How to rebuild the bottom end of your HONDA CB550?  How to assemble the crankcase? How to split the crankcase?  A google search turns up almost no information on how this can be done. Amazingly still, there are no videos on youtube showing the assembly of a CB550 crankcase.   And there are no detailed instructions on how to do this easily and without making some mistakes such as those Chris Jewell experienced when he put together his CB750 crankcase together as he showed in this video.  Kudos to Chris for posting his minor and temporary “blunders”.  It takes guts to do that.

Here are the lessons I learned when putting a HONDA CB550 crankcase together:

Clean everything thoroughly. Clean again. Especially the passage form the oil filter to the oil gallery at the bottom of the crankcase and the oil gallery itself.  Why?  Because the only way any dirt, debris, metal shavings, etc. that can get into the main bearings or the piston rods’ bearings is if they were present in these two spaces.  Anywhere else and they’ll be filtered out by the oil filter.

Clean and wipe dry the two mating surfaces of the lower and upper crankcase. Acetone is very good for that purpose.

Lubricate the main bearings. Ensure no oil or engine lube (whatever you decide to use) ends up on the mating surfaces.  The sealant will not seal well if the surface is coated in oil.

Insert the primary chain and the cam chain on the crankshaft.

Apply oil on all the crankshaft’s journals.

Apply oil on the crankshaft’s oil seals and install the oil seals on the crankshaft. It’s never a good idea to install oil seals dry.

Install the crankshaft into the lower crankcase.

Install the primary shaft as described in the HONDA SHOP MANUAL.

Install the transmission assemblies. IMPORTANT: Install the bearing setting half-rings on the transmission bearings.  See blue arrows in the image below.  Do not install them in the upper crankcase. Ensure the holes in the caps in the assemblies point straight up. See white arrows in the image below.  Ensure their respective lock pins are installed in the upper crankcase.Secure the piston rods in place using wedges or whatever is at hand that is non-shedding because you don’t want any debris to fall into the crankcase. I use short pieces of plastic tubing. See below. The idea is to be able to install the upper crankcase shell without having to work each individual piston rod through the holes in the upper crankcase.  It’s hard enough just positioning the upper crankcase correctly and lowering it into place without disturbing the gasket sealant.  Holding the crankcase with one hand while using the other to work the piston rods though their respective holes and at the same time ensuring that the sealant is undisturbed is like juggling 5 things in the air at the same time.

Here is the important part. Do not apply sealant yet.  Install the upper crankcase. If it does not fit perfectly, remove it.  Do not pound on it with a mallet or anything else. It will be of no use and will likely only cause damage.  Look at the transmission forks and make sure they are not stuck.  Ensure they will line up with their respective grooves in the transmission assemblies.  Ensure the holes in the transmission caps are at 90 degrees up.  Try again.  And again.  Keep adjusting and trying until the upper crankcase fits easily and perfectly when installed.  Repeat 3 times.  Once you have the confidence that everything is perfectly lined up and that the upper crankcase will fit perfectly when installed, you will be ready to apply the gasket sealant.

Apply 1/8” bead along all sealing surfaces. See this video to get an idea of how it is done “professionally” by a robot.

Install the upper crankcase. Gently tap into place.  Install just a single bolt to ensure the crankcase is held securely together.  Flip it over and look through the hole for the oil pan to ensure the transmission forks are in their respective grooves in the transmission assemblies.

Install and tighten the bolts as recommended in the SHOP MANUAL.  No need to worry about the cam chain as so many people seem to do.  You can always “fish it out” once the assembly of the crankcase is complete.  The chain itself is only about an inch away from the opening in the center of the crankcase.

Install the clutch mechanism (just the gear shit spindle, neutral drum stop, etc.) as shown in the image below.

Install the gear lever and shift through all the gears to make sure everything is working as it should.

Finish the assembly.


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