Today I undertook the milestone procedure of resealing the cylinders. The resources I looked at prior to undertaking this were reading the Clymer and Haynes manuals, reading Snowbum’s long article and watching the Boxer2Valve excellent video on this topic. I also watched Chris Harris’s video here.
I started with the pistons. New rings had already been installed so I installed one of the wrist pin clips into the piston. Getting these in is fiddly but I don’t think there’s a perfect technique. I used a screw driver and needle nose pliers. Make sure to avoid aligning the gap in the clip with the removal gap in the piston or you will have a hard time getting them out next time. Also, I had put the wrist pins in the freezer early in the morning.
Next I reinstalled the pistons into the cylinders. I did this from the bottom of the cylinder using a ring compression tool. I set the rings openings at 120 degrees from each other and then applied the compressor. The bottom of the barrel (crankcase side) is actually gently flared making it easier to install the piston from this side. In addition old cylinders can sometimes get a ridge at the top of the piston stroke which could make it harder to put the cylinder in from the top. I applied the ring compressor and dropped it into the bottom of the barrel. At this stage it is CRITICAL to check and double check the orientation of the piston in the barrel. There is an arrow and the word Vorn (german for “front”) indicating which side should face forward. If in any doubt check the valve cutouts on the piston face; the exhaust valve is smaller and is at the front of the head (the THREADED port which takes the exhaust pipe). Therefore the smaller cutout has to face that way. If you get this wrong the valve will impact the piston and….. who knows.
When the piston was correctly oriented in the correct barrel (you marked these conspicuously at tear down- right?!) then I gently tapped the piston down with the rubber handle of a hammer.
With the piston correctly installed into the barrel I returned to the bike. I carefully removed the pushrod lifters out of their holes in the block and inspected the surface that contacts the cam for any pitting. They all looked fine and were smeared with assembly paste (Honda M77) and replaced in the crankcase.
At this stage I replaced the large round O Ring over the cylinder base. It sits in a small groove around the base of the cylinder and you need to insure that is very clean to avoid leaks. I also placed two small o-rings over the upper two studs- the upper two engine studs are also oilways taking oil from the pump to the rocker arms. There are small grooves in the cylinder base to receive these two o-rings. If you are putting things together straight up you can put a little oil on the rings and they will sit in the grooves but they will also start to swell a little committing you to completing assembly in one session. I preferred to just put these over the studs as a “dry run”. I also put the new pushrod tube seals on with the indicator lines facing down.
Next the barrel is slid into position with the cylinder in it. This should be sticking out the cylinder base just enough to expose the wrist pin slot. I then heated the end of the connecting rod with a heat gun and took the wrist pin out of the freezer and oiled it. The pin was then introduced from the side where I had yet to replace the clip. On my bike it slides in with hand pressure (quite a bit of it) but I have also knocked up a simple puller tool to pull it in if necessary- this consists of a threaded rod, large washers and a socket. It’s pretty self explanatory. When the pin was in position against the previously installed clip then the other clip can be put it. Wear eye protection and put a shop rag to prevent it flicking into the crankcase!
When the piston is back installed on the connecting rod the barrel can be slid down to the crank case. At this stage I would normally lightly oil the o-rings (large base and 2 small ones on the upper studs) and apply a smear of sealant to the surface of the base of the barrel and the crankcase (taking care around the upper stud holes which are in fact critical oilways). However if you are doing this for the first time I recommend going through some of the later steps as a dry run and coming back to this before final torquing.
Next the head gasket is replaced with the writing facing out. This has a correct and incorrect orientation – the lower two holes for the pushrods are asymmetrical and if the gasket is on backwards these will be partially covered. Check this before proceeding. Then the cylinder head can be replaced and the pushrods and rocker assemblies.
At this stage I proceeded with the “wet” run. Everything was in place ready to go. I applied a smear of engine oil to the large cylinder base o-ring and also the two upper stud oilway o-rings. Then I applied a very thin smear of Hylomar Blue to the cylinder base mating surface on the crankcase. I was careful to make this very thin indeed around the upper studs as these are narrow oil passages and I don’t want any impediment to oil flow here. I also applied a smear to the pushrod tube seals to act as a lubricant for insertion and then a seal.
All that remained to do was install the heads, the pushrods and the rocker asseblies and torque down the bolts in a cross pattern. The bolts are torqued in stages (15nm, then 25, then 35 for this model). I was pleased to see a tiny film of hylomar come out the seal which I wiped off with a rag. I will leave valve clearance and rocker arm endplay for another day….
