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24GLX - repower notes

5216 Views 17 Replies 4 Participants Last post by  Richard-tx
Now that I have had the opportunity to spend some time on the Onan P224 powered 16G with the shop made exhaust, I figured now would be a good time to describe the experience of the engine swap and the results.

1 - It does not sound like a 24G. It sounds very similar to my 818T. Maybe a little more rumble but not much.

2 - The tractor doesn't feel all that different. The Onan is a little heavier but not a lot.

3 - The engine isn't that much bigger and yet it is. Compared to the M18 that came off, it looks to be at least 30% larger. In terms of displacement, it is 50% larger. (42 cid vs 60 cid) It is slightly larger than the B48 but not by much. The 3 qt pan does reduce the engine ground clearance compared to the M18 but the transmission is still lower than the engine. The rear cultivator will still work.

4 - As near as I can tell the rear engine adapter from any B series Onan will work with the P224. Not sure about the CCKA.

5 - I had to drill and tap two 3/8-NC bolt holes in the P224 block. There was a casting depression in the crankcase where the holes should have been so locating the position for drilling and tapping was easy.

6 - The crankshaft on this engine had a long 1/4" slot in it. That meant that the shaft seal in the adapter plate was pointless. To seal the transmission I put some RTV around the OD of the bearing plate. That has worked well so far.

7 - The crankshaft was short by about 3/4 of an inch so I made an extension from an old K301 crankshaft and held it on with a SHCS. A metal lathe made that an easy task.

8 - I tied the oil pressure switch through the ignition. To keep the cranking time low, I added a relay so that when the starter was engaged, the coil received power. Without the added start relay it would take a second or so to build pressure before it would start.

9 - A new throttle cable is required. The throttle cable for the M18 is too short. The original choke cable however is just fine.

10 - Rewiring the ignition relay was easy. I just followed the schematic for the 24G.

11 - I added a 4 wire connector at the engine. I decided to use the same connector used on the 24G. It seemed to make sense should I ever want to remove the engine.

I ran it through some wet grass and leaves. Not once did I feel that the engine was approaching maximum load. I was running my modified 50" deck with the 40" deck pulleys. Just to spin that deck with Gravely blades requires 12 hp. I have spun that deck on a 5665 with a freshly rebuilt engine governed at 3300 RPM, the throttle plate was almost wide open. Held wide open the engine would run up to about 3400 RPM. Dropping the PTO clutch at an idle just spins up the deck. No worries about stalling the engine.

I redid the exhaust system to use 1-3/8" pipe. That actually worked out better than the 1-1/4" pipe. The 1-1/4" exhaust system will be used on my 818T or CCKA when the time comes. I will be ordering muffler guards next week.

This tractor now is on the same class as the Pro16. I have to start it just to listen to it run.

All in all, it was a pretty easy job, exhaust system included. I just took my time and enjoyed the process. My recommendation is that if the opportunity arises, do the upgrade to a P224. It is worth it. It is as significant an upgrade as going from a K301 to a M18.

Two word summary? "Quiet Giant" comes to mind. One word summary? "Sleeper"

I did receive some assistance and parts from a few members here. I do have to thanks them for their help.

Don in Fla. who supplied the chunk of crankshaft
Tom, aka Popcorn, who sold me the adapter plate
Boomer - the used Onan parts guy who supplied the correct throttle pieces and engine guard that the PO lost.
Onanparts - for the exhaust gaskets, etc.

Pictures to come.
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Here are a few pictures. Everyone likes pictures.

The amount of clearance between the tire and engine - about 2.5"

Clearance between the hitch and engine. Lots of space there.

Bird's eye view of the 1-3/8" stainless exhaust. Look Ma! No rust! These pipes sat outside in the 2 day rain we just had.

Guess which muffler clamp is the chrome one. The extra clamp is there for the muffler guard. The guard will attach to the one pointing up.

I have to add some loom and a couple of zip-ties.

A clear shot for the rear PTO driveshaft.

Even with the extra 1/2" taken up by the shaft adapter, the blower pulleys line up nicely. Tailpipes to come.

Close up of the PTO adapters. I made the aluminum one.

The mounting plate and crankshaft stub installed. At this point, it is ready to be installed. I moved the snap ring after this picture was taken.

What the engine looked like before I brought it home.

The wiring was a mess. I ultimately removed it all and tossed it in the trash.

The little bit of brass protruding is the jet. There was a significant amount of dirt in the bowl. The idle jet was clogged and had to remove the idle mixture screw and blow it out. I did not remove the carb from the engine. I did this one the same as I do on my other Onans. I cleaned it in place. So far I am batting 1000 on that procedure.

The reason for all the dirt was the wrong fuel filter was used.
One more thing, if someone decides to duplicate the exhaust system I build, there is one piece of pipe that has to be turned on the lathe. In essence what is needed is a 1-3/8" to 1-5/16" adapter. That consists of a short piece of 1-3/8" pipe that is turned down a little and a piece of 1-1/4 tubing to couple the muffler and reducer to the 1-3/8 pipe. If anyone needs their pipe turned, I will do it for free. All it will cost is the shipping.

The same goes for tail pipes. 1-1/4 tubing will have to be turned down about .040 - .050

Thank you for taking the time to share the more technical aspects of this with us. While not a difficult conversion, not something I would likley jump into since I don't have some of the resources you do.

Should my 16G, (18GLX ?) ever need an engine, I will likely go the new engine route. But actually I won't be unhappy if I never need to.

Reading this last night got me thinking more about the debated differences between the M18 supplied on my tractor, marked 16hp, and other M18's, GRAVELY or other wise.

I have a Kohler master parts list for the M18, M20 engines, and after even more review of the parts used on verious spec numbers, there is no doubt in my mind that the M18 on my 16G is every bit the same engine power wise as the same year 18G engine, and many other M18's installed on various other brands and years of tractors, GRAVELY and otherwise, and advertized as 18hp.

In fact, there is nothing in those parts breakdowns to imply that any M18 produced measurably more or less power than any other M18.

And just to be clear, for those who will say that the carb is different - carburators cannot dictate horsepower, they can only limit max rpm by limiting max air flow - not a factor on a governed engine. The throttle bore of all the M18 and M20 carbs are the same - so their cfm is the same.

Cam lift and timing, ignition timing, valve size and compression ratio are what control the production of hp and torque in an engine - all of these elements appear to be the same on all M18 engines.

And now with my governor set at 3550 rpm, I am very happy with my 18 hp.

Again, Richard, great conversion and I'm sure it will serve you well, especially as you know how to treat the PTO clutch with respect.

Those Onan engiens are great - shame they are no longer made.

I agree with your assessment of the M18 regardless of what the sticker on the tin work says the HP is. I can find not any difference between the carb used on the 16 hp M18 and any other M18 or KT 19. The throat diameters are the same.

I am still debating what to do with the M18 I removed. Since that engine does not have a bolt on pan (another reason for me to hate the engine) I can't check the rod clearances unless I disassemble the engine. I am leaning toward selling the thing on CL and find another Onan. In the meantime, I think will put it on another tractor here are run it until it blows up.
A M18s is a M18s. If there was ANY difference, it was the max RPMs set on the engine. I say it boils down to a marketing snow job. With the addition of the heavier steering components, there could be justification for the bigger price tag. A 16G is one of those rare cases where you get more than you paid for.

And Richard, thanks for the info. It helps to show that are not as limited on engine choices and we may think. How about a little more detail on that shaft extension?
here are some pics


A M18s is a M18s. If there was ANY difference, it was the max RPMs set on the engine.
I think that suits me just fine to have an engine on my 16-G that has revved lower it's entire life (except when I cleaned the main jet for the first time! :eek:). I hate listening to an engine running full-throttle anyway.

- Nathan
The fact of the matter is that for mower duty the engine has to spin fast. The blades won't cut otherwise.

There are engines and then there are engines. I have heard some engines sound like they are going to fly apart @ 2400 rpm and other engines that sounded like they are at 2200 when they actually are at 3300.

For snow plowing duty I found that 3/4 throttle worked well. The added heat pushed up toward the operator was most welcome.


When it comes to selecting a replacement engine for a Gravely, there are a few things to consider.

1 - availability of an engine mounting plate. This usually stops most people from installing the engine of their dreams. A mounting plate can be made but a 12"x36" metal lathe is needed as well as a drill press and probably a mill. This is not a $50 item. Jut the raw materials (aluminum) will cost more than $50.

2 - Size of PTO shaft. Too small is no good. Too big is no good. Now one could argue that the crankshaft could be turned down and while that is true, I am not sure anyone wants to void any warranty by disassembling a new engine to have the end of the crankshaft machined.

3 - Exhaust system costs. An exhaust systems cost between $50-$400. A lot depends on how you want it to look. If you don't care, then the cost drops.

4 - Used engines. There are some people out there that have a funny definition of "runs good". There is a lot of crap out there with the occasional gem. I could say that the M18 I have runs very good...yet the crankcase is cracked. I got lucky. Very lucky.

5 - New engines. Some say there are Chinese made Honda clones out there. I cannot find any. Some say there are Briggs clones. I can't find any of those either. One obvious externally viewable difference in the alleged Honda clones is the fan. They use a plastic fan for the engine. Honda makes their fans from aluminum. Therefore they are not clones. Even the bore and stroke specs are different. A cheap imitation would be a better description.

If a throwaway engine is acceptable, then by all means get a cheap Chinese engine. There are no parts (that I can find), no support and likely won't be any...not for the foreseeable future. If you want an engine with parts support and a large installed base, then the name brand is the only choice.

6 - Premium, cheap engines. There aren't any. They just don't exist and never have. If there was a way to make an excellent cheap engine it would have been done years ago.

7 - Failure engineering. When a given engine throws a rod for example, what usually happens? Does the rod eject out the side of the engine or does it simply break with no damage to the block? This is part of why some engines cost what they do. In the case of a premium engine, the damage is usually minimal. A cheap engine will be destroyed.

8 - Power. In general and in the right hands (no abuse of power) there cannot be too much power on a Gravely 4 wheel tractor. Excess power has the advantage of increasing longevity. An engine that is loaded to 50% capacity will last much longer than an engine that is run at 100% capacity.

I believe that over the lifetime of a Gravely tractor (40-80 years) all engines cost the same. A cheap engine (Courage) will likely need to be replaced every 1500 hours as they aren't worth repairing when (not if!) an internal part fails. A premium engine on the other hand will last about 3000-4000 hours and then can be rebuilt.

Life is full of choices. It all depends on what is most important.
Richard, Excelent summation of the issue.

Call me a wild man, but I usually plow snow at full throttle in 4th gear!

Unless it's really deep, then I move it down to 3rd gear.

Because of rebuilding costs, and because I have little faith in "used" stuff, if I needed to repower the 16G tomorrow, I would likely go for a new Kohler Command PRO EFI, 23 or 25 hp.

It will bolt on, my bagger vac will work, the intake and exhaust might require some mods - that I can handle.

While it is not and ONAN, I not sure anything out there is. May people rave about HONDA, but I have had bad experiances with HONDA small engines.

The other choice is Briggs, who I have had good luck with on other equipment, but somehow the Kohler looks like the better choice of the new offerings.

In my experience, plowing in 4th did not provide the quality I was looking for. I was plowing a gravel drive. Put another way, I feel that 4th is for transporting the tractor from one location to another, not to do work. Then there is the safety factor.

When it comes to recommending new engines I just can't recommend one over the other other than to say the clones are NOT clones. The market has changed and my experience is limited. I would have to do some serious research on new engines before I could say one is better than the other and why.
I am plowing asphalt paving, and the snow is often wet and heavy. Out typical snowfall is 6".

In 4th gear the snow rolls nicely off the blade, at slower speeds not so much. I know this is an issue you have commented about regarding the rider blade design.

With a 6" snowfall I can drive right down the middle with the blade straight, then a make a pass or two on each side angled, and I am usually looking a black paving 12' wide, with maybe just a little touch up her and there - and that was before all the improvements. So As fast I can drive around the circle (the drive loops around the house) three to five times in high gear, a 6" snow is largely cleared.

Then I have claer the 40' x 40' pad, a little more detailed, and a fair about of backing up, but not more than 15 minutes for a 6" snow - when it's more than that, it starts to become "work".

I had my 300 ft drive plus my father's 270 ft drive to do. It would take a while.
I had my 300 ft drive plus my father's 270 ft drive to do. It would take a while.
I would imagine gravel is a much tougher situation? I have never done that. My "loop" is about 400', plus the pad, just a little under 7,000 sq ft. One of those big snows last year had me out there nearly 8 hours.

I just came in from test fitting the cross shaft - fits perfect!

Pictures on the thread tonight if I get time.

clones are NOT clones.
Quite so. Can anyone think of any manufactured good, durable or otherwise, for which production was moved to China that is as good or better than its domestic equivalent/predecessor and is sold at a cut-throat price point?

At work, we just got a new Powermatic drill press to replace the Delta lemon, and a Powermatic 3HP table saw to replace our WWII Unisaw that finally seized the Arbor bearing. The first is made in China, the second in Taiwan. From everything from the build quality to the trade dress, the latter beats the pants off of the former. The table saw produces repeatable work, is sturdy, quiet, and beautiful. The latter looks, feels, and acts like a Home Depot Ryobi painted Gold with a fancy extendable table. It is noisy, shaky, cheap looking, and the keyless chuck will tighten itself to the point of needing slip-joints to get it apart when it meets the hideously excessive load of a 2" Forstner bit in Poplar.

- Nathan
Quite so. Can anyone think of any manufactured good, durable or otherwise, for which production was moved to China that is as good or better than its domestic equivalent/predecessor and is sold at a cut-throat price point?
Sure. One that comes to mind is SKF bearings. The last time I checked, they had 14 plants in China cranking out bearings. No change in the quality at all. NTN also makes bearings in Taiwan ROC. For example. the NTN 6204 bearings are made in Taiwan, 6205 bearings are made in Canada and the 6206 bearings are made in the US. There is no difference in quality for either SKF or NTN no matter where they are made. That is because they apply strict QC on their products no matter where they are made.

The biggest problem with China is the Communist way of life that they are accustomed to. There is no reward for doing a superior job so doing a sloppy job pays the same. In general Capitalism rewards hard work.
There is no difference in quality for either SKF or NTN no matter where they are made. That is because they apply strict QC on their products no matter where they are made.
Right, but are the made in China bearings sold at significantly lower prices? I'm sure there are plenty of high quality items made there - such as the Iphone perhaps. The point is there is no inexpensive knock-off that approaches the real deal in terms of quality.

- Nathan
Items made in China can be any quality level desired. If someone wants to buy cheap, inferior Chinese stuff and sell it here, that is their choice. If someone wants quality Chinese stuff, that also exists.

The point I am trying to make is that it isn't where an item is made, but how it is made and from what.
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