Engine – Taking the Indian out of the Bajaj Chetak Classic

21 Apr 2015 | Author: | Comments Off on Engine – Taking the Indian out of the Bajaj Chetak Classic

The Chetak engine

You will be pleased to know if you don’t already know this that your Chetak engine is virtually identical to any large frame Vespa engine.

The two differences are as follows:

The stator wiring is different


The exhaust is bolted onto studs like a T5 (but not the same size) not a stub like its Italian cousins.

The Classic SL has a starter motor and for all intents and purposes that is about the same electrically as the Vespa counterparts.

It is really a PX150 motor in closest comparison with a Sprint kickstart quadrant.

All seals, bearings, consumables except the spark plug can be used from Vespa engines, there seems to be a difference of fitted cruciforms no doubt Bajaj using up their parts store so if a cruciform goes it may pay to do a visual inspection to ensure you get the right cruciform for your gear set.

Bajaj’s use short reach spark plugs which thanks to the VW Beetle and camper van which use the same particular plug, there will not be a shortage of them anytime soon.

The flywheel covers are the same for any P200 electric start models as you will notice the difference and the longer curve at the back.

Fitment, cabling, rear suspension mount are all the same as a Vespa, the Bajaj really does respond well I would add to a T5 rear shock as the Indian units whilst OK are less precise than the sporty T5’s.

Carburettor is the perennial Dellorto SI20/20 for the 125’s and the 150, some came with Spaco carbs but all parts are interchangeable.

One thing you may encounter is Vespa engine numbers which are apparently MotoVespa Spanish engines fitted during a shortfall, this has only been suggested by other unverified sources but my engine number is not a Bajaj one although it is the original engine from the factory, it shows up as a MotoVespa 125.

Servicing these engines could not be simpler if you have the tools and the patience, a decent plug routine, oil change although I will digress here in that I only changed my oil in its third year of my ownership and the oil was dirty but still going strong, don’t do that to your own scooter as a regular change means all them nasty bits of grit, aluminium and cylinder shavings get taken away from the engine where they can do the most harm.

Bajaj 125 Classic

A standard three port full gasket set, a seal set, bearing set from a 125/150 PX/large frame are pretty much all you will need for a full rebuild.

Small upgrades

A decent 20 or 22 tooth clutch will make a lot of difference in pullaway, it does pay to lightly abrade the metal plates (not the cork ones) to give enhanced grip but when I suggest light, you really only want to give the clutch just that little bit more adhesion, too much abrading will make it nigh on impossible to let your clutch slip even with the pressure released.

Iridium plug – I have run mine now for some months with an Iridium and starting, pullaway, top end all improved from this plug and as they last twice as long as a normal plug you are not losing anything.

Multi pronged plug – Another school of thought would see better performance from a 2/3/4 electrode spark plug, either way a better spark is better burning of fuel.

Head cavity polishing with a decent metal or alloy polishing compound is a sound thing to do, for metal polishing I use Peeks metal cleaner and it brought the crown of my piston and the head cavity up like new in seconds, if you allow carbon to build up you start to develop a damper spark and it muffles the explosion as time goes on and develops into a deeper deposit.

Bajaj engines aren’t prone to web failure as much as the Vespa especially around the clutch housing web which is notorious for P200’s to go there, yet when rebuilding, do look for hairline cracks there and anywhere near the kickstart mechanics.

Please visit the links section for further information on rebuilding and tuning engines.

Bajaj 125 Classic
Bajaj 125 Classic
Bajaj 125 Classic
Bajaj 125 Classic
Bajaj 125 Classic

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