LO 206 exhaust brace mounting holes

R

RPMotor

New member
I have two customers just break taps in the unthreaded exhaust mounting holes in the head on new engines. Any one else here had any issues with this. I believe we need to get the holes threaded at the factory. Any thoughts about this?
 
They were both using 1/4-20 to match the RLV 5506 pipe mount bolts. What thread size are you using. BTY they both said they used the proper tap drill. a #7 I believe. They also said the existing hole was slightly larger already. I personally have not tapped any. Engines were sold in box.
 
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When we get a LO206 engine ready for a customer we tap the head with a 6mm-1.0 tap it works perfect. Spray a little cutting fluid or oil in the hole and tap 2 to 3 treads back off 2 turns cut 2 more treads back off and so on till the hole is tapped. Alum will gall up and bind the tap or break it if you try to tap whole hole with out backing off the tap
 
The holes are made for 6 mm bolts not 1/4 X 20.
That's why you broke the taps
For get the tap and use 6 mm self tapping tri-lobeular flange head bolts.
Use your 1/4" impact gun and a drop of taping fluid and it's done in about 10 seconds.
 
Bernie
Yes you are right. I don't think you will find them at the big box stores.
ACE hardware stores here have a great selection and then there is always Fastenal.
I buy them 50 at a time from Fastenal
 
Thank all for the great information. Sounds like I may need to unbox engines and tap the holes before selling them. I would still like to see them tapped at factory by Briggs.
 
I now helicoil that as well as the head bolt holes even before running them. Then you wont have an issue in the future and you will trust me. Make sure that the brace hole is lined up when pretightening the head bolts. Otherwise it puts an unnecessary preload on the pipe and it may crack at the thin point on the bend. If neccessary elongate the brace hole with a file or tweak it before tightening.

Greg
 
IMHO
I support RLV and their products and i appreciate what they do for karting.
Their 5507 pipe leaves a somethings to be desired.
As i see it there are a couple of issues.
1. The pipes actually will burn through under the header wrap.
2. The brace for the pipe is not stiff enough to support the pipe properly. It should also extend to the end of the pipe to provide a stop when installing the silencer.
While the price is reasonable i would encourage them improve the whole product.
The pipe itself could be made of a better or thicker material as well as the brace member for the tail end of the pipe.
The last order of 5507 pipes i got included another brace member that goes from the fuel pump mounting plate to the pipe a few inches above the mounting flange.
While this is an improvement it is a band aid for the root problems.
Neither the cylinder head nor the aluminum that the head is made of is the problem
You will not see Briggs change the design or the material that the head is made of so it's up to the aftermarket to solve the problem.
You will not see helicoils installed from the factory and you should not have to install them yourself.
The 5511 pipe that is legal for the Pro Gas class (thank you Steve Baker) is an improvement that should be allowed for the LO 206. If you are not familiar with this pipe it extends into the head about 1/2".
It adds strength and provides a better seal than the other design.
 
I thought the pro-gas pipe was slightly better (in my opinion.) BUT, I haven't installed and dyno'd any more than just the one that I had here for a pro-gas build on an actual LO206 and didn't spend any time adjusting anything else to accommodate the pipe change (which I would have preferred to do.)

Totally agree with the main advantage of the 5511 being a stronger pipe, though.
Seems I remember suggesting that the 5511 pipe be adopted (or change current -06 & -07 pipes to be more like the -11 pipe) into LO206 rules before the 4cycle crash. Jim, I think you were among many who jumped on me for that idea...glad to see you came around. :)

As far as tapping, I tap them 1/4-20 without drilling. Use tapping or cutting fluid and like suggested above, don't get too greedy at number of cut threads to chase (backwards) threads. Get greedy and you will break off taps. For what it's worth...I've used self tapping 1/4-20 bolts and they've worked too. I have broken one off though when installing with an impact - just use common sense, don't be in a rush, and get it right the first time.

--
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
 
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