Horstman muffler on Mc101

philrock · Post by **philrock** » Thu Dec 13, 2012 12:03 pm

Below are two photos of a Horstman muffler mounted on my Mc101. Note the close gap between the muffler body and the edges of the cylinder shroud. This gap is about 3/8 to 1/2". I'm concerned that the gap is small enough to restrict cooling air trying to exit the shroud. Has anyone had a problem with this?

Rob Voska · Post by **Rob Voska** » Thu Dec 13, 2012 8:05 pm

The fan is blowing from the other side. Not a problem as I see it.

I would install a 3rd bolt to secure the muffler. It will pull the exhaust inserts out.

Mike Birdsell · Post by **Mike Birdsell** » Thu Dec 13, 2012 8:30 pm

Not only do you need to put third bolt also put a spacer in there or the vibration will brake muffler.

Mike

Post by **Jeff Campbell** » Sat Dec 15, 2012 11:58 am

Mike,
No problem, I've been running the repro Horstman mufflers on my dual rear for several seasons, there is still plenty of space for the cooling air to escape. Like everyone else said, the only concern in that photo is the missing 3rd bolt ... some washers, a spacer and a good quality allen bolt with some loctite on it, you know the deal. I know you are a top notch kart mechanic guy, but for anyone else reading this ... keeping the muffler, header screws tight is a challenge... always use grade 8 or better 10-24 screws, allens are great ... use lock washers and don't be afraid to use red loctite (permanent) on the 2 screws on each side of the exhaust port, the heat degrades the loctite so the red ends up holding about as tight as the normal blue stuff ... and always use as long a screw as possible on those 2 screws at the exhaust port, but only after first checking there is NO chance of it bottoming out and destroying your block!

Jeff

Post by **Jeff Campbell** » Sat Dec 15, 2012 11:58 am

Mike,
No problem, I've been running the repro Horstman mufflers on my dual rear for several seasons, there is still plenty of space for the cooling air to escape. Like everyone else said, the only concern in that photo is the missing 3rd bolt ... some washers, a spacer and a good quality allen bolt with some loctite on it, you know the deal. I know you are a top notch kart mechanic guy, but for anyone else reading this ... keeping the muffler, header screws tight is a challenge... always use grade 8 or better 10-24 screws, allens are great ... use lock washers and don't be afraid to use red loctite (permanent) on the 2 screws on each side of the exhaust port, the heat degrades the loctite so the red ends up holding about as tight as the normal blue stuff ... and always use as long a screw as possible on those 2 screws at the exhaust port, but only after first checking there is NO chance of it bottoming out and destroying your block!

Jeff

steveohara · Post by **steveohara** » Sun Dec 16, 2012 4:53 am

Some good advice here, in particular about using the third bolt and proper spacers to assure the muffler is well supported.
That being said, I don't recommend using Loctite for the two primary mounting screws. I have seen two many cases where the Loctite would not let go and when the exhaust is removed the steel thread inserts back out of the block. Unfortunately, for the inexperienced mechanic this often leads to damage as the mechanic is not aware of what is happening and he messes up the threads in the block.
A much better solution is to drill the heads of the two primary screws to allow for safety wiring. If you are running a header that leaves the third screw head exposed it should be drilled and all three should be safety wired together to prevent any from coming loose.
If you are running an exhaust where the third screw is buried inside the header then care should be taken to use a fresh lock nut in the pocket in the head. DO NOT use a Nylock... the nylon will just melt. The standard locknuts used in the Mac blocks work great as long as they are pretty fresh and still have a good degree of pinch on the bolt.
Before assembly the exhaust port gasket surface and the header mounting surface should be checked to make sure they are flat, smooth and clean. Never use a paper exhaust gasket, the only type that holds up is the copper gasket.
Regarding the length of the screws, the thread inserts are approximately 3/8" long so anything longer will not add to the strength of the assembly but too much will bottom out in the pocket and break a hole through to the intake area. Put your screws through the header and gasket and measure to make sure you have no more than .4" and no less than .3" of thread sticking through and you'll be in good shape.
Oh, by the way, good luck drilling the heads of the hard black allen screws... what a PITA! You'll want to buy a few extra bits. Here's a tip for drilling.... grind a small flat on the OD of the screw head that is parallel to one of the six sides of the inside hex. Use a center punch to make a starter point for your drill on the flat you have ground and then make sure you hold the screw securely with the flat surface perpendicular to the drill bit. The position of the flat spot is critical... if you don't make it parallel to one side of the hex inside the drill will penetrate and when it crosses over to the oppposite side it will hit land on a sloped surface and the slope will cause the drill bit to snap off. The tip of the bit needs to land square to the inner surface of the internal hex when you start drilling through the second side or you'll have nothing but trouble.
Steve O'Hara

Rob Voska · Post by **Rob Voska** » Sun Dec 16, 2012 9:05 pm

Good info all. Try drilling with a center drill to get the first hole in. Then switch to a regular GOOD QUALITY HIGH SPEED drill bit & run it slow so you don't burn it up. Also a good cutting fluids or oil helps. When you are about to break through ease up the pressure so it don't grab. I have also drilled with my center drill first from one flat then turned the bolt 180 degrees and drilled the second hole like the first. But I admit I cheat & use my mill.

philrock · Post by **philrock** » Mon Dec 17, 2012 5:57 pm

Guys,

Thanks for your help with this.

I was aware of the third bolt issue and have taken care of it. The hard part was that the third bolt hole on the 101 is in a different location than on the engine the muffler was designed for - I had to plug the hole and re-drill .140" farther from the exhaust port.

I ran the engine this weekend and saw no ill effects from the close shroud / muffler clearance.

Thanks again,
Phil Rockwell

Horstman muffler on Mc101

Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101

Re: Horstman muffler on Mc101