Blog
013-2014 RZR 900 Head Inspection, Repair, and Performance Guide
The ProStar 900 engine powering the 2013 and 2014 Polaris RZR XP 900 generates impressive power density for a naturally aspirated side-by-side, but it packs a well-documented mechanical flaw. The cylinder head on these specific model years suffers from premature valve seat recession, soft valve guides, and thermal warping. If left unaddressed, tightening valve clearances eventually result in zero clearance, holding the valves open and causing complete compression loss or dropped valve heads.
Diagnosing and repairing the RZR 900 head requires understanding how heat stress, dust ingestion, and factory valvetrain tolerances interact over hours of operation.
Technical Overview: ProStar 900 Valve Dynamics
The dual-overhead-cam (DOHC) four-valve-per-cylinder layout of the 2013–2014 ProStar 900 relies on direct-acting bucket shims to set valve lash. Unlike hydraulic lifters that self-adjust, mechanical bucket systems transfer every bit of thermal expansion directly to the camshaft lobes.
Factory Specifications & Tolerances:
├── Intake Valve Clearance: 0.006 in - 0.008 in (0.15 mm - 0.20 mm)
├── Exhaust Valve Clearance: 0.008 in - 0.010 in (0.20 mm - 0.25 mm)
├── Cylinder Head Warpage Limit: 0.002 in (0.05 mm) maximum across deck
└── Camshaft Journal Clearance: 0.0009 in - 0.0024 in (0.023 mm - 0.061 mm)
As the soft factory intake valve seats pocket into the head casting under severe heat, the valve stems move upward toward the camshaft. This movement narrows the clearance between the shim bucket and the cam lobe. Once clearance reaches zero, the valve stays cracked open during the combustion cycle. Superheated combustion gases blow past the valve face, burning the valve edge and ruining cylinder compression instantly.
Common Failure Modes & Diagnostic Matrix
| Symptom | Root Cause | Inspection Method | Primary Fix |
| Hard Cold Starting | Intake valve seat recession holding valves open when cold | Feelergauge measurement under cam lobes | Reshim valves (temporary) or CNC cut valve seats with fresh valves |
| Popping through Intake | Burnt intake valve face due to zero clearance | Cylinder leakdown test (>15% leakage through intake manifold) | Replace intake valves and cut multi-angle valve seats |
| High Oil Consumption | Worn valve stem seals or egg-shaped valve guides | Inspection of intake ports for wet oil pooling | Press out worn guides; install manganese bronze replacements |
| Coolant Overpressurization | Deck warpage causing head gasket breach between combustion chamber & water jacket | Straightedge precision measurement across cylinder deck | Surface-grind cylinder head deck surface (max 0.005 in) |
Diagnostic Procedures for Compression Loss
Before pulling the engine, run two diagnostic tests to pinpoint whether low cylinder pressure stems from the head assembly or the bottom-end piston rings.
- Dry & Wet Compression Test:
- Thread a calibrated compression gauge into the 12mm spark plug port.
- Hold the throttle wide open and crank the engine until the needle stops rising.
- Healthy ProStar 900 engines register between 165 PSI and 185 PSI per cylinder.
- If pressure reads below 135 PSI, squirt 10mL of motor oil into the spark plug hole and retest.
- A jump in compression indicates worn rings. If compression remains low, the issue is internal valve leakage inside the RZR 900 head.
- Cylinder Leakdown Test:
- Rotate the crankshaft to top dead center (TDC) on the compression stroke for the target cylinder.
- Supply 100 PSI of compressed air using a dual-gauge leakdown tester.
- Air escaping out the intake plenum indicates leaking intake valves.
- Air rushing out the exhaust tip confirms burnt exhaust valves.
- Air bubbles inside the cooling reservoir reveal a blown head gasket or cracked internal coolant passage.
Machine Shop Rebuild Steps
Rebuilding a 2013-2014 casting demands specific machining processes to correct factory metallurgical soft spots:
- Guide Replacement: Press out original sintered iron valve guides. Heat the casting in an oven to 300°F (149°C) before pressing in bronze replacement guides to prevent galling the aluminum ports.
- Seat Cutting: Cut 3-angle valve seats (30-degree top bowl, 45-degree seating surface, 60-degree throat) concentric to the new guide centerline within 0.0005 inches.
- Deck Resurfacing: Precision mill the deck face using PCD (Polycrystalline Diamond) tooling to achieve a Surface Roughness (Ra) finish smoother than 30 microinches for optimal MLS (Multi-Layer Steel) head gasket sealing.
- Valve Spring Pressure Check: Test intake and exhaust springs using a spring scale tester. Reject any spring showing less than 45 lbs of seat pressure at installed height.
Frequently Asked Questions
What are the signs of a bad cylinder head on a Polaris RZR 900?
The most common signs of a bad RZR 900 head include hard cold starting, erratic idle, loss of top-end power, and popping through the intake plenum. You may also notice high coolant pressure or oil consumption. Performing a leakdown test quickly confirms if combustion pressure is escaping past the intake or exhaust valves.
How do I adjust the valves on a 2013-2014 RZR 900?
Adjusting the valves requires measuring the current clearance between the camshaft lobe and the valve bucket using feeler gauges. Remove the camshafts, lift the bucket, and read the thickness stamp on the underside of the shim. Calculate the correct replacement shim size using target specifications, then reinstall the camshafts and torque the caps to 88 in-lbs.
Why does my RZR 900 engine pop through the intake?
Intake popping happens when the intake valves fail to seal completely during the power stroke. As intake valve seats wear into the RZR 900 head, valve lash drops to zero. Superheated combustion gases blow back into the intake manifold during firing, igniting incoming air-fuel mixtures and causing a distinct popping sound under load.
What is the factory compression specification for a Polaris RZR 900?
A healthy ProStar 900 engine shows a dry compression reading between 165 PSI and 185 PSI per cylinder at sea level. Variance between the two cylinders must not exceed 10 percent. Readings under 140 PSI signal severe ring wear, valve seat recession, or burned valve edges that require immediate teardown.
Can you resurface a warped RZR 900 cylinder head?
Yes, a machine shop can resurface a warped casting, provided warpage does not exceed 0.005 inches. Machine shops use PCD diamond fly-cutters to maintain an ultraclean Ra finish necessary for multi-layer steel head gaskets. Machining beyond maximum tolerances alters valve-to-piston clearance and cam chain tension, requiring custom thickness gaskets.
What torque specs are required for installing an RZR 900 cylinder head?
Torque the main head bolts in a cross-pattern sequence using three distinct passes: first to 22 ft-lbs, second to 40 ft-lbs, and a final 90-degree angle turn. Clean all bolt threads completely and apply light engine oil beneath the bolt heads to ensure accurate torque readings during assembly.
Properly clearancing your bucket shims, using bronze guides, and installing heavy-duty stainless valves eliminates the structural shortcomings of the factory casting, restoring compression and keeping your machine running reliable trails for years.
Click Here Fie More