Volvo Penta AQ bensin sterndrive AQ131, AQ140/140A, AQ145, AQ151, AQ171 - rebuild and common faults
A family guide to the whole AQ petrol series: marinised Volvo redblock (B21, B23, B230) with a cast-iron block, aluminium cylinder head and cam belt drive. The internal engine hardware is identical to the car engine, so parts are cheap through the car engine trade. With factory-verified torque figures and workshop prices.
The AQ petrol series is classic Swedish boat engineering built on Volvo's redblock. AQ131, AQ140/140A, AQ145, AQ151 and AQ171 are all marinised versions of Volvo's B-series car engines - a cast-iron block with an aluminium cylinder head and cam belt drive, marinised with a saltwater-adapted cooling circuit, marine exhaust manifolds and carburettors. Because the internal engine hardware is identical to the car engine, parts are still cheap and available through the car engine trade, and the torque figures are the same as on the B21, B230 and B234. The big problem is corrosion - decades in a saltwater environment eat away at the cooling passages, exhaust manifolds and the head gasket sealing face - plus wear on the drive and sterndrive. During a rebuild, cylinder head pressure testing is all but mandatory. We carry out cylinder head reconditioning, cylinder boring, crankshaft reconditioning and complete engine reconditioning in our own machine shop with 12-month warranty. See also our boat engine rebuild hub page.
The AQ petrol models at a glance
Every AQ petrol engine is a marinised Volvo redblock. Displacement, power and base engine per model. Identity data compiled from Volvo redblock documentation and Volvo Penta AQ sources.
| Model | Displacement | Base engine (redblock) | Valve config. | Power | Period |
|---|---|---|---|---|---|
| AQ131 | 2,3 L (2 316 cc) | B23 / B230 | 8v SOHC | ~120 hk | 1985-1993 |
| AQ140 / AQ140A Slug/URL | 2,1 L (2 127 cc) | B21 | 8v SOHC | 138 hk SAE / 125 hk DIN | 1975-1979 |
| AQ145 / AQ145A | 2,3 L (2 316 cc) | B23 | 8v SOHC | ~138-139 hk | 1979-1988 |
| AQ151 | 2,5 L (2 490 cc) | B230 (bored/stroked) | 8v SOHC | ~146 hk | 1990-1993 |
| AQ171 | 2,5 L (2 490 cc) | B230 + 16v head | 16v DOHC | ~167 hk | 1989-1993 |
About the base engines: The AQ140/140A is the marine application of the B21 (Volvo's move from pushrod OHV to SOHC with a cam belt). The AQ131 and AQ145/145A are based on the 2.3-litre block (B23/B230). The AQ151 and AQ171 use the same 2.5-litre block - a B230 block bored and stroked with a forged crankshaft and 86 mm stroke - where the AQ151 has an 8-valve SOHC head and the AQ171 a 16-valve DOHC cylinder head.
NOTE - the AQ171 is not turbocharged. The AQ171 is a naturally aspirated 16v DOHC engine on the 2.5-litre redblock. Unlike the car engine B234 the AQ171 also lacks balance shafts - it is a 16-valve cylinder head on the standard redblock bottom end. No turbocharged factory variant of this 4-cylinder redblock marine engine ever existed.
Torque figures AQ petrol (redblock)
The internal hardware of the AQ petrol engines is marinised Volvo redblock, so the torque figures are the same factory values as on the car engines. Verified against Volvo factory manual TP-30170 (Reconditioning B 17, B 19, B 21, B 23). All values apply to oiled threads per Volvo; degreased parts must be oiled before assembly.
Cylinder head & valve train (8-valve AQ131/140/145/151)
Cylinder head 16-valve (AQ171, DOHC)
Engine block & bottom end
Timing belt & timing
NOTE - Head bolts: Volvo allows reuse up to 5 times if stretch is checked. Meksta always fits new bolts on disassembly. The reason: stress accumulation on stretched bolts is invisible and can give a false torque reading, and the cost of new bolts is negligible against the risk of head gasket failure. Lubricate the new bolt threads with 30-weight engine oil. Tightening sequence from the centre outwards: 7-3-1-5-9 above / 8-4-2-6-10 below.
NOTE - 8v versus 16v cylinder head: The AQ131/140/145/151 has an 8-valve SOHC cylinder head with the early/late bolt procedure per TP-30170. The AQ171 has a 16-valve DOHC cylinder head and an entirely separate head torque (20 + 40 Nm + 115 degrees, the same as the car engine's 16v redblock head). Never mix up the 8v and 16v values. The 16v values are taken from Volvo's greenbook for the 16-valve redblock (TP 31311/1).
NOTE - Con-rod bolts: Volvo specifies two torque values depending on the stud type. Identify the bolts and use the correct value. If in doubt, always fit new studs and run 70 Nm.
NOTE - Crankshaft centre bolt: Use holding tool 5034. Secure it in the bolt holes for the harmonic damper, not in the pulley. For the full redblock torque table, see B230 (8v) and B234 (16v).
Common faults on the AQ petrol sterndrive
Faults common across the AQ petrol family - partly redblock-specific, partly marine (drive, corrosion, carburettor). Cross-checked against the marineengine.com forum, Volvo Penta technical bulletins and YBW Forum AQ threads.
Corrosion in the drive and sterndrive
Saltwater • High- Symptoms
- Stiff or juddering drive, water ingress in the drive oil (milky oil), corroded seals and gearcase, noises when manoeuvring.
- Cause
- The sterndrive unit sits partly in the water and corrodes inside and out. Drive oil seals age and let water in. Sacrificial anodes that have not been replaced accelerate galvanic corrosion. Common to the whole AQ family's drive package.
Corrosion in the cooling water passages
Decades in saltwater • High- Symptoms
- Saltwater on the side of the engine, overheating, dropping compression on a single cylinder.
- Cause
- Saltwater in the cooling passages erodes the cast-iron block and the aluminium cylinder head. The corrosion is hidden and only comes to light at disassembly or pressure testing. Affects the whole redblock family.
The exhaust manifolds' internal partition corrodes
8-12 seasons • High- Symptoms
- Saltwater on the exhaust side of the cylinder, white smoke, sooted spark plugs.
- Cause
- The exhaust manifold's internal partition between the water side and the exhaust side corrodes through. Water gets into the exhaust passage and can reach the cylinder. A marine-specific fault source on all AQ petrol engines.
Head gasket blows
On overheating • High- Symptoms
- White smoke, coolant loss, "mayonnaise" under the oil filler, poor compression.
- Cause
- The difference in thermal expansion between the aluminium cylinder head and the cast-iron block. Made worse by overheating from a blocked raw water cooling system. The same weakness as on the car engines' redblock.
Cam belt and belt tensioner seize
During periods of standing • High- Symptoms
- The engine will not start after winter storage, the cam belt slips, failure on first start.
- Cause
- The redblock are cam belt driven (toothed belt). The belt tensioner seizes after periods of standing and the belt can break. The 8-valve AQ engines are free-wheeling (non-interference) - a belt failure stops the engine but normally causes no valve damage on the standard cam. The 16-valve AQ171, however, has less margin and should be treated more carefully. Change the cam belt and tensioner as preventive maintenance.
Carburettor diaphragm dries out
Common • Medium- Symptoms
- Starting problems, running rich, heavy hesitation on acceleration, problems when the engine is hot.
- Cause
- The accelerator pump diaphragm in the carburettors dries out and cracks, and fuel runs down into the intake. The AQ140A runs twin Solex 44 PHN-3 carburettors; later AQ petrol models have their own carburettor specifications. Rebuild kits are sold by specialist Volvo Penta suppliers.
AQ petrol rebuild prices
Based on the redblock configuration (4-cyl SOHC/DOHC, 92-96 mm bore). Excl. VAT and parts. Main operations - cylinder boring, crankshaft grinding, cylinder head resurfacing - are carried out in our own machine shop.
Cylinder head reconditioning
Bottom end
Full rebuild
Manifold + riser
Cylinder machining
| Service | Price |
|---|---|
| Cylinder boring 4-cyl inline block (92-96 mm) | 3 318 kr |
| Plateau honing 4 cyl | 1 050 kr |
| O-ringing block 4 cyl | 2 800 kr |
| Deck decking block 4 cyl | 1 974 kr |
Crankshaft work
| Service | Price |
|---|---|
| Crankshaft grinding (5 main + 4 big-end) | 3 010 kr |
| Polishing standard | 1 022 kr |
| Cleaning 4-cyl crankshaft | 784 kr |
| Straightening (medium) | 1 190 kr |
Cylinder head and pressure testing
| Service | Price |
|---|---|
| Resurfacing aluminium cylinder head 4-cyl | 1 330 kr |
| Pressure testing cylinder head 4 cyl | 1 876 kr |
| Valve seat cutting 8 valves (8v) | 910 kr |
| Valve seat cutting 16 valves (AQ171) | 1 820 kr |
Pressure testing & balancing
| Service | Price |
|---|---|
| Pressure testing cylinder head 4 cyl (small) | 1 876 kr |
| Pressure testing cylinder block | 1 400 kr /h |
| Balancing rotating assembly straight 4-cyl | 3 742 kr |
| Flywheel balancing | 2 100 kr |
Indicative prices for the AQ petrol configuration (marinised redblock, 4-cyl, 92-96 mm bore, alu cylinder head on a cast-iron block). Labour prices excl. VAT and parts. Marine-specific components (exhaust manifolds, riser, drive seals) are extra. Request a quote for an exact price after inspection.
See also
The car engine siblings in the redblock series and other Volvo Penta marine engines.
Questions and answers about the AQ petrol sterndrive
Are the AQ petrol engines the same as Volvo's redblock?
Yes. AQ131, AQ140/140A, AQ145, AQ151 and AQ171 are marinised Volvo redblock (the B series). They share the block and internal engine hardware with the B21, B23 and B230 car engines, but have a saltwater-adapted cooling circuit, marine exhaust manifolds and carburettors. Because the internal hardware is identical, the torque figures follow Volvo's factory manual TP-30170, just as on the B230.
Which base engine does each AQ model use?
The AQ140/140A is based on the B21 (2.1 L 8v). The AQ131 and AQ145/145A are based on the 2.3-litre block B23/B230 (8v). The AQ151 is a B230 block bored and stroked to 2.5 L with a forged crankshaft and 86 mm stroke (8v SOHC). The AQ171 is the same 2.5-litre block but with a 16-valve DOHC cylinder head - and lacks the balance shafts that the B234 has.
Is the AQ171 turbocharged?
No. The AQ171 is a naturally aspirated 16v DOHC engine on the 2.5-litre redblock (~167 hp). There was no factory turbo in this AQ family of redblock sterndrives. The AQ171 is often incorrectly described as a turbo in third-party sources.
What are the torque figures for the cylinder head?
For the 8-valve engines (AQ131/140/145/151) the redblock's early type applies (60 + 110 Nm, warm up, back off 30 degrees, tighten to 110 Nm) or the late type (20 + 60 Nm + 90 degrees). For the 16-valve AQ171 the separate 16v value applies: 20 + 40 Nm + 115 degrees. Main bearings 110 Nm, connecting rod 63 Nm (old bolts) or 70 Nm (new), flywheel 70 Nm, cam sprocket 50 Nm, crankshaft centre bolt 165 Nm. Meksta always fits new cylinder head bolts at disassembly.
What does it cost to rebuild an AQ petrol engine?
Cylinder head reconditioning 5 500-7 500 kr in labour. Complete engine rebuild 24 000-36 000 kr in labour, plus parts 6 000-14 000 kr. Marine-specific components (exhaust manifolds, riser, drive seals) can add another 4 000-9 000 kr.
What are the most common faults?
The marine ones: corrosion in the drive and sterndrive, corrosion in the cooling passages and exhaust manifolds, plus carburettor diaphragms that dry out. The redblock-specific ones: a head gasket that blows on overheating and a cam belt/tensioner that seizes after periods of standing. Everything must be assessed before the scope of the rebuild is decided.
Does the cylinder head have to be pressure tested?
At every rebuild. The AQ engines' light-alloy cylinder head often has hidden cracks from decades of saltwater exposure. Pressure testing is the only reliable way to find them before assembly.
Is it worth rebuilding an AQ petrol engine in 2026?
Often yes - parts are cheap through the redblock car engine market, the engines are robust, and a rebuilt AQ in a classic boat is worth considerably more than a repowered replica. We service all types of boat engines - see the boat engine page.
Do you have a Volvo Penta AQ that needs looking over?
Call us or send a quote request. Reply within 24 hours. We service all types of boat engines - see boat engine page. All rebuilds with 12-month warranty.