Kubota Diesel Engine Main Bearing Assemblies

[gondola993]

Folks,

I've never seen the style of main bearing cap assemblies that Kubota uses. It's clear that they end up with a very stiff block. Below is a photo album of the bottom end plus some snippets from the engine service manual showing the assemblies. I'm interested in the tolerance of the assembly fit to the engine block. The bolt coming up from the bottom cinches each assembly to the block. The manual says that each bearing cap assembly is of a slightly different diameter requiring that they be placed on the crankshaft in proper order. Is there a name for this style of main bearing assembly? The engine runs fine; this is just for information. Thanks!

Google photo album.

Thanks

 

[MikeHalloran]

I think cam bearings are sometimes stepped in diameter so that you won't accidentally scratch them during axial assembly, since the distal cam bearing journal must pass through all but one of the bearings on the way its final destination, and so forth.

Given that engine's construction, there exists the possibility that the bearing carriers' outside diameters are stepped for the same reason; axial assembly of the crank + bearings into the crankcase.



Mike Halloran
Pembroke Pines, FL, USA

 

[PJGD]

That is a Tunnel crankcase and is a well known architecture that has been widely used by many better class engines in the past including several diesels. The Italians are very fond of it and it can be found in several VM Motori engines and also CMD engines:

http://www.cmdengine.com/index.php/en/products/aeronautical-engines.html

The WO Bentley-designed pre-war Lagonda V12 used that construction, as did the post-war Aston-Martins and several other engines. The aluminium bearing disc assemblies were colloquially known as "cheeses" since they look about the size and proportions of a cheese disk. The Offy engines used it too.

PJGD

 

[gondola993]

Thanks Mike and PJGD. What you wrote gave me a lot to go on. Now that I know it's a tunnel crankcase design there's a ton on the web describing them.

Best,
David

 

[tbuelna]

I don't think this type of crankcase construction is actually better overall than a conventional ladder-type lower end. Plus this tunnel arrangement involves more parts and machining operations.