[NSRCA-discussion] NMP Headers

Sun Feb 12 10:56:12 AKST 2006

Bob,

There were changes made to the headers to make them better. However I can help you make a change to yours to make it as good.
Basically I will give a story of the way the headers were designed since I was involved. I can also tell you what the changes did and why they were made. The result is the functional part of the header is the same for even the early prototypes that I ran back in 2003

The original ones I flew and I don't know that many of these got out other than "Prototype versions" They had an aluminum bushing nut to hold the header onto the  motor. These work well However it was difficult to tighten them up as the material was aluminum and so was the head. Yes it was a different aluminum alloy than the head as we felt this would help in the heat and expansion properties to keep it tight. Remember back we had been using steel nuts on the headers. So a change was made very very early on to use a steel bushing nut. This was a simple change and the bushing was just replaced. No other change was made at the time and the header was put into production for the first batch. Some people were still having trouble with the bushing nut coming loose. If you continued to run the header after it came loose...the harder bushing nut would tear up the header body. This was a result of the header coming loose. The other thing we were doing was using a High temp silicone. The copper colored stuff. This kept the header from leaking and would seal it up so it didn't come loose...but some guys still had it coming loose. Perhaps the threads in the head were not clean or who knows.

By the way I was not having trouble along the way in keeping it tight. What I did do was fly it. Then pull the header and tighten it up while the motor was hot right after the flight. If you put a little smoke on it while hot they would stay great.  An idea came up to but put a stop screw on the bushing so it could not back out. A few tried it and the result was the bushing would loosen just a little then the stop screw would kick in and the thing would tear itself apart. Again same deal the bushing was hard material and the header was soft.

Then we started to re-examine the problem with fresh eyes. The Hatori headers and old NMP headers never came loose? Why. The copper washers inside the head of the motor. If these would smash down too much then the header would come loose. Light bulb went off we need a copper washer in there. But it can't go inside the head. This would prevent the bushing nut from tightening up on the head. So it needs to go on the bushing right inside the header right?

In the mean time I had helped some guys with their headers and noticed that some of the motors had a casting line that cut right through the exhaust port. Since this surface was not flat or near flat there was no way for the header to stay tight. In the mean time we were redesigning the body of the header to take internal copper washers. So we decided to put a washer inside the header on the bushing nut like an internal lock washer...and stick one between the head and the header to seal a not so great fit sometimes at this connection point. When the design was changed the header got slightly bigger to accommodate the internal washer and the mounting surface was made thicker to help prevent the tear itself up action. We also put a groove on the face to accommodate a washer between the head and header. At this time another change was made to the bushing nuts. We were adding 2 washers and the thread depth of the bushing nut was not as good as we liked. SO we decided to change and make the bushing longer to account for the washers. In doing this we found out something we learned years ago. Not all the YS engines have the same thread depth inside the exhaust port. Some are deeper than others Even 2 160's from the same batch would be slightly different.. So in some case a 3rd washer was needed to keep the bushing nut from bottoming out inside the head. Again this was not a functional change the change was made to use a longer bolt because we were stacking washers on it.

OK lets back was up. The design physically changed to make it more robust. But the mechanical function has not changed at all. I had about 10 different headers that were testing going back to the original concept about a year or more before this final stage. The way the system works is the same its just that we now have a soft material that will expand faster than the aluminum to keep everything tight. On these older headers what I did do was install a single copper washer between the head and the header. This is an easy accommodation and requires no changes to the header or its parts just the addition of the washer. So you get the exact same properties even though it may not accommodate all the improved features. I am still running these old original headers with a single washer between the head and header. This is 2-3 yrs later.

So you need to contact Central and get some of the copper washers. It is a special size made just for this header. But they are cheap.

Then look at a couple things.

1) remove all internal copper washers that may be down inside the exhaust port from using older headers. These will make the bushing tighten up but the header will not be tight on the head. 

2) make sure the surface of the exhaust port flange is flat. It need not be a machined surface just no mold flashings or bumps.

3) Clean the bushing with acetone or the likes to remove the oil and grime from it. Carb or Brake cleaner works well too.

4) Install the header and stick a single or maybe even 2 washers between the header and the head. I think you only need one but others with argue. I helped design it and am confident one will work as good as two.

If it ever comes loose again.....

5) run the motor and while its hot right after shut down tighten the bushing nut again. It won't come loose.

There are some other guys that run the newer header brace and it works well also. Again its probably not needed but depending on how your pipe/muffler is supported it might be an advantage. I always mount my pipe at the front neck where the header attaches to the pipe and then at the stinger. If you do this then the pipe is not whipping around and putting forces on the header. Some guys feel mounting the pipe at the CG of the pipe is the best way. Ok fine if this is you then use the brace to keep the forces from being transferred to the header and the bushing nut connection.

If you continue to have any problems let me know and I can help you out offline.

troy_newman at msn.com

Troy
  ----- Original Message ----- 
  From: THERUPMAN at aol.com 
  To: nsrca-discussion at lists.nsrca.org 
  Sent: Sunday, February 12, 2006 11:23 AM
  Subject: [NSRCA-discussion] NMP Headers

  Help needed,
  If this has been covered before, just point me to it.
  I've got a YS FZ in a QQ Yak with an early NMP hdr.
  I'd like to say I've installed it per instructions, but sometimes I miss something.
  Anyway. Every flight loosens the header connection to the head. The cap connection stays tight, but it does have the small screw to keep it from backing out. Engine runs fine. Any help would be appreciated.
  Bob Ruppel in Nashville

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