Just a word on your comment about the last bit of throttle not doing anything. Your kind of running the engine at a low max RPM. When you do this the throttle response changes. you might find that by increasing your rpm another 1000 (flatten the pitch) your throttle will behave a little different and you may even get better full economy. I know it sound counter intuitive. remember these engines develop their max HP at just above 10,000 RPM and the snowmobile racers are running them up to 11,000 RPM frequently.
I think the this biggest factor as far as starting is the prop diameter and moment of inertia. I don't have any problems starting on my trikes but Im running 68-70" 3 blade light propellers. I usually start with the enricher (choke) open and the throttle cracked open. When it fires I throttle up a bit and close the enrichener. Most important thing to remember, if it ever fires up but wont get past a really low idle just shut it down because it will just shake and idle really low. Enough shaking to possibly knock your airbox off or damage of stuff eventually.
One thing to note: the Yamaha engines do have an oil cooler it is just built into the side of the engine next to the oil filter. It is a liguid to liquid heat exchanger and it uses the engines coolant.
I bit of more information on steves bearing failure. It appears that the thrust shims that are installed on the pinion shaft may have contributed to the bearing failure. Rotax claims that if the shims are not set correctly then premature bearing failure will occur. I have in my instructions to install the shims but some gearboxes dont have the shims just depending on the clearances. I should enphasize to everyone that it is a good idea to check this clearance if you get a used gearbox and everytime the gearbox is assembled. The shims are basically just a thin washer and are available from rotax. Now that steves bearing is bad we cant take that measurement to conclude that this was the cause but its pointing in that direction. On a side note while going through rotax service bullitins i found a that the c gearbox load rating is the same as the 912 gearbox.
Steve henry made it back f to idaho from the copperstate flyin. He noticed his clutch drum was rubbing on the gearbox housing so investigated more and noticed one of the rotax ball bearings had failed. The cage was missing and the balls were free to float. It is the lower shaft bearing. We are just hypothesizing right now that maybe the clutch drum causes heavier loads on the in put shaft bearings. He is going to go back together with the stock rubber dampener and no clutch drum. Put hours on it on and inspect the bearing around the 50 hour mark and repeat.
When you say the springs were loose, did they loose some of their elasticity or did the face plate bolting come loose? I heard that the main killer to these clutches is running them up and down at around engagement rpm so they are slipping a light perhaps in a amphip application. I heard if you go past the engage point and don't hangout there a lot heat wont build up and ultimately causing the spring to weaken. I know for a fact Steve started having that noise almost right away after installing the clutch and he called the designer of the clutch noises and he assured Steve that it was nothing to worry about. He questioned Steve on the application and the HP and he said it would be fine at the higher HP because of the high RPM since it will push the weights out even hard into the drum and that the drum is robust enough to handle the extra centrifugal force. But knowledge and experience being king here I am really interested in your specific failure parts and what exactly came loose. At what hour interval did you experience a failure. At what rpm did you run the engine at primarily. Sorry for all the questions I just want to gather as much data as possible a compare to the RX operating conditions and to possibly save Steve Henry from a failure. Thanks
yes, I did but soon after a purchased the kitfox a Avid came up for sale that needed an engine. So I decided to do the engine install in the Avid. The kitfox does prrtty good with 80hp 912 thats in it so im considering selling the kitfox now and focusing my efforts on the avid
I would aim for level on the float bowl mounting surface but if you wanted to lean it either way within 15 degrees to optain a particular engine position or thrust line you wouldnt affect anything. I have ran the engine on the run stand in all kinds of positions to see if it affected fuel flow or overflowage and it didnt miss a lick or drain fuel. On the snow machines I would imagine they are put in more extreme positions than most of us would.
Greg, thanks for posting im sure everyone loves the pics and the info. I cant wait to see steve's apex engine adapter he gets from you. Heck i might buy one from you if steves works out. i dont currently have plans to build one for the apex engine if your works good.
Greg mills, some of your information here is not true. I do appreciate you sharing some personal experience with the engine as it may be helpful to others. You kind of make me out like a copy cat and i dont appreciate it. Early on when i first started hearing about the yamaha snowmobile engine i did in fact inquire to you about your adapter kit and after i found out you were using the stock cover with a chain drive bolted on top of it I wasnt interested and came up with my own that completely replaces the stock cover and bolts a gearbox directly to the engine and my intentions were not to mass produce these or even make another but my friends wanted some so i got the cnc program and now i can make them as needed but i in no way have a business doing this as you. After i came up with a good adapter with some reputation you in fact inquired to me about buying my adapters if i would modify them to accept your chain drives and i told you i wouldnt do that. Over last couple years i have been watching to see if you have completed kit ready to sell and not just acepting deposits. Are you now actually shiping out kits? Because some people on here might be interested in the chain since it brings the prop closer to the top of the engine where it could be easier cowled. I know I sold a adapter kit to Steve Henry of wild west aircraft and he told me he gave you deposit of $1500 for one and that you were still in development but that was about a year ago. Did you get steve out one yet? It would be interesting to see how it works in the highlander. He is currently flying with Skytrax adapter.
Angle the engine to the left 3 degrees. For pitch angle make the prop. Flange paralel with the firewall that is if your firewall is set up to be perpindicular with flight angle. If you font know for sure the set the prop flange perpindicular to what ever is on the fuselage that is level during flight. If you make shim changes later to the engine mount you may have to modify your cowl