Ok Matt, I'll bite. I'm sitting here not doing much today.
First. I am conservative.
Second. I am cheap.
Third. I have put over 400,000 miles on various B series engines.
Fourth. I am lazy and prefer to drive rather than maintain my car.
Observations
Smog port B series heads are prone to cracking. I have not figured
why, but I will lay odds poor maintenance has something to do with it.
B series exhaust valves tend to burn. Again, I think poor
maintenance has lots to do with this too.
Suggestions:
1. If it aint broke, don't fix it. I have put over 40,000 miles on a head
that was so cracked, I had to protect the distributor from water spray with
a cardboard box. Typical #3 sparkplug cracks will not kill an engine, and
it will continue to be drivable. Once heated up most cracks will seal and
only weep slightly.
2. Before doing any machine work, get the head crack tested. Machined junk
is still junk.
3. Correctly repaired cracked heads are more expensive than buying a new
aluminium head. And the repaired head will not look or run as cool.
4. Any used head is probably going to need exhaust seats. Assume the
worst.
5. A used head is worth $175-250 with a warranty of being crack free. If
you buy a head without such a warranty, I have some swampland for sale, it
may or may not support a building.
6. The original valves were adequate for unleaded fuel, as were the seats
cut in the head, and the cast iron valve guides. Any one who tells you
differently will also suggest esoteric magnetic devices to attach to your
fuel lines.
7. The original head design was good for about 40,000 miles given correct
maintenance.
8. Correctly adjusted valves and carburetion reduce the likelihood of burnt
exhaust valves.
9. Hardened seats and stellite valves should give longer life than the
originals and will be less likely to be damaged by poor maintenance (this is
a good thing).
10. Incorrectly sized bronze guides will bugger up your nice new engine big
time (this is not a good thing).
11. Bronze guides can corrode with lack of use, seizing the valves and
resulting in the bad thing.
12. I have never had a complaint of cast iron valve guides resulting in a
bad thing.
13. Short of a valve head falling off, most head problems do not result in
instant undrivability. This does not include head gaskets which have a
party life of their own. This also does not include the bad things listed
above.
14. You can drive around with a worn out head until the smog man gets you,
or you get passed by too many Volkswagons.
15. If the valve guides get bad enough the Volkswagons will not be able to
see to pass you.
16. Heavy valve springs allow the engine to rev to destruction and will
decrease the life of the valve seat.
17. If you have the time to port and polish the head on a street car, you
should be more responsible with your time.
18. The time between valve jobs is directly proportional to your ability to
set valves, carburation and timing.
19. A correctly torqued head is a happy head.
20. No matter what you do, expect coolant seepage between the head and
block on the distributor side. If there is no seepage, check coolant level
immediately. If the level is correct, be very happy and tell us all about
it.
21. There are two types of valve seal normally available. One is an O ring
and comes in the head gasket set. Somehow it gets squeezed into the top of
the valve guide. Seems like magic to me. The other type fits over the
valve guide and makes sense. Neither do any good if the guides are not
machined correctly.
22. In 73 the heads came with a 1.625" intake valve. All others use a
1.562" intake. Zenith carb heads have a water port at the rear. Late water
port and some UK heads use an offset oil hole rear rocker pillar. Apart
from that everything interchanges. Water port heads are worth lots because
most Zeniths were never adjusted correctly, and the later cooling systems
didn't for a number of reasons.
Hopefully these pearls of wisdom are helpful. My suggestion for
your situation at this time is to locate a crack free used head, or cough up
the money for the new alloy one. Figure that the used head is going to need
at least a couple of valve seats. It is just as easy to install all of them
and quit worrying. Stellite is the way to go on exhaust valves. Standard
valves supplied mail order may not be to the original AE spec. I am very
torn about valve guides. I have had too many problems with them to be
really happy. For ease of mind I would install cast iron, unless there is
someone out there who has a machining spec which they guarantee will not
seize. (I do not care how many people have gotten away with using
something. I want the exact tolerance their machine shop used!) I am not
going to give a preference on valve seals. Tight guides need the
lubrication. Loose guides need the sealing. You can put the seals on the
intakes only as per Jag. Leave them off as per Triumph. Or anywhere in
between, it depends on the clearance in the guide.
Ok enough for now. Lets see what others think.
Kelvin.
> -----Original Message-----
> From: Gaetke [mailto:gaetke@ix.netcom.com]
> Sent: Sunday, January 10, 1999 12:16 PM
> To: mgs@autox.team.net
> Subject: cylinder heads
>
>
> I guess I've found an opportunity to show my ignorance.
> I know little to
> nothing about cylinder heads, and their various options. I
> guess this is
> the time to learn, being in the market for one, so here goes:
>
> What are the advantages of (and what type of driver should get):
>
> bronze guides?
>
> hardened seats?
>
> stellite exhaust valves?
>
> Do valve seals just cut oil consumption, and do they
> require any of the
> above modifications to be made practical? Worth it?
>
> What does one do to a head to make it ready for unleaded fuel?
>
> If the main advantage to all of these things is a
> longer time between
> valve jobs, how long does a valve job with none of these
> features last?
> with all of them?
>
> If it matters, I'm not going to put a ton of miles on
> this car each year,
> but those miles will include four drives of 900 miles to and
> from school,
> so my primary concern is failure during a long drive. In
> fact, that will
> make up a large part of the mileage put on the car each year.
> How does
> that effect what I should be done to my head?
>
> I want long and detailed answers! :) I know some of
> you have to be
> passionate about cylinder heads... I feel like I need my own head
> magnafluxed (couldn't resist the pun).
>
> TIA,
>
> -Matt Gaetke
>
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