Spark plug blow out

[Eric12171]

Hello again
79 xs650 special on going project.

The one plug hole was warbled out when I got it .
Figured it was a matter of time til it went .
Went to Kick it over last night and POP!!!
It went.

At least I was at home when it did it.

Picked up a save a thread thing today.
It’s the insert type not the coil.
We will see how this goes .

I’m sure this isn’t the only one .
How have others fixed yours , and how well did it hold ?

 

[Jim]

That's the good kind. The tap uses what's left of the original threads as a pilot of sorts. Still doesn't guarantee you'll tap straight/square, but it makes it a hell of a lot easier.
The way I set up for it is put the piston going down on the power stroke, tap the threads, then continue rotating the crank until the exhaust valve opens. Then use a blow gun with a skinny tube to blow the crap out of it..... so it all comes out the exhaust valve.

 

[Eric12171]

I got it tapped out,
That seemed to go smooth enough.

I bought high heat locktite to put on it ,
It’s rated to 400 degrees f
Now I’m wondering if that’s enough or should I put the high heat job weld on it ?
I think it’s closer to600 degrees.

How hot does a spark plug get ?

 

[Jim]

CHT's (cylinder head temp) on an air cooled aluminum engine will typically be around 300-400°f.
Add-on CHT gauges usually use a sender that replaces the spark plug washer/gasket.... so that's about what it'll see.
I've used J B Weld in the past with good results. Use it sparingly though. You don't want to get any on the inner threads... the ones the plug uses.
But I wouldn't be afraid to use the thread locker you've got there. Should work just fine.

 

[atom4488]

That's the good kind. The tap uses what's left of the original threads as a pilot of sorts. Still doesn't guarantee you'll tap straight/square, but it makes it a hell of a lot easier.
The way I set up for it is put the piston going down on the power stroke, tap the threads, then continue rotating the crank until the exhaust valve opens. Then use a blow gun with a skinny tube to blow the crap out of it..... so it all comes out the exhaust valve.

Dry tap or greased flutes to trap swarf as the tap cuts?

 

[Jim]

I do it dry. Easy enough to blow the swarf out.
My fear of the grease is what if a gob of swarf/grease mix falls into the cylinder? Sticky as it is, would be a bear to clean out.
That's how I see it anyway....

 

[Jan_P]

Permatex is a good brand been around since the 60 ies at least

 

[atom4488]

I do it dry. Easy enough to blow the swarf out.
My fear of the grease is what if a gob of swarf/grease mix falls into the cylinder? Sticky as it is, would be a bear to clean out.
That's how I see it anyway....

Agreed. Better odds of a full cleanup of the cylinder.

 

[Eric12171]

CHT's (cylinder head temp) on an air cooled aluminum engine will typically be around 300-400°f.
Add-on CHT gauges usually use a sender that replaces the spark plug washer/gasket.... so that's about what it'll see.



I also ended up taking about 1/8 of an inch off of the longest insert ,
Seemed like it was a bit too long.

 

[40north]

In VW days I much preferred measuring the oil temperature. If I were going to measure cylinder head temperature I would not use plugbase location, as the tightness influences the reading. An IR sensor would be my choice, properly compensated for emissivity of Al. I have never managed a nice job of insert repair plug hole...but it does happen, so they say! Good luck! BTW, PN junction temperature sensors are notoriously nonlinear, ie not very accurate. Best! 40N

 

[Kevin Werner]

I did a spark plug re thread once. I removed the exhaust pipe and the cam cover (XJ650RJ) so I could insure that the intake was closed and exhaust was open. Then I stuffed a shop vacuum cleaner hose into the exhaust port with rags and duct tape sealing and securing the hose. Dry tapping was easy and I could hear the swarf going into the vac.. 52000 miles later I sold the bike running as good as ever...

 

[Jim]

I did a spark plug re thread once. I removed the exhaust pipe and the cam cover (XJ650RJ) so I could insure that the intake was closed and exhaust was open. Then I stuffed a shop vacuum cleaner hose into the exhaust port with rags and duct tape sealing and securing the hose. Dry tapping was easy and I could hear the swarf going into the vac.. 52000 miles later I sold the bike running as good as ever...

Don't know about the valves on that one....
On the XS, there's a good possibility of grinding the tap into the exhaust valve if it's open. Even a skinny bump stop has a tendency to interfere with the valves. A big ol' spark plug thread tap will almost certainly hit the (open) valve. I wouldn't recommend having either valve open during the tapping.

I do like the idea of the vacuum in the exhaust though. Finish tapping, open the exhaust and use a combo of the vac and the blow gun in the plug hole. Any swarf in there won't stand a chance.

 

[Kevin Werner]

Don't know about the valves on that one....
On the XS, there's a good possibility of grinding the tap into the exhaust valve if it's open. Even a skinny bump stop has a tendency to interfere with the valves. A big ol' spark plug thread tap will almost certainly hit the (open) valve. I wouldn't recommend having either valve open during the tapping.

I do like the idea of the vacuum in the exhaust though. Finish tapping, open the exhaust and use a combo of the vac and the blow gun in the plug hole. Any swarf in there won't stand a chance.

Thanks Jim.

 

[46th Georgia]

Thanks Jim.

Ya' gotta' love this forum. Someone here has more than likely either done it or thought it through, saving the rest of us a whole lot of money, headaches and heartbreaks.

 

[Eric12171]

Got it together last night,
Everything looks good , looks like I actually got it in straight.
Fired it for a second just too see if it ran , it did

Tonight the goop should be set up enough to run it longer .