hugger-4641

My Feedback: (6)

I have a Saito .82 mounted @ 90 degrees in a .60 sized T34, was flying it yesterday and the muffler seperated at the threads. About 2" of pipe still attached to the engine but the muffler and fuel tube were hanging loose in the bottom of the cowl. I noticed the change in noise about 2 minutes into my flight, but I continuedto run outthat tank outwith no noticible difference in performance. It stillstarts up and runs fine, butI won'tfly it again until Ifix the muffler. My question is: Why didn't the engine quit when it lost pressure to the fuel tank, and why does it still run fine?

earlwb

The engine has pretty good fuel draw, and you likely had it adjusted on the rich side, which is good, so it continued to run OK and just leaned out a little more. Good luck on not losing the muffler parts. yeah, sometimes they aren't as tightened down well as as one might think.

fordman1

Most engines will run without pressure. Just adjust a bit richer.

MetallicaJunkie

try some plumbers teflon tape..wrap it around the header and tighten the muffler.... i used to have that problem with the saito 150 when i was using the big "firehose" muffler back in the 90s

scooterinvegas

My Feedback: (1)

I safety wired my muffler of my Saito to the head. If it ever comes lose, it can only move about a 1/8 turn.

daveopam

My Feedback: (9)

The teflon tape works for me. I also run the motor for a couple minutes after the initial install and retighten while hot.

david

spaceworm

Tightening the muffler bolts when the engine is hot is an approach cited by many, and I guess it must work. But since an aluminum muffler must expand with heat more than the steel attaching bolts, when the engine is hot the muffler flange is "bigger" than when it is cold. Tightening is this hot condition will result in a looser bolt when it cools down, or not? Can someone explain how this "tightening while hot" works?

Thanks

daveopam

My Feedback: (9)

I wish I knew the science and maybe we are fooling ourselves. But I think the bolt will expand along it's length more than the flange will expand on it's thickness. The steel bolt is 2" long or so and the flange 1/4" thick. So the percentage the flange is expanding is more, but in inches the bolt is more.
On the Saito we are talking about, there is no bolt and flange so I can't explain the logic there. As far as the teflon tape. It basically fills the voids in the threads and removes the room the muffler has to vibrate.
Those are my stories and I am sticking to them.

david

nonstoprc

My Feedback: (90)

Teflon tape method also works with YS engines, well. Several wraps on the header will make it very tight.

The trick works with almost all places on the plane where a bolt could loose because of vibrations.

hugger-4641

My Feedback: (6)

Thanks for the info fellas! I'll definitely try the teflon & safety wire, and tighten again while it's hot. I'm still amazed that it runs so good with no pressure to the tank, none of my two strokes will run good enough to fly without tank pressure.

maxtenet

four strokes don't need muffler pressure because of the relative small carb size and the much better suction on the intake down stroke that two strokes don't have. Most four strokes have ineffective mufflers anyway. The OS .60 and .90 mufflers do nothing at all. They are as effective as Harley Davidson mufflers.[8D]

Max

rv9-a

Are you talking about the small allen bolt, about 2 inches long, that holds the two muffler pieces together? Is so my method is to tighten the bolt as tight as you feel comfortable. Then clamp a drive punch in a vise slip the exit end of the muffler over the punch. It will stop at the head of the allen bolt. Hold the muffler in one hand and hit the threads on the other end with a small hammer until you distort (destroy) the threads. It will not come apart again, and I can't think of a good reason you would want to take it apart. Tried red loctite and because of the heat it didn't work.

I have owned several Saito engines with this type of muffler and most of them came apart and were successfully fixed in this manner.

Recycled Flyer

If you assemble any engine part at its operating temperature it will always be more stable in use, BMW has been doing this with their motorcycle engines for years, alloy castings, steel bolts all respond well to being preheated upon assembly.

For example, the aluminium muffler does not expand evenly all over, it will expand more along its length than its width, lets call this 'anamorphic creep.'

It you assemble the components at the operating temperature you have resolved this anamorphic creep already and are far less likely to suffer part movement from then on in.

Does that help?

Rudolph Hart

So does this mean i need to assemble all my saitos only when they are peaked out to the max..this sounds like a dangerous practice to me

Hobbsy

My Feedback: (102)

On the Saito the aluminum is outside of the steel pipe so being hot allows it to be tightened more taking up the slack created by the expanded aluminum.

Recycled Flyer

Well, no but you should torque down all bolts whilst the engine is the warmest that you can handle and typically re-torque just after the first few runs.

Just as an aside here, I have ye olde screw in liner diesels, the liner is steel and the case is aluminium and they do not stay put unless you heat up the parts firstly with a heat gun.
If I assemble the engine cold I am just asking for the liner to unscrew during running and that can ruin the engine real quick.

Cheers.

jetpack

My Feedback: (1)

The reason the engine must still have ran good is it must be able to develop a lot of vacuum by itself so it didn't need pressure as you had thought. Most engines do not need muffler pressure, only if they have problems is it suggested in the ones that don't.

Kostas1

Jerry,

my engine didn't quit also.....
[youtube]http://www.youtube.com/watch?v=jOrKvF4xNqE&feature=youtu.be&hd=1[/youtube]

Kostas1

Have you also tried Teflon;