[timotoi]

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!

Tim

 

[longdistancerider]

Drain the oil, remove the starter, clutch ass'y, stator, shift rod and it's ready to split
I use a couple of 4x4's to support the engine upside down.
Start tapping the seam split and work your way around slowly, when it starts to come loose the sound will change to a hollow type sound.
DO NOT try driving anything between the case halves to separate them.
Replace the starter drive pinion shaft O-ring, output seal and shift shaft seal
Use a very thin coat of Honda Bond to seal the cases together, you're only filling minor flaws in the machined surfaces so it takes very little.

 

[longdistancerider]

For the broken bolt file the end flat and center punch it. Use a smaller left hand drill bit running the drill in reverse. With luck the heat and vibration will break it free as the drill gets a bite and back it out. If not then soak it in PB Blaster and let it sit for a couple of hours. Then you can try a screw/bolt extractor, not the cheap ones you find at Home Depot/Lowes/Harbor Freight. If the extractor breaks you're in serious trouble so get quality ones. If it still won't come loose then proceed to use larger bits until the remainder of the threads will come out. Don't over size the drill bits, you're trying to save the original threads here so you don't have to use a Heli-coil or Time-Sert.
If you succeed in getting the bolt out without any case damage then be sure to run a tap into the hole to clean the threads up.
In Fact you should run a tap into all the bolt threads to clean them.
Cleaning the lower case is just scrubbing it out using Dawn liquid detergent

 

[Gixxer-18]

You can't just replace the bottom half, you'll need to get a top half as well, because the crankcases are line bored, and that will get expensive. You can however get the crack welded and spot faced to seat a new drain plug. That's the route I would take.
Just an opinion.
Nigel.

 

[Dabba]

I wonder how tight you need to gorilla that thing to crack it. I wrenched mine down pretty tight and now I'm paranoid. Seems like a feat to do though!

 

[Gixxer-18]

I'm a diver, and we use O rings extensively. If they leak, you replace them. Sometimes on our filling panel, which works at 300 bar pressure, some times the o rings leak. We don't tighten them, we loosen them, and with a Phutt.. They seal. If yours are leaking, don't gorilla them . It won't help.

 

[longdistancerider]

You can't just replace the bottom half, you'll need to get a top half as well, because the crankcases are line bored, and that will get expensive. You can however get the crack welded and spot faced to seat a new drain plug. That's the route I would take.
Just an opinion.
Nigel.

The lower case on these engines can be swapped, that's why I have oil cooler on my 400.
The match machined parts are the upper case and crankshaft carrier.
There is an aluminum crush washer on the drain plug that people forget to change periodically, that's why the drain plug gets over tightened to get it to seal.
The figure 8 O-ring mentioned earlier should also be changed, IIRC David Silver Spares has them.
Also after cleaning the lower case of all the crud I run it through the dishwasher, nice and spotless clean then.

 

[timotoi]

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.

 

[longdistancerider]

#9 in that fiche is the shift shaft seal, the out put shaft seal is found in the transmission fiche
The starter drive O-ring is found in the crankshaft section 91304-216-000 plus there's a O-ring that goes on the starter that would be good to replace, 91312-MG7-003