Rotax manifold 2 OR 3?

[Allantat]

About ready to mount my exhaust manifold on my 582. There are four holes in which to mount the manifold...but only 3 are useable.I visited our local ultralight hanger yesterday to ask questions about the 582. Several members mentioned when attaching the manifold to ONLY use 2 of the mounting holes (criss-cross) instead of the 3 useable holes. Looked at several aircraft and ALL were using 2 holes in a criss-cross pattern. Any particular reason for this?

Feedback? Thanks.

[gyropilot]

Allan.

Every Rotax 2-cylinder 2-stroke I've ever seen uses 2 bolts per flange (or 4 bolts total per manifold) to mount the exhaust manifold to the cylinders... this is despite there being 4 bolt holes per flange (or 8 holes total per manifold). This is how Rotax ships the engines from the factory.

I presume Rotax stamps out the exhaust manifold flanges with 4 holes for ease of assembly. That way, no matter which way they're welded to the exhaust manifold, they're the correct orientation!

Best regards,

John L.

[mark treidel]

I use 3 bolts on the exhaust manifold of my 582. The lower inside ones are left unused. You cant get a wrench in there anyway. Criss-cross is ok but in this case, 3 is better. I also use a small drop of locktite 242 since the bolts are prone to loosening after time and cannot be saftey wired. They should be retorqued after a few hours of initial usage. (update 1-15-06), Just read a small article of interest in the Jan. EAA magazine regarding this issue. If you are having the aircraft inspected for certification, ALL 4 HOLES have to be used (fancy that?!) They are selling a 'kit' which is simply a stud, lock washer & nut for the bottom inside holes. I couldn't find that anywhere in the regulations but thats what the article claimed. Incidentally, the proper torque for the exhaust bolts is 16 ft. lbs.

[scottessex]

You can use a stud and a nut on the ones that are hard to get at, it seems that if you use just 2 they leak, not good on a 2 stroke.

[GyroRon]

I have always used just two per jug and never had a problem. I just tighten them RDT - real dam tight - by hand and forget about them.

[scottessex]

Chris wilson's was leaking like a pig, and getting crap all over the engine, He put all the bolts in and it was fine. I think that Phil's 618 only has 2 and so far it seems to be fine.

[Allantat]

Thanks for the feedback guys.Did some research and found some archived audio on the Ultra-Flight web site. Tom Olenik was the guest and mentioned it is BEST to use all 4 attach points. He echoed Scott and suggested inserting a stud in the #4 "Impossible to get to" hole. If you use a crows foot socket the nut can be properly torqued.
If the manifold only needed 2 bolts...and it would be cheaper to manufacture....why did Rotax design it for 4?

[GyroRon]

Mine had started to leak on my White gyro around the 60 hour total time mark, so I took the manifold off, put some black high temp silcone gasket goo on both sides of the exhaust manifold gasket and then re installed everything making sure I used my RDT torque methods and no leaking anymore.

[scott heger]

I use high temp automotive gasket sealer on both sides of the gasket, three bolts and one stud/nut per side(8 total). No more nasty oily mess ever since, 250+ hours.


Scott Heger, Laguna Niguel, Ca N86SH

[Chuck Roberg]

Ron and Scott, which high temp gasket sealer do you mean? All the ones that I found are only good to about 600 degrees. The ones I tried melt from the heat and the goo gets blown out.

[gyroplanes]

Originally Posted by Allantat

If the manifold only needed 2 bolts...and it would be cheaper to manufacture....why did Rotax design it for 4?

So you could mount the manifold or engine either way. Plugs up or down, manifold up or down.

I have over 30 installations, used 2 bolts, locktite, proper torque and never a leaker.

[gyropilot]

I'd like to pass on a tip I use at home which can help you obtain a leak-free seal from a Rotax exhaust manifold.

When you're reassembling a 2-cylinder Rotax engine after having the cylinders loose, prior to tightening the head bolts, use the exhaust manifold itself as your "alignment tool" to insure the cylinders are positioned correctly on the crankcase.

Let me explain...

The factory sells a special alignment tool (basically just a steel bar with holes in it) which is supposed to be bolted across the intake ports of the cylinders to hold the individual cylinders in alignment with each other prior to the head bolts being tightened. This is probably the best procedure in the factory assembly environment, because they likely don't know yet which exhaust manifold will be used for a particular engine. Now later, *if* the exhaust manifold flanges aren't perfectly aligned with each other, then it might not yield a perfect seal on the cylinder's exhaust ports.

However, if you use the exhaust manifold as the "alignment tool" instead, you're guaranteed to have the cylinder's exhaust ports perfectly aligned to the exhaust manifold flanges... even if they're slightly out-of-true.

It's been working great for me. And like Tom, no leaks whatsoever even though I use only 2 bolts per flange and no sealant (just exhaust gaskets per usual).

Happy wrenching,

John L.

[GyroRon]

Chuck, I used High temp Black silcone. Not sure of the make, whatever they had on the shelf at Autozone.

[jdalexa]

If it was leaking like that, I would check

- to make sure there were 2 gaskets per cylinder
- that the cylinders were in line
- that the mating surfaces of the "Y" was in line and flat.

If the engine has been rebuilt and the cylinders weren't properly aligned, that would cause a leakage problem. Part 876-904 is the alignment tool for the liquid cooled engines exhaust.