broke a spark plug... lots of backfire

[peterman]

While checking my plugs one night I pulled one out noticed it was black (expected as much) and then put it back in. While screwing it in, it broke, it was still warm (yes I'm that much of an idiot at times). Anyway I was able to use some needle nose plyers to get the threaded portion of the plug out. I looked to see if the plug had any parts missing, I couldn't find any. However Since then I have gotten a lot of backfire and now it won't even start.

I am concerned that there was a piece that fell into the chamber and has caused me to lose compression.

Any ideas?

1982 Yamaha xs400

[BuzZz]

It's possible you did indeed get some plug-guts in the cylinder. Best take a compression test and see if that cylinder reads abnormally low. That should tell you if you buggered anything.

[peterman]

What's the best way to remove the cylinder head from the cylinder? I've checked diagrams and appear to have every bolt off. I am sure it has just seated itself over time. Is there a good way (not going to do more harm than good) to remove the head?

[TechTMW]

Dude.



Did you do a compression test?

You can use a rubber mallet and knock on the head to loosen it up a bit, but there is usually one bolt that you just haven't gotten.

[peterman]

I didn't do a compression test. But I am getting almost no air out of the spark plug hole, whereas I know I was getting a noticable gust before the sparkplug broke.

I am also interested to see what I got going on in there. If the cylinder walls are scored or the piston rings are worn then I may consider boring the engine and getting the larger pistons that are available.

[mydlyfkryzis]

Before pulling the head, you should of checked the valves. Maybe a valve is hung up.