On a passenger car engine, a rebuild usually requires machine boring of the cylinders, honing; matching of oversize pistons and rings, etc. Never thought too much about it. Then, as I learn more about machinery, I learn that most heavy duty diesel engines have you REPLACE the wear surfaces with new ones on a rebuild–not just “wet sleeve” design, but Detroit Diesel sleeves, for example, are removed, new ones installed, and put back in service that way.
It just seems a better system overall: build tolerances are those set by the factory; you aren’t limited to a finite number of rebuilds; the need for specialized engine rebuild machinery is lessened (making the job potentially cheaper due to not needing to send so much work out).
Does anyone know why? What is the downside to just replacing all wear surfaces? Cost or something else? (Is it an implicit indication you aren’t really expected to rebuild a gasoline engine?)
I used to be a certified diesel mechanic in my younger days and the answer is simple. Diesel engines are designed to have cylinder sleeves installed and gas engines are not. That’s from my early 70’s diesel training and I don’t think much has changed today. There is a limit to how far the cylinder walls can be bored before the engine block has to be replaced on most gas engines.
Yes, I get that, just asking “why?” I mean, you could design either engine around either system–it’s just that diesels are built one way, and gassers another.
The obvious explanation is that the gasser strategy is simpler and cheaper if you assume the engine will be disposed of, rather than rebuilt. I thought that, maybe, there was more to it than that.
Gas engines can be sleeved. I had one done on a big block Ford to increase displacement from 406cu in to 427 cu in when I had new pistons, rods, and crank that were much superior (Le Mans). It was done by a professional race engine builder. I don’t see why doing this to maintain original bore would cost much more than replacing pistons but what do I know. I remember 283 cu in Chevrolet small blocks being bored .30 over creating a 301 cu in Many experienced piston slap and compression problems with stock pistons.
The Renault Dauphine did have cylinder liners that wee replaced when the engine was overhauled. An overhaul kit was available that included the cylinder liners, pistons, rings, bearings, etc. The overhaul kit wasn’t terribly expensive, but the engine required an overhaul about every 20,000 miles and had the durability of a potato chip.
Yes…gas engines can be sleeved but they are a rare animal. The only one that I know of personally was a '94 Vega GT. It had sleeves installed because of the flaky aluminum bore but it overheated at the drop of a hat. We fixed the overheating problem with a powerful electric fan but it was very noisy. My brother was the owner and he sold the car after it was able to go 100 miles without spewing the coolant everywhere.
Today, very, very few automobile engines are rebuilt in the field…It’s very uncommon now…If the factory did not use replaceable liners, then engine builders seldom did it, unless the engine was a rare one and a cylinder was badly damaged…After all, it’s just a CAR engine, a disposable consumer product…It boils down to a matter of cost…
There’s a huge cost differential between boring and replaceable sleeves with the former being cheaper. Cars are also not designed to go for millions of miles as trucks are.
The older Subarus used wet-sleeve engines with replaceable liners. Those liners set on copper gaskets of varying thicknesses which were designed to create a liner protrusion above the block and promote head gasket sealing.
There was a ton of head gasket issues with those engines even if they were redone by the book with a new liner/piston set.
Copper is a soft material which rested on an aluminum block and the head bolts require retorquing every 15k miles. It doesn’t take much thinking to see what’s going to happen after a while when that copper is continually being crushed and liner protrusion starts to disappear.
Sleeving a cylinder on the vast majority of gasoline engines is relatively expensive. The block must be bored precisely to allow the proper fitting of the sleeve and when installed the sleeve must be machined to get a proper seal at the deck and possibly bored and honed to match the piston. If more than one sleeve was needed I sourced a used block in better condition to cut the cost.
Big trucks are expected to go several hundred thousand miles, get a rebuild, and go several hundred thousand more. Since their useful lifetime is so long, the extra expense of sleeving is not the cost killer that it would be in a car or light truck. Big trucks can cost a couple hundred thousand and the cost to sleeve the cylinders is not a huge part of the initial expense, either. Saab tried providing a significantly safer car at a slightly higher cost and they went out of business.
The chassis of big trucks are built to go more than a million miles. Downtime being so expensive to a big rig, the engines are designed to be rebuilt over and over quickly and cost effectively. Big rigs can go over 3500 miles weekly on cross country deliveries. They can rack up a few hundred thousand in a year.
One point about trucks too is that operating hours are more important than miles. A dump truck can experience heavy duty operation for eight hours a day, even sixteen, five or six days a week, yet never put on many miles. Off-road equipment, including off-road dump trucks, can put on less mileage than you do in your car yet run under heavy loads for 5,000 hours/yr… some even more. Fast rebuilding capability is essential for this environment. No contractor wants a $200,000+++ piece of equipment sitting idle for any longer than absolutely necessary.
Cars’ chassis are not designed to go more than a million miles. There are numerous cars out there right now whose engines outlast the chassis. I myself have put hundreds of thousands of miles on a few cars without ever wearing an engine out or ever having to rebuild one, 338,000 being my personal best. My current car has over 217,000 and it’s still in excellent shape.
Mentioning Renault here brought some memories back. I think it is a cost issue. Last time I worked on engines, was many years ago and I remember the Renaults would cost the owner more because they needed a new sleeve with each rebuilt. This was in an era that 80K miles was good use out of any engine, so rebuilts were part of life. I remember some asking for pistons that had a scoop to increase engine size too.
I had to put a sleeve in a Jeep engine and it worked out well. I was boring out the cylinders for oversize pistons. On one of the cylinders, I accidentally set the boring machine’s cutting diameter too large. Oops.
The solution was to re-bore that cylinder to the specs needed for a sleeve. We “froze” the sleeve to cold temps, and then dropped it quickly into the cylinder before it warmed up.
As others have noted, the economics aren’t there for car engines to have sleeves by default. And the need isn’t there either. The failure rate of car engines today doesn’t warrant it.
I bet over 90% of cars built today will never see a rebuilt engine, the vehicle is scrapped either with the original engine or a used engine. I imagine well over 50% of heavy duty diesels will get a rebuilt engine.
The local auto machine shop here gets about 10 bucks a hole to bore them.
They get about 100-200 bucks a hole to sleeve them; all depending.
The only time sleeving is really feasible is if a repair is being done on a valuable engine; say an early Boss 302 or Vette 427, early Hemi, or the need to keep that original date coded old engine going.
The only one that I know of personally was a '94 Vega GT.
I think you meant 74.
I rebuilt my 73 Vega, and had the engine steel sleeved. Chevy should have done that with the original design. It added a total of 10lbs to the engine…and made the engine 1000 times more durable.
Engines and lubricants are so good now that we have few opportunities for rebuilding engines. Shops that do this are fewer and fewer. Heavy duty diesels have liners because the trucks they are in go several million miles before being scrapped.
Liners add to the cost of an engine and a properly designed engine block in cast iron or aluminum will last the life of the rest of the car which nowadays is getting close to 300,000 miles, as opposes to 100,000 maximum in the 50s.
The Vega aluminum block engine without liners was a very poor design and a half hearted effort by GM to build a small car to compete with the VW Beetle.
I know of people who have re-sleeved the Suzuki G-series engines used in the Geo Metro, Suzuki Swift, and others. These can also be bored over a couple times. It sounds like they have to flash cool the old and new sleeves to get them out and back in.
That being said, I think this is about the same price as overboring and junkyard blocks for these are not getting too rare yet. I have some engine cores for my Geo Metro sitting out in a shed.