Repair of the crankshaft of the Tohatsu outboard motor: from diagnosis to assembly

The kneeshaft (kelvinshaft) is the “heart” of the outboard motor TohatsuIt's a very powerful, stable, and resource-conscious engine, and even minor defects like scratches on the necks, beatings, or wear on bearings can cause compression to fall, increased vibration, and even a motor to jam. diagnose malfunctions of the kneelRepair yourself (including grinding and replacing liners), and avoid typical errors that shorten the service life of the repaired site.

Feature of motors Tohatsu (series) MFS 9.8/15/20/25/30 In compact design and high revs, which imposes higher requirements for accuracy of repair. Crashing more than 0.03 mm is considered critical and requires a mandatory flow or replacement.And many owners mistakenly attribute the crankshaft wear symptoms to problems with the carburetor or ignition system, and we'll help you figure out when repairs are appropriate and when it's cheaper to buy a contract shaft or a new engine.

Signs of malfunction of the crankshaft: when you need repairs

The first "bells" about crankshaft problems are often ignored until the motor begins to "crash" literally in front of your eyes.

• 🔊 Metal thumping It's at the bottom of the engine, which is enhanced by the speed of the engine, most often caused by wear on the root or rod bearings.
• 🌀 Idle vibrationIt's not lost after the carburetor is adjusted, it could indicate a shaft beating or an imbalance.
• 💨 Compression fall In cylinders (dispersion of more than 10% between cylinders), the reason is wear of the necks of the crankshaft and increased gaps in the friction pairs.
• 🛢️ Oil starvation: rapid blackening of the oil or the presence of metal shavings on a magnetic plug.

On the engines. Tohatsu system Oil Injection (for example, MFS 25 EFI) crankshaft wear is often accompanied by lamplighting of emergency oil pressure If you have a problem after changing the oil and filter, it's a direct signal to diagnose the shaft.

⚠️ Attention: If you can hear the engine squeal Or it suddenly dies with a characteristic "blow" -- stop the engine immediately! These are signs of a jamming of the bearings, and further work will lead to the destruction of the crankshaft and the cylinder block.

Diagnosis of the crankshaft: tools and procedure for checking

Before you disassemble the motor, make sure that the problem is in the crankshaft.

• 🔧 Micrometer (for measuring the necks of the shaft).
• 📏 Time-type indicator (to check the beat).
• 🔍 endoscope (To inspect the bearings without complete disassembly).
• 🧲 Magnetic plug. (for analysis of metal shavings in oil).

Procedure for verification:

1. Pour the oil And look at the magnetic cork, and if you have a large chip (more than 0.5 mm) or a melted particle, you're going to see the bearings break down.
2. Take off the pallet. And look at the root liners. bullying, painting or wear greater than 0.1 mm - a replacement is required.
3. Check the shaft beat. Place the motor on a flat surface, hold the indicator on the block, and rotate the shaft behind the flywheel. Tohatsu - no more 0.02-0.03 mm.
4. Measure your necks with a micrometer. Compare the nominal sizes (see table below).

Motor model	Diameter of the necks (nominal), mm	Diameter of the rod necks (nominal), mm	Max. allowable wear, mm
Tohatsu MFS 9.8/15	35.000–35.010	30.000–30.008	0.05
Tohatsu MFS 20/25	40.000–40.012	35.000–35.008	0.06
Tohatsu MFS 30/40	45.000–45.015	40.000–40.010	0.07

If the wear of the necks exceeds the permissible values, the crankshaft is subject to repair-size Or a replacement. Tohatsu Usually provided for 2-3 repair sizes of liners (increased) 0.25 mm).

Disassembly of the engine and dismantling of the crankshaft: step-by-step instructions

Disassembly Tohatsu It's nuanced because of its compact design, so keep it in order to avoid damaging the parts.

Dump oil and fuel | Disconnect battery (on models with electric starter) |Remove casing and air filter |Remove high-voltage wires |Detach gas cables and reverse->

Then proceed as follows:

1. Remove the cylinder block head (GBC) On motors. MFS 25 EFI Turn off the sensor connectors and fuel ramp.
2. Demount the pallet And the oil pump. Be careful with the gaskets. Tohatsu They often get stuck.
3. Remove the lids of the root bearingsMark them with serial numbers (for example, a marker) so as not to confuse them when you build them.
4. Remove the kneel. Some models require the flywheel to be removed (use a filmmaker).

Pay special attention lockingOn. Tohatsu they're often attached tension-bolt, which cannot be unscrewed without a dynamometer key, and if you don't properly dismantle the bolts, they stretch and lose strength!

⚠️ Attention: If there's a kneecap on the necks deep-rooted risks or bulliesDon't try to eliminate them with sandpaper, it will break geometry and accelerate wear after repair, and these defects are only eliminated by grinding on the machine.

Grinding the crankshaft: repair dimensions and nuances

Grinding is the most important part of repairing, and it can only be done on a specialized machine (for example, a machine). Berco RTM 270 Or similar. For motors. Tohatsu The following rules apply:

• 🔄 Repair dimensions necks increase with step 0.25 mm (e.g. 35.00 → 34.75 → 34.50).
• 📉 Minimum neck diameter After the resurfacing, there should be no less minus 0.75 mm.
• 🛠️ After the grinding, it is needed polish your necks with diamond paste to remove microbarbs.

Example Tohatsu MFS 20:

• Nominal size of the root necks: 40,000 mm.
• 1st repair size: 39.750 mm (The inlays are marked with green paint).
• 2nd repair size: 39.500 mm (The inlays are marked with yellow paint).

After grinding. Make sure you check:

1. The shaft beating (should be no more) 0.01 mm).
2. The ratio of the root and rod necks (tested on prisms).
3. Surface hardness (must not be lower than) HRC 55 for steel shafts.

What happens if you ignore the beating of the shaft?

If the crankshaft beat exceeds 0.05 mm, this leads to uneven wear of the liners and necks, increased vibration and the risk of shaft failure at high revs. In practice, such a motor will work no more than 50-100 hours before re-repair.

Replacement of liners and assembly of the motor

When replacing the liners with Tohatsu Consider the following points:

• 🔄 Inlays are selected strictly for the repair size of the necks.For example, for size. 39.75 mm We need a labeled liner. 0.25.
• 🧴 Before installation, lubricate the liners with engine oilBut don’t use a consistent lubricant – it can clog up oil channels.
• 🔧 Tightening of bearing covers Perform in 3 stages:
  1. Preliminary tightening of the moment 20 Nm..
  2. The hull to 40 Nm..
  3. Check the moment after 10 minutes (due to shrinkage of the gaskets).

Assembly order:

1. Install new liners in the block and lids. fixative The liners got into the grooves.
2. Put the crankshaft in place, lubricating the necks and liners with oil.
3. Tighten the lids of the root bearings, observing the moment and order (from the central to the extreme).
4. Check it out. shaft-turning - it should rotate smoothly, without jamming.
5. Install rods with new liners and tighten the lids in the moment 25-30 Nm. (For the exact values, see the manual for your model.)

After assembly of the lower part of the motor, install the oil pump, the pallet (with a new gasket) and the head of the unit. hydraulic pusher (for example, MFS 30 EFI) after assembly will be required valve clearance.

💡

Do not use a sealant on pallet and HBC gaskets - on Tohatsu they usually do not require additional sealing. Excess sealant can get into the oil channels and clog them.

Running the engine after repair of the crankshaft

The first 10 to 15 hours of work after repairs are critical. Failure to run the rules can nullify all efforts. Tohatsu The following recommendations are in place:

• ⛽ Fuel.Use gasoline with an octane number not lower 92 and oil for two-stroke engines with class TC-W3.
• 🔄 Working hours:
  • The first 2 hours are no more 50% maximum speed.
  • Next 5 hours, until 75% of turnover.
  • After 10 hours, you can go to full capacity.
• 🛑 Forbidden.:
  • Long-term work on idle turns (more than 5 minutes).
  • Excessive gas surges (especially on a cold engine).
  • Overload operation (skier towing, heavy loads).

After the break-in Make sure to replace the oil - it's gonna have a lot of metal dust from the finishing of the parts.

• No leaks of oil from under the pads.
• Stability of work at idle speeds.
• No extraneous noise when dialing.

If it stays after the break-in thumping or vibrationThis is a sign of assembly errors (e.g., improper bearing tightening or crankshaft imbalance), in which case the motor must be re-disassembled and the shaft geometry checked.

Typical errors in repairing the Tohatsu crankshaft

Even experienced mechanics sometimes make mistakes that reduce the life of a repaired engine.

• 🔧 Use of used insertsEven if they look normal, their geometry is already broken, and they won't provide the right lubrication.
• 🧴 Savings on oil When you run it, cheap oils don't form a strong oil film, which leads to bullying.
• 🔄 Failure to observe puffing momentsFor example, pulled rod bolts can deform the liners.
• 📉 Ignoring the shaft beatEven. 0.05 mm It can cause vibration and accelerated wear.
• 🛠️ Resurfacing without subsequent polishingMicrosausins on the necks act like an abrasive, breaking the liners.

Another common mistake. flywheel-mountingOn. Tohatsu It sits on a cone and it's locked in a veneer, and if the flywheel is not mounted to the point, it leads to:

• Unstable turnovers.
• The veneer damage.
• Risk of flywheel failure at high loads.

⚠️ Attention: On the engines. Tohatsu MFS 25/30 EFI After the repair of the knee is required ESIBecause the crankshaft position sensor (CRP) can give incorrect signals because of the changed shaft geometry, without which the motor will be malfunctioning.

FAQ: Frequent questions about Tohatsu crankshaft repair

Can I repair the crankshaft without grinding, if the wear is minimal?

If the wear of the necks does not exceed 0.02-0.03 mmThere is no beat, you can do it. substituting the nominal sizeHowever, before doing this, be sure to check the roughness of the necks with a profilometer - if Ra > 0.4 μm, it's gonna need polishing.

How much does it cost to grind the Tohatsu crankshaft in the service?

The cost depends on the region and the complexity of the work:

• Resurfacing for the 1st repair size: 3 000–5 000 ₽.
• Full complex (grinding + polishing + beat check): 6 000–10 000 ₽.
• Replacement of liners (work): 4 000–7 000 ₽.

For engines. Tohatsu Over 10 years is often cheaper to buy contract-shaft around 15 000–25 000 ₽ depending on the model).

How often should I check the crankshaft for wear?

Recommended interval:

• For motors up to 15 hp: 300-400 motor-hours or once in season 3.
• For engines. 20-40 hp: 200-300 hours of motor-training or once in season 2.
• After hydrostrike Or work with detonation - immediate check!

Signs for unscheduled diagnosis: compression drop, knocking, vibration.

Can I use repair liners from other engines?

No, the linings are coming up. strictly according to the model of the engine and repair sizeFor example, the inserts from Yamaha or Mercury not fit for TohatsuAnd even if the diameters are the same, the differences might be:

• The thickness of the antifriction layer.
• Material (e.g., material) Tohatsu frequently uses inserts with additions lead, not aluminum.
• Oil channel configurations.

The use of “non-fair” liners will lead to their accelerated wear and the risk of jamming.

What to do if the engine smokes blue smoke after repair?

Blue smoke indicates ignitionPossible reasons:

• 🔧 The rods are pulled over → The oil is squeezed through the gaps.
• 🛢️ Sapoon's full. → High pressure in the crankcase.
• 🔄 Wear of oil-removable rings (Unless they were replaced by a repair.)

Decision: Check the compression, inspect the candles (if they are in oil - a problem in the rings or liners) and clean the sapoon.