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Discussion Starter #1
I'm wondering if anyone has dismantled a water pump for the 4518 or 5518 GX640 engine? Part No. 19200-ZG8-000 and/or 19200-ZG8-010

I want to attempt a disassembly but don't know which direction the waterpump shaft can be pressed out. I bought a brand new pump to get my tractor mowing again, but I have the old one with bad (VERY bad!) bearings and a tiny coolant leak.

Anyway, even if I damage it beyond repair, I will post my result. If it goes well, maybe another $100+ Honda part can be fixed for $25 worth of bearings & seals?

Pictures of brand new water pump below. Note: This pump does not include a new o-ring.
 

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It looks like the impeller is crimped on so I'd guess that would be the last part to go on when assembled in the factory. The sprocket side looks like it might be a press fit though, maybe it's possible to use a puller and remove it and press out the shaft to get to the bearing. Japanese automotive water pumps are built similar, maybe researching how those are rebuilt would give better options.

I had a similar idea with HT3813 water pump, I also have one with really bad bearings that's far from usable in it's current shape.
 

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It all depends on how you value your time. @.17/hr you might come out ahead. But by the time you factor in the learning curve and special tools you might not have...?

All of a sudden a C-note with a guarantee seems mighty reasonable, imo. Ymmv.
 

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Discussion Starter #4
It all depends on how you value your time. @.17/hr you might come out ahead. But by the time you factor in the learning curve and special tools you might not have...?

All of a sudden a C-note with a guarantee seems mighty reasonable, imo. Ymmv.

Point taken... If I valued my time properly, I would have pushed this tractor in the scrap heap 11 years ago. I have done a TON of "dealer only" type maintenance on this 4518 well beyond the tractor's worth. I do value my time, but the $114 waterpump was "backordered forever" so I got a $147 waterpump. There are others listed over $200. Next thing could be that this waterpump goes NLA, so I figured it might be beneficial to the 4518/5518 owners to tinker with one and see if $25 worth of bearings & seals could fix one. For motorcycles & ATV's? Honda sells a very similar looking impeller & shaft ***'y and the drive pulley is absent. Looks JUST like this 4518 impeller & shaft, so my first attempt will be to press the shaft through the drive gear toward the impeller. If I break it, I'm out nothing, but then we will know what's inside and can proceed from there.
 

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Fair enough, sounds like a Plan... I do fully support this kind of repair and often do, and didn't realize this pump was a possible endangered species.

:trink39:
 

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Discussion Starter #6
On a very good note, I did finish my new waterpump installation today, reinstalled the engine and fired it up.

Success !! This crazy thing has not run so smooth & quiet as long as I have owned it ! I'm pretty dang happy.

A few notes from the job...

Don't do this without a factory service manual... Just don't.

Take pics. Bag & label your parts as you remove them. There is a CRAZY amount of stuff to disconnect and parts pile up quick.

Parking the tractor on level, solid ground is good. I carry a moving blanket from side to side with me to kneel on while working.

After you drain & remove the radiator, spend 1/2 hour flushing it inside & out. I was SHOCKED how much sediment I flushed out of the inside with my pressure washer. I was shocked again at all the clogged fins on the outside, even after I periodically had pressure washed it after mowing. Remove the screen guard because it shields a 1/2" top & bottom of more fins that will be clogged.

Don't loose the plastic cap/cup from inside the coupling, and if it falls out, the wide end is "out" toward the driveshaft.

Since my parking brake is stuck/nonworking, I park with the tractor slightly in forward. That turned out well, because turning the driveshaft by hand allowed me to EASILY move the tractor forward & backward to line up the engine for re-installation.

Order a new timing cover gasket (o-ring?). Mine was trash and I wish I had one but reused my old one.

I did not replace my timing belt. It's hot as heck here and I'm working outside under a portable tent. I'll do it later when my new garage is built and I can work on it when the **** grass isn't growing so fast :tango_face_angel:

BEFORE you remove the idler pulley & water pump, set your cam and crankshaft timing marks up. That way, as long as you don't turn them while it's apart, it goes right back together with correct timing. Pictures below show the cam timing marks. There are two and you pretty much set them perfectly horizontal, but the crank timing mark also has to be horizontal to the left at the same time. Turn it more, clockwise only, if they don't all line up the first time.
After the cam belt is back on with the idler pulley loose (spring connected, center bolt finger tight only), turn the engine crank counterclockwise by two teeth on the cam, then clockwise 4 teeth on the cam then tighten the idler bolt. (clockwise as viewed from the camshaft end of the crank, and you can reach the front fan or flywheel to do this by hand).

Most of this was just the reverse of disassembly, but wire harness routing and hose connections are just about overwhelming on this tractor... Best to take pictures and make notes while you pull the engine.
 

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Nice photos/documentation.

I'm the same way, if I valued my time at a dollar amount, I probably would be homeless from throwing money at all my problems. I enjoy this kind of work, so I view it more as a hobby.

Parts for this age of machine (20-25+ years old) are at risk of being unavailable, Honda does pretty good at keeping parts in production, but at some point most things go unavailable. Look at some of the early 80's 3 wheelers, just about nothing is available anymore, so I'd agree finding a way to repair the old ones would be beneficial if and more likely when the part is no longer in production. Kind of doubt a company is going to step in and reproduce them since it probably has way too little of demand to be profitable.

Anyway, the 18hp engine is pretty interesting, seems to be somewhat related to the 13hp in the HT3813 machines. Is the flywheel on the front on the engine instead of the rear? If so Is suspect getting to the starter is a lot easier on that model.

Good luck with the water pump repair, hopefully pressing the pulley off works out. $75+ savings for hopefully a 15-30 min job once it's figured out. There's companies out there that rebuild automotive water pumps, so it has to be possible to do fairly quick with out too much costs to repair it (bearing + seals, maybe new impeller). Don't forget to sand blast the body (if you have one) so it looks like a refurbished unit :).
 

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Discussion Starter #8
Anyway, the 18hp engine is pretty interesting, seems to be somewhat related to the 13hp in the HT3813 machines. Is the flywheel on the front on the engine instead of the rear? If so Is suspect getting to the starter is a lot easier on that model.
Yes & No... The starter is under a heat shield, under the muffler, under another heat shield. The exhaust flanges on the head come off easy enough, but where the heat shields bolt to the muffler body, the 10mm bolts tend to snap off in their rusty holes. I left them loose this time and bent the heat shield(s) quickly with the engine running to eliminate the rattling. It worked fine. Changing the starter is a matter of uncovering it from the exhaust parts.

Good luck with the water pump repair, hopefully pressing the pulley off works out. $75+ savings for hopefully a 15-30 min job once it's figured out. There's companies out there that rebuild automotive water pumps, so it has to be possible to do fairly quick with out too much costs to repair it (bearing + seals, maybe new impeller).
For a 2000 Honda Accord, there are three aftermarket waterpumps available... It's nearly identical to my 4518/5518 waterpump. I installed my deck with new blades this morning, added some more antifreeze, topped off the oil and proceeded to mow about an acre of wet grass. Very happy with the way my 4518 ran today.

-Tom
 

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The 13hp engine you have to pull the engine, fly wheel, lighting coil & ignition coil to remove the starter. Not super crazy of a job, but takes plenty of time. Another route instead of pulling the engine is to take the tractor apart, but it seems like that route would take longer, there's only 4 bolts that holds the engine in + electrical, removing the hood, radiator etc.
 

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Discussion Starter #10
I found this online pictorial of a similar water pump being disassembled and rebuilt. I've been trying to figure out which way, to drive what component and since this one is pretty close, I will attempt to drive the shaft out of the housing (toward the drive gear) by pressing through the small hole on the end of the impeller.

How to replace the Water Pump Bearing and Seal ( ST1100 ) *

I still might try a two-jaw puller to get the cogged drive gear off first. I think after it's off I will make two gains: 1. I'll know which way the bearings & shaft need to be driven out. 2. I'll be able to better support the housing if the shaft needs to be pressed toward the drive gear.

This will take me a couple days to get to it...
 

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Discussion Starter #11 (Edited)
Ok, I have tracked down the tiny stamped characters on the end of my H4518 waterpump shaft. It's a shaft, bearings & seals assembly for water pumps all over the world on Honda products (cars, trucks, power equipment, etc...)

"WPB1730071" Decoded, this means Water Pump Bearing with 1730071 being the specs of the bearings & shaft assembly.

It appears the Honda 4518/5518 waterpump is very similar to a Honda ST1100 motorcycle pump. Under the pump impeller, there is a ceramic seal that presses in. That rides against another ceramic seal in the spring loaded seal assembly that presses into the coolant side of the pump housing. I now know for certain, the pump shaft & bearing assembly presses out in the direction from coolant side to outside and the impeller comes off easier than it looks.
Here is a vendor for aftermarket (not in the USA, of course.) https://preview.tinyurl.com/y2jmx8dp

Pic below shows a naked waterpump bearing for our 4518/5518 tractor waterpumps. I have not pressed my old one apart yet, but will take pictures and post when I get to it. Minimum order is 10, so I'm not going to be buying a box of these any time soon...
 

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Discussion Starter #13
just so you know, all 4518 and 5518 water pumps are the same regardless of part number.
Got it... Thanks. More than likely, just the seal assembly inside (against the coolant) changed for the part number change at Honda. It has a spring loaded ceramic seal riding against a polished silicon carbide surface and relies on the coolant for lubrication. (I.E. Don't run just water in your Honda cooling system or you can damage your waterpump seal.) This is the exact same seal technology used in both my SeaDoo PWC and my Nautique ski boat.

I still have not pressed my old pump apart, but I'm 100% confident that I have it figured out now. There is a Honda motorcycle popular in Europe that uses the exact same shaft/bearing/seal assembly as our tractors, but the coolant impeller is different because it rotates the opposite direction as our tractor engine. I will make a horseshoe shaped shim to place under my impeller prior to pressing the shaft out so I don't damage the impeller. They even have a couple "How To" videos online showing the motorcycle pump rebuild. The ebay seller for the shaft/bearing/seal assembly did his homework and is keeping the part numbers hidden so I can not source them locally.

I think it's worth continuing my experiment... These pumps may be NLA in the near future. Here is a relevant example of a guy in Arizona rebuilding a very similar motorcycle pump as a cottage industry: https://www.ebay.com/itm/361465308318

Pictured below are the actual parts needed, identical to the Honda 4518/5518 waterpump, that a guy is selling in the UK for the Honda ST1100 Pan European motorcycle. Everything in this kit is exactly that same as the 4518/5518 pump. For $70 + my time, I could have a "like new" waterpump for my tractor sitting on the shelf. https://www.ebay.com/itm/113695793839
The shaft/bearing assembly is WPB1730071 same as stamped on my waterpump shaft.
 

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Great Post and pictures many Thanks, very much appreciated!

Looks like you can still find them these days for around $100-150 online - unless they are not actually in stock..

My water pump and timing belt have never been touched in my ownership of 10 years - no idea before that - I imagine my 5518 is at least 25 years old. Are there symptoms of a failing water pump - other than the obvious over heating? I imagine the bearing shown fails - and the timing gets thrown off or possibly breaks the timing belt?
 

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Discussion Starter #16
Are there symptoms of a failing water pump - other than the obvious over heating?
When the inner seal fails, it allows coolant to leak on the bearing and wrecks it. Coolant does not completely evaporate, so you'll have signs of coolant leaking out of the weep hole on the side of the waterpump and you'll have a drop of coolant level in your radiator overflow bottle.

Interestingly, as I mentioned somewhere, when I wsa mowing with my good hearing protection on, I could hear the waterpump bearing growling. I really thought it was a mower deck pulley bearing but the missing coolant from my overflow bottle caused me to search more and I found the leaking waterpump.

Changing the waterpump takes only a few minutes; Removing the engine from an H4518 to get to the waterpump to me several hours! :tango_face_surprise
 
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