Need factory numbers for your Bolens QS or QT garden tractor? This 93-page Bolens QS, QT, 1660, 1666, 1900, 1966 service manual PDF (OEM #552974-2) walks you through the hydrostatic drive, transaxle, and PTO clutch on the QT-16, QS-16, and QT-17 as well. You get wiring diagrams broken out by serial number range, so an early 1660 gets its own charging and light circuits instead of a close-enough guess. Inside: hydro repair for both Eaton and Sundstrand units, carburetor adjustments, interlock switch checks, plus mower deck, snow thrower, and tiller service. Set the Kohler idle on a 1660 to 2350 RPM; the Onan in a 1666 runs 1900. Swap-meet parts, forum threads, faded memories: none of them beat the factory book. Bookmarked PDF opens on laptop, tablet, or phone; carry it out to the barn and get it running this season.
What's Inside This Bolens QS, QT & 1900 Series Manual
| System | Pages | Key Topics |
|---|---|---|
| General | 1-9 | Serial Number Information, Specifications, Maintenance Chart, Lubrication Points, Lubrication Chart |
| Electrical System | 10-28 | Troubleshooting Guide, Electrical Wire Color Guide, Wiring Diagrams, Light Circuit, Charging Circuit, PTO Clutch Circuit, Seat Switch Circuit |
| Drive Train | 29-58 | Troubleshooting Guide, Hydrostatic Transmission, Hydrostatic Identification, Transaxle Removal, Oil Seal Installation, Bearing Installation, Hydro Installation |
| Fuel System | 59-64 | Troubleshooting Guide, Servicing (Fuel Valve, Duel Valve, Fuel Filter, Air Cleaner, Carburetor Adjustments) |
| Chassis | 65-74 | Steering Assembly, Hydrostatic Adjustments, Brake Assembly, Interlock Switches, Power Take-Off |
| Hydraulic System | 75-80 | Trouble Shooting Guide, Testing Hydraulic System, Hydraulic Power Lift |
| Engine | 81-85 | Troubleshooting Guide, Qt-16 Onan Engine, Qs-16 Kohler Engine, Qt-17 Kohler Engine |
| Tractor Attachments | 86-93 | Mower Decks, Snow Thrower, Tillers |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| All Models | ||
| Battery voltage | 11.5 to 12.5 volts | p. 27 |
| Transmission Oil Capacity | 10 quarts | p. 6 |
| Transaxle Housing Capscrew Torque | 30 ft-lbs | p. 49 |
| Front Tire Pressure | 12 PSI | p. 86 |
| Rear Tire Pressure | 8 PSI | p. 86 |
| 1666 | ||
| Onan engine idle speed | 1900 RPM | p. 62 |
| Engine Oil Capacity (Model 1666) | 3 pints | p. 5 |
| Engine Oil Capacity (Model 1666 Onan) | 2 quarts | p. 6 |
| 1660 | ||
| Kohler 1660 idle speed | 2350 RPM | p. 63 |
Bolens QS, QT & 1900 Series Common Problems This Manual Covers
Hydraulic lift will not raise the mower deck, or raises slowly under load
Check transmission oil level before touching anything else; the hydrostatic and lift circuits share the same 10 quart reservoir, and low oil starves both. Test system pressure using the hydraulic testing procedure on page 75, then inspect the implement relief valve for a stuck plunger or weak spring. Trace the schematic on page 76 to hunt down leaking lines.
Manual Section: Hydraulic System p. 75Engine cranks but will not start after the tractor sat in the barn all season
Verify the brake pedal is fully depressed and the PTO is off; the interlock switches kill spark otherwise. Check battery voltage against the 11.5 to 12.5 volt spec on page 27, then clean corroded terminals and the frame ground. Follow the electrical troubleshooting guide on page 10 to test the ignition, brake and PTO interlock switches.
Manual Section: Electrical System p. 10Engine runs hot and loses power partway through mowing the yard
Check engine oil level first; these air-cooled engines run hot fast when low. Clean grass clippings and chaff out of the cooling fins and blower housing, and verify the fan turns with the engine. Check tire pressures too (12 PSI front, 8 PSI rear), since dragging tires load the engine. Work the overheating checks in the engine troubleshooting guide on page 81.
Manual Section: Engine p. 81Frequently Asked Questions
How do I reset the carburetor on a Bolens QS-16?
To adjust the carburetor, turn the 'MAIN FUEL' needle clockwise until it bottoms lightly, then back it out 2 turns. With the engine running at full throttle, turn the screw in until the engine slows down, then back it out until it regains speed and slows down again. Position the screw halfway between these settings. For the 'Idle Fuel Screw', turn it clockwise until it bottoms lightly, then back it out 1/2 to 3/4 turn. p. 63
How do I troubleshoot Bolens QT-19 hydrostatic drive problems?
If the unit will not operate in either forward or reverse, check if the free wheeling valve is open, if the system is low on oil, or if the oil filter is plugged. If the unit operates in only one direction, check the control linkage for faults or if a check valve is stuck open. Refer to the Drive Train troubleshooting guide for specific remedies. p. 29
How do I reset the ignition timing on a Bolens QS-16?
The ignition timing for the Kohler engine on the Model 1660 is set by aligning the 'S' mark in the timing hole. The breaker point gap should be set to .020 inches (0.5 mm). p. 5
How do you fix bolens QT-16 will not move forward or reverse, hydrostatic drive dead after sitting all winter?
Check the free-wheeling valve first; push the control fully in so it seats closed. Verify transmission oil level, since the system holds 10 quarts and low oil kills charge pressure. Then work through the drive train troubleshooting guide starting on page 29, checking charge pressure and oil lines before you condemn the hydrostatic unit itself. p. 29
Is this Bolens QS manual a PDF I download?
One searchable PDF covering 93 pages, delivered instantly. No disc, no shipping, no waiting on the post.
Am I able to print pages from this Bolens QS manual?
Print away. There is no DRM and no page limit. Many buyers print one chapter at a time and leave the rest on a tablet.
Can I trace circuits with this Bolens QS manual?
Complete wiring diagrams are included, covering all electrical circuits, harness routing, and connector pinouts for the Bolens QS & variants. There is one on page 13, for example.
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