why groco why

[markxengineerin]

Spoke to Paul, who assembled this head back in 1994. He has been doing it for 30 years, nice guy. The original design is from the 60s. There is no logic behind manufacturing undersized rings vs. oversized ones that would have end gap filed down to fit (an easier and better process IMO) besides that back then, they never considered rebuilds. Suggestions are that grooves in the side walls aren't that bad, since the plastic ring will wear into them if installed tightly enough, that making a piston with larger diameter is a good idea to prevent rocking, and that "some circulation will always happen". He has not heard of X rings being used.
I have my own opinions on the above, so will be coming up with a different strategy, likely involving a bore-out, new piston, and X rings.

Suggestions for piston material?
Marine-Grade 485 Brass-- $393
Easy-to-Machine 936 Bearing Bronze - $223
Oil-Filled 841 Bearing Bronze- $165
932 Bearing Bronze- $152
Wear-Resistant Easy-to-Machine Delrin- $16
Teflon impregnated delrin- $80

I am guessing the regular delrin would last many years?

[mvweebles]

Great update. Thanks. I realize a little recirculation is expected, but I do remember having excessive amount once. Any guidance on what causes that? I thought the little black ball was the culprit as it acts as a check valve to make the piston stroke double action. But maybe not.

I never perceived any issues with the rings. I also didn't perceive any issues with the bore becoming oval shaped, another oft cited issues. I did run a cylinder hone through the bore on my last rebuilding but just to dress the surface.

Beyond the joker valve which is universal wear part, the items that led me to rebuild were the two flap assemblies: one in porcelain bowl (spring breaks); and the one on the back that controls water intake. This had should never be installed fully below waterline in my opinion.

Good head. Tremendously out of fashion. Can't give them away these days.

Peter

[markxengineerin]

Paul said that the only cause of recirculation was the piston rings, and I agree based on my understanding of the check ball. I think the symptom of having no check ball at all would be "head pumping air instead of seawater".

I do understand the logic of everyone saying "buy the $200 head and immediately replace with new when it stops working". It is a balance of guilt about filling up landfills with garbage vs. the unpleasantness of dealing with a nasty job that requires a lot of patience. If I had others on board waiting for the head to work again, and less interest in improving old stuff, I think my decision would be different. I do wish Groco would make tiny changes to improve the rebuild kits, but, they're doing something right to still be in business, hard to judge.

[markxengineerin]

Here's the new piston, and bored/honed cylinder. I went 0.015" over what I believe was originally 3.000" on the cylinder, plus a little more than that in the top section which has no function other than making the piston harder to install when it gets crudded up. The piston has .005" clearance. X rings are nominally 3/16" cross section and interfere about 0.015" with cylinder wall, which is the spec for reciprocating applications. I hope this works better. Lifetime supply of o rings was $10.

[peghall]

If you cured the problem, I hear from enough owners of recirculating Groco K that I'd love to have step by step instructions of exactly what you did for my files. Those who aren't mechanically inclined enough to follow 'em (most of 'em actually) would have 'em to give to someone who is. I'll send you a PM with my email address if you'd be kind enough to send 'em to me.


--Peggie

[wsmurdoch]

My wife is not a fan of the harness rivet in the center of the flapper. It is installed with the burr and protruding end of the rivet sticking up into the bowl, snagging toilet paper, and taking an extra stroke or two to get it out of the bowl.

[markxengineerin]

Ok, I'll make a drawing of the piston and list part numbers if it works. On the bench test, I'm getting a 100% seal but also a little bit of black rubber swarf left on the cylinder walls after pumping. The x rings are lubricated with grease, so I'm not sure what's up, maybe I didn't get the walls smooth enough. I used 220 grit stones. I'll give it a go in the boat and hopefully it breaks itself in/ wear stabilizes while still maintaining the perfect seal.

[markxengineerin]

Document attached, I'm going to send it to Groco in case they decide to make a Groco K version 2.0. As is, I would not recommend the Model K to anyone, but with these small changes, it might be pretty good.

[donradcliffe]

Originally Posted by markxengineerin

I would not recommend the Model K to anyone.

Ditto. One rebuild with the coat hanger was enough, and it only lasted a year.

[markxengineerin]

Do you know what the failure was, after 1 year, or the symptoms?

[wsmurdoch]

I ran across this note at https://downeastboatforum.com/thread...rebuilt.18077/ He seems to have used rubber o-rings in the factory piston.

************************************************** *******

As I understand things- these units run a 3" bronze piston that separates raw water (or fresh if one chooses) from the turds. The water below the piston is the flush water, and when handle is pumped and foot pedal is appropriately located you get that flush water out from under the porcelain similar to a household unit. The control rings on the bronze piston are white and made of some sort of plastic, and they leak turd water from top side of the piston to the bottom side chamber when at steady state, no pumping. Not a lot, but enough so that when the wife flushes I get yelled at cause the flush water has a colored tint to it, from the turds of course.

I bought a model K and had it rebuilt at a very reputable shop in Seattle specifically because my boat is classified as the boat with a crapper on it and I got tired of unclogging the princess model jabsco pump toilet so I sourced a model K which will flush a live cat and a beer can at the same time. I love it, but wife gave me grief last summer (first summer with the model K) about the flushwater mentioned above, so I pulled it out this winter and stuffed rubber o rings on the piston which will no doubt fail long before factory plastic control rings would have so I just set myself up for new o-rings every year or so. But with O-rings the seal is tight and you don't get recycled turd water coming out the flushwater, wife is happy.

So since you write you would rebuild the above for sale toilet you must know if the standard operating conditions of the model K allow for the leak by of the turd water or do I just have a worn cylinder chamber and the reputable company in Seattle sold me a unit that I should toss back through the front window? Or take to a motor shop and have it bored out and a piston sleeve installed…..

Don't get me wrong, I love the toilet, tall, sturdy, flushes anything, doesn't need power, and I even hooked fresh water to it through a commercial kitchen water foot pedal so to fill the bowl simply push pedal and it fills, no pumping till you flush. Freshwater, so no holding tank stench.

Thanks for any expert toilet advice, Chris

[markxengineerin]

Interesting, I'm surprised that worked even for a few flushes- o rings are sized to have 10-20% compression on the cross section, and the odds of finding a standard size to hit that tight window with the original piston seem low. I didn't look, but wanted X rings anyway. O rings can twist up as piston goes up and down until they break, called spiral failure. I've seen this happen even with tiny amounts of micro-movement, and very likely to happen here with the stroke of the piston being relatively long and lubrication poor.

To answer the question that guy was asking- the piston ring design will always have some leak, but it should be very small, maybe too small to notice when all parts are brand new. The problem with a standard rebuild is that the ring wants to be sized for the worn out bore to minimize leak, but can't be because it has to fit through the un-worn top part of the cylinder during install. So the ring is made smaller to fit, and then leaks too much, at least for my judgement. The ideal piston pump style head would have a replaceable insert for the working part of the cylinder, and a bigger bore everywhere else, to make piston/ring/oring/xring installation easy.

[BlueH2Obound]

Mark,
I have two Groco Model K heads that I removed and am replacing with Raritan Marine Elegance toilets. Well, one was replaced in January of this year, and the other will be replaced as soon as I receive it. Anyway, they both work just fine, just wanted to go with fresh water. I'll post them in the next day or so in the classified section. Selling them CHEAP! Where are you located?

[markxengineerin]

I'm in Maine, not in the market at the moment for any more Model K's, but good luck w/ the sale!