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About PRO50 4 Stroke Gas Backpack Concrete Vibrator Parts by Northrock
Genuine OEM PRO50 4-Stroke
Backpack Vibrator Parts
Find every replacement part for the Northrock Pro 50-4S 4-stroke gas backpack concrete vibrator. OEM components for the Honda GXH50 engine, transmission, clutch, frame, throttle and shaft system, shipped from an authorized Northrock supply channel.
The Northrock Pro 50-4S is the 4-stroke evolution of Northrock's flagship gas backpack vibrator. Powered by the commercial-grade Honda GXH50 engine (part 555C2), it runs on straight unleaded gasoline with no fuel mixing, delivers 10,000 VPM through a high-efficiency belt-drive transmission, and ships with a universal quick-disconnect adapter that accepts Northrock flex shafts as well as compatible shafts from other major manufacturers.
DanseUSA is an authorized Northrock dealer stocking genuine OEM components for every sub-assembly on the Pro 50-4S, from the complete frame assembly (440AV1) and complete clutch (25BA1) down to individual bearings, springs and hardware. Every part number on this page matches the official Northrock Pro 50-4S parts manual, so the part you order is the part Northrock built the machine with.
Looking for the older 2-stroke variant? See Northrock PRO50 2-Stroke Backpack Vibrator Parts for engine and drivetrain components specific to that model.
| Specification | Detail |
|---|---|
| Engine | Honda GXH50, 4-stroke, 50cc, 2.5 HP (part 555C2) |
| Fuel | Straight unleaded gasoline, no oil mixing required |
| Vibration Frequency | 10,000 VPM (vibrations per minute) |
| Transmission | High-efficiency synchronous belt drive in cast aluminum housing (635A1 box, 635B1 cover, 390B1 belt) |
| Clutch System | Centrifugal clutch with double-shielded bearings (25BA1 complete assembly) |
| Shaft Connection | Universal quick disconnect, square drive with spring-pin lock (factory installed) |
| Flexible Shaft Lengths | 7 ft, 10 ft, 14 ft standard, up to 21 ft available |
| Compatible Head Diameters | 3/4", 1", 1-1/4", 1-1/2", 1-3/4", 2", 2-1/2" |
| Frame | Tubular steel with breathable padding and 4-point engine mount (440AV1 complete frame) |
| Country of Manufacture | Bohemia, NY, USA |
The Pro 50-4S parts manual organizes the unit into five sub-assemblies. Identify your part by reference number, then order the exact OEM component:
Honda GXH50 Engine
Complete Honda GXH50 4-stroke engine (555C2). For carburetor, recoil starter, ignition coil, air filter and other engine internals, refer to the Honda GXH50 service manual.
Transmission Assembly
Transmission box (635A1) and cover (635B1), driven pulley (295N1), micro V belt (390B1), double-sealed bearings (140C300), end cap (215M1), drive core adapters (160CW1, 160CW2), casing adapter (150DE1).
Clutch Assembly
Complete clutch assembly (25BA1), clutch drum pulley (295S1), clutch adapter (630A1), clutch shoes (625A1), clutch springs (465D1), double-shielded bearings (140D005), retaining ring (255F1), key (575D75).
Frame Assembly
Complete frame assembly (440AV1), frame (440AT1), frame pad (445E1), engine mounting plate (215BR1), engine plate stand-offs (200AJ1), frame spacer (200AW1), engine mount screws (190J30), frame nut (211F1).
Throttle Assembly
Throttle control assembly with cable (605F1) and mounting screw (190F217). Ships pre-attached from the factory.
Flex Shafts & Heads
Flexible shafts in 7 ft, 10 ft and 14 ft standard lengths (up to 21 ft custom). Vibrator heads from 3/4" to 2-1/2". All heads are factory sealed in an oil bath and require zero maintenance.
Based on typical contractor use, these are the components that wear first on the Pro 50-4S:
- Micro V belt (390B1) - The single highest-wear component on the Pro 50-4S. Replace when you hear belt slip on engagement, see glazing or cracking on the ribs, or notice reduced VPM under load. Inspect every 100 operating hours.
- Complete clutch assembly (25BA1) or individual clutch shoes (625A1) and clutch springs (465D1). Replace when the clutch chatters on engagement, slips at idle, or fails to drive the shaft at full throttle. The springs and shoes wear together and should be replaced as a pair.
- Flexible shaft inner core - Inspect and re-lubricate with high-quality lithium grease every 50 hours of operation. Replace when the core shows dry spots, kinking, reduced flexibility, or any visible wear on the square drive ends.
- Throttle control assembly (605F1) - Replace when the throttle sticks, returns sluggishly, or the inner cable frays at either termination point. The complete assembly ships with the cable pre-installed.
- Double-shielded clutch bearings (140D005) and transmission bearings (140C300) - Replace if you hear grinding from the transmission housing or feel rough rotation when spinning the pulley by hand with the engine off.
- Honda GXH50 spark plug, air filter, and engine oil - Service intervals follow the Honda GXH50 owner's manual. The Pro 50-4S uses standard automotive 10W-30 in the engine sump, not pre-mix fuel.
The Pro 50-4S and the older Pro 50 2-stroke share the same frame, shaft system, vibrator heads and quick-disconnect interface, but the engine, transmission and clutch sub-assemblies are not interchangeable:
| Pro 50-4S (4-Stroke) | Pro 50 (2-Stroke) | |
|---|---|---|
| Engine | Honda GXH50, 4-stroke, 50cc, 2.5 HP (555C2) | 2-stroke gas engine |
| Fuel | Straight unleaded gasoline | Pre-mixed gasoline and 2-cycle oil |
| Engine Maintenance | Oil changes per Honda GXH50 manual | No oil changes, but must mix every fill |
| Drive Belt | Micro V belt (390B1) | Different belt and pulley geometry |
| Shafts & Heads | Universal inventory. Likely reusable across both models (confirm fitment before ordering). | |
| Best For | Lower emissions, easier starts, no fuel mixing | Lighter overall weight, fewer fluids on site |
Honda GXH50 Engine
Follow the Honda GXH50 owner's manual for oil changes, spark plug replacement and air filter service. Use straight unleaded fuel only. Never add 2-cycle oil to the gas tank, this is a 4-stroke engine with a separate oil sump.
Flexible Shaft
Lubricate the shaft inner core approximately every 50 hours of operation. Remove the inner core, wipe it clean with a lint-free cloth on a clean surface, then reinstall with a 1/16" coating of high-quality lithium grease. Do not over-grease, excess lubricant causes drag and overheating.
Vibrator Heads
Heads are factory sealed in an oil bath and require zero maintenance. Replace the entire head when you notice reduced amplitude, leaking oil, or visible wear on the eccentric tip. Apply adhesive sealant to the head-end shaft threads on every install for a water-tight seal.
Quick Disconnect & Clutch
Keep the square drive on the quick disconnect free of dried concrete. Inspect the spring pin for wear before each use, the shaft must lock with no rotational play. Inspect the clutch shoes and springs anytime you replace the belt, they wear together as a system.
Need Help Finding Your Pro 50-4S Part?
Share your model and serial number with our parts team. We confirm exact fitment against the Northrock parts manual before every order.
Frequently Asked Questions
Match the Ref. # on the diagram to the row in the parts list at the right. Click a part name to see details, price, and add it to cart.
Confirm your model/series and serial number range on the product page. Many manufacturers have serial breaks, when in doubt, share your model and serial with us and we’ll verify fit.
The Ref. # points to the callout on the drawing. Qty shows how many of that item your machine uses. Parts are sold individually unless noted as a kit.
Yes, we supply genuine OEM parts for all our brands. If a part has an approved replacement, we ship the latest superseded revision
Manufacturers often supersede numbers. Our pages list the current orderable number and show older numbers in the description when available. Your old number will cross-reference to the correct part.
Yes. Some items are not pictured or are shared with other assemblies. Send us the model, serial, and a description (or photo) and we’ll locate it.
Yes. DanseUSA passes the manufacturer’s warranty to you. Coverage applies to defects in materials and workmanship under normal use for 30 days from the purchase date, in line with the manufacturer’s warranty policy. Terms can vary by brand; the product page reflects the applicable policy. If a claim is needed, we’ll help coordinate with the manufacturer.
Yes, most new, uninstalled items can be returned under our standard policy. Please see our Returns & Refunds Policy for eligibility, timeframes, and any exceptions.