I am a happy guy right now. My wife’s Subaru Forester developed “rod knock” at the tender age of 58K miles, and after a couple of weeks of biting my nails as the warrenty status of the work teetered on the edge, I am pleased to say that I have a piece of paper in my hand that says she got her engine rebuilt at no cost.
Now for the questions…
What exactly is rod knock? I have heard of it before, and I understand that it is a terminal engine disease, but the actual details are hazy. Why would it go away after warming up (10 mi or so)? It also went away completely at highway speeds.
The receipt says this:
“R&R Engine” and “Replace with Short Block” among other things.
In the parts list is “REMAN SOHC SHORT BLOCK”
What is “R&R Engine”? “Remove & Replace?”
What is a “Short Block”?
When I was faced with the possibility of having to pay the whole cost, I spoke with my own mechanic about having him do it instead of the dealer. He told me that he would likely replace it with a “Long Block” since it would be easier.
What’s a “Long Block” and why is it easier than a “Short Block”?
What does it mean to have a remanufactured short block? What do they do to it? How does it differ from a brand new one?
R&R is remove & replace. SOHC is single overhead cam.
Short block is the central core, so to speak - the crankcase and pistons. A long block is that, plus the cylinder heads. It’s easier to swap a long block as you’re not disassembling parts off one engine to transfer to another. You have to remove the entire engine in one lump from the car for either sort of job, if you can afford the full engine, you do save on labor.
Rod knock means the bearings at the ends of the piston connecting rods are worn and have loosened, leading to a knocking as they move.
Remanufactured means they’ve stripped the engine to its individual bits, inspected them, and rebuilt it using whatever’s good enough to go into a new engine and replacing whatever’s not. It’s not going to be all new parts, so they can’t call it new, but it’s a much more thorough job than just (as an example) dropping the oil pan and replacing the crankshaft bearings without inspecting everything.
R & R = Remove and replace
Short block = Engine block assembly with pistons, and crankshaft and typically the other items that are inside the block such as oil pump, and distributor drive. Does not inculde cylinder head(s) May include oil pan
Long block = as above but inculdes head(s) Typically this is a complete engine less manifolds
Reman vs rebuilt. Typically a reman engine is done on an assembly line where some parts are replaced and others are reused or re-machined. Rebuilt usually means a one off rebuild (done by a mechanic vs a shop that does hundreds. Which is better? Depends. I have seen remans that rival factory new for quality. I have seen remans that are junk. Depends on who is doing the work. Same with rebuilts. Pretty much semantics.
Connecting rods connect the pistons to the crankshaft. The bearings at the bottom end (rod bearings) run with a very slight clearance (measured in hundredths of a millimeter, or for those who are not metic savy, thousandths of an inch.) This gap is filled with oil under pressure. So the oil does the bearing of the loads. However if you don’t change your oil, it runs low, or other bad things happen, the oil does not protect the bearing, and the crankshaft starts to hit the actual bearing causing a knock. This is a bad thing.
Hope this helps to answer your questions.