Onan 7000 Cracked Block Cover Repair - Welding vs JB Weld Fix

Tools & Parts Needed

Find these on Amazon: JB Weld Original Steel Reinforced Epoxy , Brake Parts Cleaner , Wire Brush Set

Quick Answer

Yes, your cracked Onan 7000 block cover can be successfully welded by an experienced aluminum welder, and JB Weld can work as a temporary solution. The key is proper preparation and understanding that aluminum welding requires specific expertise. JB Weld can hold for 6-12 months if applied correctly, giving you time to plan a permanent repair.

Welding the Cracked Block Cover

SAFETY WARNING: Working with pressurized oil systems and aluminum welding requires proper safety precautions. Always depressurize the system, wear appropriate PPE, ensure proper ventilation when welding, and be aware that aluminum welding produces intense UV radiation that can cause severe burns.

Welding aluminum block covers is definitely possible, but it requires the right approach. The block cover on your Onan 7000 is aluminum, which means you'll need TIG welding with AC capability or specialized aluminum welding equipment. Here's what you need to know:

The block cover must be completely removed from the engine and all oil must be drained before welding - welding on installed components with any oil residue presents serious fire hazards. The crack area must be completely clean of oil residue - this is critical for welding success. Even microscopic oil contamination will cause the weld to fail. You'll need to degrease thoroughly with brake cleaner or acetone, then use a wire brush or grinder to expose fresh aluminum. Complete chemical cleaning and degreasing is essential - never attempt to burn off oil residue as this can ignite vapors.

Find a welder experienced with aluminum engine components. Not all welders can handle aluminum effectively, and the heat-affected zone around the repair needs careful consideration. A good aluminum welder will likely V-groove the crack slightly to ensure full penetration, then build up the weld and machine it flush if needed.

JB Weld as a Temporary Solution

JB Weld can absolutely work as a temporary fix for your situation. I've seen it hold on similar cracks for several months, though the high-temperature, high-pressure oil environment may reduce effectiveness compared to other applications - monitor closely for any seepage. Here's the proper application process:

1. Clean the area thoroughly - Use brake cleaner or degreaser to remove all oil residue. The crack and surrounding area should be spotless.
2. Roughen the surface - Use coarse sandpaper or a wire brush to create texture for better adhesion. Clean again after roughening.
3. Use JB Weld Original or WaterWeld - The original steel-reinforced formula works well for this application. WaterWeld can be applied to slightly damp surfaces if needed.
4. Apply in thin layers - Build up the repair in 2-3 thin coats rather than one thick application. Let each layer cure partially before adding the next.
5. Shape and smooth - Before final curing, shape the repair to match the original contours. You can sand it smooth after full cure if needed.

Critical Preparation Steps

Whether welding or using JB Weld, preparation is everything. Oil contamination is your biggest enemy here. The oil pressure sensor area is constantly exposed to pressurized oil, so any residue will compromise your repair.

Consider this cleaning sequence: Initial degreasing, wire brushing, second degreasing, acetone wipe, and final inspection under good lighting. For JB Weld repairs, some mechanics recommend slightly warming the area with a hair dryer to improve adhesion and help drive out any remaining contamination.

Temperature cycling is another concern. Your Onan 7000 heats up and cools down with each use, causing expansion and contraction. Both welding and JB Weld repairs can handle this, but proper application is crucial.

Long-term Considerations

While you mentioned not wanting to replace the cover right now, start planning for it. A cracked block cover often indicates the aluminum is aging and may develop additional cracks over time. Keep an eye on oil levels and watch for new seepage around the repair area.

Monitor your oil pressure readings more closely after any repair. A compromised block cover can affect pressure readings, and you want to catch any issues early. The oil pressure sensor itself should be inspected - the over-tightening that caused your crack may have damaged the solenoid threads or sealing surface.

Prevention for Future Repairs

Over-tightening is a common cause of this situation. Onan specifies torque values for good reason - aluminum threads are much more fragile than steel. For the oil pressure sensor, torque to manufacturer specifications for your specific model (typically much lower values - consult your Onan service manual for exact specifications as over-tightening can cause cracking).

Invest in a good inch-pound torque wrench for small fasteners like this. When working with aluminum components, hand-tight plus a quarter turn is often sufficient for sealing applications. If you feel significant resistance, stop and investigate rather than forcing it.

When to Call a Professional

Call a professional if the crack is longer than an inch, if you see multiple cracks, or if the crack goes through a bolt boss or mounting area. Also, if you're not comfortable with the cleaning and preparation process, it's worth having a shop handle the repair. A poorly prepared JB Weld repair that fails can make a permanent fix more difficult later.

For welding, definitely use a professional unless you're experienced with aluminum TIG welding. The heat input needs careful control to avoid warping the cover or affecting nearby areas.