Rotax 912 ul repair

[foxkit3]

Hello.

I have a older rotax 912 ul. it has 1800 hours on it. The engine runs great. No oil burning or excessive blow buy. when a cylinder differential test was performed all were 80/80. From the records that i have the engine has been maintained properly. The gear box chatters a bit bit at 1800 r.p.m's. the carbs have been sinked properly. This winter I was going to reshim the gear box, repl all brass and rubber components in the carbs. also repl the oil pump shaft. I have installed the New updated fuel pump and new carb boots. My question is, Is there any other things I should be looking at? I have been doing my studying reguarding the 912 ul and these are the most common things I have found with a older high hour 912.

Thanks

chris

[Slyfox]

rocker arms.

[Jeremy MacGregor]

Rocker arms are defiantly a good thing to look at. Chances are you wont find much wear on the rocker arms them selves but the bushings can start to wear over tolerance. Depending on age you may have the old style rockers with the pressed brass bushing or the new style with replaceable plastic bushing. Just be sure to measure them and know what your working with. Other than that all rubber externals (carb flanges,coolant hoses, diaphragms), replace the gearbox springs,and carb overhaul. Once you start going deeper than that a full top end or case split and reseal is the way to go.

[Slyfox]

on the rocker arms, if you have the brass inserts, put the cylender on top dead and remove them and inspect, chances are real good with the brass they are gauled and show signs of seizing, no good. must move freely, these things move at increadable speeds at 5600rpm.

[Dorsal]

Do you know approximately what year they changed them?

[Slyfox]

no, they had a bulletin out on it.

[foxkit3]

Thanks for the info, I appreciate it. I am a mechanic for G.M my brother inlaw is a a/p mechanic. And a friend of mine went to the rotax 912 heavy repair course. So I hope between the three of us we should have a good handle on it. Im just trying to get info and peoples opinions on what they have seen before. I have been doing alot of studying and reading bulletins on the 912. I dont beleave in fixing something that is not broken, But a good inspection and replacement of updated parts is in order per bulletins pertaining to to my serial number. Any other info or things I should know about the 912 is appreciated

[Paul Z]

The TBO would bother me. 1500 hours I believe is the TBO recommended, I would recommend checking it on the Rotax page, serial number of engine will give you that info. A major Overhall requires heavy Maintenance, and that is not cheap!

[foxkit3]

Well I have been going threw my 912. Amazed of the condition, No signs of wear present, All components of the engine that I have measured are at new spec. Cross hatch still present in the cylinders. The gear Box has some wear present. The thrust washer is way out of spec. spring tension is low. Going to replace with new. Cant beleave the amount of lead build up in the heads and piston crowns. The exhaust valve and exhaust port
had a excessive amount. I have been running mogas the 90 hours I have owned the plane. I will try not to ever run 100 ll threw her again if I can help it.

[Av8r_Sed]

If you use Decalin additive and change the oil at 25 hr intervals you shouldn't experience serious lead buildups with 100LL.

-- Paul S