When Should I Rebuild My Dirt Bike Engine?

Why?

Staying on top of engine rebuilds is important to ensure your dirt bike continues to perform as it should while also preventing major engine failure that can cause costly damage or worst case an accident while out on the track or trail. All manufacturers will provide a rebuilding schedule in the owner’s manual of when you should be rebuilding the top and bottom end of your bike and we always recommend sticking to the numbers given. Dirt bikes are high performance machines requiring unique maintenance intervals and unlike a car, they are generally ridden hard and ridden in some treacherous conditions!

Rebuild times provided by your manufacturer are a guide as there are plenty of variables involved in our chosen sport. These include riding conditions, how the bike is ridden, air filter maintenance, the quality of oil used and more! All of these if abused can drastically reduce the lifetime of your engine and in turn make rebuilds more frequent, so it is extremely important to carry out your routine maintenance to stick to those rebuild times as much as you can.

Two Strokes:

Usually, there are a few ways to tell when a two-stroke needs to be rebuilt - a noticeable loss of power, lack of compression or it has reached a certain amount of hours where a rebuild would be appropriate. It’s also important to keep in mind that if you’re running your two-stroke on the lean side, it may need more frequent rebuild intervals.

When rebuilding the top end the general time frame is every 25 hours however like we said earlier every bike is unique and rebuild times also vary with engine sizes. A KTM 50 or a fire breathing CR500 will have totally different rebuild times so we always recommend checking your owner's manual for the most accurate intervals!

The bottom end of a two-stroke can usually last around 70-80 hours before rebuilding. It’s always advised that when you rebuild the bottom end to also rebuild the top end. Tell tail signs of a bottom end about to let go is a rattly, noisy engine or heavy vibration through your handlebars or again lack of power and drop in compression.

Four Strokes:

A four-stroke has slightly different intervals between rebuilds, the top end is generally rebuilt at the 25-30 hour mark if you’re a regular racer, and more importantly on a 250F, which is typically ridden more aggressively. On a 450, or if you’re riding the bike under an ‘easy’ load, then rebuilding the top end between 30-40 hours will be adequate. Again these are just a guide and you should always follow your owner's manual.

The bottom end on a four-stroke engine can typically see 100 hours of life, however, to be on the safe side, most riders will rebuild it at approximately the 80-hour mark or sooner. Again, when you’re rebuilding the bottom end, always rebuild the top end and throw in a new piston at the same time. It’s also always advised to check your valve clearances every time you tear the engine down.

Takeaways:

Check your owner's manual for the accurate service intervals between rebuilds for your bike! Stay on top of other routine maintenance items like oil changes and clean air filters to get the most out of your dirt bike. However, when rebuilding your bike it is a perfect opportunity to give it a birthday by replacing coolant, spark plugs, air filters, engine oil, oil filter, and muffler packing to keep your bike in the best running condition. When rebuilding your engine make sure you replace your gaskets and o-rings or head gaskets in your cylinder head because there's nothing worse than having to do it all again because of a gasket or o-ring.