ONAN twin cylinder head temperatures

[JackC 616]

SOI, That display looks great. Every ONAN twin should have one and every Kohler and Briggs also.

As to your questions:

1. On the alarm setting, 5 degree increments should be good enough.

2. For over temperature, a single alarm should be good for both. I would be happy if the alarm triggered on either cylinder hitting a trigger point. For over temperature, could the display for the hot cylinder blink and an audible alarm go off?

3. I am not sure we know enough about delta yet to know where to set limits. The delta may increase slowly over time as some condition deteriorates. An ONAN engine will start and run on one cylinder so in that case the delta would indicate a dead cylinder even though no temperature is exceeded. In that case it seems that it would be good for an alarm to go off. If the displayed delta number could blink that would be good also.

4. Not sure about under temp. Perhaps the temperature display could blink until a normal operating temperature is reached at whatever temperature that may be. Would that have to be pre-programmed or could the user specify that?

Is it possible to make the display characters blink when the displayed numbers are below or above specified values? There may be times when the audible alarm may not be desired, for example when troubleshooting a known poor running engine, but the displayed numbers could always blink if lower and upper bounds are exceeded.

[JackC 616]

Don and Nick, with the temperature monitors installed we would be able to collect a lot more data and learn a lot about the conditions that influence temperature and temperature differences. The monitors should be able to alert us to conditions that need attention to avoid engine failures.

[Save Old Iron 1,563]

A few additional thoughts.......

with the conversation heading toward fuel mixture differences contributing to cylinder temp differences, I have the sneaking suspicion we will be talking about EGT (exhaust gas temperatures) in short order. I think I will be proactive and put an EGT display on this monitor too. It would require one or two exhaust system thermocouples to be installed but they would be optional to operate the monitor - not required.

I'm convinced EGT would give a faster and more responsive indication of cylinder performance than CHT (cylinder head temperature).

I always viewed EGT to be a useable tool than CHT, especially for live tuning of fuel air mixtures. EGT is more of "here it comes" where CHT is more "oh crap ! it's already here!"

The other common discussion relates to the intake screen clogging up. Clogged screen = less air passing thru the cooling fins of the engine. Last night I had the image of an automotive mass airflow sensor come to mind. Mass airflow sensor technology could be placed behind the inlet screen to monitor the actual airflow thru the inlet grating. The "heated element" airflow sensor is actually quite easy to implement and might allow us to "step out in front of the problem" of overheated cylinders by monitoring one known cause of overheating - a clogged air inlet.

Today's task - get the CHT alarm setpoint menu to function. Guess I'll start off at 300 degrees F and increase the alarm setpoint by 5 degrees F per key press ?

[Save Old Iron 1,563]

Jack, et al,

I just received a package containing the 4 x20 displays. As anticipated, they are larger than the 2 x 16 display.

4x20 = 2.5 inch by 4 inch

2x16 = 1.5 inch by 3 1/4 inches.

This brings up a design question. What style enclosure do you envision for housing either display? Where on the tractor do you envision this enclosure being mounted? Is the addition of two lines of info worth the increase in the size of the enclosure?

[JackC 616]

Initial thoughts are as follows:

The 4 line display dimensions are similar to my iPod or a smart phone and the monitoring device could have a similar look.

Any set buttons would be on the right side (most are right handed) not the top or bottom if that is doable otherwise bottom is OK.

The 4 line display could be used as follow:

TEXT

TEMP

TEMP

RPM

The two line would have a similar look but not as tall.

The mounting location options should include the following:

1) top of hood for maximum visibility above the dash (older tractors and the 520Hs),

2) on the maintenance decal above the dash on a 300, 400 series,

3) on the dash,

4) on the shift cover below the dash.

For mounting on top of the hood, a triangular or hinged stand of some kind would be needed and a means to attach without damaging the finish on the hood would be needed such as a padded magnet or double sided tape or both or sticky feet of some kind. Adjustable viewing angle would be good to accommodate different height drivers.

For mounting on the maintenance decal or directly on the dash, something like double sided tape could be used. Not sure if the plate behind the dash is aluminum or steel on the C series for a magnet to be used or not. The top of the tower is aluminum.

For mounting on the shift plate the triangular stand could be used if angled up against the front on an 8 speed or just the double sided tape if there is room to mount it flat like on a hydro. Different users will want different mounting options. There could also be some mounting brackets designed for those who prefer permanent mounting and don't mind drilling some holes.

I will see if I can draw some diagrams or take some pictures over the weekend.

[JackC 616]

Additional thoughts:

1) If RPM can be implemented, an alarm would be triggered if the RPMs are too low (carbon built up condition) or too high (governor not working correctly).

2) For mounting on top of the hood, a sun shield over the top of the display (like the brim of a hat) may be needed.

3) I edited the previous post to indicate buttons on the right since most drivers are right handed. Bottom is second choice.

4) So as not to distract the eye from the displayed information, the case would be black plastic (or metal) and be as small as possible to house the display and set buttons.

[Save Old Iron 1,563]

submitted for your comment - I'm still waiting on a few components but decided to investigate a graphical display as opposed to a text display. Instead of being constrained by lines of text, this display is just a field of addressable "dots". Shapes are possible - boxes, circles. logos, graphs, varying sizes of text.

These displays are surplus from Nokia cell phones and are super easy to interface to computers. Another really nice feature is they fit inside the standard 52mm gauge housings. You can build you own custom gauges to mount in existing dashboards. The gauge face is TOTALLY CUSTOMIZABLE to whatever appearance you could want. I have 2" polycarb tubes on order for the gauge body and laser cut polycarb faceplates for the gauges. I'm hunting down the chrome trim rings for the face of the gauges. Maybe back to the Harley dealer.

My thoughts are now going to a dual display of analog pointers for both head temps and a digital readout in the middle. Let's see if that can be done! Then there's always COLOR readouts too!

[baerpath 517]

Stop down to the chrome shop in Fonda. He should have trim rings in a variety of sizes

[JackC 616]

Stop down to the chrome shop in Fonda. He should have trim rings in a variety of sizes

Does the shop in Fonda do chrome plating?

When dealing with colors, many men have red green color blindness so some colors combinations would be hard for them to see.

Also, maximizing visibility of the displayed information in sun light is a consideration.

http://www.toledo-bend.com/colorblind/Ishihara.asp

[philpjuk 19]

I run a prewar douglas motorcycle with fore and aft cylinders,these always run cooler on the rear cylinder which is masked by the rest of the engine,this is said to be caused by the crank throwing more oil to the rear cooling it,maybe the Onan does the same?

[Save Old Iron 1,563]

Maybe SOI can come up with a recommended hook up with a relay so we can all add the loud horns to our twin ONANS 520s and 416s. It would be good if the test switch also tested the horn. 12V boat horns are really loud.

Be happy to do up a circuit. We still need to come to some consensus as to what temperature to trigger the alarm at. The rest is really quite easy to implement.

There is a company on Ebay called Ordoer that sells thermodisc style temp switches.

http://www.ebay.com/itm/2pcs-Temperature-Switch-Thermostat-155-C-N-O-KSD301-311-F-2548-/221085678446?pt=LH_DefaultDomain_0&hash=item3379bbbb6e

They appear to have a good selection of switches that trigger in the low 300 to 350 degree F region. Maybe worth a look for $4 for 2 pieces shipped to your door.

[Save Old Iron 1,563]

And being that I never leave well enough alone, always seeking that adrenaline rush from unexpected discoveries .....

a 2 stage alarm with a visual indication (or a muted pre-warning audible alarm if you put a resistor in the horn circuit)

p.s. I'm guessing at these trigger temperatures. I have not concluded any research on what constitutes "over temperature" of an Onan cylinder head.

From the "Demystification manual":

The contacts inside the switch are normally open. As the body of the

switch warms, the clearance between the contacts narrows, until the

switch closes at 320-340 degrees F. It does not reopen until the

temperature falls to 280-310 degrees F.

[varosd 1,185]

great info Chuck and the video clip! 03:57! I thought I get up early!

[JackC 616]

"p.s. I'm guessing at these trigger temperatures. I have not concluded any research on what constitutes "over temperature" of an Onan cylinder head."

According to page 3-26 of the Demystification guide, the trigger point would be 320 to 340 degrees F. That is where the 520H over temp switch closes and it does not re-open until 280 to 310.

When mowing or putting the engine under load and being preoccupied with operating the machine, I would much rather be blown out of my seat by a loud horn rather than smoke a rod or a valve seat.

Due to the Holidays and cold weather I have not collected any more temp data on my horses. I am curious how the various engines I have measure out.

[ericj 1,576]

i'm in the process of tearing down a blown P216 that i picked up for parts awile ago. when i pulled the pan the oil had a very strong burnt smell and the oil in the filter looked like tar, now the motor has been sitting for well over a year and for some time out side uncovered in the elements. will try to post some pictures when i get time to take them and post, might be alittle while

eric

[Save Old Iron 1,563]

A quick update

I have just received an automotive intrusion alarm which may prove useful for the Onan temperature monitor circuit . This little device (2 inch diameter by 1 3/4 inches tall) produces a 110 db screech sure to be heard even if it tucked in the hoodstand of a tractor with the Onan at full rpm. Current draw is less than 2/10ths of an amp while on.

For those who may be interested in following along and build a prototype alarm - about $4.50 to your door. Careful, this device is PAINFULLY LOUD at 12 volts. It is meant to be placed inside a car to make the interior of the car uninhabitable if the alarm is sounding. If this device proves to be too loud in use, the sound intensity can be adjusted down by addition of resistors in series with the power leads.

http://www.ebay.com/...984.m1439.l2649

I'm also investigating a yellow 2 line LCD display to see if it is more legible in sunlight than the white on blue LCD pictured earlier. Reports to follow once the sun shines in upstate NY.

Finally, I am able to reduce the size of the computer board needed to run this whole mess down from 3 x 5 inches to a mere 1 x 3/4 inch profile. This will help in reduction of the case size and allow the size of the display to determine the overall size of the enclosure. I would still like to be able to stuff all this into a 2" gauge case. If not, the case size for the temperature monitor would not be too large as to be offensive looking when mounted on the tractor.

More to follow

[JackC 616]

Keep up the good work. We do not want to lose any more of those sweet running ONANs. Especially the ones on my tractors.

[artfull dodger 329]

Here is some real world data, just adusted the valves on a JD318 with a Linamar P218 engine, 497hours on the clock. Both intake valves were greater than .013 and the exhaust was tighter than .005. All valves were reset to factory spec. Tractor is much easier starting as that was his complaint, that it was very hard starting when cold. Starts up much better. My 518 has always started easily. I am wonder if shutting down an Onan without any cooling down helps the valve seat issue happen? Have you watched what the heat values do right after shutting down and block heat soaks from loss of cooling air? Mike

[doc724 924]

I'm goning to add my 2 cents here, and I aplogize if someone else already suggested this somewhere in the previous 6 pages (I admit, I did not read all six pages). If, as several have mentioned, think that residual heat (after shut down, temperatures will continue to rise until natural convection cooling brings them down) is the culprit, why not have a 12V fan connected to one of those small thermostats that another poster suggested. The thermostats are NO (normally open), also known as "close on rise" style. As temperature goes up, the switch will close, energizing the fan. The fan will not shut off until temp drops below a preset limit (the differential). The reset temp is always lower than the close temp. This is the same method used on many automobiles that has the cooling fan still running after you whut off the car. I know this is not an elegant solution, but is is really low cost.

[roscoemi 245]

SOI, you can always use a layer of duct tape to quiet the alarm down! :ychain:

[Save Old Iron 1,563]

Here is some real world data, just adusted the valves on a JD318 with a Linamar P218 engine, 497hours on the clock. Both intake valves were greater than .013 and the exhaust was tighter than .005. All valves were reset to factory spec. Tractor is much easier starting as that was his complaint, that it was very hard starting when cold. Starts up much better. My 518 has always started easily. I am wonder if shutting down an Onan without any cooling down helps the valve seat issue happen? Have you watched what the heat values do right after shutting down and block heat soaks from loss of cooling air? Mike

Mike, the whole temperature monitor thing is still in the development stage. I'm learning as I go with some new microprocessors and software on the market and we are still trying to determine exactly how and WHERE to measure the head temperatures. So we don't have any live data yet. We haven't even reached a consensus on what the "danger point" is for head temps.

I'm thinking with the ability of aluminum to transfer heat, the instant you shut off the heat supply produced during the combustion cycle, the aluminum fins will cool down rapidly - but that is why were are doing this experiment to begin with - to know things - not to guess at what's happening.

[artfull dodger 329]

I will watch with baited breath for the results of the experiment. I plan to pickup an analog gauge made for air cooled snowmobiles to watch cylinder head temps and put it in the dash of my 518h when I upgrade it to a 520 dash with full gauges. Probably ditch the air filter gauge. I used to see a twin needle gauge for twin cylinder Rotax sled engines. I used to have one on my Skidoo 550 blizzard. It is a shame we cant sit down with a couple of the old Onan designers of the P series and get thier input to these failures and why its more prone to the garden tractors and not the gen set engines. Unless the fixed 1800 rpm and more constant load is the key, along with a cool down period after unloading the generator before the engine shuts down. Mike

[wheeledhorseman 573]

I’ve just read through the whole thread which is fascinating and of great interest as I have a 316 with ONAN that I bought last year originally for parts but decided it would make a nice project. Despite over 1000 hours the engine runs and sounds just so sweet with bags of power though it does suffer from the notorious hunting when it gets hot (well covered in other threads). Visually I’d say nothing’s ever been touched just oil, plugs and filter changes in it’s early life and probably not much at all if anything by the P.O. I got it from.

Fairly early on in the thread it was mentioned that cooling fins on these engines are not symmetrical due to the oil filter location which to my mind would certainly account for some difference in temperatures. But here’s the twist, my ONAN has no oil filter, a fact I only discovered after I’d bought a new one for it as all documentation says they do. There’s a rubber blanking disc in the tin where the filter would protrude and if you remove it you can see the machined surface on the block where it would normally attach. It’s come up on threads before but nobody has really answered why some ONANS are without – something that I don’t believe made it to any manuals.

It could perhaps have been a cost cutting measure but then why include it in the first place if it wasn’t strictly necessary? I don’t think it was a cheaper version for the European market as I think these engines turned up on tractors in the US as well. Ok, so my 16HP flat twin Briggs in a 216 has had a long life without an oil filter by design and maybe it was a bit of over-engineering in the ONAN but then again supposing there was a known issue with these engines and not fitting the filter was an attempt to rectify it? Sorry to throw in yet another variable.

Of course, if there is any mileage in this suggestion then was it an air flow cooling issue or was it a lubrication issue i.e. an attempt to improve oil flow?

Keep up the great investigation guys! Will continue to follow with interest.

Andy

[JackC 616]

Here is some information on what happens when an engine overheats causing a piston to seize in the cylinder. I assume when the engine overheats and a piston seizes, then the rod can break. There are a number of reasons why the engine can overheat. One example is the flywheel screen getting plugged with grass resulting in insufficient cooling air getting to the heads. A good temperature monitor can alert the operator to this condition.

http://www.ultralightnews.com/engineinfo/chtwirdia.htm

[artfull dodger 329]

Some Onans in the 316's, being a strip down 318 in the first place, didnt have the filter, the engine could be ordered either way. You definatly wanna take it down and adjust the valve lash to spec, .005 on intake and .013 on exhaust with a cold engine. Then give the carb a good cleaning. The combination should clear up the hunting(running lean) problem. Keep the belly screen clean if it has one, if not get one. MIke