I just tried to fire up my 69 dt 250 and it didn’t want to fire up. It showed signs of life so I tried to bump start it. I figured the carb needed a quick blow out to make sure everything was clean. Usually if that is the issue, I can get it to run when I bump it. 
I just needed it to run for long enough to test my clutch after modifying the push actuator. I just wanted to verify that the clutch would engage and disengage. 

So, I pushed it up my street and then back down. As soon as it fired up I knew what the problem was. It was popping and snapping out of the exhaust manifold. Immediately I knew that one of the exhaust manifold studs had pulled out. It had happened a long time ago but I was able to repair it by retapping the hole and using a very small amount of high temp/pressure JB weld. I am now remembering that I think it originally just had bolts. I changed it to studs when I first fixed it. 

It held up for a long time but it now needs a more aggressive approach. I am figuring that it will require a slightly larger bolt or stud which will mean drilling the hole and retapping it. 

So after doing my usual search of the forum I figured I would throw this one out to the group and hopefully start a discussion amongst the geniuses out there and determine what works and what doesn’t. I certainly don’t want to eff-it-up and end up having to replace the barrel. 

So, who among you knows what the correct path is to get a good solid repair?

As always, I thank you for always being so helpful and supportive. 

Pmb

A heli-coil would be my preference, if there is enough material to allow for it.  There are more modern designs.  Also with an engine you need to keep in mind expansion and contraction with heat cycles, a heli-coil might be superior in that aspect?  This video will not cover that, but I like his testing methods.

 

Thanks Knutco11. That’s a very informative video. I need to investigate how much material I have to work with. 

Very good video, thanks for posting. I have personally used the Helicoil, Keensert, and Timesert systems. With the Keensert system you can also buy an additional guide to aid you in getting the correct alignment of the drill/tap to surface.

Are you going to try to do this without removing the cylinder from the bike? I have a '68, so very similar. Not a lot of clearance for tooling to get past the frame for either of those 2 bolts.

For me i'd just go the easy way & tap it to 1/4 with cylinder in place.
You should get enough thread to hold. I've gone out bigger with cylinder off though.

I've done that successfully as well...  1/4" is a little bigger than 6mm.

I’m probably just going to pull the motor out. I want to do a little cleaning and cosmetic work. I have a work bench with a metal plate for the top, so I will probably attach a few 6” (ish) long pieces of angle metal and attach them to the motor. Then I just weld the angle metal to the bench. That will make it stable while I am working on it.

I have one of those thread checker aluminum plates, like you have probably seen in a hardware store, with tapped holes and threaded studs. One of the most useful things I have purchased recently. I came to the same conclusion about the 1/4 x 20. As usual for me, I just started ordering stuff. I got a few stepped studs with M8x1.25 to M6x1.0. I don’t know if there’s enough material to drill it out for an M8 bolt or stud. 
I also got a couple M7x1.0 x40mm bolts. Not a very common size but readily available. Had to also get an M7 tap because my metric tap and die kit doesn’t include 7mm. I got 40mm long so I can cut them down and make the correct length bolts or I can run them in with a bit of red thead locker or some high temp epoxy and then cut the heads off the bolts and turn them into studs. 

My biggest concern is depth and diameter for the cylinder. I really want to avoid doing something stupid like go too deep or wide and destroy the cylinder. 

I plan on taking my time and hopefully getting a good strong that will be permanent. 

while we are on this subject, does anyone know what the torque specs are for these bolts? I figure I probably over tightened it years ago when I was a clueless newbie. I was pretty careless about torque specs when I first started wrenching on the bike. Mistakes were made… but no innocent animals were harmed!!

Thanks everyone. 

There is a schedule of torques in the repair manual according to size of threaded bolts if you go take a look.
Sneezles61

Thanks Sneezles61.
Great little torque spec chart. Now I am certain I simply over tightened the bolt. I guess you do learn the most through failure! My torque wrench just got a lot busier. 

Grampa taught me : "tight's tight. Too tight's loose again....."