SPS Mini Longtail

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SPS Mini Longtail

Postby Lane » Fri Dec 13, 2013 6:08 pm

If your running a mini or a small SPS longtail, what motor you run and what size prop? I have a 152F-3 Lifan on a mini and the 5" I have to run "deep" water(over 2') to get the shaft deep enough to hook. To my understanding these are surface piercing props so that's not right.....? The 5.5" is enough in the right direction I'm considering buying a 6" and 6.5" but hate to have 3 props laying here in my junk box. So looking for ideas from others experience. And stepping up to a 6.5hp motor is the last choice as I don't really want the extra 20lbs.
Lane
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Re: SPS Mini Longtail

Postby Mark F. Cheney » Fri Dec 13, 2013 6:22 pm

I have some 152 F motors on my shelf. I think that they have some promise. Mine have an integral syntrifical clutch. They are 53 CC I think. They are rated to 6800 RPM. To work as a mud motor they need a reduction to the drive shaft of 2.5/1 to 3/1. They also need to be mostly level which mean they need a UJ to get the prop in the water and stay mostly neutral. Lovejoy and Beldon both make a small UJ that will handle the HP and RPM. They are expensive. Chinese UJ are copies but very poorly made. I have purchased them from three different Chinese makers. None of them were good enough to use. With this combination I would start out with a 6 X 4 prop.

Mark F. Cheney
utahmarshmotors.com on the Great Salt Lake marsh

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Re: SPS Mini Longtail

Postby Lane » Fri Dec 13, 2013 8:42 pm

The Lifan 152F-3Q is a 79.5 cc OHV 2.5hp motor. Rated @ 3600rpm. It's a keen little motor. I'm under no illusions of having a 2.5hp mud motor, but rather a shallow water, air cooled form of mobility that doesn't involve paddling. :lol3: I build layout/marsh boats trying to maximize the efficiency of the hull thru shape and weight reduction. Hence not wanting to put anymore weight on the transom then absolutely necessary. The 5x5 I tried first surprised me by requiring such deep water to hook up. I didn't gps the 5.5x5 but it will put the boat on step..... Barely.
Mark, I agree, gear reduction would help, and very well may happen after sunday when our season closes. I really want to get this prop thing figured out tho first, as I doubt I"ll build a longtail for use with these motors. A shortail @ 50lbs would be good tho. I guess my thought is if I can get it to run how I want it to as a longtail then tweaking the same motor into a shortail should be fine as the gear reduction will only help. And if I can't, then the addition of 20 lbs. for a 6.5hp motor isn't optional.
Lane
hunter
 
Posts: 72
Joined: Wed Nov 21, 2012 2:44 am
Location: Cordova AK

Re: SPS Mini Longtail

Postby Mark F. Cheney » Fri Dec 13, 2013 9:39 pm

Observations:

There is a forum on the net that has had 3/4 million visitors that were looking for a small long tail with a little push. The smallest motor that gives real push that I am familiar with is a Robin 7 HP OHC motor. They are a bit spendy. The most inexpensive motor that has a little push and is readily available is a Predator by HF @ $100.00 +/- . Harbor freight sell that 79 CC that you have for $100.00 also. I bought one to experiment with as part of my obsession with a small long tail. It weighs about 21 lbs. So it is 11 lbs lighter than a 7 HP Robin.

If this project is for you personally and not for resale, Take the governor of off it and put a tachometer on it so you can hold it to 5,000 rpm. It will still need a reduction to the drive shaft. For this I recommend a belt system. Us a 6 grove micro groove J profile belt. Use an aluminum pulley for the small one on the crank shaft and a glass filled plastic and aluminum one on the jack shaft. I would use 2/1 for this motor. This system still needs a UJ. Beldon is cheaper than Lovejoy. And I would make a tubular drive shaft with solid ends on it and mount the whole thing in aluminum. With care you might get it down to 40 LBs. Use a bronze prop with a shear pin. They are a lighter prop than a stainless one and cheaper too.

Mark F. Cheney

My 152 chinese motor is a 53 CC four cycle by hausheng. it weighs 12 lbs.
utahmarshmotors.com on the Great Salt Lake marsh

801 721 3293
Mark F. Cheney
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Posts: 511
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Re: SPS Mini Longtail

Postby Lane » Mon Dec 16, 2013 7:15 pm

Mark, have you ever tried the 2-1 clutched gearboxes that can be gotten on Hondas and some of the clones? I've often wondered why no one used them for lt motors other than price? Seems to me that may be 5lbs that's worth having.?
Lane
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Posts: 72
Joined: Wed Nov 21, 2012 2:44 am
Location: Cordova AK

Re: SPS Mini Longtail

Postby Mark F. Cheney » Mon Dec 16, 2013 8:02 pm

Lane,

No, I have not

When I bought my first 50 CC Honda, several years ago they had stopped distributing them which I found out after spending big bucks for one of their 50CC motors. So I have been casting around looking for an alternative for several years. I finally have a good connection with a good Chinese clone at an affordable price. It's good to 7,400 Rpm, although the engine co. only says to take it to 6,800 rpm. At 2/1 that is about 3,500 rpm. I appreciate the heads up on the gear box availability again. When I get through doing the Coast Guard mandated clutch/neutral thing in my line I will try and get one of those for one of these motors I have under the bench. At 3,500 I can get a decent prop sized for that engine / transmission package. I used to worry about the cost of the whole motor. I have quit worrying about the cost so much and am very much concerned with the weight/ thrust thing.

Mark F. Cheney
utahmarshmotors.com on the Great Salt Lake marsh

801 721 3293
Mark F. Cheney
DHC Sponsor
 
Posts: 511
Joined: Wed Dec 20, 2006 2:53 pm
Location: Bountiful, Utah

Re: SPS Mini Longtail

Postby Lane » Fri Jan 03, 2014 8:17 pm

There is one more motor apparently Honda has a new model. 22lbs 121cc 4hp rated. GXR 120. Trying to get my hands on one.
Lane
hunter
 
Posts: 72
Joined: Wed Nov 21, 2012 2:44 am
Location: Cordova AK


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