Any more, rebuilding the Onan is no worse than rebuilding a Kohler KT or Magnum series twin and easier from a labor stand point. You will need to do the decarbon and valve adjustment right away, might just be miss adjusted valves not seating fully when closed. With the heads off to decarbon, you can inspect the bores and piston tops. Onans are powerful beasts but must be maintained, valves adjusted every 200 hours ect. Where as the old Kohlers you set them at rebuild and forgot about them after that. Onans were used in tons of RV gensets and can rack up well over 3000 hours before needing major work, but they are kept much cleaner and in proper adjustment in the normal RV set up. I myself am looking for a 446 to restore, guess I am different, give me the Onan over any Kohler opposed twin. Mike
Case 448 Hood Scoop Tractor - Should I buy it?case 448 compression
Posted March 17, 2015 - 07:09 AM
Posted March 18, 2015 - 11:51 PM
First of all, I bought the tractor in question. I now have it home, and have been playing around with it, to see what kind of condition the tractor is in. So far, better than I had hoped. It really does look like the tractor hasn't had that much use, certainly not hard use.
The motor seems to be in far better condition than what I had feared.
Here is the history to-date:
1.) Seller checked compression: Compression 75 and 50.
2.) Seller added Sea Foam additive, ran tractor for 1/2 hour, Compression 75 and 60.
3.) Got the tractor home. Attempted to run. Spitting and sputtering, backfiring so bad at 1/2 throttle couldn't go any higher RPM's. It did run pretty good from idle to approx. 1/3 throttle.
4.) I changed oil, added Marvels Mystery Oil to oil and gas. Ran for 2 hours. Noticable improvement to running sound at after about 20 minutes. Continued to improve. At end of 2 hours, drove about 1 mile with throttle wide open, ran great, except for very mild miss.
5.) Checked compression cold, 120 and 81.
6.) Ran for 2 hours more. Drove it around. Runs pretty good, except for a slight miss (could be carb. - didn't do any carb. adjustments yet.)
7.) Checked compression cold, 120 and 91.
My question: What should I do next? Is a rebuild needed? I read that 10% difference is tolerable. But the way that 2nd number keeps rising, makes me wonder if maybe its carbon under a valve?
I'm wondering if I run for another 2 hours, will that lower number continue to rise?
I do have to replace the starter (it works, but with a terrible grind), so I'm going to start with that . . .
Should I pull the heads to have a look inside? Or put it back together and run it, hoping the second number will continue to increase?
Please send suggestions . . .
Posted March 19, 2015 - 03:54 PM
Not sure what engine you have, but some BF's have pressed together intake manifold. It's top/bottom parts and kinda riveted together along sides. Sometimes the seal between them gets open and halves seperate a tiny bit and leak air, messing up carb mixture then. Myself, don't look into rebuilding engines unless they are smokey or making some mechanical noises. Just run it and enjoy! Working it more has got to be better for it than sitting.
Posted April 05, 2015 - 03:03 AM
Welcome! I also have a 448 and have found that decarboning is mandatory. The owners manual mentions it. You will like this garden tractor. Just keep using it. Mine does not have the hood scoop, wished it did as they are cool.
Edited by A.C.T., April 05, 2015 - 03:08 AM.
Posted April 07, 2015 - 08:18 PM
Time to pull both cylinder heads, decarbon them and the piston tops. Then pull the chamber covers and adjust the valves, I would bet the lower side has a valve being held partial open. Once a decarbon and valve adjustment is done, go back to working the tractor, cutting some grass or even just running the deck at full power will load the engine more than driving it around. I am leaning toward sticking rings along with needing a very overdue valve adjustment. I have the specs in my Onan manuals at work if you need them. Both intake and exhaust are set with a cold engine, and require removal of the exhaust and intake manifolds. Mike