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tbarr
New member
Username: tbarr
Post Number: 1
Registered: 01-2009
| | Posted on Sunday, February 01, 2009 - 09:28 am: | 
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Not exactly about old engines, but can someone help me:
I am trying to come up with a way to install an inboard. Space limitations, etc dictate that the engine must be installed level, i.e. I cannot tilt it doen on the back end to meet the prop shaft comming through the bottom of the boat, the shaft obviously being at an angle off of horizontal.
So, can I mate the engine to the propshaft by the use of a universal joint, same as in an auto drivewhaft. I have never seen this done, but It seems like it outght to work. Am I missing something??
If a u-joint won't work, how about a Constant Velocity joint?? Where might I get one??
Engine is a Honda commercial air cooled, 8HP at 3600 rpm (direct drive, no gear but with a centrifical clutch),plan on cruising at approx 2600, pushing an 18 ft. wooden fishing shiff that weighs approx 500 lbs.
I figure that you old engine guys have seen everything and are the best place to go to get help.I do hope I am not going to be yelled at for an "off subject" post. I think this matter is of enough interest in general to merit asking the question here, since the answer is equally applicable to any engine, new or old.
Thanks
TB |
larry_from_maryland
Senior Member
Username: larry_from_maryland
Post Number: 338
Registered: 07-2003
| | Posted on Sunday, February 01, 2009 - 12:27 pm: |
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If a single u joint is used the prop shaft will speed up and slow down as the shaft rotates. At a small angle it will be hardly noticable, as the angle gets greater the knocking and vibration gets severe. Cv joints are better. A double u joint with the joint crosses lined up and each angle egual wiill take an angle well. The speeding up and slowing down will be cancled by the second joint. I have examples on the machinery out in the yard. |
miro
Senior Member
Username: miro
Post Number: 356
Registered: 11-2001
| | Posted on Monday, February 02, 2009 - 09:33 am: |
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The DisPros use a single joint in order that the shaft kicks up into its housing inside the hull when the skeg hits a submerged object.
But under normal operating conditions, the shaft is straight so there is little effect of the acceleration / decelleration problem to cause vibration.
Typical speed is 700- 900 rpm.
When the shaft is lifted manually under full speed the vibration can be quite bad - it certainly is noticeable.
IF the speed is relatively low - say 500-600 rpm and the mis-alignment is small ( less that 5-10 degrees) and the engine is say a 3HP, then I think you could get away with a single U joint.
But for sure it would never be as smooth as a properly aligned shaft directly coupled to the engine.
miro |
George Martin
Visitor
| | Posted on Monday, February 02, 2009 - 04:05 pm: |
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Purely from an old engineering view (not marine)
a properly constructed 2 uj assembly will give no vibration. A single uj is bound to have some vibration as said earlier.
I guess the best way forward is a single CV joint with a self alighning bearing just behind the CV to hold the shaft stable. Of course there is no shaft velocity change (and hence vibration) with a constant velocity joint. |
kerrigan
Member
Username: kerrigan
Post Number: 10
Registered: 06-2008
| | Posted on Tuesday, February 03, 2009 - 09:17 am: |
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The axial trust created by the propellor must be considered. Look at a V drive configuration. |
tbarr
New member
Username: tbarr
Post Number: 2
Registered: 01-2009
| | Posted on Tuesday, February 03, 2009 - 04:31 pm: |
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Thanks to all for the info. Most informative
The last post gives me theidea that it would not be too hard to gin up a thrust bearing/collar in a u joint set up.
However, any idea if a cv joint by itself has the ability to take an axial load?
any other ideas??
Anyone know of a source of supply for small CV and universal joints? I have only been able to find things for autos, a great overkill for an 8 hp motor. I think. while i am asking for more help, anyone know of a v-drive suitable for an 8 hp motor??
thanks again
TOm Barr |
larry_from_maryland
Senior Member
Username: larry_from_maryland
Post Number: 339
Registered: 07-2003
| | Posted on Tuesday, February 03, 2009 - 06:21 pm: |
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www.surpluscenter.com page 104. They have bearings and flex couplers too. |
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