PEERPSI

So finally got a set of o-rings to hold on the BJ55. The town here is a little too small to find metric viton on the shelf. So I went with .5 mm wider. They were tough to get on the pipe, I'm what people call a big guy and I was sore trying to push the things on. Pipe doesn't move or leak now though. Two nice pee streams coming out the side!

Now for the questions. What sort of clearances do you run on the prop shaft to strut bushing, end play on the prop shaft. Do you use any thrust washers?

I drilled out the original bushings, the OEM prop shaft was 3/16", in the lathe to .252 before installing the CC pro mod. They are two piece so I'm not sure they where true when reinstalled.

Originally they had about 2 thousands clearance. Now after about 3 tanks we're at 25 thousands. Where I work we measure form and finish in nanometres so this is freaking me out!

Anyone have advice on thrust bearings?

Real happy with the way it's running now though. Even when it gets right out of the water it stays level, doesn't blow over and regains stability quickly. Definitely appears to be some torque effect on the back of the hull that needs to be addressed. Obviously torquing in the direction of the prop rotation.

I expect that twin engines with counter rotating propellors would help in that regard, hmm....

What sort of RPM's do you expect or aim for. With race cars we had shift point calulators based on gearing, rpm at peak torque/hp and tire size. The aim was to optimize where you landed in the torque curve after the upshift. I imagine with the 2 stroke boat engine we want to select the propellor size design and pitch to match the engines hp/torque curve. Anyone have knowledge to share on that point?

I'm hitting 16400 max rpm. The dyno charts I've seen for the CC Pro Mod showed peak torque/hp at 14700 RPM. I expect it's hard to judge max rpm with the boat lifting out of the water at times.

Best stress therapy I've found yet though!

dicko

The clearance between the drive dog & strut should be about 4mm if you aren't using thrust bearings. you would usuually only use thrust bearings if you are running a square drive flex. If you run a thrust bearing you want just a tick of play in the bearing. I run both depending on the hull.

Using a thrust bearing will shift the point of propulsion more from the engine mounts to the strut. Without thrust bearings the boat will have a pushing affect from the engine mounts as well as the back of the boat. The difference in handling is minimal & most people won't be able to tell the difference once the boat is set up. Just some more food for thaught for you.

As for RPM, that also will vary with the type of hull being run. Some hulls like to have a high revving (18,000rpm or more) engine with a small prop (hydro) while other hulls like cats use a lower revving engine swinging a bigger prop.

Hope this gives you some more stress relief.

MrMikeG

You want over rev in the engine, sounds like your in the ball park. Anything past 18k-18,5 will twist zenoah cranks.

Dockman

How do you adjust the play my has a lot of it (3/16"). The shaft has notches fo the set screws and I have everything in them but still have lots of play. I just figured this was normal.

dicko

I spoke to Dale yesterday about the new RCMK edition coming out shortly, apparently it's revving to 20,000 rpm stock. I can't wait to see it when he drops that in one of his hulls.

hibby

reguarding the thrust bearings, they are really designed for racing as they will only last about about 5-10 hours per tony at whw. I tried them out not knowing that and only got about 5 hrs out of them before the bearings were faling out. I use the the 1/4" thrust washers now and put 2 between the drive dog and strut and one between the ferrule and front of strut and haven't had any problems.

jtdesign

which rcmk are you talking about I really would like to know?

PEERPSI

Dockman are you still using the stock prop shaft with the upgraded motor? Several have had them break after motor upgrades taking an expensive prop to the bottom with it.

I'm using a square drive cable. I must have had something loose a misaligned because last night it was pushing on the back of the stuffing tube.

I figure my axial movement is about right then but what about radial.

How much clearance between the shaft and bushings?

dicko

It's yet to be released. I was talking to the Aussie RCMK distributor about it & he has them on order. It's an improvement on the current one being sold. I can't remember the name, but I think it was SX.... not sure. The specs he was reading to me were impressive, they had it over 92 kph stock.

Dockman

Yes still using the stock shaft. My clearance is about 1/16" total play.

Dockman

I would like to upgrade to the 1/4" shaft but not sure of everything I need? I would hate to lose the 3 blade it seems to be working awesome.
Do I have to change the strut?

How do you measure the flex shaft (total lenght)?

PEERPSI

I'll see if I can find my order for WHH on the flex shaft, it will have the dimensions. What I did is follow the instructions on their site for the solderless flex cable. It worked out fine. If you're planning to change to collet do that first as the length may be different.

I drilled out, on the vice, the bushings. One of the bushings pushed out so I had to drill that one in the lathe. Truth be told I should have done both in the lathe.

In the end I've ended up making a new bushing just yesterday. Measurements are 48.2 mm long 7.95 mm OD diameter. 3 mm on the thrust end is stepped up to 11 mm OD for a thrust surface. Press that in on the side the propellor mounts. I can send you a drawing if you like.

The prop shaft they sent with the solderless flex shaft was .2495 inches so you need to ream the hole in the bushing to a .250 and then sand the prop shaft for best fit.

One other thing, they only make two sizes of prop shaft, I thought my prop shaft would be custom sized as well. Turned out it was about 5/8" to long. They sent some plastic thrust washers out with the prop nut they short shipped. I put one on the drive side and the rest on the prop side. Be sure to ask for the thrust washers.

My mistake was thinking that the shaft was cooled and lubed by the water. Not so it's surface drive after all. So now I use the center saver grease on all the wear/load surfaces.

Ran the boat tonight in fact. Drive worked fine. In fact I was getting a wobble at speed which didn't seem to be there tonight. I'm thinking the play in the shaft, it was excessive 25 thou, might have been causing that.

Not a perfect outing though. Water was rough and I should have known better. Flipped it end for end and then rolled landing right side up. Unfortunately the roll claimed the wing on the back of the hatch and the end for end took it's toll on the rudders. One got a bit of a bend, 1/32 deflection along it's length. It also broke the servo horn.

Being as I'm braver then smart I ran again with one servo. After a few laps I figured if I ran perpindicular to the waves it seemed the most stable. So I gave her full throttle and yep over it went again. This time upside down. Decided to call it a night there!

On the plus side my CC Racing 2" band shipped Friday.

hibby

dockman, I changed over to the 1/4" prop shaft on my blackjack. I ordered octura part #OC8PS (4 1/2" 1/4 prop shaft with prop nut and drive dog), and the part #OCFSF2525 (brass ferrule), you will have to take your old ferrule off and solder the new ferule on your flex shaft. As far as the bushings the stock ones are quite brittle to try and drill them out as I tried and one cracked. I ordered the whw sl bushings and they fit perfect into our strut without having to drill at all, they are 9/16" long and are self lubricating I also got a pack of wwh 1/4 thrust washers 6 to a pack and use one between the ferrule and strut and two between the strut and drive dog and haven't had any proplems. (no more prop shafts breaking and loosing props!!) I am going to try and post a picture for you of my set-up haven't posted pictures before so hope it goes through the first time. [img][/img]

PEERPSI

Good to hear the WHH bushings fit without modification. Only think I would say about your set up versus the WHH prop shaft and solderless drive is no heat point to fail and the way their prop shaft is built it holds itself in without the worry of set screws coming lose.

hibby

If I have any problems with my flex shafts or ferrules I will go to that whw solderless cable it is a good set-up, I am just trying to use my original flex shaft and save a little money. Are you using that 6717 3 blade prop? I tried one when my zenoah was stock and it wouldn't get up on plane, but have an m-5 kit in now and use the x670 and x472 have gotten 46mph with the x472 but am thinking about trying that 6717 3 blade from dasboata.

PEERPSI

I'd be interested to see how you make out with the 6717/3. I've tried 2714/3 ABC and a 7015/3 from Dasboata. I've reached 49.25 mph with the 7015.

Dockman

Sounds like I need to order some goodies from whh. I think I will go with the solderless cable and keep the clutch. Thanks for the info guys.