Bolts Keep Coming Loose in the Header
 

Guys: I am flying an LA-2 with a very good YS 61R Long Stroke. After about 3 flights the bolts in the heading come loose or fall out altogether. I have cleaned the threads in the head as thoroughly as I can with denatured alcohol, have dropped a drop of red 271 Loctite in the bolt holes and on the threads and have screwed them in with an L wrench socket head wrench. The engine is on a soft mount. I get about three flights and the bolts always come loose or come out altogether. Anyone have any ideas on what I can try to do?

Thanks, Bill

Most of the problem is the mass of pipe, which results in it's inertia stressing the header/exhaust junction.
Soft mount the pipe at the pipe's CG.
Make an intermediate joint by cutting the header as short as reasonable and adding an additional silicon coupler at that point. You should be able to get a 3 to 6 inch piece of intermediate pipe.
The pipe will still wiggle around a lot, but the additional coupling will reduce the inertia transmitted to the header/exhaust joint.

cross drill screw heads with a small numbered drill and secure screws from turning with safety wire.

What Grotto said.

However, another great solution is to use one of Joe's excellent YS exhaust adapters that convert the YS bolt on header to a "spring on" NovaRossi header. The adapter is much like those used on OS engines such as the Hanno, the RF/VF series before that and the NR SE engines today. It's a flat to round nozzle adapter which has a silicone rand on it. The round inlet header is then seated against the rand and held against it with a spring which wraps around the cylinder - effectively a soft mount header.

splitting the header might still be needed if the engine is vibrating considerably in the soft mount to avoid stressing the header/pipe junction directly.

A side benefit is that exhaust flow (and power) is improved as Joe matched the adapter inlet to the YS exhaust outlet; something which Hatori and Macs for some reason failed to do.

See this thread for details:

https://www.rcgroups.com/forums/show...xhaust-adapter

Adapter/header kits are available from Leo Steck here:

http://klasskotemo.com/

I added some pics to show the adapters and the similar concept used by NR on their SE engines (the RE engines have the nozzle cast into the case). The last OPS engine shows their adjustable tuned length exhaust header. The pipe slides into the header allowing for a variable length. While this can't be done with the NR headers (unless modified), it shows the concept of using a "stub" header at the engine attached to the main header via a coupler (OS used this system too on their RE engines as mentioned above). If one uses the same idea as described by Grotto with the NR header cutting it close to the adapter junction and dual couplers, the result is a built in "soft" mount for the exhaust. One can even hard mount the pipe with this setup. However, with the spring mounted header, dual couplers and cutting the header at the root should be unnecessary.

David

HI David:

For some strange reason Yamada uses 3.5MM socket head bolts on the 60 long stroke instead of the 4MM ones on the short stroke. It's hell trying to get he 3.5'd any way, Home Depot has the 4's. I just left my engine with a machine shop to drill and tap it to 4MM. The info you just gave me looks very interesting and will check it out. Thanks, Bill

I definitely agree with grotto2, It may be a little work, But it will be worth it in the long run.

I always installed HeliCoils in those holes. Then you can really torque them tight....I flew those engines for years and never had one loosen up.

You can try just putting some teflon tape on the header bolts. Works for me.

Thanks guys for all the tips. I am waiting to get my engine back from the machine shop with the new 4MM taps. I will also try grotto2's suggestion and cut an intermediate piece and see if that relieves the stress on the head/exhaust joint. Will let you guys know how it goes. Bill