477cc Upgrade FAQ – Royal Enfield Himalayan Big Bore Kit

This FAQ last updated: 29.12.2021

Please ask questions in the FORUM where issues are discussed in greater detail.

Warning: we had one case where our liner did not fit the engine body. This is a RE QC issue, the body had a small protuberance that had not been machined properly in the factory. The liner can then be fitted to the body by using a lathe. Or using a dremel you can carefully remove the protuberance (make sure no metal residue falls into the engine housing e.g. by stuffing it with an oild cloth). Check the fitting before you proceed to bore.

Q: When can I expect the 477cc upgrade to ship?
A: Now.

Q: What power increase can I realistically expect?
A: We have researched this issue in depth and verified it with Dyno runs. The naked 477 (all stock except cylinder/piston) will give you 27 RWHP, that is 6.5 RWHP (not BHP as RE uses) over stock which is 20.5 RWHP. You can further enhance this with: K&N air filter plus open exhaust: plus 1 RWHP. A polished head with bigger inlet etc.: also 1 RWHP extra. Now you are at 29 RWHP (or about 34 BHP). Futher enhancements are available with a performance cam. They can give you additionaly a maximum of 5 RWHP (our new HT-b cam) or -only in the highest rev regions-  3 RWHP with the TEC cam. Our earlier cam design (HT-cam) gives you only extra 1 RWHP but enhances torque in the low rpm which is more practical in daily use. For a more detailed discussion please visit the forum.

Q: What is the difference between the two sets?
A: The complete kit with the ready-to-install cylinder requires no work (other than replacing it with the old cylinder of course).
The kit with piston, liner and gaskets requires removal of your cylinder, then fitting of the liner and drilling and honing by a professional engine rebuild store, and insertion of the new cylinder into the engine.
Depending on expertise and equipment, some may be able to do this themselves. For normal mortals who need a specialist workshop for this, it may be cheaper to purchase our complete set, especially since original cylinders and pistons then remain with the owner – just in case.

Q: How much is the upgrade kit?
A: Please check the main 477 page for this information. It differs between individual distributors, e.g. Australia makes its own prices.

Q: Is the piston professionally produced or homemade?
A: The piston is made in a large Indian factory (the maker of KIA car pistons, among others) according to the pattern of a prototype made by an Italian engineer in Italy.

Q: Do I need special fuel or octane booster for this piston?
A: No, we run it with Indian standard fuel without problems. That is one of the the lowest quality you get world wide so it should run fine everywhere else.

Q: What are the advantages of a bigger piston/increase in displacement?
A: Mainly these are:

  • More displacement means more mixture can fill the larger cylinder and be burned.
  • Larger bore size means larger area on the top of the piston, so the combustion pressure acts on a larger area, providing more “push”, resulting in increased torque.
  • Larger piston area creates a harder “pull” on the intake system, increasing gas velocity in the intake port, making better use of it.
  • Larger displacement, with the same cams and ports lowers the peak torque rpm and the peak hp rpm, approximately equal to the displacement increase, this giving more power at a lower range on the rpm band. 15% more displacement lowers the working power band by about 15%, or about 700 rpm.
  • More power in the useful mid range, you don’t have to rev as high for power. You ride lower rpm before lugging.
  • Larger bore size increases compression. Without being a higher compression piston by design, just by virtue that you are compressing a larger volume into the same size combustion chamber, you are getting a compression increase.
  • Although larger size pistons could be heavier, this one is lighter thereby decreasing the reciprocating mass, and causing less stress on the rod and bearings which will add to engine life expectancy.

Q: Will the new 477cc sleeve fit into the engine body without widening it?
A: YES, that was the idea behind this upgrade, to keep it plug & play.
A bigger piston would need you to change the housing as well as the head which would make it way more expensive. We have had one case where the engine housing was too small to accept the liner as-is, which is a RE quality issue. Please check the fitting with the naked sleeve before continuing on with boring/honing and if necessary use a lathe to make the liner fit.

Q: Will overall reliability suffer from this upgrade?
A: Reliability in terms of life expectancy is very much a function of maintenance. The 410cc engine is very robust. Well maintained it should last well over 80.000km. The 477cc upgrade will not change that because with more power it is likely you won’t drive it at it’s limits quite so often.

Q: What total cost must I expect for a 477cc conversion?
A: That depends on you doing the work of changing cylinder and piston or if you outsource the work – then add ca. 3 hours worth of a local technician’s pay to the set price. If you have an EFI version you will need some fuel flow regulating device like the Powertronic. On top of the sales price there is shipping and possibly import tax, depending on your country’s laws.

Q: What is the difference between your kit and that from Hitchcock?
A: We drove both. In fact the Hitchcock piston was our initial motivation. It is a good upgrade, but as always, the better is the enemy of the good. Our set just delivers more for less money.

Q: Do you provide a map for the 477cc and the Powertronic?
A: We do. Please consult the forum where these maps are made available.

Q: I have a BS3, do I need to change the carburetor configuration or the carb itself?
A: The standard issue carb of the Himalayan is identical to the one on the 500cc Bullet. So the upgrading to 477cc is no issue as such. We have re-jetted to 130 main and one up the pilot as well to be able to get a low idle and reasonable cold run. But the bike will run with the 125 stock jets as well. If you go over 2000m change to a 110 main jet.

Q: Will the 477cc bike use more fuel than the 410cc?
A: No, it will use less, given comparable driving conditions.

Q: Will you publish measurements, charts etc. on your setup?
A: There are plenty Dyno charts done by our Australian partner available on the forum with all kinds of different configurations. There is also a customer in New Zealand who has anounced a Dyno with the 477 in the near future. Please check the forum – it will be more up to date.

Q: Are you using the factory liner bored to 477cc or are you providing the cylinder with a new liner when upgrading to 477cc?
A: For this upgrade it is necessary to use a new liner that will however still fit into the engine body without any changes to the latter (however, see the warning on top of this page).

Q: Is this a cast or a forged piston?
A: It is a cast piston. We used to offer a forged version but apart from a huge price difference the forged version also posed problems with some boring/honing companies which where not familiar with this kind of piston and made a too narrow liner that consequently lead to a jammed piston. A good explanation of the difference can be found here.
And a video explanation here:

Q: In your upgrade set do you provide everything I need for the upgrade or do I need special tools/other stuff to do it?
A: We provide everything except the tools. But the tools you need are very common and are all listed in the “How To Upgrade” video. We did it without even a torque wrench (if this is your first engine upgrade it may be a good idea to use one). There is one special tool for valve adjustment, you can order it from Hitchcocks if you can’t source it locally.

Q: Will this piston give me a greater top speed?
A: Yes and no. If you are heavier than most or ride with pillion and luggage it will because you likely never red-lined the engine in such a configuration. However, if you are a small lone driver – then no. The red-line RPM is the same. To change that you would have to change the number of teeth on either sprocket – You would want to add one tooth to the front or subtract three from the rear. Make sure the chain fits after that change. Hitchcock and others offer such sprockets. As of our latest test a 16 teeth sprocket does a lot for a much smoother an quieter run especially at highway speeds of around 100km/h.

Q: Are there specific break-in rules I must follow?
A: Yes, there are. This piston should not be moved beyond 3000rpm for the first 500km. Then an oil change is needed and for the next 1500km 4000rpm should only be surpassed for take over. It can take up to 2000 km to reach full free running, up to this point top speed can be used for short moments but not sustained.

Q: My engine has run for over 30.000km, is there anything I should exchange/renew with the upgrade?
A: It is advisable to change the timing chain which is suggested at 30.000km for the older versions and at 50.000km for the newer ones.

Q: Does your piston come with any kind of warranty?
A: The warranty is limited to delivery failures or damaged delivery goods see here. This is a high performance upgrade, it requires you to handle your bike accordingly. E.g. we have no influence on how the break-in is done. For that reason we do not warranty the upgrade set as such. As unlikely as they are, failures could have any number of reasons outside our responsibility. BUT we do offer to sell anyone who bought an upgrade set from us and experiences a problem at any time a factory new 410cc cylinder+piston set for 100.- € plus shipping.

Please ask questions in the FORUM

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