You can do a static pressure test on the system. The tester is a
modified radiator cap that air can be blown into. Blow it up to
5 PSI or so and see where it is leaking.
The water pump pumps water into the engine. It is possible to have
a leak in the lower raiator hose or heater hose that allows air into
the system but doesn't let water leak out. This may also be a symptom
of a plugged radiator. The key here is that you were using the old
hoses and the old engine did it too. This can be especially bad
if the lower hose collapses. I would suggest running a little pressure
on the system. Don't know what your radiator will stand up to, but
5 psi should help.
Since you are running without a thermostat, I would assume this is
not trapped air in the head suddenly coming out.
I would assume that you checked for a warped head. Did the head
gasket you replaced show any signs of damage? Usually a blown head
gasket shows some obvious damage when the head is taken off.
Only three ways air can get into the cooling system. The first is
a blown head gasket. The second is a cracked head or block. The
third is through the suction side of the water pump when the system
is at 0 pressure.
Good luck. Let us know what you come up with. There is very little
that Chevy designed in these trucks that can't be explained or thought
through.
Bruce K
57 3200
Mt. Iron, MN
At Sunday, 25 August 2002, you wrote:
>This is a fairly long post and explanation. Any good mechanics.
.please
>take the time to read - I REALLY need your expertise and experiences.
I
>have two days before I have to get this on the road for a 10 hour
trip, and
>am running out of time. As much as I hate to even think about it, if I
>can't get this solved, I am seriously thinking about selling the
truck. I
>just spent almost $900 to rebuild the new engine, and am now where
closer to
>fixing it than before. I can't afford to keep throwing money at
a problem
>that doesn't seem to me to be solvable.
>
>Well, I am absolutely and totally at a loss as to what is wrong.
During the
>breakin, I followed the advice I've always heard as to how to break
in an
>engine, ie. to run it up to around 2000 rpms, and let it sit there
for 15-20
>minutes. So I did that. Everything seemed to go pretty normal.
The temp
>gradually got up to 190 or so (no thermostat yet installed), and
held there.
>I didn't see any small bubbles during this time and just before
the end of
>the 20 minutes, I put the radiator cap on. BUT, as I reached the
end of the
>break in, and as I reduced the rpms to idle, all of a sudden the
water from
>the radiator started spewing (with sufficient force to shoot to
the fender)
>out under pressure out of the overflow tube at the filler neck (cap
is a
>zero pressure cap). I immediately shut down the engine, and looked
inside
>the radiator and saw nothing of concern. I started the engine again
and
>gradually added water so it wouldn't be hit with a large volume of cold
>water at once. That went fine, but at idle, I am seeing the same
damn small
>bubbles!
>
>As some may recall, I originally rebuilt the 235 because of bubbles
in the
>radiator and pressure getting into the water system (I had a thermostat
>installed and when it hit opening temperature, a rush of water and air
>caused the radiator to volcano. I had originally suspected a blown
head
>gasket was allowing air to enter the system, causing it to not only
>overheat, but was the source of the air getting into the system
which, when
>the thermostat opened, allowed this air to rapidly escape and cause the
>volcano effect. So I put on a new head gasket, but the same problem
was
>there. So, suspecting I may have messed up the head gasket somehow
when I
>put on the head (I did it myself and thought I might have somehow
scored the
>gasket while setting the head on), I tried again with a new head
gasket, but
>before that, I took the head and had it magnafluxed and surfaced.
.but after
>putting on the head and new gasket...same thing, same bubbles and air
>getting into the water jacket. So, suspecting a cracked head (as
235 heads
>are prone to do) and that was missed by the machine shop, I found a
>replacement engine (thanks again Skip) to use the head. I took
that head
>and had it pressure tested and the surface checked...it checked
out ok. So,
>now the third new gasket went on with the second head. Same problem.
That
>pretty much, at least in my mind, left only the block as being the
>cause....so out with the engine, and I began rebuilding the engine
I got
>with the replacement head.
>
>The "new" block was able to be bored to .040...I also had the crank
turned
>to .010. Anyway, I put in new pistons, bearings, timing set, cam,
lifters,
>and everything was within specs. I mic'd everything, and also used
>plastigauge to be sure. All clearances (bearing and rings) were
perfect.
>So, I don't think anything was wrong with the machine work. I am
getting
>good compression on all cylinders and all within acceptable range.
>
>So, I have now rebuilt the engine with new everything at least internally,
>and am still at the same point I was at in the beginning, ie. with
small
>bubbles getting into the water system, and judging by the way the
water shot
>out when I dropped the RPMs after the breakin, I suspect the system is
>building up pressure somehow. The water pump is the original pump,
and all
>hoses are the ones from the old engine.
>
>I have to believe my rebuild was done accurately. I followed torque
specs
>to the letter, and torqued the head following the torque pattern in the
>manual, and did it in 3 stages. I took my time and was always careful
and
>thorough. The last time I rebuilt a 235, it was able to do two
crosscountry
>trips and all was good (until this saga with the bubbles and overheating
>began), and have never had any other engine rebuild go bad. I consider
>myself a pretty good mechanic, and follow the manual to the letter.
This
>problem has me totally stumped.
>
>Assuming then that all the machine work was done correctly (block
boring and
>head checking), and my rebuild done correctly, where else might air be
>entering the system? Could it be coming in from the water pump
even though
>the pump is showing no signs of an external leak? Could it be coming
in one
>of the hoses and not show any external signs of a leak?
>
>The system is a zero pressure system...so, my thinking is that maybe
somehow
>air is able to be sucked into the system, but since the system itself
>doesn't build up pressure, it is not "squeezing" water to the outside.
.just
>sucking air. Does this make any sense to anyone? If so, how do
I determine
>what is behind this if not the head or head gasket? Can the system be
>pressurized to see if the reverse occurs, in other words, if air
can get
>into the water jacket, if the system is pressurized, could it cause
water to
>follow the air path?
>
>ANY thoughts are VERY much appreciated. If anyone wants to discuss
this in
>person, my phone number (cell) is 360-551-2490.
>
>Thanks for your patience with this long post and in advance for
any help you
>can offer.
>
>P.S. I am thinking of going ahead and replacing the water pump and all
>hoses, but know I need a shortshaft water pump, which is not generally
>available at the local auto parts but has to be ordered from one of the
>truck vendors, but unfortuantely, I don't have time now to wait
for it to be
>shipped. SO....if I buy a long shaft at one of the local stores,
can't I
>simply have the plate that the fan and pulley mount to, pressed
down the
>shaft and then have the excess cut off? If so, as I suspect I can, can
>anyone tell me how far down to have the plate pressed (ie. when
to stop so
>that the pulley would line up).
>
>Rob
>----- Original Message -----
>From: "Rob J." <robertjacobs@ureach.com>
>To: <old-chevy-truck@yahoogroups.com>; "_Oletrucks"
><oletrucks@autox.team.net>
>Sent: Saturday, August 24, 2002 1:39 PM
>Subject: [oletrucks] Engine troubles
>
>> Got the 235 rebuilt...build went just fine. I got it dropped in just
>fine,
>> but am having trouble firing it off. I am getting spark, good
>> compression...checked all cylinders and they range from a low
of 105, to a
>> high of 113. I suspect it is either a timing issue, or carburation.
I
>have
>> the rotor set at dead TDC for the #1 cylinder...checked and rechecked
my
>> valve lash, but it just won't fire...actually, I am getting combustion,
>but
>> I just can't seem to get it to sustain and run on its own. As
long as I
>am
>> pumping the gas, and using the foot starter, it is hitting, but
as soon as
>I
>> let off either, it dies.
>>
>> The previous engine was a 235 overbored to .060 and was running dual
>> rochester 1 bbl carbs. This new engine is only a .040 overbore,
and set
>up
>> with the same carb set up. I suspect it may be running a bit
rich since
>> there is less total displacement, but should that be enough to
cause it to
>> just not run at all?
>>
>> How can I check various items to see what it needs to run right?
>>
>> I have a single intake I could put on, and could put points in
instead of
>> the Pertronix I am currently using (forgot to mention I was using a
>> Pertronix dist on the last engine and it has moved to the new engine.
>>
>> Any thoughts or what I can try to maybe lean out the carbs without
>resorting
>> to changing out the jets (ie. just to see if that is the problem?).
>>
>> I put new spark plugs in (correctly gapped) and the rotor and
dist. cap
>are
>> nearly new.
>>
>> I have to get this running as I am due to drive to Idaho from
Seattle next
>> Wednesday.
>>
>> TIA,
>> Rob
>> oletrucks is devoted to Chevy and GM trucks built between 1941
and 1959
>oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
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