Just a reminder of sorts to myself so maybe I don't have to learn the whole process everytime I change bearings. I changed main bearings (front and rear) on my OS 120 Surpass III the last two days. Not a whole lot of fun, but very satisfying once all done! Here are some notes to self:
1. Bought these bearings for just over $10 for the pair from McGuire Bearing Co at 2125 N Commercial St, NE. They are both shielded on both sides, but I still don't fully understand shielded vs sealed vs not. Main thing is Bax at OS Engine Support on RCU says it's ok to go unsealed or sealed. Got the dimensions (IDxODxWidth) from places selling the bearings for certain engines, such as Boca Bearings.
2. When dismantling the engine, remember stuff like where the little dot on the cam was at TDC. For the 120 Surpass, the dot is at the bottom of the cam directly in line with the pushrods.
3. To remove the piston requires (on the OS 120) sliding out the cylinder sleeve first, by pushing from the bottom. Then I have to hold my tongue just right to slide the stirrup under the piston off the cam shaft. Putting it back on is even harder.
4. Once left with just the crankcase, the crankshaft, and the PITA bearings, it's time to heat the mess up in the oven. Guys recommended 275F for 20 minutes and 400F for 10 minutes. These removals never work easily like everyone seems to say they do. I heated the case up 400F for about 15 minutes. When I rapped the engine on the rear, the rear bearing inner race and ball bearings fell out. The outer race stayed in the engine. I did more heating, and the front bearing came out in one piece with a little help from a screwdriver and dowel. I gave up last night with the outer race stuck in the engine. This morning I tried heating the engine at 400F for 10 minutes in the oven...NADA. Went to 450F for another 10 minutes...with my needle nose pliers, I think I saw the outer ring of the rear bearing rotate a smidge. Went to 500F and it rotated more and I got it pulled out half way. Went to 530F and after 5 minutes more, a gave the engine a tap on the wood block, and the outer ring of the bearing FINALLY FELL OUT!
Here is a quote from Bax for future reference: "You can use a regular kitchen oven to heat the case, but make sure you've completely degdreased/de-oiled the case and bearings. You don't want any petroleum smoke inside a food overn. You can also use a heat gun, such as used for shrinking film covering. A butane torch will also do the job. j With both the heat gun and butane torch you have to keep them moving around the case to make sure it gets evenly heated. The heat won't affect the bearings. The aluminum case will expand more than the steel bearing races and will allow them to come out. If the bearings are especially stubborn, we've added more heat. As long as the case is heated evenly, we've not had problems." Some guys are concerned that 500F can damage the engine, but we'll see when I try to start and fly this engine!
5. The sad thing is that the new bearings would not simply drop in place. I had to heat the engine up again to 500F to get them back in, and I also froze the new bearings for half an hour. Had to tap on the crankshaft to get the rear bearing seated, and then had to slip the front bearing on over the prop shaft and that required some tapping with hammer and wood block to get it seated, but luckily the assembly went together with just one heating in the oven. Only burned two fingers on my left hand when I missed the pot holder while grabbing the engine.
6. Reassembly was not bad, the only hard part being getting that piston stirrup back on the camshaft. Took many tries and a little tapping. Seems it fell apart but would not just fall back together.
7. Gaps seemed fine, so I did not readjust. Not a hard thing to do with this engine since the head is exposed on the Yak-54 cowl. Also the plug looks ok, and it is easy enough to change if need be later.
Anxious to try her at the field...it won't sound like a farm tractor anymore!
This is just a place for me to ramble (sometimes rant) about my hobbies which include radio controlled airplanes, oil paintings, my sports cars, and any other random blithering from me.
Aloha and Welcome to my small speck of cyberspace! Dec 8, 2010 is the birth date of my blog. Never had one before, but my son encouraged me to have one, and it seemed like a good way to at least keep a log of my RC airplane building and flying. With the initial design kicked off by my son, I'll carry on from here and have fun with it. Now that I have it, I will use it to also keep track of my oil painting efforts, and any other ideas, hobbies, travels, or whatever else that come up. LIFE IS GOOD!
Update on 02/25/2011. It's been a few months since I began this blog, and I am enjoying creating and having it! I like documenting the things I have done in my hobbies, and sharing with my small family. I think Jer and Tad actually view it fairly regularly, as a means to see what I've been up to lately. At worst, it serves as a reference for my own use.
Update on 12/22/2011. This blog stuff is habit forming. My blog is a year old now, and I make an entry about every other day or so as that seems to be the frequency of doing something in one of my hobbies. Like my hobbies, this blog is a lot of fun, and it has become in itself another hobby that I enjoy.
Years are flying by...update on 01/11/2013. Still enjoying maintaining this blog even though hardly anyone sees it. I don't advertise it anywhere or to anyone, and it is mainly just a way for me to keep my own notes and thoughts on my flying, painting, and cars. If a stranger happens upon it, I think it is by pressing NEXT at the top of the current blog they are visiting, lol. It's a great device for me.
August 2014: still here! Took up flying RC helicopters one year ago and got hooked. Had flown micro Helis up to then, but got serious with 450 size for a couple months, then bought the Goblin 500 and Gaui X5 . Also got my Boxster in April 2013. Most importantly, Ariel was born 12/02/12 followed by Skylar 07/20/13, and they are little beacons of joy in our lives. Life is indeed good!!!
No comments:
Post a Comment