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Exhaust Gasket
Exhaust Gasket  
So I have a '75 Cb400F that is in very good shape. I bought it to learn how to wrench, so everything is pretty new to me. I know electronics, and rewired the bike with no problem.
So, I did pull a rookie move and accidentally stripped the oil pan bolt when doing an oil change. I read the manual and used a very good torque wrench, but in talking to a couple of vintage honda guys...this was too much. (didn't take into account age, etc)

Anyway, I got a new pan, have been cleaning it out.
Got a new gasket for the pan, and everything looks good there.

To get the pan off though, I ended up removing the exhaust.
There are a couple of really tricky bolts, and I didn't think I could get them off without removing it.

No real problem getting the exhaust off. I've cleaned it up removed some rust, etc....and got some new parts.

Another mechanic in the city here said I should probably replace the exhaust gaskets when I remove the exhaust. (In other forums I've heard the opposite) Anyway, I've tried to remove them, but I really dont know how without damaging the surrounding metal. They are very solidly in there. (Image attached)

I have new ones to replace them with, but should I replace them?
If so, how do I get them out? I've been going at them with a 90 degree pick...but I've not moved it at all.  

Also when I get to putting the oil pan back, I've heard a bit of grease on the gasket is a good idea?

Thanks much!

ANSWER: Chris, those are fine bikes... I have owned about 10 of them over the last 35 years.

In regards to the exhaust gaskets, I use either a long thin flat blade screwdriver or I also have a bent ended cotter pin pulling tool that gets beneath the gasket then I can tap on the end of it and drive it beneath the gasket and then they pop out. You can do that with the screwdriver too.
If you happen to scratch the cylinder head a little, it is okay, as the gasket will mold into the depressions.  

If the gaskets are all okay and sealing properly, you might just leave them in if removal proves to be too much for you. If there are exhaust leaks evident at the flanges, then new gaskets should be installed. The photo you sent looks like the gasket was sealing okay, though.

Either some silicone grease or othe tacky grease might help keep the pan gasket packing in place while you put it up in position.

Bill Silver

---------- FOLLOW-UP ----------

QUESTION: I got them out after swapping to the screwdriver. Just needed a couple soft taps on the handle. The stuck one was the #1 exhaust ,which I found was actually stuck in place more due to a lip in the cylinder mold for the surrounding metal.

So I actually stripped the oil pan origianally by following the manual on foot pounds. Apparently I've been told you have to take age into account here. That said any tiricks to putting the exhaust back in? The pipes didn't seem too tightened down when I took them off. Flanges , collars, anything to should know there?


ANSWER: Chris,

Frankly, I have never used a torque wrench on a drain bolt before. Hand tightened is fine. You just want to secure the bolt against the crush washer firmly. I have never heard of anyone losing a drain bolt in service.

The exhaust is a bundle of snakes. Put a box or jack under the muffler towards the back to help support the weight of the muffler. Some people will put some low-adhesive tape on the headers to help keep the flanges up towards the top of the exhaust pipes, then put the whole system up into the ports. Then you just have to feed in the split collars a pair at a time, until they are all in place. Go easy with the exhaust flange nuts, working them down a little at a time from one side to the other.

Wipe down the exhaust headers and muffler of all leftover fingerprints and grease, etc. before starting the engine.

Bill Silver

---------- FOLLOW-UP ----------


Everything ended up really great!
Oil pan and gasket on with no leaks, exhaust back on and sounds good, everything overall is running well.
Only thing I have trouble with now is getting the muffler attached. It's not stock, but looks very close to the original muffler (I know these mufflers had rust problems). It has 2 bolts that attach to the frame.
The holes look aligned up, but I can't seem to get it to thread....seems like its coming in at a slight angle.

Should I back out all of the exhausts and secure the muffler first?
I tried to loosen the collar where the muffler attaches, but it's not moving / rotating.

As I said it looks completely aligned, I can see right through the holes...but somethings not right.

Is there a trick to this?

Chris, no tricks really, but some of the aftermarket mufflers were made quite right.

Just get a round file or a drill motor and a correct sizes bit and open the slot up a little bit so the bolt holes are perfectly aligned with nut plates.

Don't loosen the header system to get the bolts in. If you do and the bolts do get installed, the rest of the exhaust system will be in a bind and something is not going to fit properly somewhere else. If the header is all secured nice and tight, then just remedy the problem with the muffler. I recall having similar issues with the last CB400F I had. You just have to adjust what you have a little bit. They probably had a bad day at the muffler factory when they made yours. If the muffler nut retainers are rotated out of a vertical plane you will have to get the muffler and header separated so you can change the orientation of the parts. I have some of those lead-shot plastic hammers for nudging parts into place without leaving big dents behind.

Bill Silver

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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