740 rattle noise on deceleration

Hi all:

Thanks to all who commented a couple of years ago on a flashing oil
light. I tried a different oil pressure sensor; and it's been fine
since.

Now, the 86 740 turbo has a new rattling noise, mostly on
deceleration. Seemed to happen after I drove it harder than normal in
a rush to make an appointment. Different than the piston slap I'm
told is normal for these engines. Sounds high in the engine. One
mechanic thinks it's time for a new (used) engine. (He found one noise
in a contact in the alternator, repaired it but that wasn't it.) This
mechanic has been good, but is sometimes a bit of a pessimist.

Another mechanic thinks it's valve dampeners, about $200-400 to
replace depending if it's top and or bottom (?), but says there is no
immediate need to.

I'm not a mechancic by any stretch, just looking to make the right
choice.

Thanks!

L

 

Could it be a loose heat shield or the finger guard on the alternator belt?

 

I will ask. It sounds more like something in the engine than on it to
me though. More like a 'knock' than a 'rattle' really.

 

That usually makes a pretty distinct gurgling popping noise, my 242 was
doing that while I was getting megasquirt tuned up.

 

Sometimes engines that are running rich will misfire on
deceleration, as the extra gas detonates at irregular intervals. Older
hotrods and race cars did it all the time. Check your fuel system.

 

Thanks for posting. The rattle/knock is very regular; every
deceleration, same sound, rate seems matched to rpm; ie slower as rpm
drops.

 

That probably rules out both misfiring and a loose heat shield. It
does indeed sound mechanical.

 

Hi all:

Update. Booked the car in for the valve dampener job, but the
mechanic says it has gotten worse and is not the valve dampeners, it
is likely piston wrist pins. He says he can't fix it, maybe time get
a new car. But he wasn't sure it was wrist pins.

While looking at a used 99 v70, the owner turned out to be a retired
mechanic, (mazda I think). Listened to it and said he thought it
might be the cam shaft (a flattened section?) instead. It sounded
like it might be more repairable than the wrist pin problem. He's
checking around for an acquaintence that might be able to do it.

In the meantime, does this sound likely?

On another note he said the knocking sounded like one cyclinder only.
Would that make the problem, even it's wrist pin, more fixable?

More info: knock is almost always present now, quite distinct at
idle. It does seem to dissappear when cruising at 1500-1600 rpm, with
the motor pulling; lifting off the gas brings it back. Does that say
anything?

 

Could be piston slap perhaps, it's hard to say without getting in there.
If it were me, I'd just grab a junkyard motor and swap it, those are
cheap and plentiful, at least around here, but it helps that I have
access to a hoist which makes a motor swap a simple weekend project. No
idea what it would cost to pay a mechanic to do it.

 

Has the mechanic ruled out a valve / the valves being out of
adjustment?

 

Both non-dealer volvo specialists in town have ruled out piston slap,
or rather, say it's in addition to the existing piston slap. Another
shop is indeed recommending replacement, but they have a all-Volvo
salvage yard which made me wonder if the diagnosis was made partly
because they have engines to sell. Estimated cost is about $3000
cdn. (I'm not even close to being able to do anyhting like this
myself, though it would be fun to learn.)

 

I think so. Aren't the valve dampeners related to this? The guy who
thought it might be that, ruled it out.

 

Yeesh! That's a lot of cash! Prices on used motors vary widely, several
U-pull yards around where they're only $150, but it can be tricky to
pull one at a yard. I've had to get creative with 2x4s, rope, and a few
guys to help. Worst case I guess you could sell the car to a shadetree
mechanic type.

If the noise is getting worse that's not a good sign. It's possible you
might have a loose connecting rod cap, if that's the case you'll find
out pretty soon because it'll rapidly get more loose.

 

I wish I had your skills. Now I'm looking for a newer 740 or 940; at
least I will be able to use my third seat, dog/luggage gate and snow
tires in those. Unless I get lucky with a lead on an engine repair
under $2000.

On that note, Is $2000 too much to spend? Is $3000? I have done the A/
C (redone to modern standards), clutch, fan motor, timing belt,
brakes, turbo hoses, and a bunch of minor stuff in the last three
years. No rust. Does it make sense to get more use out of that
before I give up?

We're kind of stuck with volvo wagons too, because we have two kids
and like to ski, cycle and kayak. Any other vehicle has smaller
luggage space (39 cubic feet vs about 34 for accord, passat, camry or
legacy wagons. New v70's are down to 33 cubic feet.) or too high to
reach the roof to load stuff on the roof. Don't need or want 4wd. And
camping and mountain biking with four people, we're packed to the roof.

 

Update. The quote on a replacement engine seems to have come down.
Another mechanic, who can't do the work, says that a non-turbo motor
is a better option for longevity; he recomends the 92-95 740 or 940
also because they had better lubrication of the pistons, which he says
leads to less chance of piston slap. It requires changing the
computer, but that has to be done anyway with the wiring harness.
How's this sound to you engine swappers?

 

Putting a non-turbo motor in a turbo car sounds stupid. Just how much
longevity do you need? I know of several Volvo turbo motors with over
300,000 miles on them, my own is at 293 something now. If you maintain
it properly and don't beat the crap out of it every day it will hold up
longer than the rest of the car, and there's no screwing around changing
computers, wiring, exhaust, intake, etc and you don't lose all that nice
power and end up with a half-assed hack job. If you're gonna spend the
money to pay someone to do the job, then do it right, otherwise sell the
car and buy a different one.

The '92- turbo motors have piston cooling oil squirters, some of the NA
motors did too, but in most of them have plugs in their place. They are
nice if you are building a hotrod motor, but not really necessary for
normal use. I wouldn't turn down a deal on a late turbo motor if I found
one, but I wouldn't insist on one either.

 

Thanks James. The shop that would do the work thought a non-turbo was
dumb too.

They have a 91 turbo 740 motor from a car with 250,000 km. 90 day
warranty. Not much info on the car. The garage is part of an outfit
with an all-volvo wrecking yard that would supply the motor.
http://www.chapmanmotors.ca/ . What questions can I ask about the new
motor, before I commit, without annoying them?

 

Not really sure what there is to ask. Obviously it should be leak-free,
seals should be replaced while the motor is out and accessible,
compression test would be good, and there shouldn't be any funny noises.
A used motor is always a gamble when you haven't had it open.

 

I was going to suggest throw in a can of STP and run it until it kicks
the rods out. May run six months or a year...
Then put a new bullet in it.
But I see you're up where it's cold. Don't want to get stuck on the side
of the road when it's freezing out.

 

I would also recommend pulling some things apart and having a look
before replacing the motor. Could be something simple, loose rod cap
bolts, bad bearing, something that could be replaced without pulling the
whole motor.