Speedmaster Sport 20 hydro strut

[785boats]

You won't need the 7/32" tubing inside the 1/4". The tolerance is too tight & will bind on the flex when you adjust the angle of the strut.

[Old School]

Many thanks.

[CraigP]

You won't need the 7/32" tubing inside the 1/4". The tolerance is too tight & will bind on the flex when you adjust the angle of the strut.

I think he’s saying short 7/32” at the motor coupling end of stuffing tube. I do that on all my boats so I can leave the distance of the exposed flex shaft a bit longer to the coupler, in order to clean it before it’s inserted into the coupling.
It just keeps it from starting to whip around. You have to keep the distance to a minimum on a 0.150” flex though...

[IRON-PAWW]

Great topic. Exactly the discussion I need at the moment. I've fitted 1/4 brass tubing on a gsx380 on advice I got at ose. I have that going going all the way into a sport 20 strut - leaving the 1/4 inch gap at rear of the strut for the bushing head as described above. 3/16 ose flex with no teflon. Problem I'm getting though is terrible vibration in the flex when I bench test. Brass tube even begins getting hot. On a the gsx380 it results in a fairly long flex cable..... is 3/16 really ok on this hull? Can't figure why it vibrates like it does beyond an alignment issue....

[rol243]

1/4 inch brass logs are fine for 3/16 inch shafts so your problem must be either the motor collet is out of true or the flex shaft join to stub shaft is out of true. where does the brass log get hot ? strut end or motor end ??

[IRON-PAWW]

Closer to strut end but near as I could tell maybe 3/4 of the way from motor to strut. So mid way is getting hot. Motor end is ok. Can't see any wobble in the flex at motor end when I spin it by hand with collet done up. But I have another so I'll try it. I have another flex too so I'll try that as well. Gentle bend as I could make it. Frustrating.

[Old School]

I went with a 9/32" tube with teflon liner. At the strut end of the stuffing tube I soldered a short length of 1/4" tube protruding about 3/16", with the end chamfered to allow a degree of strut angle adjustment. It will be sometime before I can test my install but I did spend some time getting the alignment correct. The flex rotates very easily by hand.

I wonder if the weld alignment on the flexshaft is accurate as mentioned in previous post. If not then the flex will tend to whip inside the stuffing tube at the strut end of the tube causing vibration.

[rol243]

I have had some pretty badly made collets and flex shafts that had to be tossed so you should try another collet and or flex shaft as it does sound like one of these parts is your vibration issue. just one other thing, is the motor lined up well with the shaft log ? if the motor is out of alignment you will also get a bad vibe in the drive line.

[IRON-PAWW]

Thanks guys. Really appreciate the assistance. I did spend the time getting the motor alignment as true as I could get it. But I did note that after I nipped up a slightly loose motor rail mounting bolt the motor alignment did shift a shade. I've corrected that - so I'll try another bench test first. Then I'll swap collet and flex. I too have suffered bad parts in that department before. It's an OSE flex and those have been good to me so far. Octura coupler though.... I think its got to be some sort of cable whip or wobble I've got going on right now. Cheers muchly again.

[rol243]

There was some mention about the Octura Collets being not so good. you shouldn,t get any whip in the 1/4 inch tube , more likely its the collet or shaft. easy fixed.

[Old School]

I use TFL collets and these flexshafts. I have purchased quite a few of these with no issues at all. They seem to welded very well with no misalignment. Seller is excellent to deal with.

https://www.ebay.com.au/itm/3-16-X-2...72.m2749.l2649

[MarkF]

It's normal to get some rattle when you don't use teflon. That is why I always use teflon in all my boats that run 6s or less. I also use 3/16 in my 380 and it's butter smooth even with the long length. Using teflon offers a better seal and more adjustment and is just as fast as boats that don't use teflon.

Mark

[IRON-PAWW]

Well. I've still got some type of issue going on. Swapped out the Octura Collet for an MBP. Tried a different Flex. Problem remains. It's a type of knocking mid-flex. To me it seems to be about where the brass tube goes through the hull. If I gently jiggle the prop back and forth I can hear the flex knocking on the brass tube at around that point. No matter how I align things - that happens. Bench testing gets up one hell of a vibration at faster revs. I just don't know how to solve it. A different curve maybe?









[

[rol243]

seems very unusual as you have a very good quality collet and the brass tube log has a very even and slight bend which is perfect so what else could it be. ??? are the bearing / bushings in the strut good ? are you sure the flex shaft is perfect at the welded join with no out of trueing ? is there anything inside the brass stuffing tube at the top end area ? also are you leaving a good 3/16 inch gap at the strut to drive dog ? plenty of oil or grease on the shaft ?

[IRON-PAWW]

Hey Rol243. Thanks for helping mate.

I can't detect any defects in either of the flex shafts I tried. They both appear wonk/bend free at the join. Both roll evenly across a flat bench top etc. Bushing is not loose or worn - they are brand new. Yes - even though there's no gap at the drive dog in the pics I *am* leaving one when I run it. I packed as much grease as I could get into the tube - and that helped. That did quell the vibrations out a reasonable bit - maybe it just needed more grease for testing. But the whole tube starts getting warm with a few high speed blips on the bench - with the hottest part being mid-way. Is that expected? I might try a few very small runs (20 - 30 sec) with it tomorrow and see what transpires. My first build like this so I'm not sure how things should behave. I might try some speedmaster flexes perhaps if I can't get any breakthroughs.

[Norwest]

Use liner and bend is too gentle coming out of hull!

[properchopper]

Use liner and bend is too gentle coming out of hull!

I've experienced this situation before. I arrived at this exact conclusion FWIW.

[IRON-PAWW]

Ok. I wondered if the gentle bend might have something to do with it. So. I need to throw away the 1/4 tube and get the size that will take a liner? Re-doing the bend with this 1/4 tube and no liner isn't going to work? Can someone show me a photo of the curve I need? Cheers muchly. Think my RC Boatbuild FE30 uses no liner :-)

[properchopper]

I believe that there's a certain stuffing tube/shaft bend angle that, when exceeded cancels out the harmonics. I've been on both sides of the issue. The bend I put on FE30's seems to be on the happy side, and being teflon-less seems to be the hardcore race setup (although I'm willing to side with Mark on this). Teflon surely won't be hindering full P setups but my thinking is that for P-Ltd Power even a teensy bit of (probably imagined) greasy teflon induced parasitic drag could knock off a few needed RPM's.

pictures will follow

This is a bit noisy with a smooth, gradual curve:

shaft some noise.jpg


This is the original production FE30 (with a later cowl) - I didn't build this one - No noise/harmonics with an initial sharper curve (then going straight back)

shaft good.jpg

[Norwest]

Many years ago I posted on here about sanding the liner liner and the original poster asked and said it worked to a T and said thank you , so it should work here too!

[Norwest]

Check here on OSE, Steve has a chart regarding stuffing tube with liner and a chart without liner.

[rol243]

with some luck to might have to raise the strut closer to hull bottom after testing / trimming, if so you could add a slight bend in this log so help this issue and save re fitting another size.

[Norwest]

Check flex to see if the smallest portion has a tiny kink under the scope which maybe unseen by the naked eye. Remember the flex will vibrate in the middle of flex if the whole flex lay near flat. Coupler jaws spacing maybe and will show up right away just off the coupler tip and you'll see it right away if looked real close . Now if set screws in coupler have 3 screws , they can be used to compensate.

[Norwest]

rol- you could remove s/tube and add by soldering brass tube and use a next size bigger for a sleeve which will make a better curve. Do your bending before soldering which will make a bigger angle down.

[Old School]

Do not know if this helps but click on the FE30 image and a Word document opens giving info on setting up the hull and tuning.

http://www.insaneboats.com/setups/

[rol243]

I would firstly email Mike from ML Boatworks and ask him what is the good strut height for the 338 sport hydro and with abit of luck you might have your strut alot deeper than is required so this means you should be able to add a slight bend near where the brass log exits the hull to bring the stut to the desired height. if this works it will save you alot of extra stuffing around in regards to changing to another log etc. fingers crossed.

[IRON-PAWW]

Ok Thanks guys.

Thanks for the pics Tony. I do still have that FE 30 here you built me so I might refer to that as well regarding getting a better bend.

I spent a few hours at the lake today setting different strut heights and trying different props & flexes. I even tried bending the stuffing tube a little more. I was able to get the boat running better - but still sometimes I'd get the awful vibrations set in though. Just couldn't get it running smoothly every time. So I came home and ripped the stuffing tube out :-). Time to admit it just wasn't going to work the way it was. From what I found during testing - It does seem that just slightly more of a bend would probably help things. I'll go the 9/32 tube with liner and get a more pronounced bend and see where I end up. Live and learn. Watch this space :-) Damn nice boat the GSX380 when it gets up and goes... I'll say that.

[Norwest]

When flex came out, they found a small S in stuffing tube bend close to hull and thru the hull near coupler. This took the whip our of flex especially in the .130 flex. Make sure the s/tube is straight from motor to prop. Now if s/tube has a slight bend to either side of hull flex will whip, I found this out! Let the group know how things turn out .