RV Generator Spark Plug & Tune-Up - Mobile Service Florida
Coast to Coast RV Repair provides mobile spark plug & tune-up service on-site at your campground or driveway across Florida - certified technicians, same-week scheduling.
Coast to Coast RV Repair provides mobile spark plug & tune-up service on-site at your campground or driveway across Florida - certified technicians, same-week scheduling.
Certified technicians. $299 service call. Same-week scheduling. Call (866) 887-1199.
Spark Plug Electrode Erosion and Its Effect on Generator Starting and Load Performance
Onan QG and QD engines specify a 0.025-inch plug gap because the ignition system's coil energy output (measured at 40 millijoules for the QG 5500) is optimized for this gap at the compression ratio of 8.5:1. As the electrode erodes, the gap widens at a rate of approximately 0.001 inches per 25 hours of operation for standard copper-core plugs. At 0.035-0.040 inches, the ignition coil must develop 30-40% more voltage to jump the wider gap - and in Florida's humid air, which reduces the dielectric strength of the ignition circuit, the coil may misfire 2-5 times per 100 firing events. These misfires are silent at low load but cause rough running and RPM hunting at high load because the combustion timing is irregular. Starting difficulty in humid conditions is the first observable symptom because the wider gap requires peak coil voltage that an aging coil may not achieve reliably during the first 3-5 cranking revolutions before the engine warms. Replacing plugs at the 150-hour interval (when gap is approximately 0.031 inches) prevents this progressively worsening symptom pattern. Iridium plugs (Champion QC14PYPB) maintain gap integrity to 300 hours but cost 4x more per plug - the math favors standard plugs at the standard interval for most RV users.
Valve Clearance Service on Onan QG OHV Engines - Measurement and Adjustment
The Onan QG 5500 uses an overhead-valve design with hydraulic lifters on the camshaft and solid pushrod adjustment at the rocker arm. Valve clearances must be measured with the engine cold (below 85 F) and the piston on top dead center of the compression stroke. Onan spec is 0.004-0.006 inches intake and 0.006-0.008 inches exhaust. Clearances tighten over time as the valve seat recedes into the aluminum head and the valve face wears - a tight exhaust valve (under 0.004 inches clearance) holds the valve slightly open at full lift, causing the exhaust valve to burn and lose sealing integrity within 50-100 hours. This is the primary cause of compression loss on high-hour Onan generators. Adjustment is via a 10mm locknut and 0.050-inch hex adjuster screw at the rocker arm pivot. Jesse Earl measures valve clearance at every tune-up regardless of hour count - tight valves on a low-hour engine indicate an aluminum head that is seating faster than normal, a condition worth tracking over multiple service intervals.
Also see: Generator Service Services
This page covers spark plug & tune-up specifically. For the full range of generator service services we offer, visit our Generator Service service overview.
Case Study: Spark Plug & Tune-Up Repair
RV: 2020 Thor Palazzo 36.2 • Location: Encore Fort Pierce, Site 71 • City:
Symptom: Onan QG 5500 difficult to start in morning - required 6-8 cranking attempts over 90 seconds before firing; once running, ran smoothly; owner reported plugs had never been replaced in 5 years and 290 hours of use
Diagnosis: Jesse Earl removed both spark plugs (Champion RC14YC, Onan P/N 167-0241) and measured electrode gap: 0.037 inches (spec: 0.025 inches). Gap erosion of 0.012 inches over 290 hours is consistent with normal wear. Plug electrode color was light gray with minor white deposits - no oil fouling or carbon buildup, indicating a clean-running engine. Valve clearance measured with feeler gauge: intake 0.004 inches (spec: 0.004-0.006 inches), exhaust 0.006 inches (spec: 0.006-0.008 inches) - both within spec. Air filter showed 60% surface blockage by visual inspection. Fuel filter was original, with visible discoloration.
Outcome: Generator started on second crank attempt at ambient 78 F; fuel consumption measured 0.58 GPH at 75% load (spec: 0.55-0.62 GPH); no-start issues not repeated at follow-up call 2 weeks later
Time on-site: • Total cost: • Dealer alternative:
Generator Spark Plug Options - Standard vs. Extended Life
| Plug Type | OEM P/N (Onan) | Aftermarket P/N | Gap Spec | Expected Life (hours) | Cost per Plug | Florida Humidity Resistance |
|---|---|---|---|---|---|---|
| Champion RC14YC (standard) | 167-0241 | Champion RC14YC | 0.025 in | 150 hours | $4-6 | Good |
| Champion QC14PYPB (iridium) | N/A (approved for use) | Champion QC14PYPB | Pre-gapped 0.025 in | 300 hours | $18-22 | Excellent |
| NGK BPR5ES (standard) | N/A (cross-ref) | NGK BPR5ES | 0.025 in | 150 hours | $4-6 | Good |
| Bosch W8AC (standard) | N/A (cross-ref) | Bosch W8AC | 0.025 in | 150 hours | $5-7 | Good |
Signs You Need Spark Plug & Tune-Up
- ✓Record hour meter reading and last service date
- ✓Remove spark plugs and measure electrode gap before cleaning (document wear rate)
- ✓Inspect plug electrode color: light gray = healthy; black = rich mixture or oil; white = lean
- ✓Gap new plugs to OEM spec with feeler gauge before installation
- ✓Torque spark plugs to spec (Onan QG 5500: 18-20 ft-lb)
- ✓Measure valve clearance cold with engine on TDC compression (intake: 0.004-0.006 in, exhaust: 0.006-0.008 in)
- ✓Replace air filter (Onan QG 5500: P/N 140-1751)
- ✓Replace fuel filter (Onan QG 5500: P/N 149-2457)
- ✓Clean spark arrestor screen - replace if screen wires are broken or over 60% blocked
- ✓Run generator 20 minutes under 75% load and verify smooth operation
Spark Plug & Tune-Up - Pricing
Typical price range: $185-$345
All calls start with a $299 service-call fee that covers the technician's trip to your location and the first hour of diagnosis. That $299 applies toward any repair you authorize - it is not an additional charge on top of the repair. Pricing shown is a national average range; your exact quote is provided in writing on-site before any work begins.
Spark Plug & Tune-Up - Common Questions
Straight answers from our spark plug & tune-up service call log.
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More Generator Service Services
Other specialized repairs under generator service - all done at your location, no tow required.
Where We Provide Spark Plug & Tune-Up in Florida
Coast to Coast RV Repair runs spark plug & tune-up jobs across these cities. Click your closest one for local-specific info, response times, and campground coverage.