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

[CraigP]

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!

[srislash]

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

Shawn

[CraigP]

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...

[srislash]

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.

[CraigP]

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!

[CraigP]

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...

[srislash]

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

[srislash]

TFL struts look a little beefier.

[ray schrauwen]

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

[srislash]

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.

[ray schrauwen]

Possibly a different supplier. I never looked past Boca.

[ray schrauwen]

Actually I did search all over.

[srislash]

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.

[CraigP]

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.

[CraigP]

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..