Ultimate Guide to Pit Bike Engines

Quite a few manufacturers make pit bike engines and they can range in price, power output and durability dramatically.

Unlike a lot of traditional motorcycle manufacturers, pit bike companies don’t tend to design or manufacture their own engines.

Many pit bike engines are bought in ready-built by other companies ready to drop straight in as a kit. This is especially true when we’re talking about the various Chinese manufacturers of pit bikes and their motors.

The positive to this is that lots of these little motors are interchangeable and easily upgradable too. Full pit bike engine kits are readily available on the market.

The vast majority of pit bikes use the same engine mount bolt pattern which over the years has remained unchanged making pit bike engine swaps ridiculously easy to do.

Esteemed Japanese motorcycle manufacturers have also made motorcycles with the same layout and engine style in the past, featuring that distinctive and compact forward-facing single cylinder layout. A great example of an older Japanese bike with a pit bike engine would be the Honda CT70.

However, no Japanese motorbike company has made a pit bike or minibike quite like this. The latest pit bikes feature tall suspension front and back with a very small frame making them tiny by motorbike standards with an extremely short wheelbase, but still suitable for adults to ride comfortably.

The reason these mean looking little bikes are called pit bikes is because at motorcycle racing events riders are not allowed to ride around the place on their competition motorcycles when they’re not on the track, but they are allowed ride around on a smaller bike in the pit area for example or between the pit and their trailer.

These little mini dirt bikes started off with comparatively tiny 50cc engines but over the years these pit bike engines have got bigger and so has their suspension. These days, pit bike engine 140cc are very common, and they are now probably the most popular displacement which is a big step up.

Starting out as a cool custom scene, eventually companies sprang up and started making specific pit bikes in this style.

If you are based in the UK, we definitely recommend checking out the range of Fun Bikes pitbike engines (reach out to them too – they should be able to help you with any specific queries you might have).

Pit Bike Engine Diagram

One of the best things about pit bike engines is their pure simplicity. Being such simple engines, they are also remarkably affordable to purchase, especially compared to a normal motorcycle engine from one of the big manufacturers.

With these factors combined, many peoples first motorcycle experience is with pit bikes, and this low cost of entry to riding on two wheels can only be a good thing.

The simplicity of pit bike engines can also give people their first opportunity to work on their own engines and tune and tinker with them at home DIY style.

Pit bikes engines are configured in the classic format as listed below:

1. Single Carburettor
2. Chain driven overhead Camshaft with two lobes
3. Exhaust and intake valves (2 valves per cylinder)
4. Single traditional piston and conrod
5. Crankshaft with single journal
6. Clutch and 4 speed gearboxes with shared oil

Looking at the engine diagram you can really appreciate how rudimentary these pit bike engines are featuring a single piston, conrod and crank journal. Plus, there is a single overhead camshaft with two lobes to actuate the two valves for the cylinder, one for intake and the other for exhaust. The camshaft is also chain driven which makes for less maintenance burden.

The clutch and gearbox is included in this one engine unit and the majority of pit bikes have 4 gears, usually in the default layout with neutral just between gears one and two. Some pit bikes however have neutral at the bottom below first gear which adds to the simplicity of finding it.

Whether your pit bike features a 50cc, 70cc, 110cc, 125cc or 140cc engine, this configuration and layout is always the same. However, there are lots of opportunities to tinker with a pit bike engine and get a little more power and torque from them.

Pit Bike Engine Oil

The fact you can order a Chinese pit bike on Amazon for next day delivery encourages the idea that they are ready to ride. However, these bikes are still contraptions that require a degree of mechanical sympathy if you want them to stand the test of time.

From the manufacturer, any pit bike engine kit you buy will come with oil in it already, whether its in a bike or separate. This oil is generally used by the manufacturer to lubricate parts during assembly and to ward away corrosion and rust from the inside of the engine during storage and transportation.

Its recommended that you don’t run a pit bike engine for more than a moment with this oil, but it is advised that you check it starts up for the first time so you can confirm your new engine is a runner.

Following this the correct procedure would be to carefully break your pit bike engine kit in using special break-in oil with added zinc for the first two hours or so of running. By “carefully” I mean without too much engine load. Riding around on relatively flat ground without revving the motor too high would be the ideal.

Following the break in period of around two hours run time, you should drop this oil and replace it with a good quality non-synthetic 10w40 engine oil which is generally the universally recommended oil for pit bike engines.

Avoid running more modern synthetic oils as they have a tendency to work their way past the piston rings and glaze the cylinder walls causing rough running. This type of oil is also much more likely to make it past the seals on the engine and lead to a pesky oil leak.

Pit Bike Engine Parts

The most common pit bike engine these days is the 140cc motor built by a variety of manufacturers to varying degrees of quality. You can get cheap non-branded Chinese 140cc pit bike engines which are generally considered to be quite weak from a durability standpoint, but you can also get branded Chinese engines such as the Piranha 140 which is generally considered as a quality pit bike motor.

Of course you can get engines in this layout from older Japanese bikes, and these will without doubt be the most durable, and maybe even “bombproof” engines designed to go on forever, however they often have a smaller displacement and lesser power outputs which needless to say makes them less exciting. In fact, this reduced power and reduced stress on the engine components in a lower state of tune is one of the key factors in making those Japanese single cylinder engines so durable.

Thanks to the fact these mini bike engines are so similar in their design, there’s a wide range of aftermarket support for them too and you can very quickly modify your pit bike for all-round improvements in power, torque, durability and smoothness of running.

In stock form and healthy condition, a 140cc pit bike engine should be able to propel you to around a 55mph top speed, which is remarkable considering their physical size. But the temptation is always there to tune things a bit further, which is part of the joy of motorcycle ownership.

But if you’re having running issues with your pit bike engine, it’s easy to get carried away replacing parts for uprated and modified components, however it’s worth nothing that they are quite often poorly assembled.

Before you dive into swapping parts out for new, it’s better to inspect the pit bike engine closely and maybe even partially strip it down and rebuild it with the correct torque specs. This quite often solves issues and you may even notice some glaringly obvious problem that would otherwise have been missed.

A great example of this would be exhaust or intake manifold gaskets that are commonly left out by accident leading to unwanted leaks, loss of power and rough running.

Beyond the engine itself, you can also play with the gearing to lengthen the powerband of your pit bike engine and in turn raise the top speed. The gearboxes for these engines often have very short gear ratios which feels great when your shooting up and down through the gears on a twisty dirt track, but if you need to ride your pit bike on the open road, it can quickly become tiresome and you’ll wish you could cruise at a higher speed.

One option is to exchange your front sprocket for a larger one. The standard pit bike front sprocket is a 420-pitch 15-tooth item which is generally consistent no matter which minibike you get. However, you can throw on a 17-tooth replacement for very little cost and raise your top speed by up to 10mph.

You can also change the rear sprocket for a smaller one to increase this gearing even further. This combined with some tuning and maybe an uprated carburettor has lead to individuals managing to get 75-80mph out of a 140cc pit bike engine which is as incredible as it is dangerous.

Some of the most common engine and gearbox upgrades for pit bikes are as follows:

• Larger Carburettors
• Larger front sprocket
• Free-flowing Air Filter
• Exhaust pipe Kit
• Race Camshaft
• Big Bore or Stroker Kits
• Electric start

You can easily swap and change these parts and they are interchangeable between different pit bike engines quite often too, so it can make sense to purchase and enjoy these knowing that you can carry them forward or swap them onto a new engine kit if you have any issues going forward.