Mitsubishi 4M51 Workshop Manual

If you’re diving into a Mitsubishi 4M51 engine, you’ve probably realized the factory service info is not easy to find. The internet is full of translated snippets and conflicting torque values. That’s where this Mitsubishi 4M51 Workshop Manual comes in. It’s a direct factory document—36 pages long—and it gives you the exact clearances and procedures Mitsubishi engineers specified. No third-party messing around.

Factory tolerances are printed on page 1. You want the nominal clearance between the camshaft gear and the intermediate gear? It’s 0.05–0.15 mm (0.002–0.006 in). Wear limit? 0.20 mm (0.008 in). Don’t guess. Use the damn spec.

Camshaft Removal and Intermediate Gear Clearance

This manual walks you through pulling the camshafts without bending valves. The intermediate gear mesh is the first thing you check. The manual shows a specific bolt removal sequence for the camshaft bearing caps—23 bolts in a numbered order. If you skip that sequence, you risk warping the caps or damaging the camshaft journals. The Russian original uses a diagram, but the English version here has the same numbers. You’ll follow that order when reinstalling, too. The intermediate gear clearance check requires placing the camshaft on a surface plate and using a feeler gauge. The nominal clearance is 0.05–0.15 mm (0.002–0.006 in). The wear limit is 0.20 mm (0.008 in). That’s the data you need before you button up the timing cover.

Does This 36-Page Manual Cover Wear Limits?

Yes. Camshaft lobe height wear limit is listed at 25 mm (0.984 in) from a nominal 61.78 mm (2.432 in). The journal clearance is spec’d: nominal 0.03–0.07 mm (0.0012–0.0028 in), max 0.10 mm (0.004 in). These are the numbers that determine whether you can reuse the cam or need a new one. Aftermarket manuals often leave these out. This one doesn’t.

2 Critical Specs on Page 1 You Cannot Ignore

First, the gear backlash. Nominal 0.05–0.15 mm. Second, the intermediate-to-cam gear clearance max. Both are on the same page. Page 1 also includes the bolt removal diagram. If you ignore these and just reassemble, you’ll be chasing a timing noise next week. I’ve seen it happen.

Check the Intermediate Gear Backlash with These OEM Numbers

Set the camshaft on a surface plate. Use a feeler gauge between the gear teeth. The manual says the nominal gap is 0.05–0.15 mm (0.002–0.006 in). The maximum allowable is 0.20 mm (0.008 in). That’s tight. If your gear is worn past that, replace it. Don’t try to shim it—the manual doesn’t list shimming because it’s not a field repair.

Mitsubishi 4M51 Workshop Manual: Why 36 Pages Is Enough

This isn’t a 2000-page complete service manual. It’s a focused workshop manual for the 4M51 engine’s valve train and timing components. You get camshaft removal, intermediate gear service, and wear limit data. That’s all you need for a top-end overhaul. If you need transmission specs, check the Mitsubishi R4AW2-1, R4AW2-3, R4AW2-7 1996 Workshop Manual”>Mitsubishi R4AW2-1, R4AW2-3, R4AW2-7 1996 Workshop Manual for automatic transmission rebuild data. For smaller diesel engines, the Mitsubishi 4D68 1996 Workshop Manual – 70 Pages of OEM Specs”>Mitsubishi 4D68 1996 Workshop Manual – 70 Pages of OEM Specs covers the 4D68. And if you’re doing a transmission overhaul, the Mitsubishi F4A4 F4A5 1999 Workshop Manual – OEM Transmission Rebuild Specs”>Mitsubishi F4A4 F4A5 1999 Workshop Manual – OEM Transmission Rebuild Specs has what you need.

36 pages. No filler.

Is this manual in English?

Yes. The factory translation is direct, though some original Russian diagrams remain.

What exact specifications does this manual include?

It includes camshaft removal and installation procedures, intermediate gear backlash checks, and wear limits for the camshaft lobes and journals. You’ll find nominal and maximum clearances for the gear mesh (0.05–0.15 mm nominal, 0.20 mm wear limit) and camshaft bearing clearance (0.03–0.07 mm nominal, 0.10 mm max). Cam lobe height wear limit is 25 mm (0.984 in) from a nominal 61.78 mm (2.432 in). The manual also covers the 23-bolt removal sequence for the camshaft bearing caps. It does not include head gasket torque specs or overall engine rebuild data—it’s focused on the valve train and timing components.

For background on diesel engine architecture, see Automotive Industry Overview”>Automotive Industry Overview. The intermediate gear system in the 4M51 is similar to that in a manual transmission’s idler gear; you can read about Manual Transmission”>Manual Transmission designs for context.

Stop relying on generic spec sheets. Put the factory data on your bench. Download the Factory Manual now.