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How to Re-thread a Flange Bracket on a Loncin Water Pump using a Helicoil Kit

Laura Published on Jun 30, 2020 View Comments

In this video, we show you how to Re-thread a Flange Bracket on a Loncin Water Pump using a Helicoil Kit.

Health & Safety Warning - Please ensure that you have safely prepared the machine and workspace. If you are unsure about any aspect of the task please seek professional advice.


Today we're going to show you an easy way to rethread the bolts located on the flange bracket on a Loncin (25zb21-1.2Q) Water Pump using a M8 X 1.25mm Helicoil Kit. The flange bracket holds the pump case securely to the machine. Therefore with consistent vibration over time, this could have an effect on the bolts and the threads. Before starting you will want to remove all the components attached to the flange bracket. To determine the size of the helicoil needed to rethread, you will need to use the original bolt to find the diameter (measure the diameter with a caliper) and pitch (the size of each thread on a spring) using a Screw Pitch Gauge. Get the 8mm drill bit provided in the Helicoil Kit, then drill out the hole using a power drill. Now using the tap from the helicoil kit (knowing the size and the pitch). Place this in a ratchet to easily re-thread the hole. Place the ratchet in straight. Start off slowly to make sure you have aligned the tap correctly. Turn until you have rethreaded the hole and then release by unscrewing the ratchet. Now get the installation tool and adjust so you know the measurement of the hole depth for the new insert. When you know the size, attach the spring on the end of the tool making sure the tang is in the slot. Now place this in the hole, twisting the new helicoil until it is secure. This should be half a turn below the surface. Do not twist against the direction of the thread, as this could damage the spring. Then to remove the tang at the end of the spring, gently tap this with the break tool provided. You can now reattach the parts back, including the check valve and suction flange. Aline the bolts and washers back and then tighten with a 13mm socket spanner. That's how you rethread the bolt/s located in the flange bracket on a Loncin 25zb21-1.2Q Water Pump using a M8 X 1.25mm Helicoil Kit.


Parts and tools included in the Re-Thread how-to video.

  • 8mm Helicoil Thread Repair Kit: - 902 1539

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