Onans - to rebuild or not

[DavidBarkey]

Like Steve said it is mostly due to the design of the Flat head / low compression and and poor flame travel though the head . I have an NHC big block Onan I would like to try making OHV heads for one day .

Dave

[Timj]

I only notice it when I have it running in the shed. No trouble outside with my p218.
I have noticed that I've become more sensitive to these kinda odors, you would think after all these years around it everyday I wouldn't smell a thing.
Even if I couldn't smell a thing, my wife would let me know. she knows if I even walked past a running motor or a gas can.
I sure love to hear that Onan working. I think/hope I will get many more hours out of it. If/when it fails I don't know what I will do, rebuild or replace.

[Gordy]

It will still make your clothes stink.

If you want an Onan that does not do that you would like a 4-digit model better. It is all about which way the engine cooling air is moving.

The Onan is a dirty engine and that is why they were discontinued. It is a wasted spark flat head. That means that for every stroke both pistons come to TDC. The cam only makes 1/2 a turn per crank full turn. The ignition fires on both sides but one of the two sides alternates having the exhaust valve cracked open. They burn about 2/3rds of the fuel that they use. The rest goes out of the exhaust. So, it is not burning oil that is the problem. It is a simple and robust design that as most things have, has trade-offs.

I read that they are also a 1930's designed engine that because of its "simple and robust design" was never really changed or upgraded till the EPA got involved.


Gordy

PS: Anybody know of a good group for knowledge on rebuilding a Kohler KT- 19 opposed twin? Still a strong engine BUT smokes like a Army smoke generator

[Eugen]

@Gordy you're not going to like this discussion

https://www.mytractorforum.com/threads/ ... od.236554/

[Eugen]

@Timj maybe the p218 engine isn't the same type of engine design wise as the b43 or bf-ms?

[DavidBarkey]

@Timj maybe the p218 engine isn't the same type of engine design wise as the b43 or bf-ms?

Basic design is all the same even up the big block P224 and the NHC. A lot of the parts in the smaller sized group interchange and the same for the big blocks . You can even take a generator long block , swap some parts and put it in a GT.

Dave

[Timj]

@Timj maybe the p218 engine isn't the same type of engine design wise as the b43 or bf-ms?

Basic design is all the same even up the big block P224 and the NHC. A lot of the parts in the smaller sized group interchange and the same for the big blocks . You can even take a generator long block , swap some parts and put it in a GT.

Dave

As @ssmewing said, the 4 digit tractors were better because of turning the motor around.
I would think there is probably some other improvements in the newer models.

[Eugen]

@ssmewing and @Timj sorry guys, I don't understand this. If both B43 and P218 are dirty engines, they both put out smell in the exhaust. My 446 has the tip of the muffler at the front of the tractor in that slot in the hood, on the left hand side. The 4 digit tractors have the exhaust coming out also at the front of the hood, but on the right hand side. Why would that make a difference? The air cooling the fins goes front to back in both tractors. Unless there are exhaust leaks at joints before the muffler exit, there should be no difference. Just trying to understand what you guys are saying.


The fact that at least two of you guys like the Onans so much makes me think I may want to give my 446 another try. Maybe a really good carb tune up, making sure there are no air leaks in the intake and exhaust joints would improve the stink.

[Timj]

@ssmewing and @Timj sorry guys, I don't understand this. If both B43 and P218 are dirty engines, they both put out smell in the exhaust. My 446 has the tip of the muffler at the front of the tractor in that slot in the hood, on the left hand side. The 4 digit tractors have the exhaust coming out also at the front of the hood, but on the right hand side. Why would that make a difference? The air cooling the fins goes front to back in both tractors. Unless there are exhaust leaks at joints before the muffler exit, there should be no difference. Just trying to understand what you guys are saying.


The fact that at least two of you guys like the Onans so much makes me think I may want to give my 446 another try. Maybe a really good carb tune up, making sure there are no air leaks in the intake and exhaust joints would improve the stink.

I was thinking the same thing. That is why I think fuel delivery is better/ leaner on the newer ones. I don't have an older one to compare to, yet.

[Gordy]

@ssmewing and @Timj sorry guys, I don't understand this. If both B43 and P218 are dirty engines, they both put out smell in the exhaust. My 446 has the tip of the muffler at the front of the tractor in that slot in the hood, on the left hand side. The 4 digit tractors have the exhaust coming out also at the front of the hood, but on the right hand side. Why would that make a difference? The air cooling the fins goes front to back in both tractors. Unless there are exhaust leaks at joints before the muffler exit, there should be no difference. Just trying to understand what you guys are saying.


The fact that at least two of you guys like the Onans so much makes me think I may want to give my 446 another try. Maybe a really good carb tune up, making sure there are no air leaks in the intake and exhaust joints would improve the stink.

The 3 digit tractors have the engine oriented flywheel forward, so the cooling air is directed back at you. With that air flow the exhaust gets sucked in with the cooling air, so the exhaust comes at you too. The 4 digit tractors have the engine turned around, flywheel to the rear. So the cooling air is blown forward and would push the exhaust away from you.


Gordy