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Some good comments so far, and I'd like to add/expand/comment on some:
Lisa wrote:
> Should I be worried about: 1) Valve-to-head-chamber clearance, 2) Length of head
> bolts (too long after re-surfacing), and 3) Increased compression ratio (should I
> cc the head and calculate it?). I plan to have the machine shop vat the head.
Hopefully, we're only talking about removing a few thousandths of an inch during
resurfacing. However, on the 230, you should be able to shave quite a bit off without
valve clearance problems, assuming that the head has not already been milled. Just to
be on the safe side, measure the fully raised valve height above the deck, then add
another say, 15 to 30 thousandths for "float factor." (Valve "float" is the distance
that the valve travels beyond the point to which it would normally be raised at a low
engine speed. Float generally only happens at high engine RPM and/or if the valve
springs are weak, in which case the valve gets "flung" up beyond its normal travel
range. However, if the valve springs are OK...and given that the redline on the 230
is somewhere around 3200-3400 RPM...there really shouldn't be much valve float.)
Then, measure how much depth there is to the area of the combustion chamber above the
valve. There needs to be some margin to work with, plus the thickness of a compressed
head gasket. I've heard of people taking .030" (and more) off of a 230 head with no
valve clearance problem, but without going out to measure it myself, I will NOT
guarantee any particular amount as being safe. Perhaps some of the listers can relate
their experience here.
> > <snip>Always use new headbolts if possible. The 230 bolts are cheap, at $1 to
> > $2
> > each, a small percentage of a very expensive engine rebuild.
>
> Yeah, but there are a lot of them! :-) This I must do, luckily the two special
> bolts that have a bolt threaded into them are OK.Should I find hardened washers
> for underneath the head bolts, and has anyone found if headbolts from a common
> engine will work, like say from a Ford 302 or Chevy 350?
If you're on a budget, I'd suggest replacing at least those head bolts that are in
poor condition. The 230 engine's head bolts can be safely re-used, provided that they
were never torqued beyond their yield point. The original bolts are not a
torque-to-yield design like those used on a lot of newer engines. In case you're
interested, many newer engines have "torque-to-yield" head bolts or studs that are
designed as throw-away fasteners. Torque-to-yield fasteners are designed to be
torqued until they stretch to somewhere close to, but not beyond, their design yield
point. These fasteners provide an increased useful elastic range that allows the
fastener to maintain proper tension over a wider expansion and contraction range.
When you torque a torque-to-yield fastener the first time, it imparts some permanent
changes to the metal and perhaps a small amount of permanent stretch. If you remove
and re-torque a torque-to-yield fastener, it can be stretched even further, beyond
its design yield point, which seriously alters the metal and weakens the fastener.
Many of the U-bolts that hold leaf spring packs to an axle are also torque-to-yield
fasteners that should be replaced each time.
> > <snip>One thing that is often overlooked is to renew the "spot face", or the
> > little circular seat
> > on top of the cylinder head that each bolt head tightens on. It's often
> > galled, and prevents proper torquing. There is a spot facing tool for use in a
> > drill press that does a nice clean job.
>
> Yes, a few are really galled. Should the machine shop do this, or can I find this
> bit and do it myself?
That was a good comment about the condition of the "spot face." If the inner portion
of the face is ground away, the bolt will contact the head further out under the bolt
head instead of against the shoulder area near the shank. This will result in the
tension on the bolt being a little lower than it should be at the proper torque
reading. Generally speaking, the smaller the diameter of the bolt head relative to
the diameter of the shank, the less of an effect this will have. As mentioned, these
surfaces can generally be cleaned up without any sophisticated equipment. A few pits
won't hurt much, but if it's quite chewed up, you should resurface it. The spot
facing tool mentioned above should have a pilot shaft that fits snugly in the
cylinder head bolt hole; this assures that the new surface is perpendicular to the
axis through the bolt hole.
I would NOT suggest adding washers to make up for metal removed as the result of
refacing spot faces, unless you took a LOT of metal off and the bolt bottoms out in
the hole (this is quite unlikely). Adding washers can affect torque readings.
> I wonder about using that new red coolant that Chevy uses; straight coolant, no
> water to cause steam pockets. There is no way to put an overflow bottle on, is
> there?
>
> > <snip>I'm not sure why so few folks understand this about the 230. Study
> > the engine and you'll see! One last thing: You MUST use the proper bypass
> > thermostat in the 230. There are a dozen variants that will fit and operate,
> > but only ONE which handles bypass flow correctly in the military engine.
Another good comment about the bypass thermostat. A bypass thermostat allows the
coolant to continue to circulate inside the block while the thermostat is closed.
Without this kind of thermostat, you'll get hot spots and boiling in the block during
each closed-thermostat interval.
NOTE: While it's a good idea to keep the coolant level reasonably high, a little air
in the radiator tank of your M37 (say about 1/2 inch) is actually RECOMMENDED, as it
allows for some expansion and contraction of the coolant, radiator, and block, plus
the inevitable odd bubble production here and there inside the block...without
forcing coolant past the pressure cap and onto the ground (ethylene glycol is a
sweet-smelling but deadly poison). Also importantly, the air acts as a pressure
"reservoir" to maintain a reasonably constant pressure inside the system during
engine operation, which is necessary to keep the boiling point of the coolant higher
than it would be at normal atmospheric pressure. As the pressure builds up inside the
system, air is forced past the cap instead of coolant, keeping the pressure
approximately constant. When the system cools down and starts drawing a vacuum, air
is drawn back into the system through the one-way return valve in the pressure cap.
If you fill the M37 radiator all the way to the top and there are no bubbles in the
system, you will soon have some air in the system anyway, since it would just force
coolant past the pressure cap when it heats up and pressure builds up, and then it
would suck air in through the one-way return valve in the cap when it cools down and
draws a vacuum. So, you might as well just start out with a reasonable amount of air
in the tank. I've found that about 1/2 inch is generally enough to prevent coolant
loss past the cap. Also, the cylinder head is somewhat below the bottom of the
radiator upper tank, so as long as there is coolant in the tank you should not get
any air bubbles in the head. Besides, the coolant flow pattern is out of the bottom
of the radiator and up through the engine block and up through the thermostat, then
into the top tank of the radiator, so once the engine/pump is running, if there were
any air bubbles in the head, they would be purged from the head as soon as the
thermostat opened (or even before, since most thermostats don't seal tightly).
You could also add an overflow tank, which would allow you to fill the tank all the
way to the top. On an M37, there really isn't much advantage in this, other than a
very slight increase in coolant capacity since the air space would no longer be
required.
Overflow tanks have been added for several reasons, but here are the basic ones:
First, many newer vehicles have low-profile radiators with side tanks instead of an
upper tank. The side tanks can't hold much air without the coolant level dropping
below the level of the water jacket in the engine, and in some cases, the tanks may
actually be below the level of the water jacket! On these vehicles, the overflow tank
allows the pressure to build up in the system and force coolant past the radiator cap
and into the overflow tank as necessary to maintain a constant pressure during
operation. Then, when you shut off the engine, it draws the coolant back into the
system through the one-way return valve in the radiator cap, instead of drawing air
into the system. The second major reason for the overflow tanks is that they help
prevent highly toxic...and expensive...liquid from being spilled onto the ground.
If I were you, I'd just leave 1/2 to 3/4 inch of air in the tank, measured when the
system is cold. On the other hand, an overflow tank is not a bad idea, either.
As to what kind of coolant to use, I prefer to use "propylene" glycol-based coolant
instead of ethylene glycol, since it's MUCH less toxic and it seems to work equally
well. When it first came out in the market, it was quite expensive, but the prices
have dropped down lately to where they're more competitive.
Have fun,
Alan
This archive was generated by hypermail 2b29 : Tue Apr 04 2000 - 21:57:08 PDT