The ultimate engine upgrade for the Himalayan
For some time now we have been playing with the idea to create the maximum possible affordable engine upgrade for the Himalayan. Affordable in this context means no need for changes to the head or the engine housing. We also concurrently play with a 510cc version that is NOT very affordable.
The 477cc originated quite simply from the idea to modify an already existing piston, namely the 500 Bullet UCE version, to fit a LS410 cylinder.
This piston needs a new sleeve, (so does the 462cc). Because of the geometry of that early alpha version piston it was necessary to somehow achieve 4mm less height or else the timing chain would not fit. That was done by cutting 2.5mm off the “head” of the piston and using a 1.5mm copper gasket for the cylinder foot. We still had to get a 3mm longer chain (1.5mm both sides for the higher foot gasket) which we “harvested” from a bike that had run 25.000km already (the chains elongate with use).
The piston was now flat – as opposed to the original which has a 1.5mm groove so the compression was much higher than in the OEM engine. The added volume would have increased it to some extend already and the flat surface of the piston now made it really tough. As a result the engine would ignite too early on even the slightest acceleration when using the standard Indian fuel (which is very bad and often stretched with water or Kerosene). Only when we settled on “Power” fuel (more expensive but somehow better) and added generous quantities of Octane Booster the knocking went away. Well, almost. However it was great fun to drive this bike which was now an altogether different animal from the sluggish Himalayan we had previously known.
Initially it looked quite good and after 500km careful break-in the engine was put thru its paces and handled very well. Acceleration to red-line was now a matter of seconds and not minutes like before. Everybody was extremely impressed. We sold one prototype to a friend and he drove it 590km on a highway right out of the service center. Not a good idea. The first ring broke and took the valves down with it. This is India so the financial loss was acceptable but it meant an involuntary 5-day holiday while we rushed replacement head and cylinder to our friend during lock-down with its usual delays. No “overnight” services!
It turns out the OEM pistons are all of the cast type which is kind of brittle on the surface. Because we cut the top it got even more brittle and ultimately, after 1 hour at 110 km/h – broke.
It was clear from the start that these “home-made” pistons could only be used as stand-in for a professionally designed version. It is specifically made to reduce compression to acceptable values, similar to the stock engine. The need for fuel additives will go away, however “power” or “super” gasoline with 94-97 Octane will still be suggested. Btw: that piston is designed by the same engineer who made our successful 450cc piston.
Because of the higher expenses in making a forged piston we decided to offer both variants, a forged and a cheaper cast version. Nevertheless, both version are available – the forged only on request though as there is very little demand and the cylinder for it must allow a bigger wiggle room for the expansionof the piston – this can take a month to get done – depending on cylinder availability.
The same time and tools will be needed to do the 477cc upgrade that are also used in the 450cc version: