At 08:27 AM 11/10/98 -0800, Walt wrote:
>....
>Limped it to a local mechanic and the result is: Valve job and maybe a
lot more after the head comes off (comment written on estimate - “Valves
were 55-25 compression). Initial estimate (for valve job only) is $ 823.00.
Yikes! That's roughly what it cost me to refurbish an entire engine. This
is where the do-it-yourself type can save a lot of cash. Sweat-equity is
mostly labor time, and time = money, so if you have the time the money
stays in your own pocket. And not so much skill or experience is required
if you can just get a few key answers when you need them, like right here
on this list. If you have a workshop manual and some basic hand tools
you're already off to a good start.
>Well, there is no way I can do that right now and continue to buy food, so
will limp her home and start on the project myself.
Yep, one of the best incentives.
>.... will assemble as much of the list knowledge as I have printed over
the last few months, grab my Haynes, and blithely go forward as if I know
what to do.
Bully! Good attitude.
>.... I’ve read some on the list about “hardened seats.” Is that anything
for me to worry about?
Not to worry about, but when the head comes off for needed work, it is the
right time to think about it. If you plan on putting a lot more miles on
this car, hard seats are a good thing. I have a head with hard seats that
has done 100,000 miles of somewhat harsher than average service, including
much trailer towing and considerable autocrossing. It has gone through
three sets of valves, including most of one set of stellite exhaust valves,
but the hard seats still look like the day they were installed, and the
same head is now going onto the next engine.
Hard seats are about $5 each, plus another $5 or so for the machining and
installation, so all new hard seats will cost you around $80 installed
(depending on who you deal with). Let the shop doing the machine work
procure the valve seat inserts for you. They likely get them cheaper than
you can, and no hassle about wrong parts, material or quality issues. And
if your head has substantial wear on the original seats, it's possible that
some of the seats will be needing inserts anyway. Take this up with the
machinist when you present the head for inspection. If the existing seats
are okay, and you expect easy or average service and less than 50,000 miles
in the foreseeable future, then you may not want to spend the money on seat
inserts.
>Is lapping the valves ok or is grinding them pretty much necessary?
When the valves are far enough gone to cause bad running, lapping is seldom
the solution. At the very least the valves will likely need to be re-faced
(ground on the working surfaces), and you should prepare yourself and your
budget for the possibility that some valves would need to be replaced.
Also, depending on your driving and service conditions and expected life
miles, stellite exhaust valves may be a desirable option. For normal
driving and service conditions, standard valves can be expected to last a
good long time. For heavy driving and/or hard running conditions, stellite
exhaust valves can be expected to last about twice as long as the standard
parts. Four standard exhaust valves will cost about $30 (if needed). Four
stellite exhaust valves will cost about $75.
And if your head still has the original iron valve guides, they will also
most likely be badly worn and in need of replacement. A set of bronze
guides will cost bout $25 more then the iron guides, and the installation
is about the same labor cost, but the bronze guides are another of those
likely once in a lifetime fixes. Again the decision rests on budget
constraints and your expected service requirements. Talk to the machinist
about this when you take the head to the shop, and let them procure the
parts (if they have a source). Bronze guides need a bit more working
clearance for the valve stems to avoid sticky valves, but you want to be
tactful when discussing this with the machinist and not let it sound like
you're telling him how to do his job. Best to ask for his opinion to get
the discussion started.
And if you decide to use bronze guides, those things are self-lubricating
and don't need much oil, so you might consider installing "real" valve
seals to reduce oil consumption a bit. This can also reduce carbon
deposits on the intake valves. With early engines you need to remove the
valve deflector to make room for the new seals. On engines with double
valve springs you may get a charge of a couple dollars per guide to reduce
the diameter of the top of the guide to fit a seal with a smaller OD.
Again, let the shop procure the parts, seals are cheap, maybe $20 for the
set. If you do this, be sure to get the shop to document the work done in
the interest of future service, and get a part number for the seal that was
used so you can get replacement parts in the future.
>Since winter (read that 3" of snow) is already here I would like to get it
back on the road quickly so maybe an interim solution (lapping) would work
instead of a full rebuild. Sound reasonable?
Ah, one of my favorite subjects, Grapes of Wrath repairs. And the answer
is, probably not. However, suppose you're on a really tight budget and
just want to get the valves to seat and seal so you can drive it a while
longer before the hit for the real valve work. J.C.Whitney sells a "Valve
And Seat Facer" for $9.99US. It's a small hand held jig with a free
wheeling grind stone. You spin the valve with an electric drill to grind
the working surface against the free wheeling stone. It actually works
quite well (surprise) as long as the valve head is round and concentric,
and there's enough metal left to clean it up without producing a sharp edge
on the valve head. You can also do a multi-angle grinding job on the
valves with this tool. Once the valve edge is clean, you put a couple bits
of sticky backed sand paper on the edge of the valve, drop it into the
head, and spin it again to clean up the mating valve seat. This also
works, as long as the seat is not too badly burned and recessed into the head.
How long this repair lasts is greatly dependent on the condition of the
valve guides, among other things. The finished valve to seat contact area
should be about 1 mm wide. If the contact patch is too narrow, the valve
may over heat and burn prematurely because of insufficient heat transfer
from the valve head to the seat. If the contact patch is too wide, the
mating surfaces can accumulate carbon deposits because of insufficient
contact pressure, and these deposits can contribute to leakage of hot
combustion gasses and erosion of the valve and seat.
For such a Grapes of Wrath valve job, the work is only warranted by the
person doing the work, you. Having said that, I have performed this
procedure on several engines (not all my own), and in each case have gotten
at least a few more years of continued service (YMMV). But if the valve
guides are quite sloppy, don't expect too much additional life, and you
will still likely have excess oil consumption and smoke.
Good luck and happy tinkering,
Barney Gaylord
1958 MGA with an attitude
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