing that holds the wheel tightly in place.

After the oil pump wheel is fitted with the fine smear of oil, the gaer can be put onto the crank. There is a chamfered side at the wheel this side should face forward to the engine casing. Otherwise the whhel and crank could touch. Mainly depending at the crank design.

Once fitted you can see the beauty and nice design of the bgm crankshaft together with double lipped oil seal.

One of the most important thing is to get the power of the top end transmitted to the bottom end. Therefore we highly recommend the well proved bgm Superstrong clutch.

Design to be used with 10 clutc springs there are plenty of variations to cope any power!

For the expected power delivery we opt for 10 XL springs.

Once again: oil! This time to lubricate wave designed hub.

Now we are going to fit the clutch sprocket and clutch plates. If you are going to purchase a complete bgm SUPERSTRONG all this will be done for you. And you receive a complete Plug & Play unit.

For first fitment some drops of oil will do it!

For the steel plates the positining of the curved one is of importance.

This one needs to be slightly bended, only a few tenths of a millimeter to get the clutch working properly right from the start of the lever action.

If the plates, steel platees and securing clip are fitted it is done.

The self locking nut is tightened to 60Nm.

Once the engine is completed, the proper tuning action can start. Tomorrow we are going to have a look for the port timings!

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Vespa Polini 210, bgm PRO 60mm ,Dellorto SI26 – Tuning Test engine – part 2

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Today we took a closer look at the Air intake filter / bellmouth from Polini as well as for the Dellorto SI 26 carb. And we will answer the question what the glory hole on top of the carb is good for?

In the end it has a good effect on the working of the carb. Simplified it works like a bigger carb, the carb sucks harder and gives more fresh air for the engine. The result is well known: more power, good!

If your engine gets more air you need to richen the mixture with the right amount of more fuel. The delivery of the Polini air intake includes a138 main jet for the SI carb (this is at the P200 version).

At the idle jet and atomizer there is a relief groove at the venturi. This guides the fresh air thru. This is similar to the mods done to the SI air filter base. To get a bore in there gives a better and easier jetting and better throttle response. This does the groove in the Polini kit as well.

Because you can’t put the air filter on top anymore, Polini found a nice and well working solution for this too.

An adaptor kit is tightened down at the carb box. This makes it easily possible to fit a modern day foam filter.

The adaptor should be fitted in a way that you still can get to all connectors, fuel pipe connection as well as cables for choke and throttle cable.

The fact that Polini included a 138 main gives a rough indication on how much more air will get thru with this neat mod. Experience on engines with bigger SI main jets than 130 showed us that some mods to the carb are needed to get the show reliable. Otherwise the fuel starvation will happen.

You need to sort this out properly and start where the action starts. At first the fuel tap should deliver enough fuel. We recommend for tuned engines the bgm FASTER FLOW taps. These are capable to deliver more than enough fuel. If your fuel tap gets 280-300 ml/min thru everything should be fine. But check the video at the fuel tap out to get the full story.

Except for a working air vent in the fuel tap cover you can’t do much more for the fuel tank. It is sorted with the bgm FASTER FLOW.

Now we come to the blue printing of the carb that is needed-at least- from 130 main jets on.

The small float bowl of the SI carb needs to be topped up with fuel all the time. Even under full throttle for long distances. The main bottle neck here is the float bowl valve. The best way is to swap this for the Vespa Cosa one. A straight and easy fit that cures this problem.

To the right: the standard SI item. At the left corner: The Cosa one.

Except for the larger float needle the bore diameter for the valve is bigger to. And for sure the of the valve.

The fuel channel for the float valve is opened up to 3mm.

Now all the needed mods are done to have a proper blue printed SI carb that gets enough fuel even on powerful engines.

One hidden design fault is still there though.

The small hole in the middle of the picture has a 1.5mm diameter. This is the channel for the main jet. All the fuel for the main jet has to go thru this.

This is too small as well. It is good for a 150 main jet but a design fault. We drill this out to 2mm. Better safe than sorry!

The bore at the left is for the choke system only and fine as it is.

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Vespa Polini 210, bgm PRO 60mm, Dellorto SI26 – Tuning test engine – part 1

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Lots of scooterists out there and here in Scooter Center to, dreamt about a Polini 207 kit made of alloy with the hard wearing Nicasil plating. This dream already came true!

We had one of the first kits fitted to a 10 hp standard P-range engine aon our P4 dyno. The bullet proof Polini layout was even better in the alloy trim. High torque low down the rev range made it t the most desired kit right from the start.

Polini introduced more and more toys for boys. Lots of stuff to get higher power output and an even bigger grint to your face. Beside the airintake/bellmouth to get the most out of the SI carbs, a Polini 210 kit for 60mm stroke is down in the pipe line. This kit is specially made for the 60mm crank and gives 221cc.

With lots of trouble free miles during the last 1 1/2 year we are so happy with the kit, that we decided to build a Polini test engine and show you what we think is worth to take care of. As soon as the 60mm version is out, we will replace the 210 for the 221.

The games started today and this is stored into the workshop. And the dyno is waiting despertately.

Cylinder kit Polini 210, cylinder head MMW and Worb5, airintake/bellmouth Polini for SI carbs, 26mm SI carb and one of the bgm PRO 60 mm crank.

All parts are carefully checked and everythings is going to be prepared for fitting.

First view is the engine casing, that will house all the other toys we saw here.

At the moment the only P 200 casings are branded as Malossi. Beside of the name nothing major changed though.

Care we have taken for the inlet area. The inlet area is carefully cleaned, blue orinted and optimzed.

For the heart of the engine we opted for the BGM-Kurbelwelle. Perfect inlet timing for high power, clean running and good fuel consumption are the key words of the good designed crankshaft. The very well made crank leaves nothing to be desired.

An additional nice feature of the bgm PRO crankshaft is the enlarged sealing area at the taper of the flywheel side. Thanks to this you can use the far superior FPM oil seal with dust lip. Compared to the common NBR oil seals the FPM oil seal has a much better reliabilty.

NNext we will have a look for the Polini air intake improvement. Watch this space!

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