Technical Advisory for the 477cc Engine Upgrade

This information is for customers who have purchased the 477 set    [last updated: 04.01.2023]

Please read before installation

IMPORTANT: Download the 477cc cylinder insertion instructions as pdf

Liner Kit: The suggested cylinder/piston clearance for the honing part of a cast piston is 0.06-0.08mm, for a forged piston 0.09-0.1mm.

If you install the 477cc piston with only one layer of bottom cylinder gasket you will achieve a compression rate which is OK for 95 RON. Use 2 bottom gaskets to reduce the compression further. Request a second bottom gasket with your order if you live in an area with low quality fuel.

If you use one of the cheap Chinese made pressure gauges (which vary up to 10% in measurements from item to item) you will see anything from 180-220 psi. Lower compression will cost a bit of power but is to be much preferred over a knocking engine.

With the 477 cylinder set comes this gasket package. It has some optional elements that may or may not be included, i.e. the OEM foot gasket no. 1 is included in some gasket packages we receive from RE but not in others. If we have them in stock we include them. They are not necessary and only serve as option to get a slightly higher compression because they are thinner. They are available from any RE dealership as part of the head gasket package. Likewise the red head gasket which was formerly the only gasket we used until we found some cases where they blew (although it may have been because the head bolts where not re-fasted after 500km). We have since then replaced them with the OEM metal head gasket cut to our 84mm size. It can still be helpful as template for cutting a 84mm metal head gasket from an OEM gasket.

You will need the following additional items to do the update: (they may be included, depending on the kit you purchased)
One head gasket, one or two cylinder bottom gaskets, one exhaust gasket (copper ring). If you do the changes yourself you will need a tool to adjust the valves (available e.g. online at ebay, from RE and Hitchcock’s) after installation. A torque wrench is advisable. Download the torque values here. If you have a carby bike you may want to change to a 130 main jet and a one size bigger pilot as well.

Break-in rules should be followed religiously.
It is recommended for the first 500km to never go over 4000rpm, onward up to 1000km 5000 rpm should be the maximum. Riding conditions should vary as much as possible which means do not sit on one rpm/speed for extended periods. If you must use a highway still vary speed and rpm. Full break-in is achieved after approx. 2000km. After the initial 500km an oil change (with filter) is needed. Also then re-fasten the head bolts (otherwise the head gasket may leak oil) and adjust the valves. While the break-in oil can be any cheap oil from 500km onward only use full synthetic oil, the brand is irrelevant as long as it follows international norms for high quality oil, examples are:

  • Motul 7100 4T 10W-50 API SN Fully Synthetic
  • Mobil 1 5W30 Fully Synthetic
  • Shell 5w-40 Helix Ultra Synthetic

Remember that oil is not only responsible for friction control, it also serves as coolant in the LS410 engine. The 477cc is a high performance variant asking for high performance oil.

If you have not done any operations on an open engine before but want to do it with this upgrade please watch our video on YouTube how to do it BUT, as mentioned above, use a torque wrench when re-assembling the parts. Experienced mechanics can do it by hand but it is a very bad idea to emulate that without years of experience under your belt. The torque values are available here.

Top and bottom cylinder gaskets are supplied with the piston. If you received a metal and a red mesh like head gasket only use the metal one. The red can be used in emergencies and also as a template to resize the hole of a OEM head gasket from 80mm to the required 84mm with a dremel.
Sometimes parts are not available or dealerships are far away. In that case you can make your own foot gaskets which are made from thin cardboard about 0.3mm thick. Such gasket material is available in sheets from Amazon and locally in hardware stores. Sometimes you will also find stores for automotive parts that can cut those gaskets for you (water cutting) or some print shops that cut labels and logos. We supply the layout for download in these formats in one ZIP packet: Corel Draw 2019, Corel Draw 12, PDF, [click here].

We are using the 477cc on carbureted Himalayans as well. The UCD33 carburetor is also used on the Bullet 500 with the same 125 main jet. We have changed that to 130 and one size bigger pilot and our bike runs OK when cold now. It will run with the 125 original jet but adjusting to a good cold idle is hard. If you venture into the high mountains change to 110 main jet or else the engine will lose ca. 50% of its power. Do not forget to change back to 125 or 130 when coming down or else the engine will run way too lean and get overheated.

EFI bikes with this piston must use a device to regulate fuel flow with a mapping according to the 477 which necessitates the purchase of the Powertronic or better our own “Red ECU” or a similar device. We supply our own 477 maps for the BS4/Euro4 PT and the Red ECU and make them available for download in the forum. Recently RaceDynamics, the makers of the Powertronic, came out with a device called FuelX (or FuelX Pro respectively). These devices are much cheaper than the Powertronic but our tests indicate they are NOT sufficient to run the 477cc without danger of damage.

While we do not offer a warranty for this upgrade we will replace a broken 477cc cylinder/piston assembly with a new OEM version (back to 411cc) for 100.- € plus shipping. It may take up to 6 weeks to get a cylinder sent to us from the factory in Chennai under normal conditions.

If you want to discuss your experience with this upgrade in the Himalayan community there are various general bike forums and some specific to Royal Enfield out there. If you are interested in replies from us we suggest you use our own forum which specializes in the Himalayan.