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Author Topic: M91 water cooled vertical H&M. A recap.  (Read 257 times)

Adirondack Jack

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M91 water cooled vertical H&M. A recap.
« on: May 22, 2021, 11:52:12 pm »
The M91 vertical hit and Miss is a nice little engine, but itís not without its fiddly aspects. With a bit of work, it can be a fun toy.

If I had it to do again: 

Iíd ignore the teasers advising Zippo fuel. Zippo works, kinda, when planets align, but itís not exactly the most energetic of fuels, so starting routines can be frustrating unless the mixer is spot on adjusted. I fought with getting the engine to start and run without frequent messing with the mixer, and frustrating sessions of flooding it, etc. Read on for the current set up. The less than energetic zippo fuel also made ignition battery life lousy. The ignition had to be pretty hot to reliably start on zippo.

Much rope pulling will tear the rubber handle off the rope, and the pulley notch may cut the knot off the rope. Iím using a chunk of 5/16 dowel and a bit of cord that began life as a draw string. A round file deburred the notch.

The cheese box base is fruitless. Longer, lower, heavier, wider. Stoppingí the hoppiní.  Maple is your pal.

When, not if, things come loose, the grub (set) screws are soft, roughly chinese number one mushy steel. You will tear the heads out trying to snug them. Buy an assortment of quality metric set screws with deep pockets and replace the originals the first time they slip. Life is simply too short.

A spark plug wire snap on terminal end fabricated from springy brass is your friend. A bit of fuel tubing makes for a boot.

Oh, fuel? I broke down and bought tru fuel, synthetic racing fuel, four cycle blend, and add about three drops of MMO per ounce. Done.

Even after sitting a month almost empty, thumb the mixer, give the flywheel a twist, ignition switch on, pull rope, enjoy. The much lower flash point and reasonably not too unpleasant fumes arenít bad.

On that note, a 200cfm computer fan running on 110v, mounted into a cardboard box, add a dryer vent flapper and duct hose, mount in window, yer in business to ventilate your test area.

Donít tell anybody, but my M91 is on my kitchen table. Itís fun to just flip the switch, give it a spin with the rope, and have it start and run nicely with one pull. I donít run it long like that, but itís fun.




Once sorted,

70Rcode

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Re: M91 water cooled vertical H&M. A recap.
« Reply #1 on: May 23, 2021, 05:03:44 am »
 Very nice M-91  H & M operational writeup !!...Your 3 drops MMO per Oz mixture is running at about 200 : 1 gas to lube ratio per gas tank full, No way close to a "typical" conventional 2 stroke gas engine lube mix ratio. And Without any cylinder wall transfer ports or cylinder wall cross-hatch or functional piston oiler, it's Impossible to have any meaningful piston skirt/cylinder wall lubrication (using fuel tank gas/oil mix only) & the typical M-90 engine series teardown inspection usually shows significant scuffing evidence despite the super Hardened stainless steel liner !! ...Obviously, that steel piston IS slapping around the bore with each firing torque "kick" !! I've been consistently directly applying 20 wt oil lube to cylinder wall & entire piston pin underside between engine runs to try to minimize the scuffing effects...With such a beautiful & carefully Machined & precision assembled model engine Without any piston underside oil slinger or piston Oiler provisions or instruction guidance, it's kinda like the Simple longtime utilized full scale engine lube oiller design features  are simply intentionally Ignored ??? ...I can't figure that simple effective important & true to full sale Deletions out ???....just my thoughts,.....tom.

Adirondack Jack

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Re: M91 water cooled vertical H&M. A recap.
« Reply #2 on: May 23, 2021, 07:53:05 am »
You are correct. I should have mentioned part of my between run routine, aside from oiling all the spinny, slidey bits, is a drop of MMO directly on the spring and guide of the top mounted intake valve.  Plenty enough oil wicks down into the combustion chamber and onward to the ring. I also note the Chinese video online shows quite a bit of oil squirted into the crankcase. I don’t think that’s necessarily a good thing, but a needle oiler giving a little 3 in 1 or whatever to the skirt isn’t a bad thing.

RedRyder

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Re: M91 water cooled vertical H&M. A recap.
« Reply #3 on: May 23, 2021, 09:23:28 am »
Hi Jack, Nice write up!

I submit to you that if you have it set up that nicely you are able to hand start it from cold. (no rope needed)

I would agree that 200:1 is likely not enough oil. I use MMO at 15 to one which many consider excessive. You might consider trying somewhere in between.

I agree that the 92 and 94 octane tru-fuel is a very good option. I use Coleman in some, tru-fuel in some and 100 LL (aircraft fuel) in some. I like to try them all and note which is best for the engine drinking it. All are mixed with MMO. I use synthetic clock oil on piston skirts and the lower bore or Mobil 1  0W-16 or 0W-20. One more thing. When I have the piston out to shave off enough to reduce the compression, I always put a very small and smooth chamfer on both ends of it.

70Rcode

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Re: M91 water cooled vertical H&M. A recap.
« Reply #4 on: May 23, 2021, 06:32:25 pm »
Very interesting & helpful info gentlemen!! Todd over on "Project Farm" has a good, exhaustive non-leaded pump gas to Tru-Fuel comparison test results, proving surprisingly, that Plain 91 Pump Gas produces a Longer Small engine Run time with Less piston & valve Deposits !! ...I've only used straight Coleman stove fuel in my Stock (weaker govenor springs mod) No head or piston mods M-91 engine...Your postings has me rethinking  gas fuel "Reid" Vapor Pressure spec. (Volatility) differences between the various mentioned fuels..My M-91 runs so Cold it never really  gets up to an optimal Carburator running temperature...I'm sure the pure, Non-Lube added Coleman fuel burns Cleaner than Any Gasoline fuel product & my non-loaded running shows No octane Knock issues..Regarding fuel Volatility, the significantly Lower (5.0) vapor pressure Coleman compared to Gasoline's 8.5 psi Vapor pressure could Possibly be Improved by adding Highly Volatility Butane to a tank full to help better Cold carb Vaporization ??...After > 1.5 yr running, still runs like new & Easy 1st flip Hand starts on original sparkplug....Ideas ??.......tom.

Adirondack Jack

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Re: M91 water cooled vertical H&M. A recap.
« Reply #5 on: May 24, 2021, 06:35:06 pm »
If I were running and storing mine in a dedicated space, Iíd probably use pump gas.
But Iím not. I needed a reliable fuel that also is relatively safe to store, and has a decent shelf life, as well as lower harmful emissions. That means a fuel designed for use without a catalytic converter. Tru fuel ships by ups and is shelf stored in retail spaces. Though I suctioned most of the unused fuel from the tank a month or more ago, using a syringe, I didnít get it all. The engine sat on a shelf in my living room. I never smelled any odor. It had developed a slipping flywheel when last run, and when finally I got around to replacing the set screws, I noticed fuel in the line when I turned the flywheel. After thumb choking, it started right up repeatedly on the little fuel left, despite the dreaded ďoil pipe bubblesĒ they warn about.  Honestly, I only have indoor storage. Tru fuel can be stored indoors. It came in a ziplock as well as the screw top can. I store the can under my bathroom sink, in a closed space with no electricity and no sunlight. No odor, and itís shelf stable for years.


RedRyder

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Re: M91 water cooled vertical H&M. A recap.
« Reply #6 on: May 27, 2021, 06:07:13 pm »
By the way, your new wood base looks awesome!

Gil

Raphael

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Re: M91 water cooled vertical H&M. A recap.
« Reply #7 on: May 28, 2021, 12:11:09 pm »
Bonjour,
I have several of these engines and for them, I tried Zippo gas but VERY expensive so now I use SP98 gasoline with a drop of 2 stroke oil.
I find them very difficult to settle and their behaviour changes when they heat.

To be able to start them with the hand suppose Gil's skillness (he helped me for my M91) ;)

And I do not know if the water pump is really useful as it is very fast :
https://www.youtube.com/watch?v=94I3FNjDup4
RaphaŽl, Membre du ModŤle Yacht Club de Paris : http://mycparis.fr/
Membre de l'Offshore Club de Paris: http://site-ocparis.wifeo.com/
Youtube : https://www.youtube.com/rhavrane

RedRyder

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Re: M91 water cooled vertical H&M. A recap.
« Reply #8 on: May 28, 2021, 02:56:07 pm »
I would not use pump gas in any of my model engines. In addition to ethanol (very undesirable) pump gas contains a littany of assorted poisons designed to be pushed through a catalytic converter at 1400 to 1800 degrees F.  My smaller hit and miss gas engines dont exceed 110 F. My largers models are no warmer than 165 and that is with no coolant.

70Rcode

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Re: M91 water cooled vertical H&M. A recap.
« Reply #9 on: June 03, 2021, 05:52:59 pm »
From Raphael's video (i hope he's ok?),...the M-90, M-91 series engines fire & torque Kick so unrealistically Violent, that despite the wooden base mount weightings & reinforcements, my M-90 tries to kick the crankshaft off the Mains !! ....Estimating the Stock C/R at about 10 : 1, does Reducing the C/R to about 5 : 1 Significantly  reduce the torque  kick ??.....thx, ...tom.

Adirondack Jack

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Re: M91 water cooled vertical H&M. A recap.
« Reply #10 on: July 17, 2021, 07:13:15 pm »
The cheaters way to model how decking the piston will behave is simply to try running it with a very loose spark plug. A little leaking compression to give you a clue.  Iíd run it first and loosen the plug once warm, so it starts easier, and see how it acts. 

70Rcode

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Re: M91 water cooled vertical H&M. A recap.
« Reply #11 on: July 23, 2021, 07:24:02 am »
Good idea AJ !!.....Wonder if Tightened up exhaust rocker arm Lash for Later valve closing timing would accomplish similar Reduced CR simulation effect ??

Adirondack Jack

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Re: M91 water cooled vertical H&M. A recap.
« Reply #12 on: July 23, 2021, 07:53:34 pm »
I donít suppose itíd do it any good long term, but yo
Model the low power version, it wouldnít be any worse than every 100,000 mile straight six anybody ever drove. Tick, tick, mushy powerÖ..

70Rcode

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Re: M91 water cooled vertical H&M. A recap.
« Reply #13 on: July 23, 2021, 09:23:31 pm »
Tightening up Lash....should quiet down some....Yes,...Mush power !!....just enough  to flywheel over Sloowly !!

 

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