95 Mercury Cougar V8 - Replace valve guides?

If you let it idle for a few minutes, then take off, it pours smoke out
the exhaust for about a minute. Someone told me that this is because
the valve guides are bad. How would you know definitively that this is
caused by valve guides, and if so, what would be the steps involved in
replacing them? I've never done valve guides so don't know what is
involved.

Thanks,
Libby

Libby Chantel wrote:

> If you let it idle for a few minutes, then take off, it pours smoke out
> the exhaust for about a minute. Someone told me that this is because
> the valve guides are bad. How would you know definitively that this is
> caused by valve guides, and if so, what would be the steps involved in
> replacing them? I've never done valve guides so don't know what is
> involved.
>
> Thanks,
> Libby
>

There are two components that both could be at fault: the valve guides
and the valve stem seals. The valve stem seals are small umbrella shaped
seals that fit around the stem of the valve inside the valve spring, and
limit the amount of oil that gets splashed directly on the valve stem.
SOME has to get there in order to lubricate the valve guides (see below)
so the seals aren't 100% oil-tight, they just prevent a flood of oil
from drowning the stem. They can be replaced by removing the valve
cover, rocker arm, and valve spring while holding the valves closed on
one cylinder at a time with compressed air.

The valve GUIDES, on the other hand, are machined metal tubes that press
into the head and form a tight (but not completely oil-proof) seal
around the valve stem. A tiny amount of oil SHOULD continually get past
the guides in order to keep them lubricated. If they are worn, the valve
will have excessive side-to-side movement which can be measured.
Replacing them requires removing the head, disassembling the valve
train, machining the head to accept new guides, and pressing in new
guides, re-installing the valves (in some cases after machining the
inner diameter of the guides to fit the valves) and reassembling the head.

My guess is that the valve stem seals are bad, and the guides themselves
may be somewhat worn but not worn out. I'd try replacing the seals
first, and measure side-play on the valve stems while in there. If the
side-play is too great, the new seals won't completely eliminate the
problem.

Well, the books all say that worn valve stem guides or seals can cause
smoke, but I'm personally not sure how often that happens, except as a
second-order effect in a generally worn engine that has bigger things
wrong with it like rings, badly burnt valves, or induction and smog
controls so knackered that you're dumping in a vastly over-rich
mixture. Certainly if smoke "pours" out rather than just being
noticeable, I think of the bigger things first.

Noting the color of the smoke is certainly an important first step:
http://autorepair.about.com/cs/troub...a/bl303a_3.htm

and so is the condition of each plug vis-a-vis the ubiquitous secret
decoder rings like the one reproduced he
http://www.verrill.com/moto/sellingg...colorchart.htm

Then you want to do a wet, dry, and bleed-down compression test.

With those three sets of data in hand, you're prepared to say
something scientific about what's happening in your engine.

Best of luck,
--Joe

Ad absurdum per aspera wrote:

> Well, the books all say that worn valve stem guides or seals can cause
> smoke, but I'm personally not sure how often that happens,

REALLY often. Valve stem seals are little rubber flaps, rings and valve
guides are machined metal parts. Which do you think will fail first?

> Certainly if smoke "pours" out rather than just being
> noticeable, I think of the bigger things first.

Except that only smoking after an extended period of idling is the
classic sign of valve stem seal leakage, NOT of oil consumption caused
by worn rings. "Pouring" does tend to make me think that BOTH the stem
seals AND guides may be worn, but just getting good seals back on worn
guides can often work wonders.

Another possibility is that the valve guides may be loose in the
cylinder head- but that's most common with aluminum heads and is prone
to happen very often on certain engine designs (Mitsubishi 3.0L v6, for
example). Don't know that its a common happening on Ford v8s- it
certainly was NOT on the Windsor v8s. The Modular v8s- I just don't know.

Ok, maybe I shouldn't have said "pours out". Too dramatic I guess. When
you take off after idling, it leaves a cloud of oil smoke in the air.
the longer it idles, the bigger the cloud. Under normal driving
conditions, it usually doesn't smoke. I am not having any trouble with
fouled plugs, the car runs very good. The thing is, when it is cold
started, it doesn't smoke. I would have thought that the oil would have
leaked down out of the heads into the cylinders during the night and
thus would blow out the exhaust when it is started the next day. Is
this right?

Libby Chantel wrote:

> Ok, maybe I shouldn't have said "pours out". Too dramatic I guess. When
> you take off after idling, it leaves a cloud of oil smoke in the air.
> the longer it idles, the bigger the cloud. Under normal driving
> conditions, it usually doesn't smoke. I am not having any trouble with
> fouled plugs, the car runs very good. The thing is, when it is cold
> started, it doesn't smoke. I would have thought that the oil would have
> leaked down out of the heads into the cylinders during the night and
> thus would blow out the exhaust when it is started the next day. Is
> this right?
>

On a cold start, the oil may sorta stick to the (cold) exhaust manifold
walls and burn off slowly, whereas when the engine is hot it flashes to
smoke much more quickly.

BTW, I got to thinking- this is probably a Modular v8 (overhead cam)
engine. So my advice about changing seals is not nearly complicated
enough :-/

Also, be aware that the Modulars have had a number of problems with some
engines showing excessive oil consumption over the years. I'm not sure
what all the various and sundry issues were, so it might be worthwhile
checking to see if there are applicable technical service bulletins from
Ford.

This is the overhead cam V8. So can you give me the repair procedure
for valve seals? Go ahead, I can take it
And what does "modular" mean? Bad news, no doubt.
Libby

> So can you give me the repair procedure
> for valve seals? Go ahead, I can take it

I wouldn't recommend doing it yourself, especially on an overhead-cam
engine, without referring to a factory service manual or at least a
good aftermarket manual.

Time was, there were some tricks for replacing some such things without
removing the cylinder heads. Never really looked at the issue on a
"modular."

As mentioned earlier, before trying to get too tricky here, I'd also
recommend compression testing and a look at each plug to make really
sure that the engine doesn't have other physical problems that would
require you to tear it down anyway. (And other diagnostics to rule out
the possibility that you're just putting too much gasoline into a
basically okay engine under some conditions.)

See, after ten years and some unmentioned but likely six-figure
mileage, and maintenance and usage unknown to me, its internal
condition could range from just broken in to generally worn and/or
specifically broken in some way, and it just doesn't make sense to
fixate on one symptom and one fix until you're resaonably sure that
that's both the main problem and the whole of the problem.


> And what does "modular" mean? Bad news, no doubt.

The current generation of Ford smallblock V8's, replacing the venerable
5-liter (which has its roots in the early 1960s). The modularity
refers mostly to an extensible design pattern. I think a '95 would be
one of the early ones.

Best of luck,
--Joe

Libby Chantel wrote:

> This is the overhead cam V8. So can you give me the repair procedure
> for valve seals? Go ahead, I can take it

I honestly don't know the specifics for that engine. But its more than
just removing the rocker arms- you may have to pull the cams too. Or
maybe not (see, I SAID I don't know).

> And what does "modular" mean? Bad news, no doubt.
> Libby

The Ford Modular v8 (in 4.6L and 5.4L versions) is the engine family
that replaced the "Windsor" v8 family (302 and 351) in the early 90s.
The Modular series had a pretty rough going in the early years- lots of
reliability problems to get ironed out, but its evolved into a good
powerplant. At the time it was introduced, it had a TON of high-tech
features not found in either GM or Chrysler engines of the time- things
like sintered-metal connecting rods with "cracked" rod caps (the rod cap
is physically cracked off the rod during manufacture so that each cap is
a specific rough-interface fit to each rod), and hypereutectic pistons.
The latter contributed to a lot of TSBs for high oil consumption and
piston slap- something that GM is just now going through with their own
engines that use hypereutectic pistons. The Modular also has some really
pain-in-the-butt features, like using jackscrews to laterally locate the
main bearing caps. And its since been leapfrogged in technology by
engines like Chryslers 4.7 SOHC and especially the 5.7L Hemi, and GM's
Gen-III v8s. But like I said, its not "bad news" anymore.