TOPIC:

Well, I found my problem. The story here is that the bike ran on a Saturday night, but after re checking valve lash and timing on Sunday morning it refused to start and hasn't started since. After chasing timing, cam timing and a couple of other things, I finally got around to testing compression, which had been a bit low but servicable before this problem. The left side was down a bit and the right side was WAY down.

So I pulled off the carbs and pipes to get a look at the ports. From the attached pictures, you can see that something appears to have gone terribly wrong, especially on the right side.

So, it's time to pull the head off of this thing and see what's going on.

Did you verify good spark? A running bike doesn't suddenly die from valve problems unless the valve clearance was set too tight and a valve is sitting open and can't close. But when you take the tank and coil off to get to the top cover, you might ding some wiring that runs the coil.

bountyhunter wrote: Did you verify good spark? A running bike doesn't suddenly die from valve problems unless the valve clearance was set too tight and a valve is sitting open and can't close. But when you take the tank and coil off to get to the top cover, you might ding some wiring that runs the coil.

Not exactly. However, I did verify that my timing light wasn't working.

Actually, what I believe happened is that the right side exhaust valve failed to open fully and as a result I had a fire going on the right side. I had diagnosed poor running as timing and so kept firing it up. Now, if nothing else, the right side appears to be a carbon mess, so opening it up to clean shouldn't be a bad thing (other than the cost of a new head gasket... those things seem to be pretty pricey).

I don't understand why the carbon out way past where the exhaust gasket should be sealing. Am I missing something?

johnbgoos

johnbgood wrote: I don't understand why the carbon out way past where the exhaust gasket should be sealing. Am I missing something?

johnbgoos

That seems to be a fair question. I don't have an answer. When it came apart, the pipe and gasket appeared to be correctly placed.

the right exht gasket, def was not sealing properly.

sounds like u may have a tight valve shimm. i would double check the clearance before u tare it apart.then make sure u have good spark at the right time.

mwriders wrote:

bountyhunter wrote: Did you verify good spark? A running bike doesn't suddenly die from valve problems unless the valve clearance was set too tight and a valve is sitting open and can't close. But when you take the tank and coil off to get to the top cover, you might ding some wiring that runs the coil.

Not exactly. However, I did verify that my timing light wasn't working.

Have somebody hold a spark plug against a head fin while you kick it over.... not a good idea to use the wife.

BTW: the spark plugs on a twin are in series. If either one fouls, it kills the spark in both.

bountyhunter wrote:

mwriders wrote:

bountyhunter wrote: Did you verify good spark? A running bike doesn't suddenly die from valve problems unless the valve clearance was set too tight and a valve is sitting open and can't close. But when you take the tank and coil off to get to the top cover, you might ding some wiring that runs the coil.

Have somebody hold a spark plug against a head fin while you kick it over.... not a good idea to use the wife.


I used one of the kids. It's fun to watch them dance.

The thing is, a timing or spark issue won't explain the sudden loss of compression on the right side. I think that I'm pretty well committed to looking inside this thing and cleaning it up. I should note that I am in possession of a new set of pistons and rings that I picked up several years ago for $35 on a whim. Assuming that the bore is within spec, I could run a hone through there and install those new bits. I kind of see that as fun (go figure) and it's an added motivation to disassemble the top end.

mwrider, how did this all work out for you?

Cheers

Maybe not so well. He hasn't visited this site for the past year and a half. Ed

They never go back together as easily as they come apart. I still don't see why he needed to take the head off based on the photos. He should have at least revisited the valve adjustment (it's just set screws on the 400/440). Very easy to do.

loudhvx wrote: They never go back together as easily as they come apart. I still don't see why he needed to take the head off based on the photos. He should have at least revisited the valve adjustment (it's just set screws on the 400/440). Very easy to do.

+1 !!

I may be wrong, but is seems like a lot of guys can't wait to disassemble things as a first step rather than first checking the most likely causes of a problem. Unfortunately, they often don't put Humpty Dumpty back together again. Ed