Sleeved Diesel Engine
Home » Tony’s Tips » Articles » Engines & Components » Understanding What A Sleeved Diesel Engine Is

Understanding What A Sleeved Diesel Engine Is

If my memory serves me correctly, the first time I heard the term “throw away engine,” was back in the early 70’s and someone was referencing the 3208 CAT. Wow, did that start something! Sure, this engine has no sleeves, but I don’t think that even comes close to implying that the engine is a “throw away.” The 3208 CAT has a great reputation and is alive and well today. I’m sure the fine engineers at CAT who developed this engine would take exception to that term, and, I’m also sure this term has become so inbred in the marine environment that many of the same fine engineers that developed our diesels today have had many sleepless nights over this undeserved label.

Some of the reasons that diesel engines like the 3208, 3116, 3126, “B” Series Cummins, the LP Series Yanmars, and the new 6LY-2 Yanmars, to name a few popular engines today, have no sleeves is strictly by design. Superior heat dissipation, compactness, and weight savings vs. overall strength, initial cost of design and manufacture, are just a few of the design reasons for the lack of sleeves, or, my preferred term, “a PARENT BORE engine or block.” If we’re talking about a sleeved engine, it can be wet or dry and both have certain advantages and disadvantages.

Wet sleeves (or liners) have engine coolant directly in contact with their outer surface and various methods are used to contain coolant properly within the engine. Dry liners, as the name implies, are pushed into the bore of a block (the Yanmar 6LY 315 & 350 are examples) and have no contact with the engine coolant. Yes, a sleeved engine is usually easier to rebuild (cheaper in some cases) than parent bore engines, but usually only if cylinder damage or excessive wear is one of the reasons for the rebuild. Many installations in commercial boats dictate the use of a sleeved engine strictly due to rebuilding down the road. Most all of the popular “parent bore” engines today can be rebuilt by either boring the block and using an oversized piston, or, boring the block and putting in a dry sleeve (except one, the 6LY-2, according to Yanmar cannot be bored.) But many rebuilds, from my own personal experience with parent bore engines, have only required good honing and rings to accomplish this part of a rebuild.

I think the most important thing I’ve learned over the years about sleeved or sleeveless engines has nothing to do with whether the engine is a “throw away.” It’s much simpler than that. It is strictly the overall cost of the rebuild. Is it economical? Can you afford to buy the parts to rebuild it? Do you really want to give this engine another life? I’m sure I’m not the only one who has seen those “green” engines in the dumpster. This is a classic example of a finely engineered “sleeved engine” advertised as being easy to rebuild because of its sleeved design that is NOT practical to rebuild because of the economics and the cost of parts. Just some simple numbers on the current rebuilding costs of a 400C Cummins: Under $325 per hole, which includes new pistons, rings, liners, rod bearings, front/rear seals, pan and head gaskets and miscellaneous peripheral gaskets. New injectors were $100 each. Labor costs what it costs, as with all boat or engine work. These costs might be used as a comparison for what I believe are realistic parts’ costs that make an engine rebuildable. Just two months ago a customer looked into the cost of cylinder kits and miscellaneous necessary parts to do a “complete top end” on a pair of 15 year old (low hour) 6 cylinder Isuzu, about $6000 per engine. That’s just parts. He bought 220 Diamonds instead. This past week, I sold a pair of Cummins B’s to a customer w/ Ford Lehmans that the manifolds had rotted thru. The engines were still in good shape but the parts to repair were $4000+ per engine. Strictly economics here. Feel free to offer your insights to this somewhat controversial subject.