A few weeks ago I reported that my 91 Civic LX (manual transmission, 170k
miles) was slowly accumulating oil in the spark plug tubes. Regular posters
Eric and Tegger proposed that the cause was aging of the O-rings that are
installed between the camshaft holders (also known as "camshaft bearing
caps") and cylinder block, and around the spark plug tubes. They advised on
how to replace them. From the archives, these O-rings do have a record of
failing after mega miles. Not all Honda designs have them, but mine does.
Today I replaced them. Here's the update and sequence of steps I took, for
the archives. Thanks to Eric and Tegger for giving their time a few weeks
ago to discuss this here.
I bought new O-rings from www.slhonda.com . Three of them appear to be
ordinary O-rings. If someone can confirm that the OEM ones are not made from
some special, say heat resistant rubber, then I would be tempted to save
several dollars and buy ordinary O-rings at my local True Value Hardware
store. The fourth seal is a custom design. One can see all the O-rings at
www.slhonda's parts drawings, under "Cylinder Head."
I referred often to two sections in my Chilton's manual, as well as some
notes I copied from this newsgroup. The two Chilton's sections are "Rocker
Arms/Shafts Removal & Installation" and "Valve Lash."
Disconnect negative battery lead.
Block the car's back wheels. Put the front driver's side on a jackstand and
remove the corresponding wheel, for access to the crankshaft pulley bolt.
Put the car in neutral, to facilitate turning the crankshaft.
Partially remove air intake housing so that the one piping connection to the
valve cover is freed.
Remove the valve cover.
Set crankshaft so #1 Cylinder is at TDC of its compression stroke. Use the
timing mark and a long screwdriver or other thin rod in #1 spark plug hole
to feel for the piston at TDC. I also watched #1 cylinder's intake valve
springs operate over a few revolutions of the crankshaft to identify when
intake, and subsequently compression, were taking place.
Loosen the lock nuts on all valves. Chilton's says to do this "two turns at
a time, in a criss-cross pattern" to prevent damage, because the springs of
the assembly are still loaded, and tolerances are close. Ultimately back off
the valve lash adjusting screws at least until they become difficult to
turn. Eric said to back them off until flush with the rocker arm, but I didn
't like the resistance I was feeling, and so just made a large gap. (Before
messing with the valve lash adjusting screws, I took some quick measurements
of the lash ( = air gap between rocker arm and valve stem). They've never
been messed with before, so I wanted to have a feel for how my gage would
Loosen the 16 camshaft holder bolts in the opposite order that one is
supposed to tighten them. (See a Chilton's manual or www.autozone.com 's
free repair guides.) Loosen them like a half turn at a time, so the camshaft
isn't distorted by the force of the assembly's springs. (This may have been
overkill on my part, but I wasn't sure, so. )
Then came the toughest part of this job: Freeing up the rocker arm/shaft
assembly. It doesn't just lift off. The old oil and perhaps the seals I was
trying to replace were baked into place after 14 years and 170k miles,
gluing the thing down. I tapped and pried a bit. Use a rubber mallet,
because the metal used under the valve cover is very soft. Tap, don't bang,
because the camshaft lobes are mated against some of the lobes on the rocker
arms, and tolerance are close. Tap in a lengthwise direction and pry only
upwards. Tabs are on the outer corners of the two end camshaft holders that
might help you to pry. A 12-inch crowbar ultimately freed one end. Then I
found some more places to pry and it came off pretty easily.
Removing the top half of the timing belt cover (two small bolts) might give
you a bit more space to pry and so free the rocker arm/shaft assembly.
Once the assembly was freed up, it wasn't too hard to maneuver it out, with
all the bolts still in place like Eric and Tegger said earlier, and walk it
over to a bench. Just don't turn the assembly sideways or upside down; then
the bolts will fall out, and the assembly may come apart, whence I suspect
life as you know it will end for a few days.
I never actually set the valve lash before. Doing 16 of these is tiresome
but got easier with each one. I double-checked (maybe triple-checked) that I
had a feel that seemed right with the feeler gage. I aimed for the center of
the specification but am sure I could be off by the 0.001 inch tolerance
(but not more than that) allowed. (E.g. the intake valves are supposed to
have a gap of 0.007 inch to 0.009 inch. I used the 0.008 inch feeler gage
but tried to go a little tight.)
The archives have some chatter about having to detension the timing belt to
remove the camshaft holders. On the other hand, the Chilton manual's steps
for removing the rocker arm/shaft assembly said nothing about this. Chilton
manuals are not perfect, so I still prepared to at least loosen the
tensioner adjusting bolt and so detension the timing belt. Getting the
rubber blanking plug off to access this bolt was not looking easy.
Fortunately and ultimately, I found doing so wasn't necessary. I did jiggle
the crankshaft a little (five degrees?) clockwise when I was trying to free
up the rocker arm assembly, thinking the timing belt was holding the
camshaft lobes fixed and so making it harder to free up the rocker arm
assembly. I thought turning the crankshaft a little clockwise would tend to
detension the timing belt. I don't know if that was really necessary.
Altogether this took about seven hours. I went very slowly and took breaks
whenever I felt tired or a bit annoyed (really, only when trying to free up
the rocker arm assembly), because doing so keeps me alert and less likely to
say things I don't want to hear the neighbor's kids repeating.
I took one short test drive and am now going to let 'er rip on a grocery
run. My biggest concern is that I didn't set the valve lash well.
My experience level and assessment of the difficulty of this job: In the
past, I have replaced the timing belt and also checked (but did not adjust)
the valve lash. I have had the valve cover off many times before, usually to
replace its gasket. I'd call the "camshaft holder spark plug tube seal
replacement" an advanced beginner or intermediate-level job.