Weed eater engine conversion

Young's props work fine

I built a weedeater motor and use the same size prop as the T-10 but with a larger hole. I can't recall the number on the prop. The one thing bad with the Young's props are that they are cast. This could cause problems if you hit something real hard with the prop spinning real fast.

My motor has pushed my fat butt, boat and gear 6.2 mph which is hull speed for the boat I have. I don't know what a different prop would do better than the Young's.

Mark W

 

Thanks for the replys to my "prop problem". I can try fabricating a prop. I started with the T-10 because instructions for building a MM back in Mar of '07 specified a T-10. By the way -- if it's of value to someone. I experienced the bearing at the motor end overheating and I determined stress on the AL tube was apparently causing enough flex that it was causing excessive friction (?). I removed the bearing and machined-down the diameter of chunk of AL rod I had the bearing pressed into, machined in 2 grooves, and installed two rubber 0-rings so the bearing "floated" a little. Problem solved.

 

I have done some rough numbers on you 16ft canoe and the 40cc motor. Assuming it will get a reliable 1.5kW at 7500rpm then a prop 6.5" in diameter will have the following configuration.

For a 1.5" diameter hub. Two blades 2.5" long made from 1" wide by 1/8" bar stock. Each blade needs to be twisted 9 degrees over its length. The tip will be at 12 degrees to horizontal when the shaft is vertical - meaning 21 degrees at the hub. Blades need to be welded to the hub so that the curved face is forward facing. Welding needs to be competent as force of 200N is not trivial. Prop should be able to handle pushing down with one hand on the hub while it is supported at both blade tips.

The blade shape should look something like the foil section attached. Blades need to be ground to achieve this shape.

The design operating conditions are also attached. The efficiency is not particularly high but I expect it will be better than your current prop. If my numbers are close I expect about 8kts.

It will be worthwhile making a prop from mild steel and then have a go at one from stainless once you check the operating point for this one.

One very important factor is the handing of the prop. Once you twist the blades you have set the handing. So you need to know the direction of twist before you start to twist. It is best to use an existing prop as a guide.

Rick W

 

Thanks Rick -- I owe you. I can't find any specs in the book or on the web for the Briggs engine (021132-0599E1). The T10 prop has a 1 & 1/8" hub and prop diameter is about 5 & 5/8" in diameter but because of the weed proof "twist" there should be more blade area than the proposed home made one. "Competent welding" will be a challenge. By the way, Youngs replied and advised their props were not for gas engines and I could try cutting the T10 down.

 

I imagined that someone with good workshop tools would have a welder and be able to use it quite well. Maybe you underestimate your ability.

If you test it as suggested by loading the hub and it stands up then it should hang in for a long time. Try to keep the shaft as flat as possible to reduce the force variation on the blades.

Props are not hard to fabricate. The best prop is one suited to the application. You can have a perfectly made prop but if it does not suit the application it will perform badly. Most of these little motors need to be geared down to get the best results with standard props.

Rick W

 

I think

you are making a mistake to try to fabricate a new prop when other ways are so much easier. There have been dozens, if not hundreds of mud motors built using the T-10 prop form Young's. Maybe your engine isn't putting out all it can.

I've built 2 motors and both have used the Young's props. The first one built out of a 31cc motor just didn't have as much upmh as I would have liked. It worked, it just didn't work great. I then built one out of a 52 cc motor and that one spins the prop with no effort. I would think the motor you discuss should easily do what you want it to do.

Other options are to cut down the T-10 by 1/2" on each blade. Make sure you get it so the prop is balanced.

Young's is saying no gas engine because of the torque of the engine verses an electric motor. Since the props are cast, they will break if they it something hard.

I have about 15 hours on my second motor and have run it through some sandy river beds. A few scrapes and all but the prop is still good.

Don't give up on what you have, it will work. One guy here used the 52cc motor with a 5:1 reducer and spun a 10.5 inch prop.

Mark W

 

We have sold hundreds of props here at the Noosa Prop Shop and have found that reducing the diameter makes little difference and once you cut it you carnt put it back ! Pitch is what its all about.Small % changes in blade area dont help .
what we dont know is what the max revs are on this 4 stroke motor and without a WOT reading for the current prop we dont know anything .Sorry mark I dont see what is to be lost in trying to make a prop..I too think .

 

I'm just telling what works

and has worked for many many people who have built these things. Fabricating your own prop will work no doubt. These motors aren't rocket science and fabricating a perfect prop to go with the motor is in my opinion a lot of time spent making something not needed when a perfectly cheap alternative is readily available.

Look back on the early posts from Turn 4 fun and Ripped off (same guy) and go to the other sites where these motors have been made. Almost all use a Young's prop of some type. I know for certain that if you were to look up my prop on the charts and mate it with the motor I have, it would show that it wouldn't work. I can tell you that it does work as evidenced by pushing my boat 6.2 mph (pictures back on page 15 of this thread). Is it perfect - probably not. Would a perfectly mated prop do a better job, I doubt it.

As far as cutting it down a little, once again theory and what works don't alway equate. There have been reports of people cutting down the T-10 to make it work better on a 31cc motor. If they are less than truthful I can't do anythign about that. They have reported it working better and that is what I am repeating.

I do like the intellectual information on mating a prop to a motor and all and I have learned much on this site and others and through emailing many who have built these things. I wish I could have a Young's prop that is forged and made of brass then things would be perfect. At $14.95, Young's is a great answer to those of us who don't think we can make our own prop. I just offering alternative's and not disagreeing with anything written on the subject.

There is another site where a guy fabricated more than one prop by looking at the prop charts and after less than stellar results, he turned to the Young's (T-10 I think) and never looked back.

You wouldn't by chance sell a nice prop that would go on the back of one of these motors would you? If you had one more "stout" than the Young's, I'd buy one in a nano second.

Mark

 

The manual for this engine is at http://briggsandstratton.com/pdf/owners_manual/100/277097-Domestic.pdf

and what we find is that its the normal 3600 rpm limit ..no HP quoted but I guess 1.5 hp as its a 4 stroke not 2 stroke

So what we need to know now is what revs its getting up to with the T10

there is no market for Thai mud motors in Australia I only run one to amuse people and get the river police going

 

That begs the question

What do the river police have against mud motors and what do they do if you get caught?

Mark W

 

its not illegal but they dont understand why there are no reg numbers on the boat ( over 4 hp) and if you lift the tail to wind them up they come and investigate because they dont understand...or if I see them first I go into shallow water and that pisses them off because they carnt follow ..ha ha ..also have a jetski with an outboard motor and they check to see if you have a PWC lisence ....but you dont need one as it does not have a sealed superstructure ...I wait till they about the write out the ticket and show them the letter from the transport department ....I hate pigs ...

 

Thanks for the additional replys and information. Re making a prop: I usually manage to get a good weld but burn more rods and do more grinding than a skilled welder. I also have some brass/bronze rod scraps as well as some 3/16" thick brass/bronze plate that maybe I could pin and silver solder (?). Re determining the loaded RPM with the T-10 prop: Umm, perhaps I could design an acoustic tachometer to read the exhaust pulses and load it into a canoe and ... that would take more time than I'd care to expend. Am I ignorant of an easy way to do it? I'm not going to possibly ruin a new-conditon T10 prop experimenting. No I don't have any other props -- sorry. I need to aim toward a reasonably low-time effort eslewise it may not get done -- not enough hours in the day. Jim H.

 

prop problems

As Mark Wo stated ; sometimes engineering theory and real-world application are in conflict. In one of my earlier endeavors at building a mini-mud-motor I used a hopped-up 31cc Ryobi with a #10 young`s prop. I estimate it made around 1.5 hp at 7000 rpm. It worked, just not well. With the blade loaded (in the water) it turned at approx. half of the rpm necessary to reach max torque. Opening the throttle further created the dreaded bog. I reduced the blade area which in turn resulted in a reduction in thrust. This acted in a sense like a gear reduction . The motor was now required to turn at a higher rpm to move the same amount of water as it previously had. The overall results were, a motor that operated at a higher rpm which produced more power and improved response. I acknowledge that this could be looked upon as a little Yankee shade-tree engineering, but it did help, not solve, the problem of motor/prop mismatch.

 

to solve your rpm problem have a look at http://www.propowerllc.com where you will find a hour tacho for one two and 4 stroke motors ..just one wire to wrap around the plug lead
In Australia contact noosapropshop@yahoo.com.au


Remember this guy is using a Briggs and Stratton ..rpm 3600 not 7000 !!
B&S fires like a 2 stroke by the way

 

Briggs N Stratton and Tecumseh both fire every revolution.Not sure but I believe the Honda and clones do also.