Yanmar 2TNV70, 3TNV70 & 3TNV76 overhaul: cylinder head and engine block
A Yanmar 2TNV70, 3TNV70 or 3TNV76 with poor compression, high oil consumption or excessive blow-by doesn't have to be scrapped: these engines are excellent candidates for a rebuild. In this blog we've listed the key measurements and wear limits from the workshop manual — for both the cylinder head and the lower block — and explain which parts you'll need.
Suitable for the entire series: Yanmar 2TNV70, 3TNV70 and 3TNV76. Note: the 3TNV76 (76 mm bore) uses different pistons, sleeves, gaskets and head components than the 70 engines. All measurements below apply to all three unless stated otherwise.
Yanmar TNV: when is an overhaul needed?
Start by measuring the compression (see also Troubleshooting Yanmar TNV problems). Below the limit value — 2.55 MPa for the 70 engines, 2.75 MPa for the 3TNV76, at 250 rpm — or more than 0.2–0.3 MPa difference between cylinders, look for the cause in valve clearance, valve seats, head gasket or pistons/rings/cylinders. Drip a bit of oil into the cylinder and measure again: if compression rises noticeably, the problem is lower down (rings/cylinder); if it stays the same, it's higher up (valves/head gasket).
Yanmar TNV cylinder head: measurements and limits
| Measurement point | Standard | Limit value |
|---|---|---|
| Head surface flatness | ≤ 0.05 mm | 0.15 mm |
| Intake valve recession | 0.4–0.6 mm | 0.9 mm |
| Exhaust valve recession | 0.4–0.6 mm | 0.8 mm |
| Seat angle intake / exhaust | 120° / 90° | — |
| Valve guide inner diameter (intake and exhaust) | 6.000–6.012 mm | 6.08 mm |
| Valve stem outer diameter intake | 5.960–5.975 mm | 5.90 mm |
| Valve stem outer diameter exhaust | 5.945–5.960 mm | 5.90 mm |
| Stem-to-guide clearance intake | 0.025–0.052 mm | 0.15 mm |
| Stem-to-guide clearance exhaust | 0.040–0.067 mm | 0.17 mm |
| Valve guide protrusion above head | 9.8–10.0 mm (cold press-fit) | — |
| Valve spring free length | 37.8 mm | max. tilt 1.3 mm |
| Pushrod runout (bend) | < 0.03 mm | 0.03 mm |
| Rocker shaft clearance in rocker arm | 0.016–0.054 mm | 0.13 mm |
When overhauling the head, always replace the valve seals and check valve recession: valves seated too deep mean new valves and/or seats need to be re-cut. Adjust valve clearance after assembly to 0.15–0.25 mm (cold).
Yanmar TNV lower block: crankshaft, pistons and cylinders
| Measurement point | Standard | Limit value |
|---|---|---|
| Crankshaft runout (½ dial reading) | — | 0.02 mm |
| Connecting rod journal diameter | 41.952–41.962 mm | 41.902 mm* |
| Connecting rod bearing oil clearance | 0.020–0.050 mm | 0.110 mm |
| Main bearing journal diameter | 46.952–46.962 mm | 46.902 mm |
| Main bearing oil clearance | 0.020–0.050 mm | 0.120 mm |
| Crankshaft end play | 0.111–0.250 mm | 0.28 mm |
| Piston diameter 2TNV70/3TNV70 | 69.960–69.990 mm | 69.915 mm |
| Piston diameter 3TNV76 | 75.955–75.985 mm | 75.910 mm |
| Piston-to-cylinder clearance 70 engines | 0.030–0.050 mm | — |
| Piston-to-cylinder clearance 3TNV76 | 0.035–0.055 mm | — |
| End gap top ring (all engines) | 0.150–0.300 mm | 0.390 mm |
| End gap 2nd ring | 0.180–0.330 mm | 0.420 mm |
| End gap oil ring 70 engines / 3TNV76 | 0.150–0.350 / 0.200–0.450 mm | 0.440 / 0.540 mm |
| Connecting rod: twist/bend per 100 mm | < 0.03 mm | 0.08 mm |
* The manual literally states "1.6497 in (42.902 mm)"; based on the inch value, 41.902 mm is intended.
The crankshaft can be reground: the manual lists an undersize of 0.25 mm for both the connecting rod and main bearing journals (finished size 41.702–41.712 and 46.702–46.712 mm respectively). Worn cylinders can be honed and fitted with oversized pistons, or — the tidier route for these engines — you press in new cylinder sleeves and stay at standard size.
Assembling the Yanmar TNV cylinder head and block
All torque specifications and the head bolt tightening sequence (including a diagram for the 2- and 3-cylinder versions) can be found in Yanmar TNV specifications & torque settings. The essentials: lightly oil the head bolts and tighten in two stages to 53.9–57.9 N·m, connecting rod bolts (oiled) 22.6–27.5 N·m, main bearing caps (oiled) 75.5–81.5 N·m, flywheel 80.4–86.4 N·m. Fit the piston rings with the end gaps staggered (never in line), and pay attention to the ring installation direction.
Ordering Yanmar TNV overhaul parts
We supply everything for a complete or in-frame overhaul, selected per variant:
- Complete overhaul kit Yanmar 3TNV76 (VAR-850047) and in-frame overhaul kit 3TNV76 (SKU-850064)
- Engine overhaul kit Yanmar 3TNV70 (SKU-850035)
- Pistons and rings: piston 3TNV76 (VAR-0121), piston 3TNV70 (SKU-100059), piston rings 3TNV76 (SKU-95090) and piston rings 3TNV70 (SKU-95072)
- Cylinder sleeves (unfinished): 3TNV70 (SKU-11111133) and 3TNV76 (SKU-11111134)
- Bearings: main bearings (VAR-0013), connecting rod bearings 3TNV70 (VAR-0049) / 3TNV76 (SKU-105022) and thrust bearing set (SKU-110038)
- Head and valves: in-/exhaust valves 3TNV70, in-/exhaust valves 3TNV76, valve springs (SKU-97075) and valve seals (SKU-410011)
- Prefer an exchange unit over a rebuild? Complete cylinder head 3TNV70 (SKU-990032) or 3TNV76 with gasket set, thermostat and glow plugs (SKU-990033); we also supply a crankshaft 3TNV70 (SKU-48001) or 3TNV76 (SKU-48004) complete
Don't forget the gaskets: a complete gasket set 2TNV70 (SKU-80034), gasket set 3TNV70 (SKU-80107) or gasket set 3TNV76 (SKU-80035) includes the head gasket, crankshaft seals and all other gaskets in one box — cheaper and more complete than ordering everything separately.
