PINASCO 251 BUILD PART 7 – CDI AND IGNITION | FEATURE

If you’ve been following our Pinasco 251 engine build features you’ll be as pleased as us that the engine is almost complete. We’ve just got a few more issues left to sort out in this episode.

Building a standard or tuned engine?

This is part seven of an eight-part series; you can read the previous six parts and the final instalment by clicking the images above. Even if you’re building a standard or tuned PX/T5, this series will provide some very useful tips, tricks and techniques.

What are we up to this time?

In this part we modify the CDI bracket to avoid it hitting the side panel, fit the ignition, pop some new brake shoes on and send Iggy home with a new engine.

This is the original layout for the 251 CDI on the supplied bracket

CDI re-mount

One problem that quickly became apparent on other 251 builds has been the proximity of the CDI to the side panel if the engine is fitted to a PX.

This is what happens when the 251 CDI touches a PX side panel; the casing breaks

This lip on the inside of a PX panel is what hits the CDI

The stainless steel mounting bracket supplied by Pinasco puts the CDI in approximately the original position on the back of the engine casing. However the CDI supplied with their Flytech 251 ignition is actually wider and heavier than a normal 4-pole CDI like that supplied with a Vespatronic ignition, for instance.

The problem occurs not when the suspension compresses, but when the shock is at full extension. In that case, the lip in the rear corner of a PX panel catches on the CDI and eventually snaps it off its bracket.

This problem was not apparent during development because Vittorio from Pinasco tested his engine in an older Vespa chassis with a different panel design.

We remounted the CDI by welding two Pinasco brackets together at 90 degrees

Rather than repeat a known issue, we chose to modify the supplied bracket in advance by welding on an extension at 90-degrees to the original. This moves the CDI round to a position occupied by the starter motor on elestart models. So far so good…

With the CDI repositioned here, it is safely clear of the panel and the shock

The Final Leakdown

The Final Leakdown is much like Europe’s dreadful poodle-rock dirge The Final Countdown, except in every conceivable way.

I think it’s fair to say that the leak-down pressure test has become one of the most essential tools in the armoury of scooter engine builders over the last decade. If you don’t test then you don’t know where the leaks are.

Once we had solved all the minor leaks through the stator holes of Iggy’s casing, the last step was to deal with the major one which is the exhaust stub to cylinder joint.

Not the flattest flange in the world…

No exhaust gasket is supplied for this face, so essentially you are relying on a small gasket area, some high-temperature silicone and the power of prayer to prevent leaks here. Those would probably be sufficient if the surface of the flange was flat, but when we checked, it wasn’t. This was probably due to distortion when the flange was welded. You can see the before and after photos above.

Video: Linishing the flange

Using a belt sander it’s possible to flatten the distorted exhaust stub.

This is the stator position we had to use to get 24-degrees as per the Pinasco instructions for the 251 kit

We have ignition

Finally we fitted the ignition system. Pinasco’s Flytech ignition is a 4-pole system like many others on the market. As such, it suffers from the problem common to all the 4-pole ignitions, namely weak light output at low engine rpm.

In its favour, the Flytech does at least have a one-piece flywheel which is a much more expensive and rugged construction method than the riveted centre-boss layout chosen by some rivals.

The Pinasco CDI contains an electronic advance-retard module offering around 8-degrees of retard over the entire rpm range of the engine.

Ignition fitting is pretty unremarkable, save for the confusing layout of the timing markings on the stator plate

VIDEO: It’s all in the timing

Since making our ignition fitting video live we’ve already had queries from people who are insistent that the ‘251’ mark is correct, so we double-checked another 251 engine. Sure enough, the other mark does give the 24 degrees BTDC setting that Pinasco suggests.

We even contacted Patrick Adam of Chiemgau Tec Production (CTP ) who has built over 40 Pinasco 251 engines. He says that for touring engines he prefers a timing of 23 degrees BTDC for the Flytech (one degree more retarded than Pinasco’s suggestion) which he says helps to keep the engine cool. In any case, he says it is important to set the timing and stator position with a strobe gun and not simply rely on the stator marks.

VIDEO: Fettling brake shoes

Next up was to fit a set of new brake shoes. We opted for a set of BGM shoes, these come complete with new shoulders, circlips and even a small tube of grease for the pivot bolts.

We had to dress the shoes to get them to seat correctly and allow the rear hub to move without friction.

Head cowling

The final pieces of the T5-based jigsaw puzzle are fitting a Vespa T5 flywheel and cylinder cowling; both of which are much harder to find than the PX versions and subtly different too.

The longer cylinder means that there is a slight gap between the cowlings after fitting but this can be solved with a dedicated BSK fibreglass cylinder cowling, available from Scooter Centre for 117 Euros.

Iggy chose to modify a standard T5 head cowling instead. He’ll show you that in the next part of this series.

With the 251 cylinder being longer than standard, you can encounter problems with the spark plug cap touching the panel when 2-up

A neat solution to this problem is to swap from standard-length B-series spark plugs (B10ES is recommended) to NGK’s shorter-bodied plug (such as BR10-ECMIX). This significantly increases clearance to the sidepanel.

My work here is done

With that final step, Iggy could take the engine home and fit it back into his PX street racer chassis. What could possibly go wrong?

Text: Sticky
Images and Video: Iggy