Exhaust Flapper Protector Valve – Fits MerCruiser, Chrysler, Crusader, Pleasurecraft (Replaces Sierra 18-4458, Mallory 9-44002, GLM 89260, Volvo Penta 834438-4)
Exhaust Flapper Protector Valve – Fits MerCruiser, Chrysler, Crusader, Pleasurecraft (Replaces Sierra 18-4458, Mallory 9-44002, GLM 89260, Volvo Penta 834438-4) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
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Exhaust Flapper Protector Valve – Fits MerCruiser, Chrysler, Crusad...
Exhaust Flapper Protector Valve – Fits MerCruiser, Chrysler, Crusader, Pleasurecraft (Replaces Sierra 18-4458, Mallory 9-44002, GLM 89260, Volvo Penta 834438-4) is backordered and will ship as soon as it is back in stock.
Product Details
This Exhaust Flapper Protector Valve – Fits Marine Stern Drives & Inboards 5" & 6" is designed for a wide range of marine stern drives and inboard engines with 5-inch and 6-inch exhaust outlets, including models from MerCruiser, Chrysler, Crusader, and Pleasurecraft (PCM).
It serves as a direct replacement for several common part numbers, including Sierra 18-4458, Mallory 9-44002, GLM 89260, and Volvo Penta 834438-4.
- External mount on the exhaust outlet for straightforward installation.
- Made with weather-resistant EPDM rubber with a UV stabilizer for durability in marine environments.
- Includes a stainless steel clamp for a secure and corrosion-resistant connection.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-4458 |
| Mallory | 9-44002 |
| GLM | 89260 |
| Volvo Penta | 834438-4 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Compatible with various inboard and sterndrive engines from Chris-Craft, Chrysler, Crusader, Pleasurecraft (PCM), and Mercury/Mariner that use a 5" or 6" exhaust flapper.
Also fits specific Volvo Penta applications calling for OEM part number 834438-4.
| Brand | Model | OEM Part No. |
|---|---|---|
| Chris-Craft | Inboard | |
| Chrysler | Inboard | |
| Crusader | Inboard | |
| Pleasurecraft (PCM) | Waukesha | |
| Mercury/Mariner | Inboard/Outboard | |
| Volvo Penta | 834438-4 |
Technical Specs
- Product Type
- Exhaust Flapper Protector Valve
- Installation
- External mount on exhaust outlet
- Connection
- Hose barb with included clamp
- Housing Material
- CR Rubber, Stainless Steel
- Housing Color
- Black
- Dimensions
- 5" & 6" (127mm & 152.4mm) diameter
- Weight
- 0.422 kg (14.9 oz)
- Fitting Type
- Barb
- Other Technical Attributes
- Made with weather-resistant EPDM with UV stabilizer; 5" installation requires two 45° cuts
What’s in the Box
- 1 x Exhaust Protector Valve (18-4458)
- 1 x Stainless Steel Clamp (6-1/16" to 7")
Installation Notes
- Ensure the engine is off and has cooled completely before beginning work.
- Locate and access the exhaust outlet where the old flapper is located.
- For installation on a 5-inch outlet, you must make two 45° cuts on the valve's housing to ensure a proper fit. No cuts are necessary for 6-inch outlets.
- Slide the new protector valve fully onto the exhaust outlet.
- Position the new stainless steel clamp over the hose barb section of the valve.
- Tighten the clamp securely until the valve is held firmly in place, preventing any potential exhaust or water leaks.
- Start the engine briefly to check for proper operation and ensure there are no exhaust leaks around the new seal.
Troubleshooting & FAQ
How do I know if this flapper valve will fit my engine?
This valve is designed for 5" and 6" exhaust outlets on various stern drive and inboard engines, including MerCruiser, Chrysler, and Crusader. The best way to confirm fitment is to measure your exhaust outlet diameter and compare your old part number to the cross-references: Sierra 18-4458, Mallory 9-44002, GLM 89260, or Volvo Penta 834438-4.
What is the purpose of the cuts required for a 5" installation?
The valve is designed to be compatible with both 5" and 6" outlets. For the smaller 5" diameter, making two 45° cuts allows the flexible rubber to conform correctly and create a tight, secure seal without bunching up or causing a leak.
What are the signs that my old exhaust flapper is failing?
Common symptoms of a worn or failed flapper include a distinct rattling or clacking noise from the exhaust at idle, visible cracks or missing pieces of rubber on the valve, and in severe cases, water being forced back into the engine (water ingestion).
How often should this part be replaced?
Replacement intervals depend on usage (freshwater vs. saltwater) and exposure to sun and weather. It is best practice to inspect the flapper annually for signs of cracking, brittleness, or tearing and consider replacing it every few seasons as part of your preventative maintenance schedule.
Is this an OEM or aftermarket part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. All our parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
How much is shipping and how fast is it?
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free to most regions, and expedited options will appear at checkout if they are available for your location.
What is your warranty and return policy?
This part is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window, provided the part is unused and in its original condition. See our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement part, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or quality control.
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