Honda Twins banner

'78 CB400T II - Questions and guidance on dropping engine to replace bottom crankcase

2437 Views 8 Replies 4 Participants Last post by  longdistancerider
Hey all. Before I've posted about my bike and it's oil leak. PO over tightened the oil drain bolt, and this resulted in a crack along the threads. He/She did a ****ty JB Weld job on it, and it's leaking. The leak has gotten worse over time. I decided that I want to fix this problem once and for all by replacing the bottom crank shaft entirely. I have a few questions about this.

1. Are there any rubber parts I will have to replace once I split the engine? To my understanding, I use the good ol' Hondabond when putting it back together. There is also this figure 8 O-ring on the upper part of the engine, and I'm not sure if I have to replace it.

2. One of the 6x35mm bolts on the alternator cover snapped off, and the screw is still in there. I know that I need to take it off in order to drop my engine. How the hell do I get it out?

3. The replacement bottom crankcase is pretty dirty. What is the best way to clean it?

4. What rubber pieces or other things are on the current crankcase attached to my engine that will come off with it? Can I simply put those things on the new bottom crankcase?

5. What is your favorite way to keep track of all the parts as I go about this? I've thought of cleaning my garage completely, then putting the different parts in a sequential order on a long work bench. I plan on getting pieces of paper and ziploc bags and labeling each along with the torque specification.

6. What do I use to hold the engine up as I am unbolting all the bolts that hold it?

7. Are there any nitpicky things I need to know about? I have the bottom crankcase, Hondabond, inch-pounds torque wrench, and a foot-pounds torque wrench. I want to do this right.

If y'all have any other tips, let me know. I thank you guys for your knowledge, and I will pass it along if anyone ever needs it. This is going to be the main thread for documenting the process so I will continue posting here. Thanks!

See less See more
1 - 2 of 9 Posts
Hey Jim, I'm currently ordering the parts you said I need to get. I did find the figure 8 O-ring on David Silver Spares. I also found this seal. Number 9 on the parts diagram below. I'm not sure if that's the starter drive pinion shaft O-ring, output seal, or the shift shaft seal.
Honda Motorcycle Parts 1978 CB400TII A LOWER CRANKCASE Diagram

Jimbo if you could give a youngster some guidance, that would be awesome. Also, about that bolt that snapped on the left crankcase cover. The hex part that goes on is gone, but the threads connecting the left cover to the engine is still there. The method with the center punch would not work because I need to get to the threads. What is the proper way to do this?

Thanks again.
1 - 2 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.