The Steamboating Forum

The thrust from the prop should be taken through a thrust bearing just inboard of the stern gland if possible. If that is impossible it is an option to make a thrust block on the outboard end of your engine bed, with enough room you can cast a bearing with a large surface flange on the after end that is a good fit onto the bearing housing, this can have either a needle roller bearing or a well machined bright mild steel collar that clamps onto the shaft and transmits load onto the engine bed rather than the mains and big ends.

Greg

Jon,

As Fred mentions, the roller chain coupling is a good candidate as well.

The Tiny Power M needs an external thrust bearing. It can be as simple as a pillow block mounted just ahead of the stuffing box( as Greg mentioned). Many of those have angular contact bearings for side loading. Ample for our purposes.

-Ron

Jon, we need to see a picture (or a few) of the area from engine to prop shaft packing gland so the best options can be suggested. A picture looking straight down on this area, perhaps with a ruler or yardstick laying along the axis of the shaft for scale. Get the engine bedding (or engine bearing) longitudinal stringers in a picture too.

Then we can all start flapping our jaws (or rather pecking at our keyboards) again, with you doing all the work and spending all the money!

A confession:

I once owned a five liter (litre?) racing hydroplane with just over 600 h.p. and capable of a top speed of 150 mph. The shock loadings on the propeller shaft when skipping over the water at such speeds can hardly imagined. These props run half submerged.

I used one of these exact roller chain couplers and it never gave any trouble through three years of racing including two catastrophic engine failures, one of which sank the boat!

I had completely forgotten these wonderful items. You will never in a hundred years break one of these and it will allow you to disconnect your prop shaft in order to run your engine without worrying about your cutlass bearing running dry. And they are remarkably tolerant of misalignment and abuse generally.

A word to the wise. Buy a couple of extra master links. The links are subject to about five times normal gravity when dropped over a bilge area.

Thank you Fred.

Mike

Mike Did you ever change spocket sizes to change the speed of the prop? Seems to me you could fine tune the prop this way rather than chasing the perfect prop on Ebay Comments? Den

Ah, grasshopper! You did not look at the picture yet.

http://www.surpluscenter.com/item.asp?i ... powerTrans

It is a one to one coupler. Two identical single width sprockets face to face with a length of double row chain wrapped around them thus coupling them together. The fact that they are sprockets confuses the issue. The chain lasts until it turns into a lump of rust but never wears out. Likewise the two sprockets.

And it can wiggle around a lot without issues. Wish I had invented it.

Mike

Howdy Gents,

To give you a little context on the garbage scow I am building.............I started out with a 22 Foot Tanzer Sailboat Hull. Someobody had already come up with the idea of turning it onto something other than a sail boat so the keel was cut out.......picture a large hole........and the deck etc was removed. The only remains from the original were the outer hull and the "seating" structure of the V berth. No Stringers, no ribs, no gunwales...............no rigidity at all.

I did a somewhat sketchy job of getting my stringers in, they walk from left to right and "float" a little toward the stern. They are bedded down hard from there forward. I am set up on motor mounts that allow me to adjust height and angle easily, they originally had rubber bushings in them but I removed those because I was getting a lot of motion on the engine. I dont have an easy way to adjust from left to right and trying to get the alignment on the engie mounts is tough given my wandering stringers and the fact that I had to cut the shaft log hole and install it etc. I was hoping to get a little forgiveness from the coupling.

I have everything pulled out of the boat right now, so I cant send pictures. As to the thrust bearing, I ran without one last year and did not notice an issue. I was hard coupled. The distance between the coupling on the end of the prop shaft is only about a foot if that and I have the engine mounted in line with the prop shaft (on an angle).

Do I really need to have a thrust bearing ?

jon

According to Ron "The Tiny Power M needs an external thrust bearing." It is difficult to see the engine bearings, but looking at the Youtube video of your boat ("Lees Mills - New Steamer") it appears that the engine crankshaft is supported with two pillow block type bearings. These are typically sealed ball bearing units, and may be rated for some thrust load. If that is the case then these bearings may be adequate, assuming they are sufficiently locked to the shaft to prohibit axial movement.

Ron, do you know what type or bearing number goes on the crankshaft here, and does it have a cylindrical outer race or spherical (self aligning)?

It also looks like the chain coupling would fit OK in the shafts, but it is a bit crowded for a new thrust bearing in this area. If a new thrust bearing is really needed, then a modification to fit one just forward of the flywheel may be the way to go.

Hi Jon, Fred,

On the Tiny Power M crank, the only thing supporting the linear forces on the crankshaft to the bearing is an external snap ring. I would only rate it's service only to keep the crank in position free running. The linear forces on the engine bearings in this arrangement can be high, hitting a rock etc with the prop. I just pulled the prop on Chief, we hit a rock last time out and the prop was pushed up on the tapers about 1/8". Had to use a puller to get it off. If the snap ring is pushed out of it's groove, it's going to do a lot of damage. And I did not cut that groove, so I don't know how deep it is.

This is more than likely the main bearing.

http://bearingsdirect.com/RLS-9-2RS-Bal ... ealed.html

Tiny Power over the years has called out two different size main bearings. Mine being about first year casting sets were offered of this engine, has a smaller main bearing. 26mm ID. Probably caught some flack about the metric dimension in the late 50's?

If there is no room between the stuffing box and coupler: Simply put a thrust bearing between the flywheel and the first main bearing housing- probably have to use a spacer of some sort. Reverse is not that much of an issue as the shoulder on the crank is heeling against the bearing and forces in reverse are typically not very high.

-Ron

DetroiTug wrote: If there is no room between the stuffing box and coupler: Simply put a thrust bearing between the flywheel and the first main bearing housing- probably have to use a spacer of some sort. Reverse is not that much of an issue as the shoulder on the crank is heeling against the bearing and forces in reverse are typically not very high.

-Ron

Reverse puts as much thrust on the engine, and you are far more likely to catch things with the prop' in astern.

This is not a problem with a good marine thrust bearing that will take equal linear force in either direction, and at your shaft size it shouldn't cost too much, a new thrust bearing for SY Gondola (4" shaft) was under £100 this winter. You would need an appropriate housing as well of course, however, again due to the shaft size, you may find you can make use of a pillow block with a bi-directional thrust bearing put in.

Greg