I'm an old fart (64) and no problem.
You don't say where you are located - always a good idea - someone might be
helpful enough to stop by.
First interesting point is how do you know that the leak occurs at 2500-3000?
And what are the symptoms - perhaps it is something else.
Any overheating??
What thermostat is installed?
Steps to take. and things to consider.
Compression check on all cylinders with air filter removed. They should all be
equal( though possibly not in your case) and ideally somewhere around 150 or
so. I think factory was 169 for the U20 i.e. lower for the U20 as opposed to
the R16 at @ 181
Is there any coolant loss - typically the overflow tank is full (if the leak
is into the water jacket) You can purchase a kit that analyses the coolant for
oil presence.
Most times the leak appears between #2 & #3 but not always.
If you determine you have a leak then as far as I know r&r is IMMEDIATELY
required (especially for the U20) While I have experience only with the R16,
my understanding is that the U20 head is more prone to warping.
So, access entails at a minimum (some of this may not apply to U20) - so sue
me!
removing intake manifold
loosen exhaust (sometimes you can pull it away from studs sufficiently)
otherwise - remove exhaust
drain radiator
disconnect all coolant/fuel lines
disconnect all cables to carburetors
valve cover
spark plug wires
and anything else that is attached to the head (temperature sender - good time
to also check that it is properly grounded)
Now be CAREFUL
Depending upon whether you have STUDS or BOLTS securing head to block
If studs - then typically the nuts will remove easily.
If BOLTS then it is always (IMHO) a good idea to TIGHTEN the bolt by about ONE
flat, then LOOSEN a flat, then TIGHTEN again. The reason for this is that if
there is rust involved TIGHTENING introduces CLEAN metal to the equation, thus
avoiding the possibility of breaking the bolt (a REAL PITA to resolve). Then
LOOSEN by 2, TIGHTEN by 1 and repeat until you are CERTAIN the bolt is free. (
If you have bolts, it would behoove you to replace with studs when
rebuilding.)
Since the U20 has an OHC, I am not sure what procedures are neccessary for
loosening the chain to allow for head removal - someone more knowledgeable
about the U20 will probably chime in.
Once the head is removed (CAREFULLY) a bit at a time (GENTLY smacking with a
BFH and a wood block should loosen enough (again depending upon BOLT/STUD
presence)
Inspect the gasket on BOTH sides - this will generally give you some clues.
Carbon deposits between the cylinders etc,
Resolution
Now check that the head is FLAT ( or at least within tolerance ) (check 311s
for appropriate tolerances ). If NOT then some milling is appropriate and then
you have to consider the impact on the cam towers. They will need to be
SHIMMED to take up the slack caused by the milling - CRUCIAL. Also note the
milling process (SMALL passes rather than BIG passes on the milling)
New gaskets all round - if coolant related might be a good idea to check the
water pump, had a vicious cycle of head gasket (fixed) then water pump failure
which caused the head gasket to blow again.
On the R16 there are 2 hoses which are IMPOSSIBLE to replace without removing
a lot of stuff. Replace ALL hoses that are inaccessible, regardless of
apparent condition.
While the valve cover is off - good opportunity to polish it and generally
"tart" up all the bits you h ave taken off.
Disassembly - about 3 hours
Reassembly - 4-6
Make sure you are aware of torquing requirements (how much and when to
retorque etc.)
That's my 2c
Hope useful
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