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Cummins/Onan DJA Engine

The Cummins/Onan DJA is a 0.49 L 1-cylinder air-cooled engine rated at 2400 rpm, producing up to 5.4 kW. It powers generator sets from Cummins/Onan and Onan (Onan Division of Studebaker Corporation, Minneapolis, Minnesota), including the 2.5DJA-51R, 2.5DJA-52R, 3.0DJA-1R and 3.0DJA-2R. It holds 2.4 L (0.6 gal) of oil.

Also known as: Onan DJA

0.49 L

Displacement

Cylinders

2400 rpm

Rated speed

5 kW

Gross power

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Procedures Wiring

Engine specifications

Oil capacity	2.4 L
Displacement	0.49 L
Cylinders	1
Aspiration	Air-cooled
Rated speed	2400 rpm
Gross power	5 kW

Generator sets powered by this engine

Shared across brands: Cummins/Onan, Onan (Onan Division of Studebaker Corporation, Minneapolis, Minnesota)

Cummins/Onan 2.5DJA-51R Cummins/Onan 2.5DJA-52R Cummins/Onan 3.0DJA-1R Cummins/Onan 3.0DJA-2R Cummins/Onan 4.0DJA-FJ Onan (Onan Division of Studebaker Corporation, Minneapolis, Minnesota) Spec T

How to read your Cummins/Onan engine serial & model number →

Common problems

Low oil pressure
Cause: Defective gage
Fix: Replace
Low engine power
Cause: Restricted air intake
Fix: Clean air cleaner
Excessive oil consumption, light blue smoky exhaust
Cause: Poor compression; worn piston, rings or cylinder
Fix: Refinish cylinder. Install oversize piston and rings
Engine does not start — blue-white exhaust smoke (engine is getting fuel)
Cause: Preheat not observed
Fix: Observe preheat procedure
Engine cranks too stiffly
Cause: Too heavy oil in crankcase
Fix: Drain, refill with light oil
Poor compression
Cause: Loose cylinder head
Fix: Tighten
Worn connecting rod, bushings and bearings
Cause: Plant run with low oil
Fix: Add oil, check cause of oil loss
Engine does not start — little or no exhaust smoke (engine is not getting fuel), little or no fuel flow
Cause: Fuel tank empty
Fix: Check fuel supply system
The engine will not crank
Cause: Possible fault with control or starting system; Fuse F1 has blown
Fix: Check for the following conditions; Replace the fuse with one of the same type and amp rating
Engine will not turn over (engine hard to start)
Cause: Restricted air intake
Fix: Clean air cleaner
Engine turns but will not start
Cause: Defective glow plug or preheater
Fix: Repair or replace
Piston, cylinder and ring wear
Cause: Close valve clearance
Fix: Re-adjust valve clearance
High oil pressure
Cause: Defective gage
Fix: Replace
Engine will not start when cranked
Cause: Air in fuel system
Fix: Bleed the fuel system
Engine will not crank
Cause: Battery discharged
Fix: Recharge

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan DJA.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			140B640	50 hr	Amazon eBay
Fuel filter			149C408	500 hr	Amazon eBay
Oil filter			122A185	200 hr	Amazon eBay $18.80 NAPA $12.88
Battery			—	100 hr
Belt			—	500 hr
Coolant	Drain water periodically from both filters and sediment bowl. Replace primary filter every 600 hours, secondary filter every 3000 hours.		—	600 hr
Coolant filter			—
Oil		2.5 quarts	—	500 hr
Spark plug			—	500 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Months	Notes
Engine	Inspect	8 hr
Engine oil level	Check	8 hr		First service — During break-in, check at least every 8 operational hours
Exhaust system	Inspect	8 hr		Maintenance schedules recommend inspection every eight hours by owner/operator for RV generator set exhaust systems.
Fuel supply	Check	8 hr		See Note 1
engine oil	Check	8 hr		Check Oil Level (Operator Maintenance Schedule)
Air cleaner	Check	50 hr		Wash filter element; replace if damaged
Air cleaner element	Clean	50 hr		Check after each 50 hours of operation
Battery condition	Check	50 hr		See Note 2
Crankcase oil	Change	100 hr		First service — Drain and replace crankcase oil after first 50 hours; drain while engine is still hot
Cylinder head bolts	Adjust	50 hr		First service — After first 50 hours of operation, retighten cylinder head bolts and check valve clearance
Cylinder head bolts	Check	50 hr		First service — Tighten head bolts and adjust valve clearance after first 50 hours on new or overhauled engine
Fuel Tank Water and Sediment	Drain	50 hr		Every 50 Service Hours or Weekly
Fuel condensation traps in lines and filters	Drain	50 hr		See Note 1
Oil level	Check	50 hr		See Figure 2
Oil-wetted-foam type air cleaner	Clean	50 hr		Wash in clean fuel; moisten with clean crankcase grade oil
Spark arrester/muffler, screen type	Clean	50 hr		Remove and scrape clean or replace screen; may be blown clean with compressed air. Every 50 operating hours.
Spark arrester/muffler, spin-out type	Clean	50 hr		Remove pipe plug in bottom of muffler and run set for 5 minutes; replace plug. Every 50 hours of set operation.
Spark arresters	Clean	50 hr		Spark arresters should be cleaned every 50 to 100 hours; routine cleaning during servicing is good safety practice.
Valve clearance	Adjust	50 hr		First service — After first 50 hours on new or overhauled engine
Spark plugs	Replace	75 hr		Annually or every 75 hours, whichever occurs first, for B43M/B48M/BF/BG/N52M engines.
Governor Linkage	Clean	100 hr		Every 100 hours; clean plastic joint only, steel joint with graphite
Oil filter	Replace	100 hr
Oil-bath type air cleaner	Clean	100 hr		Thoroughly clean and put in fresh oil
Generator armature, ball bearing, collector rings, commutator, brushes	Inspect	400 hr		Normal maintenance procedure
Air cleaner cartridge	Replace	500 hr		Install new cartridge at least every 500 hours
Battery Electrolyte Level	Check	500 hr	12 mo	Every 500 Service Hours or 1 Year
Breather standpipes	Clean	500 hr		Crankcase breather pipe must be cleaned after every 500 hours
Engine Air Cleaner Element (Dual Element)	Clean	500 hr	12 mo	Every 500 Service Hours or 1 Year - Clean/Replace
Engine Air Cleaner Element (Single Element)	Inspect	500 hr	12 mo	Every 500 Service Hours or 1 Year - Inspect/Replace
Engine Ground	Inspect	500 hr	12 mo	Every 500 Service Hours or 1 Year - Inspect/Clean
Engine Oil and Filter	Change	500 hr	12 mo	Every 500 Service Hours or 1 Year
Fuel System Primary Filter (Water Separator) Element	Replace	500 hr	12 mo	Every 500 Service Hours or 1 Year
Fuel System Secondary Filter	Replace	500 hr	12 mo	Every 500 Service Hours or 1 Year
Hoses and Clamps	Inspect	500 hr	12 mo	Every 500 Service Hours or 1 Year - Inspect/Replace
Radiator	Clean	500 hr	12 mo	Every 500 Service Hours or 1 Year
Stainless steel spark arrester screen	Replace	500 hr		For units using specially designed stainless steel screens.
Start-disconnect circuit	Check	500 hr
Valve clearances	Check	500 hr
Primary fuel filter	Change	600 hr
primary fuel filter	Replace	600 hr		Replace primary filter every 600 hours (Spec S and later)

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Brush wear limit (replace)	5/8	in
Clearance	Cam tappet hole diameter (prior to Spec P)	.7505-.7515	in	prior to Spec P
Clearance	Camshaft Bearing Clearance Limit	0.0012-0.0037	inch	At room temperature of 70 F
Clearance	Camshaft Bearing Journal Diameter, Front	2.500-2.505	inch	At room temperature of 70 F
Clearance	Camshaft Bearing Journal Diameter, Rear	1.1875-1.1880	inch	At room temperature of 70 F
Clearance	Camshaft bearing clearance limit	.0012-.0037	in
Clearance	Camshaft bearing journal diameter, front	2.500 - 2.505	in
Clearance	Camshaft bearing journal diameter, rear	1.1875 - 1.1880	in
Clearance	Camshaft end play	.007 - .039	in
Clearance	Camshaft end play	.007-.039	in
Clearance	Camshaft end play (new)	0.10 to 0.55	mm (0.004 to 0.022 inch)	Maximum permissible end play of a worn camshaft 0.60 mm (0.023 inch)
Clearance	Clearance between the bearing shell and the main bearing journals	0.057 to 0.117	mm (0.0022 to 0.0046 inch)
Clearance	Clearance in cylinder (begin Spec P)	.0055-.0075	in	90 degrees to pin, just below oil ring
Clearance	Clearance in cylinder (prior to Spec P)	.0050-.0070	in	90 degrees to pin, just below oil ring
Clearance	Clearance in guide, exhaust valve	0.0025-0.0045	inch
Clearance	Clearance in guide, intake valve	0.0005-0.0025	inch
Clearance	Clearance, Large Bearing to Crankshaft	0.001-0.003	inch
Clearance	Collector ring run-out	0.002	in	compared to generator bearing
Clearance	Commutator and slip ring run-out	.002	in.	less than
Clearance	Commutator mica undercut	1/32	in.	under the bars
Clearance	Connecting Rod Bushing Clearance	0.0002-0.0007	inch
Clearance	Connecting Rod Journal Diameter	2.0597-2.0605	inch
Clearance	Connecting Rod Large Bearing Bore Diameter	2.1871-2.1876	inch
Clearance	Connecting rod bearing clearance	.001-.0033	in
Clearance	Connecting rod bearing clearance	0.030 to 0.081	mm (0.0012 to 0.0032 inch)
Clearance	Connecting rod bushing clearance	.0002-.0007	in
Clearance	Connecting rod end play	.002-.016	in
Clearance	Connecting rod large bearing bore diameter (w/o bearing)	2.1871-2.1878	in
Clearance	Connecting rod small bushing bore diameter (w/o bushing)	1.044-1.045	in
Clearance	Crankshaft Main Bearing Clearance	0.0014-0.0052	inch
Clearance	Crankshaft Main Bearing Journal Diameter	2.2437-2.2445	inch
Clearance	Crankshaft connecting rod journal diameter	2.0597-2.0605	in
Clearance	Crankshaft end play	.010-.018	in
Clearance	Crankshaft end play	0.010-0.015	in
Clearance	Crankshaft main bearing journal diameter	2.2487-2.2445	in
Clearance	Cylinder Diameter Limits	3.2495-3.2505	inch	Bore must be less than 0.001 inch out-of-round
Clearance	Cylinder bore	105.000 to 105.025	mm (4.1338 to 4.1348 inch)
Clearance	Cylinder bore limits	3.2195-3.2505	in
Clearance	Cylinder head thickness	117.95 to 118.05	mm (4.643 to 4.647 inch)	Minimum thickness 117.20 mm (4.614 inch)
Clearance	End Play, Camshaft	0.007-0.039	inch	At room temperature of 70 F
Clearance	End Play, Crankshaft	0.010-0.015	inch
Clearance	Exhaust valve stem diameter	.3405-.3415	in
Clearance	Front gear cover oil seal installation depth	1-1/32	in	rear spring side of casing from gear cover mounting face
Clearance	Fuel injection pump installation dimension	3.260	in	new camshaft; instead of 3.254
Clearance	Governor cup center pin distance from camshaft gear	25/32	in
Clearance	Intake valve clearance in guide	.0015-.0030	in
Clearance	Intake valve stem diameter	.3405-.3410	in
Clearance	Main bearing clearance (original)	.002-.0033	in
Clearance	Main bearing clearance (replacement)	.0014-.0052	in
Clearance	Maximum permissible wear for the cylinder bore	0 to 0.15	mm (0 to 0.0059 inch)
Clearance	Original size of the connecting rod bearing journal	63.47 to 63.49	mm (2.4988 to 2.4996 inch)
Clearance	Original size of the main bearing journal	76.159 to 76.180	mm (2.9984 to 2.9992 inch)
Clearance	Piston Clearance to Cylinder Wall	0.0055-0.0075	inch	Measured 90 degrees from piston pin axis below oil control ring
Clearance	Piston clearance to cylinder wall	.0050-.0070	in	prior to Spec P
Clearance	Piston clearance to cylinder wall	.0055-.0075	in	Spec P and later
Clearance	Piston pin fit	Thumb Push Fit		room temperature
Clearance	Piston ring groove width 2nd	.0965-.0975	in
Clearance	Piston ring groove width 3rd	.0965-.0975	in
Clearance	Piston ring groove width top	.097-.098	in
Clearance	Ring gap	.010-.020	in

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Ambient	Capacity	Notes
Coolant	Commercial heavy-duty coolant/antifreeze	ASTM D4985			Do not use coolant/antifreeze that only meets ASTM D3306. Perkins recommends 1:1 water/glycol, may be increased to 1:2 water to glycol
Coolant	Ethylene glycol base anti-freeze mixed with water				Do NOT use straight 100% ethylene glycol. Normal mixture approximately 50% anti-freeze and 50% water; ratio varies with ambient temperature.
Coolant	Perkins Extended Life Coolant (ELC) 1:1 water/glycol (premixed)	Perkins ELC; freeze protection to -36 °C (-33 °F)			ELC Concentrate lowers freezing point to -51 °C (-60 °F) for arctic conditions
Coolant	Perkins Liquid SCA + water	6 to 8 percent concentration of SCA			Part number 21825755; for stationary and marine applications without anti-boil or freeze protection
Coolant	antifreeze				Replace annually in captive system
Coolant	50 Percent Ethylene Glycol	ASTM D4985	above -36°C	50.0 Percent	Freeze protection -36 °C (-33 °F), boil protection 106 °C (223 °F); 60 percent gives -51 °C (-60 °F) / 111 °C (232 °F)
Coolant	50 Percent Propylene Glycol	ASTM D4985	above -29°C	50.0 Percent	Do not use propylene glycol in concentrations that exceed 50 percent because of reduced heat transfer capability
Engine oil		API CD/SE or CD/SD		2.0 U.S. quarts	2-1/2 U.S. quarts (2.4 litres); add 1/2 quart for oil filter
Engine oil	API CD/SE				Diesel engines; use CC/SE for first fill only (50 hours)
Engine oil	API SE or SE/CC				Gasoline engines
Engine oil	Multi-grade (such as 5W-30)	API classification CC/SE (grades 10W-30, 10W-40 or 5W-30 only)	below 0°C		Recommended for service in ambient temperatures of 32 F and colder
Engine oil	SAE 10W or 5W-20				0F to 30F
Engine oil	SAE 10W or 5W-30	API CD/SE or CD/SD			For 0 F to 30 F. Multigrade oils recommended at 30 F and below, not recommended above 30 F
Engine oil	SAE 10W-30				RM92-8M0086220U6 / RM92-8M0086221U3
Engine oil	SAE 15W-40				RM92-8M0096794U3; diesel engines
Engine oil	SAE 25W-40				RM92-8M0086227U3 / RM92-8M0086224U3
Engine oil	SAE 30	API CD/SE or CD/SD			For temperatures above 30 F. CC oil for first fill only (50 hours) on new or rebuilt engine; add 1/2 quart for oil filter
Engine oil	SAE 5W-20				Below 0F
Engine oil	SAE 5W-30	API CD/SE or CD/SD			For temperatures below 0 F
Engine oil	TC-W3	TC-W3			2-cycle outboard oil; RM92-858026QB1U6 / RM92-858027QB1U3 / RM92-858037QB1U3
Engine oil	same SAE number as is in the crankcase				Used in optional oil bath air cleaner cup; do not overfill
Engine oil	SAE 0W20	EMA LRG-1 / API CH-4	-40°C to 10°C
Engine oil	SAE 0W30	EMA LRG-1 / API CH-4	-40°C to 30°C
Engine oil	SAE 0W40	EMA LRG-1 / API CH-4	-40°C to 40°C
Engine oil	SAE 5W30	EMA LRG-1 / API CH-4	-30°C to 30°C
Engine oil	SAE 5W40	EMA LRG-1 / API CH-4	-30°C to 40°C
Engine oil	SAE 10W30	EMA LRG-1 / API CH-4	-20°C to 40°C
Engine oil	SAE 15W-40 or 20W-40		-10°C to 32°C		J-series water-cooled diesel engines
Engine oil	SAE 15W40	EMA LRG-1 / API CH-4	-10°C to 50°C		Preferred oils: EMA DHD-1 multigrade, API CH-4 multigrade, ACEA E3. Minimum TBN of new oil = 10 times fuel sulfur level, minimum 5.
Fuel	ASTM 2-D or 1-D	minimum Cetane number of 45			Use 1-D fuel when ambient temperatures are below 32 F or during long periods of light/no load. Low sulfur fuel with pour point at least 10 F below lowest expected temperature

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Adjust Carburetor adjustment

⚠ Do not force needles against seats.

Open both needles 1 to 1-1/2 turns off seats.
Apply full load; turn main fuel screw in until speed drops, then out to normal.
Remove load; turn idle screw out until speed drops, then in to normal.

Adjust Decompression Release adjustment

⚠ If the screw is tightened more than one turn, the exhaust valve could hit the piston

Tools: Feeler gauge

Set valves for correct clearance first.
Leave flywheel at 10 to 45 degrees ATC with piston on power stroke.
Set arm in decompression position; turn setscrew until it just touches exhaust rocker arm.
Turn the screw exactly one revolution clockwise.
Hold setscrew and tighten lock nut 1/4 to 1/2 turn past finger tightness.

Adjust Governor Linkage (Diesel) adjustment

Loosen locknuts on governor linkage, remove link at one ball joint.
Position governor arm and fuel control arm fully forward.
Adjust linkage so both ball joints fit without moving arms.
Tighten locknuts.
Release fuel solenoid plunger.

Adjust Governor Speed adjustment

Tools: Screwdriver

Hold the sensitivity stud in place with a screwdriver.
Change spring tension with the speed adjusting nut.
More tension gives more speed.
To adjust high speed of solenoid two-speed governors, change solenoid rod length.

Adjust Valve Clearance adjustment

⚠ Check valve clearance when the engine is at room temperature about 70 F

Tools: Feeler gauge, Socket wrench, Rocker arm wrench

Turn the flywheel until the cylinder is on its compression stroke.
Turn the flywheel clockwise an additional 10 to 45 degrees.
Loosen the rocker arm locknut to increase clearance, tighten to reduce clearance.
Check clearance with a feeler gauge between rocker arm and valve.
Set clearance to 0.011 inch intake and 0.008 inch exhaust.

Adjust Valve Clearance (Diesel) adjustment

Tools: feeler gauge, socket wrench

Turn flywheel to compression stroke for cylinder to adjust.
Turn flywheel clockwise additional 10 to 45 degrees.
Loosen locknut to increase clearance, tighten to reduce.
Use feeler gauge to set proper gap.
Adjust in firing order 1-2-4-3.

Adjust Valve Tappet (Gasoline) adjustment

Tools: feeler gauge, wrench

Remove valve covers.
Crank engine until intake valve opens and closes.
Continue 1/4 turn until timing marks align.
Turn adjusting screw to obtain correct clearance.
Use flat feeler gauge between valve and valve rotator.

Adjust anti-dieseling solenoid adjustment

With set stopped, turn lever counterclockwise; set screw so plates are closed but not binding.
Check lever has approximately 30 degrees travel counterclockwise from vertical.
Start set; lever should rotate approximately 60 degrees clockwise from stopped position.
Check solenoid plunger is fully seated.
If not, adjust distance between plunger and lever arm; repeat steps.

Adjust governor speed and sensitivity adjustment

Tools: Reed-type frequency meter, Mechanical tachometer

Turn governor speed adjusting nut clockwise to increase speed.
Turn counterclockwise to decrease speed.
Turn sensitivity adjusting ratchet nut counterclockwise to increase spring tension.
Adjust for maximum sensitivity without hunting.
Secure speed stud lock nut after adjusting.

Adjust injection nozzle opening pressure adjustment

⚠ Do not try to adjust pressure without a testing fixture.

Tools: Nozzle tester

Remove nozzle from engine.
Remove cap nut over the adjusting screw.
Install nozzle on static fuel nozzle testing fixture.
Adjust opening pressure to 1,750 psi by turning adjusting screw.
Clockwise increases pressure; counterclockwise decreases.

Adjust the Vernatherm power element adjustment

Loosen the power element mounting screws.
Slide the assembly until it touches the roll pin with shutter closed.
Tighten the mounting screws.

Align brush rig to neutral position adjustment

Tools: Voltmeter

Remove end cover and band for access.
Start unit and apply full rated load.
Allow unit to reach full operating temperature.
Connect voltmeter across dc terminals.
Loosen brush rig mounting screws and rotate rig for highest voltage at full load.
Rotate rig one direction until voltmeter reading decreases; mark point.
Repeat in other direction; halfway between marks is neutral position.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		12-lead broad range reconnectible alternator	12 lead	User connects for required voltage and amperage
		X1 to VR21-5	X1	for 50 Hertz
		X1 to VR21-6	X1	for 60 Hertz
110	1	518	V1	50 hertz
110/190	3	53C	V1	50 hertz
110/220	1	518	V1	50 hertz
110/220	1	53C	V1	50 hertz
110/220	3	518	V1	50 hertz
115	1	518	V2	50 hertz
115/200	3	53C	V2	50 hertz
115/230	1	518	V2	50 hertz
115/230	1	53C	V2	50 hertz
115/230	3	518	V2	50 hertz
120	1	2-wire		Reconnectible
120	1	3C	V1	60 hertz
120	1	518	V3	50 hertz
120-volt AC/32-volt DC	single	dual purpose plant		DJA wiring diagram dual purpose plant; diagram 6100220 page 60
120/208	3	3C	V1	60 hertz
120/208	3	53C	V3	50 hertz
120/208 volt	three	4 wire		DJA revolving armature; diagram 610C187 page 59
120/240	1	3-wire		Standard connection for MCCK/MDJE/MDJC/MDJF
120/240	1	3C	V1	60 hertz. Connect X1 to VR21-5 for 50 hertz and X1 to VR21-6 for 60 hertz generators. Jumper W10 on VR21 must connect VR21-V4 to V1, V2, or V3 as listed.
120/240	1	518	V3	50 hertz
120/240	1	53C	V3	50 hertz
120/240	3	3C	V1	60 hertz
120/240 volt	single	3 wire		DJA revolving armature; diagram 6100181 page 56
127/220	3	3C	V2	60 hertz
127/220	3	53C	V4	50 hertz
139/240	3	3C	V4	60 hertz
220/380	3	518	V1	50 hertz

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the oil capacity of the Cummins/Onan DJA?

The Cummins/Onan DJA engine has an oil capacity of 2.4 liters.

What is the displacement of the Cummins/Onan DJA?

The Cummins/Onan DJA has a displacement of 0.49 liters with 1 cylinders.

Which generators use the Cummins/Onan DJA engine?

The Cummins/Onan DJA powers 6 generator set(s), including Cummins/Onan 2.5DJA-51R, Cummins/Onan 2.5DJA-52R, Cummins/Onan 3.0DJA-1R, Cummins/Onan 3.0DJA-2R, Cummins/Onan 4.0DJA-FJ.

How often should you change the oil in the Cummins/Onan DJA?

The Cummins/Onan DJA oil change interval is every 500 hours.

What is a common problem with the Cummins/Onan DJA engine?

A commonly reported issue on generators using the Cummins/Onan DJA is: Low oil pressure. Cause: Defective gage. Fix: Replace.

Cummins/Onan DJA Engine

Engine specifications

Generator sets powered by this engine

Common problems

Maintenance schedule

Repair guides

Service intervals

Service specifications

Recommended fluids

Procedures

Voltage reconnection

Common questions