Longtail motor angle

First timer here-- great site. Building a longtail motor with a 6.5 hp clone engine. According to briggs and stratton website the maximum angle for proper motor operation is 15 degrees. Due to my design i need to run motor at 20 degrees. Is the going to be problems with this? Can i add more oil to crankcase to compensate? carbuerator issues? Thanks for any replys.

 

have a look at my post " thai longtail with 6.5hp lifan/honda" you will also find posts on larger engines than weed eaters in the weedeater post...some use a universal joint so the engine is basically horisontal ..but you need a good joint !!!

 

Agreed. Heavy duty U joint. Keep is properly greased.

 

if possible get a down angle gearbox, if its a launch this angle may get worse as the bow lifts

 

but sure get a truck u.j to keep cost down

 

On a real long tail,--and I can hear one passing by me now --the engine is fastened straight to the shaft after being geared down by approx8:1

The whole thing is on swivel,--up down and 360 degrees for reverse.

when not in use you park the prop on the bow post where it keeps clean and the engine then drip oil over the transom.

Theres is so much to be admired from this simple system.

ALL parts for this including engines can be bought over the counter at most hard ware stores.

UJ? where does that go?

http://www.boatdesign.net/forums/post-tsunami/10m-thai-long-tail-8144.html

 

Most go devils have u joints inbetween the engine a prop shaft.

Look at this pic, you can see the u-joint near the engine

http://godevil.com/Images/6.5Intekenginelarge.jpg

 

I think if you look at that go devil the metal work is complex compaired to my chain drive design ( which also gives you a right hand prop) I think 20 deg is a bit high 15 more like it ....and whats this about the bow comming up ..it on a swivel joint ....if you have a "cavitation plate " over the prop it will always stay at the same depth in the water ...ie rig for cavitation plate to be horisontal ..15 deg to shaft....I think 8 :1 is a bit high for a 5 hp the driven gear will be very large dia ..mine is 2:1 and drives a 9 x 10 pitch..I trust you checked the photos in diy marinising

 

sorry guys, i misunderstood what a longtail is there, it is also used to describe a type of launch stern, ignore my post, the uj is unusable, & the bow up or down is irrelevant

 

Everybody likes their longtail a different way. There are many different ways to make one. I personally like em 1:1 directly coupled to the engine shaft with a cutlass in the water. Drill a few holes in the shaft tube for lubrication. Sit em as low as they go on the transom. 5 hp engines are easy to come by and we run em hard. An engine may last 3 years, if it's lucky.

I've seen em with u-joints too. First time I've seen a chain pistonbroke. Good way to get a better angle though. U-joints wear out, but it takes a few years. They are not designed to take the linear force.

 

I was recently watching a National Geographic program about the undiscovered tribes of the Amazon. To my great interest the preferred means of travel, in that remote area, were boats powered by long tail Mud motors. The motors were very simplistic in design. The drive shafts were directly connected to the engine (no U-joint) thus requiring the engine to be tilted downward when dropping the prop into the water. A fairly short boom on one of the boats required the motor to be tilted at an estimated 20-degrees+ when operating . The engine appeared to handle this tilt angle with no problem what so ever. The engines based on size and color appeared to be possibly Honda Gx 160 or 200`s. After that show I consulted with Dennis Scott of Scott Racing engines . Dennis builds ,dynos, and sells a lot of these type engines. I brought up my concerns about tilting the engine up to 25 degrees when operating. Dennis expressed confidence that angles approaching 25 degrees were acceptable . He did recommend adding a little extra oil to the crankcase though. I wouldn`t hesitate, tilt it and go.

 

Mudman ; I admire the simplicity of you design. You stated " Drill a few holes in the shaft tube for lubrication" Could you be a little more specific. Are you using water as the lubricant ??