Lo206, small header bolts and gummy aluminum?

R

rkcarguy

New member
Hey guys, a fellow racer and his son both have Lo206's at our track. The exhaust kept coming loose and it was pulling the treads out of the head on the forward bolt despite being safety wired. I helped him fix it because I had a tap and die set with me. I was surprised that it was only 6mm threads, we oversized the one hole to 8mmx1.25 and got a nice good set of threads in there(I've got 10 years machinist experience so I didn't nut job the new threads before you jump to that conclusion)....installed a 8mm allen bolt with a good 1/2 bite in the threads and the next race they pulled right out of the head again. The aluminum appears to be just butter soft for some reason, far worse than what I've seen in a clone.
Its the spec pipe and brace, others aren't having the same problems.....Bad batch of castings?
 
The fix that works best is a heli coil, some have headers coming loose and threads failing once we heli coil them all is well usually.
 
HMMM
Well we have about 40 LO 206's at Road America and i think i might have seen 2 of them have the bolts come loose all season.
Helicoil them with a 6 mm and they are good to go.
 
Yeah I get it that not every 206 has the problem, just a bummer because it cost Jim his points championship in light class. I found it odd that with new 8mm threads, almost 1/2" of engagement, it still wouldn't stay. It was a pretty hot on race day, probably our hottest day racing so far, maybe the header was expanding beyond normal and didn't have anywhere to grow?
 
The forward hole is blind, so not much I could do there with what I had. It was close to 2x the thread diameter...I really expected it to at least last the rest of the day if he kept an eye on it. The rear hole does goes all the way thru and allows for more threads.
 
Thinking about this for a second, you have a fairly long pipe I assume, with a heavy muffler on it that is bouncing and vibrating as the kart is raced. What I am getting at is the pipe / muffler needs to be supported better. I support both ends of the exhaust, one by the muffler with a "U" bolt type arrangement, the head end of the pipe with a strap welded onto the pipe and bolted to the top plate of the engine. End of stripped bolt problem. I have had the support by the muffler come loose / off and not stripped a header bolt because of the strap welded on and bolted to the motor. FWIW

How did you get an M8 ( roughly 5/16" ) bolt to work on the pipe? With the M6 that is standard, there is just enough room for the allen head bolt. I fear the head may be junk now.

Dave E.
 
I had some M8 allen bolts and the bolt head just cleared the header pipe by a hair.
They are just running the spec pipe/muffler as delivered from fastermotors, I didn't feel it was really too long for the bracing that came on it.
On my clones I run a piece of aluminum flat bar from one of the unused side cover bolt holes clear back to a tab I weld on just in front of the muffler, personally I haven't had any problems.
Jim is going to buy a new head and try to helicoil the old one and keep it for a spare.
 
Header support is important. Also, equally important IMO, is to not over-torque the header bolts. More is not better. As the head swells, the bolts can be pulled out if they are over torqued. Another thing to keep an eye on is if you are getting a leak past the exhaust gasket, replace ASAP. A broken gasket can let the header move and squirm which will result in a thread failure. I also prefer time-serts over the helicoils. I have not had any issue with them being too large or there not being enough material to put them in.
 
Best header design is what the QM group uses. A flange ( with port extension ) that bolts to head then the header tube slips over the flange nipple and is held down with springs. Header bolts never ever come loose...............! Next set of engine rules I write for sure will get that header design as the tech spec.

Steve


Insanity: Doing the same thing over and over again and expecting different results.
 
Loose header bolts have as much to do with the gasket type you are using as anything else. If your gasket compresses any at all, your bolts will loosen up and pull out. I LOVE Fel-Pro gaskets. I have never had a problem with them. I have never had luck with copper or other graphite type gaskets thick or thin.

In my opinion, if you drilled/tapped it for 8mm you ruined the head. If you had to drill the 206 header to fit the 8mm bolt you also ruined the header.
 
Jimbo said:
HMMM
Well we have about 40 LO 206's at Road America and i think i might have seen 2 of them have the bolts come loose all season.
Helicoil them with a 6 mm and they are good to go.
Click to expand...

Do you Helicoil them when they are new before they are put in service?
 
NO
I do not helicoil them when they are new!
I either use a copper gasket with high temp orange silicone on both sides or i use the graphite type gasket.
 
I've seen too many bolts come loose when using the graphite gaskets.
I use only the copper ex gasket now. I like Fel-Pro's too, but unlike Jamie, I haven't had issues with the copper.

Proper bracing is critical no matter what header, bolts, or gasket you use.



I prefer to use heli-coils if I need to fix stripped threads (the first time.) I can use the time-serts (Jergens or other) if for some reason the heli-coils pull, since the time-serts are available in a couple different ODs.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com

Celebrating 25 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
 
This is the gasket I use (I do not buy from Jegs, just using it as a reference):
http://www.jegs.com/i/Fel-Pro/375/FPS40001/10002/-1

Fel-Pro FPS-40001 but I buy them in the 10 pack because it's a lot cheaper that way. In my opinion, this is the best exhaust gasket made. It will not crush over time like other gaskets do (including copper). This is the only gasket I have used that I do not have a problem with.

And as Brian said, I like to start also with the heli-coil then if needed you can still go to the metal insert after that if needed.
 
If you safety wire the header bolts properly how can they come loose? I can see them stripping out if they are over tightened.
 
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