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Thread: Need a Dimension on a Speedmaster 21-1/4" Hydro Strut

  1. #1

    Default Need a Dimension on a Speedmaster 21-1/4" Hydro Strut

    Hey All,

    I'm looking to get a measurement on a Speedmaster 21 Hydro Strut for a 1/4" prop shaft. Looking to find out how wide it is at the back, across the flats running up and down on the sides. If anyone can get a caliper measurement of this and post it, it sure would help a lot! Thanks in advance!

  2. #2

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    I'll get it in the morning for you Craig.

    Shawn

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    Thanks Shawn, and can you get an overall length on the prop shaft carrier too? That's the bottom section... Looking to design in roller bearings and seals, me and Travis are tossing some ideas around...

  4. #4

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    Quote Originally Posted by CraigP View Post
    Thanks Shawn, and can you get an overall length on the prop shaft carrier too? That's the bottom section... Looking to design in roller bearings and seals, me and Travis are tossing some ideas around...
    I would go to Boca for that. I have been wanting to try needles for a long time and may even have some to fit these here. I would have to look. But back to the question, the inside measurement on the strut is .3175 and the outside along the flat which runs the length of the strut is .4375. The regular strut is 2" long and the long ones are 3.5".

    Anything else? Im just taking the dogs for a run but should be around all morn.

  5. #5

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    Well, it looks like the 3/16" and the 1/4" strut housings are the same size. That's going to make it hard to do.
    I know the 1/4" strut will take a 9/32" stuffing tube. Can you verify the ID on the front of the tapered end. It should be about 0.287", bigger than 0.250"

    Thanks so much for checking!

  6. #6

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    Hard to believe those housings are the same between 3/16" and 1/4", but it may be true. That makes a 1/4" setup a might thin... Hmmmm...

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    On the 1/4" struts you run the stuffing tube clean Thru, then run the Speedmaster bushing inside the stuffing tube. ID the same clean thru

    Best can find is a .187 X .3436 needle bearing on the Boca site. The ones with no carrier are all metric
    Last edited by srislash; 09-12-2017 at 10:39 AM.

  8. #8

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    TFL struts look a little beefier.

  9. #9

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    Can't use B series, needles fall out. Ask me how I know... Has to be caged afaik.

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  10. #10

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    Quote Originally Posted by ray schrauwen View Post
    Can't use B series, needles fall out. Ask me how I know... Has to be caged afaik.
    The available bearings are .345'ish so one would have to ream the strut out to 11/32". You would think there would be something available as did the nitro guys not use needles in their struts? I am certain I've had this conversation with Andy.

  11. #11

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    Possibly a different supplier. I never looked past Boca.

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    Actually I did search all over.

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  13. #13

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    Quote Originally Posted by ray schrauwen View Post
    Actually I did search all over.
    There aren't many choices, Boca or the Japanese manufacturer that TP and LMT uses are about it for quality.

  14. #14

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    Well, the jury is back in with a decision... The Speedmaster 21 series strut for 3/16" and 1/4" prop shafts share the same sized housing, so there is less meat to work with on the 1/4" strut. There is a 5/16" hole bore through the 1/4" strut and a 1/4" hole in the 3/16" strut. I did a drawing showing a cross section of the 1/4" unit with roller bearings from Boca and a cross section showing the Lead/Teflon bushing. The goal was to modify the 1/4" strut for roller bearings and not use the floating bushing. The second part of the goal was to provide a seal on the rear of the strut so that grease and lubricants stay in, and water stays out. Unfortunately, there is not enough room to mount roller bearings, because the smallest OD available is 3/8", which only leaves 0.032" of metal on the sides. The machining would have to be perfect and I still have grave concerns about the strut breaking under heavy use.

    The other cross section shows the Lead/Teflon bushings, available on the OSE parts store, that are 5/16" OD X 1/4" ID X 3/8" in length. So these press fit right in, no machining necessary. The small lip seal needs a circlip to retain it in place, this is 0.020" wide X 0.010" deep, which is very doable. I'm posting the drawing and folks can make up their own minds about it. I have been talking to Travis (kfxguy) and he would be willing to machine in the circlip for a nominal charge. Please work that out with him. If anybody is interested, the U-cup Rod Seal is available here:

    theoringstore.com Part # 626-008 N70 Buna-N Nitrile 70 U-Cup

    Note that this only applies to the stepped down, 1/4" to 3/16" prop shafts. The 1/4" ID seal has the same problem as the bearings, 3/8" OD on it. I have been using the bushing version on a 3/16" Speedmaster strut on my hydro and have been getting extremely good results in keeping the water out and the grease in. As a matter of fact, I have not serviced the shaft in about 12 runs now... This shaft may be serviced by first removing the strut via the single socket head cap screw and pulling it rearwards, so the seal doesn't get messed up trying to go over the 1/4" shaft.

    I want to thank everybody who was involved in the info gathering of this project. If people have a machine shop. I could post a drawing with dimensions if you want to do your own strut. It's nice not having to get into that greasy flex shaft all the time, that's for sure. Also, the bushing will last a very long time, there are 3 of them in each strut. The water getting in will rip off the Teflon veneer, because of the steel of the shaft. So keep the water out, the grease in, and good things will happen!

    This seal will also work on the 3/16" strut, same 5/16" circlip and machining required.
    Attached Files Attached Files

  15. #15

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    Here's a pic of the 3/-6" strut with the 5/16" OD C'bore in there... The seal is off to the side, resting on the bottom of the boat, by the water lines. This is the first iteration, I used a small aluminum plate as a seal retainer. I'm going to do a circlip next..
    Attached Images Attached Images

  16. #16

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    Quote Originally Posted by CraigP View Post
    Here's a pic of the 3/-6" strut with the 5/16" OD C'bore in there... The seal is off to the side, resting on the bottom of the boat, by the water lines. This is the first iteration, I used a small aluminum plate as a seal retainer. I'm going to do a circlip next..
    Craig
    I have a question?
    In your picture - why is your strut so deep?
    Bottom of the strut should be about 1/4" plus the depth of the sponson bottom from the bottom of the hull.

    By looking at your picture, the strut is down way past that, the unsharpened portion is showing down past the bottom of the hull.

    What type of prop do you run on that hull ( submerged ) ?

    Larry
    Past NAMBA- P Mono -1 Mile Race Record holder
    Past NAMBA- P Sport -1 Mile Race Record holder
    Bump & Grind Racing Props -We Like Em Smooth & Wet

  17. #17

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    Early pic, I was seeing how much adjustment range I had. Here's a pic today. The strut is the depth of the sponsons. The prop is a Octura 1742/3 blade. I run M445, M545 and M645 as well. I added about 0.20" to the sponson depth when I redid the sponson bottoms. That little bit of unsharpened strut is only in the water taking off from the shore. Boat rides nice right on the prop, like a hydro should.
    Attached Images Attached Images

  18. #18

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    Actually, there's not much difference between the two shots... This boat has hit 62, never blown over, so I'm pretty sure the setup is fairly good.

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    Here's the sponsons. This boat is very aero light stock and has a bad case of the sponson dance! I flattened the very high angles, placed in a water stiction break and increased the overall depth of the sponsons. What this did is increase the area for the air to escape back behind the sponsons, thus dumping the air buildup it has in stock configuration. My numbers told me this wasn't quite enough, so I made and installed a reverse wing in the front. Under normal water conditions, it diverts some air from the bottom to over the top of the boat. If the nose comes up due to wind or waves, it exposes more of the reverse wing, creating negative lift and bringing it back down. The system works good! It has been pointed out by others that the delta sections on the front of the air trap (referred to as "armpits" by one person) is the reason for excess air under the boat, and I concur. The wing really offsets the ability of that hull feature to grab air.
    Attached Images Attached Images

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