Smallest water cooled gas engine?

[BioHazard]

I've been looking really, really hard at the Honda CHP system, and thinking about what I can do with natural gas for my house. I'd like to try and build something similar in size...a 200cc or so gas engine making a few horsepower on natural gas is no problem. The problem comes with trying to extract the heat from an air cooled engine. I'm considering modifying a lawnmower type engine block to be water cooled much like the honda, but that's a lot of work. The plus is that engine blocks are very cheap to replace.

On the other hand, is there a ready made, water cooled engine that small already available? The smallest I've seen are about 18-20hp or so twins. Is there anything available that is single cylinder/closer to 200cc or so? Does anybody make a 4 cycle/water cooled outboard motor that small? I'd love to get my hands on one of the "Marathon" engines but they won't sell just the engine. (http://www.marathonengine.com/)

[mobile_bob]

maybe a small changfa type, like the r175
it is about 6hp or so, watercooled and could be fit with a sparkplug in place of the injector
i would think.

using an idi head on a di piston should get the comp ratio within reason, and there is no reason
that the spark plug would not work in the prechamber.

just a thought

bob g

[BioHazard]

I guess that would beg the question how can I get my hands on a Changfa R175 here in communist America? *sigh* Is there any other way besides finding one that landed here before tha ban?

I have considered maybe a lister running on a small WMO pilot with natural gas - but two things I'm trying to avoid are EPA difficulties and giant peices of iron. I just don't have enough room for that at the house...

[potter]

Try some of the RV gen sets I know Honda made a water cooled  4000 watt model that would be about 4 H.P.

    Potter

[SteveU.]

Hey great link you put up with that Marathonengine BH.
Has a good MCG education within itself and the embedded videos and links.
Sadly at $30K plus not in by budget. But just like looking at the Arrow engine info does show what is possible today using todays technology. Old, gray and grumpy now after 40 years of "promises, promises" I try hard and ignore the tomarrows tech stuff anymore.
Keep looking, asking, and kicking around ideas.
I've been through a get it under the EPA wire with an Indian 12/1 CS clone. Stumbled across literally, and bought a NOS, IDI RS175 Changfa clone with electric start for pennys on the dollar. Have had them both apart with die grinder and a spark plug thread inserter in hand. Problem is: 1) they DO run so sweet and efficiently on diesel/biodiesel fuels; 2) getting hard parts for either of these was always best just buy a whole 2nd, 3rd engine. Not possible here in the US anymore. Gaskets can be made, yeah. And I even had a fair amount of hard parts machined modified for grey market old Euro cars - $$$.
Why I keep getting pulled back to free/dime a dozen riding lawn mower aircooled gas twins for my woodgas mule engines. Oversize, RPM, power derate, use a belt drive and just acquire more pulleys, and use a 5-50 Castrol synthetic oil. Just think of that flywheel air as a free direct drive forced heating air flow source. Duct and blow it past the muffler too.
In a shop/greenhouse situation whats a little crankcase oil smell, eh?
Ha! Ha! Local lawn mower racers pass up on these and are a great ear to the ground, word of mouth source.

Regards
Washington State Steve Unruh

[mobile_bob]

it is hard to ignore the air cooled gas engines, they turn up everywhere for very good prices
just the other day i saw a 12hp kohler electric start cast iron engine, reportedly a good runner for 50 bucks

one very cool way to use an air cooled engine would be to harvest the exhaust for water heat transfer
and to enclose the unit and use it to drive a compressor and pump the aircooled heat out of the case and transport
it to final point of use via the heat pump method

i bet the efficiency  of such a unit could be quite high, with no fumes or smells in the house

i know that kohler makes its 12hp at 3600rpm, but they will run effectively at 1800 without a problem
and make about 5-6hp

motorhome onan plants are very inexpensive on the secondary market, i have seen them available for 200 to 750bucks
some are setup to run on propane, so they could be rejetted for nat gas fairly easily. one of those setup as a heat pump
with exhaust heat recovery might be a very good option, especially the onan with the full flow oil filter.

the aircooled engine would probably really live longer in a clean cabinet enclosure where it didn't have to deal with dust and dirt, and with the heat pump taking the heat out of the cabinet the ambient temp within could be just about anything you want it to be, so
if the oem engine manufacture likes 70 deg F, then set the tstat to keep the cabinet interior to 70 deg, and move the heat to the house for use.

it could be done for less than perhaps 1500 bucks if you shop it out well, but a good low hours onan plant, then retrieve a complete A/C system from a car (if you are careful you can get it out without having to lose the freon) and assemble it all into a drier cabinet or somesuch.  use dynamat insulation to help contain the heat and deaden the sound make up some ductwork, a pop riveter and drill
some duct tape and your well on your way.
bob g

[Ronmar]

Try some of the RV gen sets I know Honda made a water cooled  4000 watt model that would be about 4 H.P.

   Potter

The engine for a 4KW genset is Probably going to be closer to 8HP... 

As for a small water cooled engine, I have thought the very same thing about modifying one of the small honda's for liquid cooling as they, and all their parts, are so available...

[BioHazard]

Hmmm...I like the heat pump idea. I'm thinking about taking an old 6hp OHV lawnmower engine that I have and modifying the engine slightly so that I could literally dunk the whole thing in water up to the flywheel, and have the shaft coming out the bottom. I can get a little Briggs and stratton on ebay with a full flow oil filter for about $150 brand new. This way the short block could easily be replaced as needed.

Maybe I've been studying the honda unit a little too long, I've got vertical shafts stuck in my head now.  

FWIW, the "Marathon" engine was designed in the late 80s by Briggs and Stratton with York to power heat pumps. That idea was a failure but they have recently started putting the engine to a more modern cogen use....I just wish I could buy one.

I remember having a conversation with the Changfa factory about 8-10 years ago...diesel engines for <$200....I came so close to buying a container load of them, but I thought they would be too hard to sell. If only I knew what the bastards at the EPA were planning!

[BioHazard]

What do you guys think about the Yanmar twin from Surplus center? It's only slightly bigger than I'm looking for...you just can't beat their price. If I tried to run it on a diesel/natural gas mixture, just how little diesel do you think I could use?

[mobile_bob]

somewhere in my collection of pdf files is a paper on dual fuel operation (diesel pilot injection, nat/gas fueled)
from memory

one of the problems associated with this operation in high compression diesel engines is detonation, however
the paper related how a lean mix of air nat/gas was to stable to detonate and had to have the pilot injection to set it off.

her is the deal, you have to get from running on diesel, switch over to dual fuel and get to the lean mix condition asap
so that you can avoid detonation, there might well need to be some computer/controller control to do it.

then there is this

smaller bore sizes are more tolerant of high compression and have a lessening desire to detonate as the bore decreases
the little 2 cylinder engine's might well be small enough not to have issues with detonation running nat/gas in a dual fuel
setting.

i would expect to have to run about 10% diesel pilot injection in order to initiate combustion, anything less will likely be unstable
and also run the risk of injection pump siezure from lack of lubrication.

if it were me i would start with pure diesel, and start admitting nat/gas up until the engine became unstable under load, and back off to twice the level of diesel to provide some margin of safety.

i would also put some sort of knock sensor onto the head and connect it to a scope so that i could see how the combustion event
changes, perhaps giving me some indication as to whether i am damaging the engine.  high temp/pressure transducers suitable for
the combustion chamber (assuming you could get access) are bloody expensive and likely outside the realm of reality for us mere mortals

fwiw

bob g

[SteveU.]

Hey BH this marathonengine site is some of the best infomation I've read recently.
I was up at 2:00 with my deer barking Lab dog looking it over again and trying to load the videos.
Really is a home sized CHP tutorial.
EVERYTHING we talk about here except alt-fuels is somewhere on this site. Let them do your engineering. Wish them market susess so some day we will have a whole new generation of "Startomatics" trickling down to E-Bay and Craigs List.
Ha! Ha! Even found this:
www.marathonengine.com/intro_eco.html
Shows basic specs of thier system and a good picture of thier anti-vibration crankshft centered cradle engine mounting system for their 45 degree canted single cylinder engine.
Just like you proposed a few year back Mobile-Bob.
You should have patented that idea. Or. . . been cashing those royalty checks?

Regards to all
Steve Unruh

[mobile_bob]

i wish i got royalties off the cradle mount, but sadly it predates me by about a half century, and likely way before that.

what is interesting to me at least is the hesitance of others in the diy community to use the technology.

its actually quite amazing to see a unit running at full load, and witness the crankshaft centerline running dead true, no up/down
side/side, just humming right along. it also makes the choice of resilient mounts quite simple, they just need to be stiff enough to support the weight, without worrying much about torque action.

pretty cool seeing them use the system at marathon

i know i am sold enough on the system, so much so that i will never build anything without using it again.

bob g

[Apogee]

Why not just grab a water cooled engine off of on older motorcycle?

I'm thinking one of the single cylinder ones off of either the enduro style or atv bikes.  Would be fairly easy to convert to natural gas and I know they're out there from about 200cc to about 500cc.

I would think that either Craigslist or perhaps a motorcycle wrecking yard would be inexpensive sources...

Just a thought...

Steve

[Ronmar]

The problem with motorcycle engines is interfacing them to anything else.  They are usually one with their gearbox...

[admin]

i have seen an elegant solution to coupling a motorcycle engine to a shaft
and could also be used to couple to a generator or whatever

you simply attach a sprocket of the same pitch and number of teeth, then
place them side by side, and wrap the two with a double roller chain, which couples
the two together,

the system requires very little lube and there are plastic/rubber covers to enclose
the coupling which keeps things relatively clean and the lube contained.

a water cooled motorcycle engine direct coupled to a generator, would be pretty cool

using a modern engine with fuel injection it ought to be fairly efficient

bob g