p220 vs. p216 onan

[mrc 727]

we all dread the valve seat issue in the p220 onan powered 520H.  i hardly ever hear of the same woes from the 416 owners equipped with the p216 onan.  both are installed in the same way in our wh tractors.  why?  what is the difference?  thank you mike in mass. 

[horseyheaven 112]

From memory, I think the bores are the same.  I believe the stroke changed for different displacement/power.

[ebinmaine 63,093]

[lynnmor 6,768]

Less horsepower, less heat.  With aluminum blocks expanding at a faster rate than the steel valve seats, there can be a point where the press fit is lost and the seat starts to move.  This is true of any brand or style of engine with the steel pressed into aluminum.  Air cooled engines might have much higher temperatures at the seat area than water cooled engines so you don't see it so much in automotive applications.

 

Keep the engine cooling fins clean and the engine speed up to prevent over heating.

[tom2p 2,393]

14 hours ago, horseyheaven said:

From memory, I think the bores are the same.  I believe the stroke changed for different displacement/power.

just checked specs - you are correct 

 

P216, 218, 220 share same bore ; P224 has larger bore 

 

P218 and 220 have longer stroke than 216  (P218 and P220 have same stroke - unless I'm looking at a misprint ) ; P224 has longer stroke than 218 and 220

 

Edited January 20, 2021 by tom2p

[Handy Don 10,594]

On 1/19/2021 at 8:38 PM, tom2p said:

just checked specs - you are correct 

 

P216, 218, 220 share same bore ; P224 has larger bore 

 

P218 and 220 have longer stroke than 216  (P218 and P220 have same stroke - unless I'm looking at a misprint ) ; P224 has longer stroke than 218 and 220

 

@lynnmor pointed out that the P218 and P220 have different camshafts (220 having higher lift) and different carb main jets -- not obvious in the specs but different part numbers

[Tuneup 1,416]

Got it! Put 220 cam in 216 to get a 218. I'm tempted...

[Handy Don 10,594]

On 1/22/2021 at 8:53 AM, Tuneup said:

Got it! Put 220 cam in 216 to get a 218. I'm tempted...

Note: I've edited this post on 23-Jan to incorporate some of the comments and corrections from other posters so they are in one place! (and thanks to the posters!)

Tempting, isn't it? But there are several diffs from P216 to P218 to P220.

To recap:

Not sure if the carb body for 16 and 18/20 are equivalent - post '95 carbs are different to meet California emissions regs

Carb body is the same for 18/20 but main fixed jet is different

18 and 20 have same, longer stroke than 16; all have the same bore

18 and 20 have different camshafts (20 is higher lift) (16?)

Some units have a crankcase breather vent from front valve cover into the air cleaner (an early form of PCV valve) which draws crankcase blowby into the air cleaner to be added to combustion air -- seems to be year-dependent

20 (on WH) has tach wiring and block temperature sensor (do not affect operation-just "dressing")

All have pressure lubrication; 16 doesn't always have an oil filter but 18 and 20 always do

 

Edited January 23, 2021 by Handy Don
incorporating additional info

[ebinmaine 63,093]

Okay so forgive the silly question here because I don't have any Onans. 

 

I understand what's being pointed out above about why the 520 would be running hotter given the fact that it's literally got more fuel which is going to create more heat. But I'm not sure I'm seeing anything else. Am I missing something?

 

Or does the 520 have a reputation for running hot simply because there were a lot more of them which by small percentage is going to have more problems?

 

Does the 18 have this same tendency?

 

 

[Handy Don 10,594]

53 minutes ago, ebinmaine said:

Or does the 520 have a reputation for running hot simply because there were a lot more of them which by small percentage is going to have more problems?

 

Does the 18 have this same tendency?

 

Many have taken sides on this issue. Some valid points:

- more fuel=more heat (these are not frugal users of fuel)

- users having higher output demand (e.g. FELs, 60" decks) at higher rate = more effort by engine

- users having lower output demand and running at less than full throttle since engine has surplus power for many tasks (poor heat dissipation) - abetted by the astonishing torque these engines have even at low RPM

- boxer cylinder layout that on WH puts cooling air exit of rear cylinder "behind" the drive belt cover (impedes flow and reduces cooling?) compared to modern OHV V-twins' more elevated cylinders and one-lungers "bolt upright" layout

- layout of cooling fins (too close together and inviting obstruction with dirt?)

- oil filter within rear cylinder cooling airflow path (18 and 20 only) (does it impede airflow? does the oil cooling value offset that? do oil drips from filter changes cause dirt to collect on cooling fins? Has the user left off the filter-to-housing gasket which allows cooling air to escape?)

- high volume of cooling air can draw lots of dust and debris through intake that degrades cooling capability (trait shared with Kohler twins, though some of these have extra screening over larger intake opening)

 

18's and 20's are used in many other ways and are considered very reliable, practical, and long lived. The exterior physical layout of the 18 is identical to the 20--the differences are internal--so all of the above apply. There are far fewer 518s than 520s. The 518's never had hydro lift and had a reputedly less robust hydro pump/motor so, I suspect, fewer have been used in heavy work tasks than 520s.

 

IMHO, many users operate these robust but involved engines in the same way they use a simple low horsepower one-cylinder engine and do not follow the maintenance and operation guidelines carefully or fully. I believe the engines themselves, too, are not as forgiving of incorrect usage as are, say, 12-14hp Kohlers (or even the T or B&S equivalents!) There is a cost to pushing the high end of power and torque while maintaining the lower parts count and complexity of air cooling.

[ebinmaine 63,093]

@Handy Don

Nice right up there. Thank you.

 

I'm familiar with the airflow issues only from having read it on this site.

I've seen examples of people drilling multiple holes in the belt guard to attempt alleviation.

I take it that most or all of the other environments these engines are in don't have that same surround?

 

 

[lynnmor 6,768]

4 hours ago, Handy Don said:

18 and 20 have a PCV vent from front valve cover into the air cleaner and only some 16's have that (essentially two stacked valve covers with a reed valve between)

20 (on WH) has tach wiring and block temperature sensor.

 

 

None of my five 20 HP Onans have that style of crankcase ventilation, nor does the two I just worked on.  I think you will find that it is the year that they were produced determines the type ventilation.

 

The tachometer connection and temperature sensor are just simple things that Wheel Horse added without any engine modification.

 

I have a friend that is an expert in Onan engines and he said that every loose valve seat he encountered had dirt blocking the cooling air.  These engines were primarily made for generators where they usually run in a better environment than tractors.  Also most generator applications govern the speed to 1800 RPM, thus the enormous flywheel/fan.  While that large fan sounds good it also draws in considerable amounts of debris.  Once fins are blocked the fan size does not matter, blocked is blocked.  There was a study done a few years ago on this forum and it showed slightly cooler cylinder temperature on the rear cylinder, so maybe the alterations to the belt guide are of no value.

 

With many refusing to clean the carburetor, or keep it clean with fresh gas, filter and fuel lines, they instead pour snake oil in the fuel in the hope that will fix it.  A partially blocked carburetor will flow less fuel causing a lean mixture that will actually run hotter than the correct mixture adding to a heat related issue.

[Handy Don 10,594]

1 hour ago, lynnmor said:

With many refusing to clean the carburetor, or keep it clean with fresh gas, filter and fuel lines, they instead pour snake oil in the fuel in the hope that will fix it.  A partially blocked carburetor will flow less fuel causing a lean mixture that will actually run hotter than the correct mixture adding to a heat related issue

Excellent points that I neglected to mention. Thanks @lynnmor

[Lee1977 6,214]

9 hours ago, Handy Don said:

Tempting, isn't it? But there are other diffs from 16 to 18/20.

Not sure if the carb body for 16 and 18/20 are equivalent--jet is surely different.

18 and 20 have a PCV vent from front valve cover into the air cleaner and only some 16's have that (essentially two stacked valve covers with a reed valve between)

20 (on WH) has tach wiring and block temperature sensor.

16 doesn't always have an oil filter but 18 and 20 always do.

Part of the problem is that half circle under oil filter. If not cleaned well when changing oil filter oil and dirt will fill the air fins. Mine was completely packed when I bought it last year. The rubber vent to the carburetor was not clamped to the block either.