Where to Buy Onan Generator Rubber Isolator Mounts: Complete Sourcing

What's Going On

you're absolutely right that finding these rubber isolators for your 2008 Jayco Melbourne 29D with the Onan 4000 can be frustrating - they're not as universal as you'd expect. Based on your photos showing the split isolator, you'll want to look for the correct part for your model (verify with dealer). These are the correct rubber isolation mounts for your 4KY series generator. Cummins Onan dealers are your best bet, but you can also find them through RV parts suppliers like Dyers RV Parts, RV Parts Country, or PPL Motor Homes for around $25-35 each. Since you have the generator out already, this is definitely the perfect time to replace all four isolators even if only one is visibly damaged.

The reason your Google searches came up empty is that these aren't truly universal parts - each generator manufacturer uses slightly different mounting configurations and rubber compounds. Onan specifically engineers these isolators to handle the vibration frequency and weight of their 4KY series units. Generic motor mounts from automotive stores won't provide the same vibration dampening characteristics and could lead to premature failure or increased noise transmission to your coach.

Why This Happens

Your 2008 generator isolators are failing due to age and heat cycling - rubber compounds naturally break down over 15+ years of exposure to engine heat, ozone, and constant vibration. The isolators in your photos show classic signs of rubber degradation where the bond between the rubber and metal components has failed. This is completely normal for a generator of this age, and you're smart to address it now rather than waiting for a complete failure that could damage the generator frame or increase vibration throughout your RV.

Heat is the biggest enemy of these rubber mounts. Your Onan 4000 runs hot, and the isolators are positioned close to the exhaust system where they experience temperature swings from ambient to over 200°F. Combined with the constant vibration from the twin-cylinder engine, the rubber gradually loses its elasticity and begins to crack or separate from the metal bushings. RVs that spend time in hot climates or run their generators frequently tend to see isolator failure earlier than those used occasionally in moderate temperatures.

The loose isolator you've discovered is likely causing increased vibration transmission to your coach frame, which can lead to rattling cabinets, dishes, and potentially stress other components over time. It's also putting additional stress on the remaining three isolators, so replacing all four as a set is the smart preventative approach.

Getting Ready

SAFETY WARNING: Always disconnect battery power and allow generator to cool completely before beginning work. Ensure adequate ventilation and never work alone when handling heavy generator components.

Since you already have your generator removed, you're halfway there. You'll need a basic socket set, penetrating oil like PB Blaster for any stubborn bolts, and possibly a gear puller if the isolators are seized onto their mounting studs. Order all four isolators even if only one appears damaged - at 15+ years old, the others are likely on borrowed time. Expect to pay $100-140 for a complete set of four genuine Onan isolators.

Check the mounting studs and brackets for any signs of damage or elongated holes while you have easy access. Sometimes a failed isolator will allow enough movement to damage the mounting points. You'll also want to inspect the generator frame itself for any cracks or stress marks around the mounting points. Take photos of the current orientation before disassembly - there's usually a specific way these need to be positioned for proper weight distribution.

Have some anti-seize compound ready for reassembly, especially if you're in a salt air environment or areas with harsh winters. The mounting hardware on these generators is notorious for seizing over time, and a little prevention now will save major headaches during your next maintenance cycle. Clean all the mounting surfaces thoroughly with brake cleaner or degreaser before installing the new isolators.

Walking Through the Fix

SAFETY WARNING: Use proper lifting equipment and support when handling generator components. Never rely on isolators alone to support the generator weight during installation.

Start by documenting the current setup with photos from multiple angles - the isolators may look symmetrical but often have specific orientations for proper load distribution. Remove the mounting bolts securing each isolator to the generator frame, working systematically around the unit. If bolts are seized, use penetrating oil and let it work for 30 minutes before applying force. Heat from a small torch can help stubborn fasteners, but use extreme caution - disconnect fuel lines, ensure fuel tank is properly vented and isolated from heat source, area is well-ventilated, and keep heat source away from fuel lines, wiring, and all generator components. Consider mechanical methods first as they are safer near fuel systems.

The isolators typically press or thread onto mounting studs extending from the RV frame. Some designs use a sandwich arrangement with washers and spacers that must be reinstalled in the correct order. If an isolator is stuck on its stud, use a gear puller rather than hammering - you don't want to damage the frame mounting points. Clean all threads with a wire brush and apply anti-seize compound during reassembly.

When installing new isolators, hand-tighten the mounting bolts first to ensure everything aligns properly, then torque to manufacturer specifications (typically 15-25 ft-lbs for Onan isolators - consult your Onan service manual for exact torque values for your specific model). Over-tightening can compress the rubber excessively and reduce its vibration-dampening effectiveness. Under-tightening allows movement that will quickly destroy the new isolators.

Before reinstalling the generator, double-check that all four isolators are making proper contact and supporting the weight evenly. The generator should sit level and stable without any obvious stress points or gaps. Test the mounting by gently rocking the generator - there should be firm support with just slight give from the rubber compression.

Beyond DIY Territory

If you discover damaged mounting studs or cracked frame components, this moves into professional repair territory. Frame modifications require proper welding equipment and expertise to maintain structural integrity. Similarly, if the generator frame itself shows stress cracks around the mounting points, you'll need professional assessment to determine if repair is worthwhile versus replacement.

Some older RVs have custom mounting configurations that may require fabrication of adapter brackets or spacers. If your Melbourne has been modified from the original Onan installation or if the mounting points don't align properly with standard isolators, an RV service center with fabrication capabilities can create proper mounting solutions. This work typically runs $300-500 depending on complexity.

Consider professional installation if you're uncomfortable with the torque specifications or if access is particularly difficult in your coach. Many RV service centers can complete isolator replacement in 2-3 hours for $200-300 in labor plus parts. This might be worthwhile if you're dealing with seized fasteners or if you discover additional issues during disassembly that require specialized tools or expertise.