Hi All!
I know it has been a little bit since my question, but work took me away from the project until just this last week. So here is an update on what happened:
I did pick up the GRABIT set from Lowes and some new 1/4" x 20 bolts (and washers to match). I bought the GRABIT set that had the three bits #1, #2, & #3 and the instructions said to use #2 for a 1/4" bolt. For those that haven't used these GRABIT bits, the idea is that one side of the bit is the cutting side which you are supposed to use to drill a hole (using the drill in REVERSE) into the CENTER of the broken bolt at least 1/16" deep. Then you take the GRABIT bit and flip it around to the other side of the bit (the "GRABIT" side) and slowly drill it in REVERSE into the hole you previously drilled in the center of the broken bolt until it catches and backs the broken bolt out.
The first challenge I had is that the GRABIT bits are too short for the cutting side of the bit to reach the broken bolt without my drill hitting the valve rocker arm. I tried a 6" magnetic drill extension, but the bit was too wobbly in the extension to be able to cut into the bolt. Then I tried some left-hand drill bits to try and cut the hole in the bolt since they were long enough to reach the bolt over the valve rocker arm. But because the bolt was uneven where the bolt broke off, I couldn't get the drill bits to stay in the center of the bolt and start cutting. They kept shooting off to the side.
So, I got out my dremmel kit and grinded the bolt down to be flat and smooth (the bolt was sticking up above the head enough to do this). Once I did that, then I was able to get a drill bit to stay in the center of the bolt and drill a nice hole in the broken bolt. I would suggest using a center punch to make sure you have a nice indentation in the very center of the bolt to start drilling in. Also, I made sure to have some rags laid out around the bolt to ensure that none of the metal shavings from the drilling went onto the valve rocker arms or down any of the oil holes in the head.
It seemed that getting that nice hole in the center of the broken bolt was the hard part. Once the hole was there, I was able to take a 1/4" T-handle tool to put the "grabbing" end of the GRABIT bit into the hole in the bolt and slowly start twisting the GRABIT bit by hand counterclockwise until it finally caught and "grabbed" the broken bolt and started turning the broken bolt counterclockwise and backing the broken bolt out of its hole. Once the GRABIT bit grabbed, the broken bolt came out pretty easily. So the broken bolt was out!
However, that wasn't the end of it. While trying to test out the new bolts I bought in all of the valve cover bolt holes, I noticed that the threads in one of the other valve cover bolt holes was completely stripped and all the broken threads had fallen to the bottom of the bolt hole. Luckily, I had a friend there helping me and he had one of those telescopic magnets (looks like an old radio antenna, but with a small magnet at the end of it). We used that and got all of the stripped thread pieces out of the hole.
Most of you probably knows what came next. I had never used a helicoil before, but we ran out and got a helicoil kit for 1/4" #20 bolt holes and a 17/64" drill bit (as it did not come with the helicoil kit). We used the 17/64" drill bit to drill the existing stripped bolt hole to the 17/64" size (once again making sure no metal shavings got into the valves/head/engine). Then used the special tap from the helicoil kit to slowly create the threads for the helicoil to go down into. Once that was done, we slowly screwed the helicoil into the newly threaded hole using the tool from the kit and then backed the tool out. The helicoil was sticking out above the top of the surface of the head as those valve cover bolt holes aren't that deep. So we took some wire cutters and cut off the helicoil so that it was flush with the surface of the head. I tested one of the new bolts in the newly helicoiled hole and it went in easily with no issues!
We tested that all the bolts went nicely into all of the valve cover bolt holes, so we put the new gasket on the valve cover let it sit for a bit so the sticky part of the valve cover gasket would stick to the cover and not fall off when we flipped the valve cover over to install it. We set aside ALL torque wrenches and just used a 1/4" socket wrench to slowly tighten down each valve cover bolt in a star type pattern until they were just snug. We then went around to each bolt and snugged them down just a tad more so they were tight but not overly tight like before as I can see with the ridge on the alumnium head where the valve cover sits would definitely tear the valve cover gasket when you tighten the bolts down too much (not to mention that bolts break and threads strip!).
After all of the above, I'm happy to report that I've run the boat on Lake Washington a couple times (after testing on the muffs first of course) with no oil leaks from the valve cover at all!
Sorry for so much detail, but I'm hoping that it may help out some other newbie like me if they encounter a similar issue while trying to replace a valve gasket on these Mercruiser 3.0L engines. Thanks again to everyone for all of the help and advice!
Kekoa
1995 Bayliner 1850 Capri Bowrider
Mercruiser 3.0LX / AlphaOne Gen II Outdrive
