Trying to help out my sister-in-law with a 2008 Impreza, 64K miles that dealer just diagnosed with a broken camshaft (it’s apart, it’s broken at midpoint).
A month ago they replaced timing belt, cam seals, 3 timing belt pulleys, left OSV valve. 30 days later the car sputtered, check engine light came on, car towed to dealer with a broken camshaft. As they’re concerned about removing all metal shards within existing motor, they are recommending installation of a remanufactured engine at $5600 ($3500 engine + $1800 labor + $300 misc).
In my 50 years experience with cars, have never heard of this one! Maybe on a top fuel dragster? But a Subie with 60k? Perhaps its just one of those rare freak things
Other odd thing about timing belt, dealer had previously replaced it in April of this year at 61.5K???
So what is your question? Do camshafts break, yes, they do. Not commonly but is can happen. Is is related to previous work? Maybe. Nearly impossible to determine without expensive analysis. Is it worth a reman engine in an 11 year old car? Only your sister can decide that.
The car is 13 years old with very low miles. I wonder if the light use and depending upon the oil change regimen if the engine sludged up and cut off oil flow to the camshaft which then led to it seizing and breaking.
Metal shards seems to be a pretty weak reason to me to recommend 5600 dollars worth of engine. If engine sludge is not a factor then it seems that someone should figure out WHY the camshaft broke before suggesting a new engine.
I would not replace the engine just for a broken camshaft. Any metal shards will be visible in the area under the valve cover or they will have migrated to the oil pan. The oil pick up has a screen that will stop most shards. Anything that can get through the mesh of the screen will next go through the oil pump which has pretty good clearance and into the oil filter. Anything that gets past the oil filter won’t be big enough to do any harm.
BUT, the head with the broken camshaft may need to come off because there is a chance that a valve or two may have hit a piston. The top of the piston may need to be smoothed off. But the valves that hit it will be bent and need to be replaced. You could do both head gaskets at this time if you want but if money is tight, one will be enough for now.
At this time you could drop the pan and clean it out. Even if you don’t drop the pan but are still concerned about shards, the camshaft is steel and there are these really strong magnets that you can stick to the bottom of the pan that will attract and hold any metal particles.
The oil pan drain plug may already be magnetic but if it is not, you can get this:
Every time you change the oil, you will be able to wipe off any metal particles off the drain plug.
Edit: to determine if a valve or two are damaged, the mechanic can do a leak down test before pulling the head. If it passes that, you just saved a bunch of money.
I’ve seen a few broken cams over the years and the cause was always lack of lubrication in the camshaft saddles in the cylinder head. It doesn’t take much in the line of neglected oil changes to start plugging up those small oil pressure ports.
I just don’t think a broken cam justifies the need for another engine; unless the existing engine is oil sludged.
Something strange going on here. In my limited experience, the only broken camshaft was caused by a piston hitting a valve. Do you know why it was necessary to replace the OSV?
Actually the most likely scenario is. Part of the cam stops spinning because of a break. This can possibly hold a valve open allowing a still spinning crank to slam a piston into the open valve.
Timing belts have a specified elapsed time replacement interval, as well as a specified odometer mileage replacement interval.
IIRC, the elapsed time interval for your engine’s timing belt–regardless of odometer mileage–is 8 years.
So, if anything, that belt was overdue for replacement if it was done for the first time when the vehicle was 11 years old.
I also tend to disagree with the use of the word “shards”. That denotes larger pieces other than minute filings. The few broken cams I’ve seen always broke the shaft between a pair of cam lobes with little ir any debris.
As Keith mentioned. any metal that does exist will go to the oil pan and get stopped by the pump screen or the oil filter for the tinier bits. It seems to me a new engine is overkill. It’s similar to some shops that recommend a new engine because the timing belt broke and some pistons got nicked by some valves. Very, very seldom is that necessary.
I realize that sorting out causes and effects can be tricky when looking at a blown engine, but I happened to know that this motor had been over-revved (incident dates back to my hot-rodding days in 1970s). It seemed to me far more likely that valves floated, a piston hit one, effectively slamming a brake on the cam, than the camshaft just snapping under no more resistance than that from the valve springs.
So the timing belt was replaced at 61K, earlier in the spring, then again recently, at 64 K? That seems very unusual. What was their stated motivation to replace the timing belt the second time?
Doesn’t work that way. You float a valve and it hits a piston, then does not fully close after that but it won’t stop the cam from pushing the valve down the next time the lobe comes around.
I’ve seen a lot of broken timing belts and valve damage along with nicked pistons over the years but I’ve never seen a broken cam because of it. The piston is aluminum; it’s going to give before the camshaft does. The super hot valve is trying to cant sideways while open with piston contact so all of the force is not applied directly to the cam lobes.
In the case of the OP I still think they need to examine a potential lubrication problem. IF that is the case it should be easily apparent on the cam journals and cylinder head saddles.,
Floating the valves on a 2008 Subaru? I’m not inclined to think so. The rev limiter should prevent that: UNLESS someone has been in to the engine before for say head gaskets and botched something.
You used the term “float”. If a valve hits a piston while the cam is pushing it down, either the cam has already broken or the timing belt or timing chain has broken. If the cam is already broken, then it wasn’t due to a floating valve.
