Installation of a New Top End - Step By Step - KTM 85 SX, Husqvarna TC 85, and Gas Gas MC 85

September 27, 2023

Follow these detailed steps for a smooth and successful new top-end replacement. KTM 85 SX, Husqvarna TC 85, or Gas Gas MC 85 - engines which are all from the KTM Group.

Preparation: Before you begin, make sure to drain the coolant from your bike. Then, remove the seat, side panels, fuel tank, exhaust springs, and the exhaust pipe.

Disassembly: Next, remove the spark plug and head stay bracket. Disconnect any hoses connected to the engine and consider removing the radiator (although not necessary) to provide more room for working. Remove the power valve cover, clip, and control rod.

Cylinder Head Removal: Loosen the head bolts in a crossing pattern to avoid damaging the engine. Inspect for damages or excessive carbon buildup in the cylinder head's dome and remove it with a scotch brite pad.

Cylinder Removal: Remove the base cylinder bolts in a crisscross manner as well. Carefully lift off the cylinder while supporting the piston.

Inspection & Cleaning: Inspect both the cylinder plating condition and inspect the crank shaft and connecting rod for damage or excess play. Use a ball hone to lightly break any glazing in the cylinder to creating a better seal for piston rings to cylinder.

Piston Removal & Replacement: Use a small pick tool to remove the piston pin c-clip carefully not to drop it.

A Step-by-Step Guide to Preparing a Piston for Installation

Check the Ring End Gap: Before installing the piston rings, you need to check the ring end gap according to your service manual's specifications. To do this, place the piston ring inside the cylinder with its marking facing up. Push it down using the piston until it's about an inch below the top. Measure and adjust the gap as necessary to align with the service manual's requirements.

Install the Rings on the Piston; Remove the ring from the cylinder and install it on the piston, ensuring that the marking is facing up and aligned with the center locating pin on the rear of the piston.

Secure Wrist Pin Clips: Install one of the wrist pin clips into its groove on the piston before installation of piston. Ensure that it's secure in grove, with its open end either facing up or down, but never towards the rear open area on the piston.

Lubricate and Install Wrist Pin Bearing: Lubricate the wrist pin bearing with 2-stroke oil, then install it within your connecting rod.

Attach Piston on Connecting Rod: When attaching your piston to your crankshaft's connecting rod, make sure that its arrow is pointing forward (facing toward exhaust port). Next, install your second wrist pin bearing clip in a similar manner to how you installed your first.

Remove Rag and Install Base Gasket: Before proceeding further, remove any rags protecting your engine components and install an appropriately sized base gasket. I like to reuse the same size as I removed during dissemble.

Best way is to check squish clearance and choose the correct gasket that way.

Lubricate Piston and Lower Cylinder: Lubricate your piston's skirt using 2-stroke oil. Compress your installed rings around your piston, ensuring they remain aligned with their respective locating pins. Carefully lower your cylinder over your piston, ensuring that the rings and pins are correctly positioned.

Torque Cylinder Base Bolts: Torque your cylinder base bolts to 14-15 foot-pounds in a crisscross pattern to ensure even pressure distribution.

Next steps installing cylinder head and O-rings and properly torque down the cylinder head bolts.

When I have time, I like to always install new bolts to reduce the risk of the head bolt stretching form past installation.

Install New Cylinder Head O-Rings: Begin by installing new cylinder head O-rings, making sure that the location pin is correctly placed. You can lightly grease the O-rings to help them stay in position during the installation process.

Touque Cylinder Head Bolts: As you proceed with attaching the cylinder head bolts, be sure to use a crisscross pattern when tightening them. Torque each bolt to 7.4-foot lbs.

Install New Spark Plug: Install a new spark plug (BR9ECMVX) for a late model bike, and torque to 14-foot lbs.

Reconnect Power Valve; Reinstall the power valve rod and clip so that they are secured. Next place a new gasket on the power valve cover and reinstall the three bolts and torque to 4 to 5 foot lbs..

Reinstall Head Support: Reinstall the cylinder head support bracket and tighten it to 24-foot lbs.

Install Exhaust Pipe: Carefully reattach the exhaust pipe and springs in their designated spots on your bike.

Install New Air Filter: Don't forget about air intake! Install a new, clean air filter for improved keep fresh motor clean debris, and maintain performance.

Now that your engine components are properly assembled, focus on reconnecting the cooling system hoses & add fresh coolant. A good choice is to use a performance coolant like Engine Ice, Maxima Cool-Aide, and Bel-Ray Moto Chill Racing Coolant. The three brands mentioned will lower coolant temperature.

Note - Before starting your motorcycle, give it a thorough inspection for any potential issues such as missed connections or leaks in the coolant system.

If everything looks good and no problems are detected, you're ready to start your bike, let it warm up, and enjoy a smooth ride on your now well-maintained motorcycle. By following these steps and investing in regular upkeep, you'll keep your motorcycle in top condition for years to come.

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What Piston kits are available for the KTM 85 SX, Husqvarna TC 85, and Gas Gas MC 85

Vertex Top End Kit 85 SX, MC 85, and TC 85

Vertex Piston Kit 85 SX, MC 85, and TC 85

Wiseco Top End Kit Armorglide Coated - PK1921

Wiseco Piston Kit - Racer Elite Series - 47.00 mm - RE910M04700

Wiseco Piston Kit Armorglide - 855M04700

Namura Piston Top End Kit 85 SX, MC 85, and TC 85

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Tools That will Make the job Easer

Motion Pro Deluxe Piston Pin Puller - 08-0472

Motion Pro Hose Removal Tool - 08-0646