Replace pistons when replacing head gaskets?

subaru
outback

#1

I have 195k on my '97 Subaru Legacy Outback. I blew the head gaskets and while replacing them (along with new timing belt and water pump) for $2k, the dealer mechanic is suggesting replacing the pistons since he says there is a slight slap in atleast one of them - another $1200. I have seen no loss of mileage (24 in city and 30 in highway) or have lost any oil. Is it a good idea to change the pistons or wait until it becomes necessary? Thanks.


#2

I think at 195k miles you are better off not going into the pistons. That leads to other issues that involve cylinder bore wear, taper, and so on. To cure cylinder bore faults require boring the cylinders. That in turn requires diassembling the entire engine and means a complete engine overhaul. To me, that piston recommendation is kind of goofy and can open up a can of worms.

It might be added that any top end noise might not even be a piston slap and could be related to excessive valve lash. It’s actually best that lash be inspected and adjusted as needed every 30k miles but that is seldom done.


#3

I wouldn’t. That would require rings and a rebore I would think. Old rings and a new piston aren’t a good idea.


#4

I say “go further”. At those normal prices, why not replace the whole car? It makes some sense to keep the car but you will also need a lot of luck.

Once you replace half the brake system and get the automatic transmission rebuilt or run into clutch problems with the other kind you could get the $1400 computer code. Fix that and get a $950 alignment with the $500 CV joint job and you’re still not done.

If your interior is starting to look bad and smell odd, you might consider a newer car. Your current air bags might work.

If it all works fine and there is an accident, all the money could be down the drain. It just seems like a lot of negatives and not enough rewards.

Now, for the advice you asked for. If you end up needing new pistons the head gaskets have to be redone. It would be better to get the ring job done now with the new pistons, main bearings and valve job. Better to get a remanufactured engine really.


#5

Thanks all. I will put off replacing the pistons - hopefully won’t need to anytime soon.


#6

In all seriousness, if they’re doing head gaskets and a timing belt job the valve lash procedure I mentioned should be done after the heads are reinstalled and before the valve covers are put back on. It’s not difficult to do and with the engine out it’s a piece of cake.


#7

Years and years ago I’ve done a head-off ring replacement. Drop the pan…unbolt the connecting rods from crank…then push the piston through the top. Replace rings…then put the piston back in and reconnect and torque bolts. Not the best thing to do…but it can be done.

But that’s a lot of money and effort on an almost 20 year old car.


#8

The Subarus that I am familiar with are quite unique in their design, @Mike. The wrist pins must be removed to remove the pistons From the information here I would discourage going any deeper into the engine than necessary to repair the head gasket(s).


#9
The wrist pins must be removed to remove the pistons

Yes you have to remove the wrist pins to remove piston from connecting rod. But if you’re just replacing the rings…you don’t have to disconnect the piston from rod.


#10

Subaru pistons can be removed without block disassembly or connecting rod removal as they’re Boxer style engines. There are holes (sealed by plugs) in the block both front and rear on each side. A wrist pin circlip is removed from each hole and the wrist pin withdrawn through the hole with the piston being somewhat awkwardly forced out of the top of the bore.

The downsides are that a special factory tool is needed for wrist pin removal (although that can be worked around) and that any cylinder honing as to be done with great care as the end of the connecting rod still occupies a spot in the cylinder bore. It’s also a bit awkward to line that connecting rod small end back up with the wrist pin holes in the piston during assembly

Still, makes no sense to go into pistons at almost 200k miles because more than likely the cylinder bores are out of spec in one way or the other.


#11

That’s why I recommend avoiding dealers for older cars.
Your goal was, I assume, to get the car up and running again. Not to return it to “like new” condition. Replacing the pistons is definitely not required to get it up and running again, and once you get into that level of work the cost skyrockets.

IMHO the dealer’s suggestion is way out of line. But it is what I’d generally expect from a dealer shop.


#12

The wrist pin must be removed first to remove the piston from the block.

http://www.rs25.com/forums/f105/t74366-tearing-down-ejxx-block-pictures-head-removal-splitting-block.html