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
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 read, etc.)
Loosen the 16 camshaft holder bolts in the opposite order that one is supposed to tighten them. (See a Chilton's manual or
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.