Onan Moving Too Much Air?

[Tuneup 1,452]

Hi gang,

 

I've read before that these engines were designed primarily to run at 1800 RPM under load to a generator so the flywheel is designed to move adequate air at that RPM. With the 3600 RPM machines we run, the flywheel is likely unchanged? If so, it would explain why I can't mow the lawn (weeds and dirt) without that blower sucking up grass clippings and dirt - not good for the fin cooling.

 

Soooo, the natural question, and keep in mind that my 216 DOES NOT have an oil filter in the way of the cooling air stream: Why not consider cutting some of the air flow by either removing the alternate fin (retaining balance) or, in red neck fashion, taping around the alternate two fins and reduce air flow to be more appropriate to the higher speeds?

 

It would also save some horsepower for the PTO.

 

All that said, I wouldn't want to test this without a baseline of running head and oil temps. I could run a thermocouple on for these and make a measurement on the 516. My lazy butt might get around to doing that one day but was wondering if it even makes sense to try - I don't know that the flywheel was or was not altered for the higher RPM we utilize.

 

Flame on?

[Tuneup 1,452]

Well, flea bay gave me the opportunity to buy a couple K thermocouples cheap so I might be able to test this simply enough. Stay tuned.

[tom2p 2,394]

the engine will generate more heat running at higher / 3600 RPM - so it will need more air / cooling (compared to running at lower / 1800 RPM)

 

[Tuneup 1,452]

Hmmm, yes, maybe, or does the load on the engine determine the amount of heat regardless of RPM? If that is a given, would our typical tractor load mowing at 3600 = the load demanded by a gen at 1800? If so, less than 3600 RPM cooling needed. Heck, I don't know. A generator works those engines hard. Those sensors will get here next week and I'll measure oil temp during a mow since that's just an immersion setup and is quick and dirty. Getting a good reading on a head will be trickier. I'll probably drill out a fan housing bolt on the head and sink the sensor in epoxy. Should be fun.

 

Then, what is a good air-cooled engine head temp. On my Beetle of long ago, we kept it less than 350F. Curious to see the Onan values.

 

An 1800 RPM flywheel? I can feel the wind this thing generates across the garage and that flywheel is a beast. Anyway, measurements needed.

[lynnmor 7,815]

Yes, they do suck a lot of debris but I would attack the source of the debris before altering a cast flywheel.  Watch the left front tire as it tosses grass up into the air stream, and then think about making a fender for the tire.

[8ntruck 7,833]

If you have the chance, baseline an Onan on a working generator to see what the operating temps are in that application.

[Tuneup 1,452]

1 hour ago, lynnmor said:

Yes, they do suck a lot of debris but I would attack the source of the debris before altering a cast flywheel.  Watch the left front tire as it tosses grass up into the air stream, and then think about making a fender for the tire.

 

I will certainly focus on where it's coming from. Seems to stop the grass but plenty of dirt getting in there. My 'good yard' is perfect Bermuda and I hand mow it but the rest is whatever wants to grow.

[Tuneup 1,452]

49 minutes ago, 8ntruck said:

If you have the chance, baseline an Onan on a working generator to see what the operating temps are in that application.

 

Now, that would be nice. I USED to have one on an nice little RV we had long ago. It was perfect. Kept the rig warm in the Walmart parking lot. One trip to Nova Scotia and back for the wife's parents and...gone.

[tom2p 2,394]

8 hours ago, lynnmor said:

Yes, they do suck a lot of debris but I would attack the source of the debris before altering a cast flywheel.  Watch the left front tire as it tosses grass up into the air stream, and then think about making a fender for the tire.

possible a ribbed front tire would reduce the problem ?

Just yesterday was watching grass clippings get sucked from the tire to the air intake - and wonder if a ribbed from tire (as opposed to the OEM Dico or similar) would be less likely to retain the grass clippings as it rolls (and therefore less clippings sucked from tire into the air intake)

 

 

Edited April 25, 2021 by tom2p

[tom2p 2,394]

12 hours ago, Tuneup said:

Well, flea bay gave me the opportunity to buy a couple K thermocouples cheap so I might be able to test this simply enough. Stay tuned.

thermocouple ?

 

get a FBGS (Fiber Bragg Grating Sensor) and imbed into the piston crown 

 

lol

 

[lynnmor 7,815]

4 hours ago, tom2p said:

possible a ribbed front tire would reduce the problem ?

Just yesterday was watching grass clippings get sucked from the tire to the air intake - and wonder if a ribbed from tire (as opposed to the OEM Dico or similar) would be less likely to retain the grass clippings as it rolls (and therefore less clippings sucked from tire into the air intake)

 

 

 

 

A ribbed tire might help a bit, but the perfectly smooth front tires on my zero turn gather up grass till the yoke around the tire is stuffed full.

[Tuneup 1,452]

6 hours ago, tom2p said:

thermocouple ?

 

get a FBGS (Fiber Bragg Grating Sensor) and imbed into the piston crown 

 

lol

 

I'm too old. Messing with simple thermocouples and thermistors in data acquisition systems is more my bag. I used to troubleshoot and repair those systems. I miss those days - like working on cars or tractors without the dirt. The closest we got to fiber was in early UV communications. I think this will be some fun. The 516 is purring and might be up to a little experimentation without getting grumpy.

[Tuneup 1,452]

I like the ribbed tire idea. Will keep it in mind - always up to wrestling with tires, rims and Ru-Glide.