How-To: Honda Z50R XR50R CRF50F Engine Rebuild 1968-2015

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I’ve put together a full engine rebuild video that is 3.5 hours long for the 1989 Honda Z50R I recently acquired. The engine was fully disassembled in a large plastic tote, and I spent the past month piecing it back together. I was able to find a shifting problem, which made someone take it apart in the first place.


Year, Make, Model

The video features a 1989 Honda Z50R. However, I have flipped through all the manuals from 1968-2015, all these motors are all basically the same. Sure, there are a few differences, but this video covers the bulk of the information you will need to properly rebuild one of these motors. Also, the CT70 model is similar as well! If your motor looks anything like in the sample vid (OHC horizontal) then this video will be huge help, along with the service manual.


Service Manual

Below are some links to FREE service manuals in PDF format.

Honda Z50A / Z50R Service Manual

Honda XR70R 1997-2003 Service Manual



Here are several symptoms that indicate your engine may need to be rebuilt or disassembled for inspection:

  • Low engine compression
  • Engine is burning oil
  • Any strange noises
  • Transmission shifting issues

….or maybe you need a visual aid for adding the following modifications

  • Big bore kit
  • Cam swap
  • Clutch spring and plate upgrade
  • High volume oil pump
  • Stroker crank
  • Race head



This post covers why this engine was taken apart.


What is covered in this video?

  • Complete top and bottom end disassembly
  • Splitting the cases
  • Complete transmission disassembly and reassembly
  • Clutch disassembly and reassembly (including plates and springs)
  • Oil pump disassembly and reassembly
  • Cylinder head disassembly and reassembly (with valve lapping tutorial)
  • New valve stem seal installation
  • Cam timing procedure
  • Piston ring end gap inspection
  • Some measurements (cylinder bore & piston O.D.)


What is not covered in this video?

  • Engine removal & installation from frame. Video begins with engine on workbench
  • Transmission blind needle bearing removal in engine cases
  • Main bearing removal from crankshaft
  • Some engine parts are missing during disassembly (parts are added during reassembly and covered in detail)


Special tools required

Lisle 21200 Small Valve Lapper (intake only)

Tusk valve spring compressor

BOA BO13010 Constrictor Aluminum Strap Wrench

Motion Pro 08-0015 Oil Filter and Clutch Hub Spanner 24mm ID

Motion Pro 08-0026 Flywheel Puller M27X1.0 L.H External Thread

Vessel Megadora 980 Impacta P2x150 #2 JIS Cross Point Impact Screwdriver

Vessel 125943 908 P3x150 Impacta Screwdriver


Other helpful videos

How-To: Honda 50/70cc Valve Adjustment (XR70R)

Honda 50 Flywheel Removal & Installation with Puller

How-To: Z50A Carb Clean & Rebuild / Pilot Adjustment

How-To: Z50A Oil Change

How-To: Carburetor Idle & Pilot Screw Adjustment Honda XR70

How-To: Motorcycle Carburetor Clean Honda XR70R

How-To: DIY Soda Blaster – Cleaning Motorcycle Carburetor

How-To: Install & Remove Crankcase Bearings With Your BBQ Grill


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