Prop to Strut clearance

[INEEDAV]

What is the acceptable distance for prop to strut clearance?

[johnmiller]

We always added 5" to the length of the shaft when measured from the v-drive to the end of the strut. So, you should have app. 5" of shaft past the strut.

[schiada96]

1/4 to 3/8 between the prop and end of the barrel so a prop puller works.

[superdave013]

from the back of the strut to the hub of the prop should be between 3/8" to 3/4". I've seen NJBA tech let up to 1" slide but they didn't like it.

[INEEDAV]

Well crap, when I put the v-drive in yesterday after rebuilding it I reconnected the prop shaft. Looks like I am going to have to spend at least 2 more quarters on this project.
What should the maximum space between the output shaft and the prop shaft be before it becomes and issue?
Thanks for the replies.

[johnmiller]

I wouldn't do that. You want them kissing each other in the split coupler. Too much risk of it pulling out!!! If you're too short, order another propshaft. As I said, you should have about 4 1/2 - 5" of shaft hanging out of the end of the strut.

[superdave013]

John, it's common for racers to move the prop back and forth by putting nickles between the 2 shafts. The Key will clear a nickel on a 1" shaft. I had 4 or 5 in mine for years when I was racing.
What is safe I don't really know. That would also depend on your coupler. Do you have the big long one or the short 4 bolt model?
This is a good thread as I'm getting ready to buy a shaft for my new set up. Maybe I'll start off with 5" past the end of the barrel like John's suggesting. But I'll put all my props on to make sure that there is no more then 3/4" between the prop and strut barrel. If there is I'll cut the shaft down a bit.

[INEEDAV]

John
From what I have read, mostly on here, it is standard practice to use spacers between the two shaft to take up space when you move the prop. Don't get me wrong, as I am just getting in to this type of boating and have a lot to learn, but doesn't 4.5-5.0 inches allow for a lot of prop "whip", especially on a boat that should be in the 700-750hp range?

[superdave013]

I think he means 4.5 ~ 5" from the end of the strut barrel to the end of the prop shaft.

[INEEDAV]

Sorry John, misunderstood your first post. 4.5~5 in makes sense with it through the prop, looks like my reading comprehension skills are fading:confused:, thanks for giving that last little tug to get my head out Dave.
Still yet, how much spacer is it acceptable to run between the two shafts? I do have the long coupler.

[Razors Edge]

I was taught by an old racer/engineer dude down here that the distance between the front of the prop boss and the back of the strut barrel should be a maximum of 3/4's of the shaft diameter. eg with a 1" shaft you should have NO MORE that 3/4" gap.
The closer to the strut the better, keep in mind that the prop will also move up the shafts taper slightly when you first run it, you will need some clearance so as not to hit the strut once you are running. Keeping in mind that you also need to have plenty of clearance between the blade and the bottom of the boat.
I have also experimented with spacers between the output shaft and the propeller shaft like superdave has but have learnt the hard lesson of running the prop too far back, (snapped shaft right behind the strut and prop lost to the fishes). I try to get mine set up with about 1/2" clearance between the prop and strut (on 1" shaft) and then re tighten the nuts after running for 3 or 4 laps.
This puts the prop too close to the strut to get my puller on but I prefer to drop the shaft out of the box to get a puller on as opposed to risking breaking another shaft. Props are too damn expensive to loose let alone the over-rev your engine suffers when the load comes off. My 454 pulls 7300rpm flat out but showed over 10,000rpm on my tell tale after throwing the prop and dinging the rudder on the way out. Not good for a 454.
Be sure to run good strut bushes also, I replace mine annually. I currently use a product that we call oily bush. It is like a nylon but impregnated with oil I believe, and cut 3 water grooves in them and run about 8-10 thou clearance when they are new. There is a product being marketed here by the name of Thorndon that some guys are now using for strut bushings, it is a bright orange colour and is quite rubbery. Has anyone there had experience with this stuff. Or what do you mostly use.

[johnmiller]

Dave's right, it depends on how long your split coupler is. I'm sorry I didn't word my statement very well, I meant exactly what Dave stated, (end of the strut barrel to the end of the prop shaft).
I guess I worry too much about this kind of stuff, because as a boat builder, you have to make sure the customer will have no problems. I have seen several props/shafts get ripped right out when you back out of the throttle at high speeds, causing the prop to smash into the rudder which instantly blows the boat out of the water. When I install a split coupler, I take out the set screws and drill into the shafts, and then lock tite them in. I also would do the same to all the safety collars including the rudder safety collar. I would also drill a 5/16" hole through the rudder and tiller arm!!! I just don't take any chances with stuff that can come loose or get pulled out.
All of you on this web site are experienced V-Drivers, but we had to worry about joe blow customer who never checks anything, and then looses his boat!!!

[Moneypitt]

When installing a prop and checking the gap to the strut, the first check should be done without the key in the shaft. Push the prop all the way on, and carefully check the gap. (A known size spacer and feeeler gages work well). Then install with the key in place, the gap should not be larger, if it is you are not flushed up on the taper, and are riding on the key. If this is the case you need to trim the key down on some sandpaper until the prop bottoms on the taper, and the gap measures the same as without the key. I've seen boats shake like crazy because of this, trimed the key, shake went away.........Moneypitt

[superdave013]

Originally posted by johnmiller
All of you on this web site are experienced V-Drivers, but we had to worry about joe blow customer who never checks anything, and then looses his boat!!!
And alot of us are learing things from guys like you.
I know I've learned alot from this site. I try to help when I can but I still know that there is lots to still learn from others.
That's what makes this place so great!

[johnmiller]

Moneypitt is absolutely correct. Never install a prop before checking what he stated. I have never been able to use a key as is. I've always had to grind them to fit. What I used to do is slide the prop up without the key and apply a piece of tape on the shaft right where the front of the prop hub ends, then start playing with the key till the prop slides all the way up to the tape. Most of the time I couldn't find a feeler gauge, but always had masking tape on me! Ha Ha
If you don't do this, you stand a chance of cracking the prop hub when tightening the prop nut, or the prop can rock on the key which is not good either, as MoneyPitt stated.

[stix818]

I believe ours is around an 1/8 from the back of the strut to the prop barrel. If the prop clears but you can't get a puller behind it you can always losen the coupler and slide the prop shaft back a tad. We have to do this on my old man's boat.

[Lookin for Liquid]

Originally posted by superdave013
from the back of the strut to the hub of the prop should be between 3/8" to 3/4". I've seen NJBA tech let up to 1" slide but they didn't like it.
Dave, with a couple of years of experience in this question we have found that .250 is perfect and adequate clearance for Flats and Hydro's up to say 1000 HP. We set the TAF with .375 clearance and the TAH with .400. Anything less and you would be risking hub to strut rotational friction.
Some people seem to think that the prop only pushes forward but to add to that, every time it rotates 1/2 turn it is trying to push water up and out, which the bottom of the boat redirects back and creates a tremendous shear load on the shaft.
Bottom line is closer the better as long as the hub does not rub on the strut barrel.
Another case to point out is how well your V Drive is braced for the forward push of the propshaft. I really wish people would take a minute and sit and comprehend what pushes their boat forward as the V Drive and plate are transferring all the forward momentum to the complete boat. Bracing is very important to calculate what clearance you may need between the barrel and the prop hub. We try to pick up the engine rails with radius rods that have heim joint ends as to take up any slack and to give correct propshaft to V Drive tailshaft alignment.
Sorry to ramble but when I see a prop 1" back of the strut, I can't stop shaking my head which leads me to an ice chest sooner than anticipated.

[Hallett]

I just want to say thanks for all the great info on this topic.
i am installing my new prop and didn't know what the
clearance should be. looks like mine is 5/8" from the strut
to the prop Barrel. thanks moneypit. superdave and others.
for the post. Hallett :cool:

[lost boy]

have been told that a bit of lapping compound on the shaft and new prop
(twist back and forth to help seat a new prop w/o key)is a good thing?
You may want to ask about that. Makes sense to me.
lb

[Cole Man II]

Can someone elaborate further on the use of the lapping compound.

[058]

Can someone elaborate further on the use of the lapping compound.I lap the prop with valve lapping compound to the shaft and check contact with machinist blue. When done I install prop without key to insure full seating of the prop, snug it up with the nut and then install the key, it should slide in with light tapping using a small hammer and punch. You shouldn't need a jack hammer or an air chisel to drive the key in.

[old rigger]

I just want to say thanks for all the great info on this topic.
i am installing my new prop and didn't know what the
clearance should be. looks like mine is 5/8" from the strut
to the prop Barrel. thanks moneypit. riverdave and others
for the post. Hallett :cool:
Riverdave? I think you meant Superdave? No offense to RD.
I learn something new everytime I read a v-drive post by 058, superdave and a few others on this VD forum. Great info being shared.

[superdave013]

Most of the time I couldn't find a feeler gauge, but always had masking tape on me! Ha Ha
hey John, I hear it's worth up to 10MPH if you use DUCT tape instead of masking tape. haha :cool:
I've never done that lapping compound trick. I'll be sure to do that this time.
Old Rigger, you da man! Are you going to Pomona sunday?

[Hallett]

[QUOTE=old rigger]Riverdave? I think you meant Superdave? No offense to RD.
I learn something new everytime I read a v-drive post by 058, superdave and a few others on this VD forum. Great info being shared.[/QUOT
Yes your right old rigger i meant superdave. :)

[Moneypitt]

058, most shafts I've seen are cut just where the key rides, not all the way out the back of the prop.......This is why the right keys are rounded on the ends, to fit in the recess in the shaft. I would be afraid of a slot long enough to drive the key in with the prop installed............And what, if anything keeps the key in??................MP

[Norseman]

058, most shafts I've seen are cut just where the key rides, not all the way out the back of the prop.......This is why the right keys are rounded on the ends, to fit in the recess in the shaft. I would be afraid of a slot long enough to drive the key in with the prop installed............And what, if anything keeps the key in??................MP
That must be where you use the Duck Tape! :D

[058]

058, most shafts I've seen are cut just where the key rides, not all the way out the back of the prop.......This is why the right keys are rounded on the ends, to fit in the recess in the shaft. I would be afraid of a slot long enough to drive the key in with the prop installed............And what, if anything keeps the key in??................MPAll the shafts I've seen have the keyway cut all the way to the threads allowing the key to be installed with the prop on the shaft. I do it this way to insure the prop is fully seated to the shaft and not offset by riding on the key. The prop nut will hold the key in just fine.