[midwest_eng]

I went to start up my 1979 CM400T yesterday and she wouldn't start. A little firing, but no combustion. I eventually noticed that the cylinder head around the right side spark plug had a bunch of white residue around it so I took out the spark plug and a helicoil insert came out with it, wrapped and tangled all around the spark plug. I had replaced this spark plug when I bought the bike last summer but at the time I didn't know what a helicoil was and didn't notice it in there. It's very likely that I wiggled it loose during that initial spark plug replacement and it just now got loose enough to where I was losing compression and the bike wouldn't start (plausible?).

There is also a hole near the bottom of the machined surface around the plug opening, is this a concern?

Both plugs seemed a bit black, so I will look into leaning out the fuel-air mixture after I repair the plug hole.

My main questions are on the Time-sert. I contacted Time-sert and they said that the regular spark plug repair M12x1.25 won't work for me because of the previous helicoil, and the M14x1.25 which is designed to go over previous repairs is in fact a 14 mm inside thread, so that won't work for my NGK D8EA's. They said that the regular thread oversize repair may work but it's not spark plug specific.

Any thoughts are appreciated,I read quite a few of the spark-plug-issue threads here in the past couple of nights and it seems like the Time-sert is my best option. I did recently learn to TIG weld but I'm a major amateur and I don't think I want to try welding this hole on my own to re-tap, but it is a possibility.

Update: I'm planning to buy a used 1979 CM400T cylinder head on eBay ($62 shipped) and go for the swap. The seller said the threads are in good condition for the spark plug holes. I have a couple riding friends nearby who can assist me on the swap if needed. I'll keep you all posted.

 

[jdvorchak]

I think replacing the head is a great idea. That one, in the pics, is too far gone for my liking. Don't forget a new head gasket and valve cover gasket. Good luck.

 

[longdistancerider]

Heads are plentiful and cheap. That's the way to go on this, you'll spend as much getting it repaired or more.
That hole you mention at the bottom of the machined surface is a water drain hole, frequently they are plugged up with dirt.

 

[midwest_eng]

Thanks for the replies. I got the replacement cylinder head today and I'm going to be cleaning things up and taking apart my current cylinder case until the new gaskets arrive on Monday.

 

[midwest_eng]

I got everything put back together last night and tried to start her up. It turned over for a while and then ran at low rpms (~1,000) for about 10 seconds then died. I only tried starting it once after that and same thing. Tried the kickstarter after that and nothing at all. The valves didn't leak and I set the clearances to spec, torqued things to spec, new gaskets. Could be losing compression somewhere? Maybe just not running it for over a week has it bogged down? I'm going to troubleshoot tomorrow. Pictures of the replacement head after hours of cleaning.

Also: cam chain tensioner was a pain in the butt. Had to put on and take off the cylinder head about 4 times to pull up the tesioner as far as it could go without seeing any change and then finally got the chain over the cam sprocket part way and turned the engine with the stator crank and the chain pulled itself on. I'm not sure if this is part of the issue now with not starting but I don't think so. I'm having a friend help me out later to trouble shoot in person.

 

[longdistancerider]

Hmmm. You leak checked the valves but didn't do anything else to them? Could be your fuel, it goes bad real fast nowadays. Plugs new and correct ones?
Hint on that tensioner. Pull all the way up with the blade disconnected and the tighten the adjuster nut to hold it in place. Bend the blade with a screwdriver to get the pin to align and insert and the the clip.

 

[midwest_eng]

Hmmm. You leak checked the valves but didn't do anything else to them? Could be your fuel, it goes bad real fast nowadays. Plugs new and correct ones?
Hint on that tensioner. Pull all the way up with the blade disconnected and the tighten the adjuster nut to hold it in place. Bend the blade with a screwdriver to get the pin to align and insert and the the clip.

Thanks for the tip. I didn't do anything else to the valves (besides tapping with a rubber hammer to make sure they weren't stuck) after trying to get one of the valve springs out and then stopping because I didn't want to deal with putting them all back in. I ran out of spare money to put into this repair at the moment and with other obligations (graduating from school in a few weeks) I didn't spend too much time on them... they could be an issue so I'll see what my friend and I can come up with. Plugs are new and gaps were checked. If it's fuel, that would be an easy fix.

 

[midwest_eng]

Back on the street! Adjusted the idle speed screw and she got running. Had to adjust my exhaust headers (loosen and re-tightened) and then cam chain tension lock but and it's good to go. Vieeo:

 

[bilbikek411]

That sounds ok.