Crank/Bearing compression from prop

[Gbenzx]

Can anyone comment abt big block engines w/o gear & belt boxes?

We know lot of 454 & like motors run direct but how abt an engine that hasn't run a prop before like the diesels we're looking at?

Navistar people has said(said) they are employed on drilling jobs that result in 1000lbs push or more but is that the whole story. May be a minute or few minutes where the temps don't get otta whack. Although we know one must pay more attn to what is written in their warrantee than the said words.

An engine at almost full power & 680lbs torque may be absorbing 680lbs of push from the right prop, we just don't know yet. Due to the low rpm torque & weight consideration these engines cannot rightfully accomadate any kind of box that we know of. Is there any other choice to protect an engine from the prop thrust?

Wouldn't be very much fun with a temp gun in static testing learning we've bought the wrong prop & engine in the wrong place to add a box?

What would you do to avoid the unmerciful?

Thanx, Gben

 

[Anonymous]

Excellent topic. Chevy engines are so common because they have been proven to work well as DD (for a while anyways until the rear main finally goes out). I think this is due to the large journals and a pretty good oiling system.

Diesels are not common on airboats and when you do see one it's on a high dollar boat which probably has a gear box anyway.

So how DO you know if it's going to stand up over time? I think you have to look at the oiling system and the location of the thrust bearing. It needs to be at the back of the crank. Not sure where it is on any diesels

On a side note, I have been thinking about an add-on rear roller bearing for use on direct drive applications. I think it's time we look at direct drive not as "cheaper" but as a way to provide SIMPLE, and light weight power. Auto engines can be built for 0-3000 performance just like aircraft, and with all the cylinder head, cam and EFI tech available for autos now I don't see why it is not feasible.

Diesels already have a leg-up on the torque aspect, but not the light-weight. Someone should make an all-aluminum diesel for GBen's boat

 

[cntry141iq]

Hey guys If you run a dd plan on changin bearings every season if you want to be ahead of a failure I believe the term is preventitive maintenance. Now anytime you start experimenting with stuff it gets expensive unless you get lucky thats why comnpanies have r & d divisions. No guts no glory covers it pretty well. I believe I still have a few failed experiments layin around the yard LOL it goes with the territory. Now the good news is that what seperates us from monkees is the fact that we can learn from the mistakes of others instead of making them ourselves. If you build the boat and decide you want a box on it then I would go with the lightweight belt drive " blue lightin" I believe it is called then you will still be spinnin the same direction as a dd but the prop will be too little pitch unless you went with an adjustable one which is what I would do if I was experimenting. Now you will need to modify the engine stand of course but that is no biggie and the cage should already be as big as possible anyways so it should be ok. Just plan as much as you can to allow for modifications and be ready to revell in the glory of being first when you gitter done.

 

[Gbenzx]

Thanx Guys,

Red,
How abt a thrust plate + thrush bearing like you say outside the rear of the block? The plate can be fabed to whatever size & shape that is needed & distribute the pressure to the block where it should be. May use alum & weigh very little. The bearing can be sized to match whatever thrust level is needed. Of course we'll have the terrible ezpense of a zerk fitting = My welder!

IQ,
Can't remember for sure but the belt/box they said we should use was close to 200lbs.
Pleased to hear that at least some of us have been seperated from monkeys Both Hollywood & washington will be upset to say the least

Your right on that trial & error can become very expensive. But luckily most our fixes have been the other way around. When fuel was 9 cents p/gal I was at an age where I still hadn't learned that the big dogs got big by extracting the $$$ out of our pockets. Not only fuel but in all walks of life we now look for better & less expensive ways of doing things.

Gben

 

[cntry141iq]

I know floral city airboats has a belt drive that weighs less than a gear box which is way less than 1/2 of 200lbs. There aint nuthin wrong with better and less expensive all for that. That is the purpose of this site to maybe find better less expensive ways. My time is limited so I like ridin more than wrenchin any more so I usually go with the tried and true as often as I can but if nothin is available I get more involved then. One of these days I am gonna build or have built the prop shroud that gives me the super boost on the thrust and cuts the noise in half. I belive it can be done and safely mounted on a boat Just gotta take the time to find the right fabricator and be willin to blow a couple of props in the process and hope not to get hurt when testing in the real world as opposed to runnin it in the yard. It can be done it has been done on a stand just have to get it in the water and keep it outta the trees cause bumpin it would be a bad thing for sure 3/8 of an inch is tight.

 

[Anonymous]

Gben, that is exactly what I had in mind.