RZ21 OB

[Joern Markset]

Larry

Can I get more info on the Novarossi water jacket you used. I'd like to buy one for my Rody OS

Perhaps a part number or?

any other ideas for a carb other than the OS 21D carb

This is the waterjacket for your OS VS PTO, I`m using the same my self (without watercooling) https://www.worldchampionproducts.com/en/vspto-01/1271-culasse-vspto-02-vs01001m.html

There is a lot of carbs that will fit your engine. The 60L carb is a good option, however it is almost identical to 21D which is by far the best carb for this engine (and many other 21 marine engines)

 

[Joern Markset]

The more posts the better, happy for this thread to take any direction. Especialy interested in anything OS related, including Rody's engines.

Brad, are you searching for info on measurements, interchangable OS parts (+ 3rd part items that may fit) and so on?

​Cause I would be more than happy to share info I have, I`m also constantly searching for the same info, however it is kind of expensive when you have to buy all material just to check measurements.

 

[BradSpencer]

The more posts the better, happy for this thread to take any direction. Especialy interested in anything OS related, including Rody's engines.

Brad, are you searching for info on measurements, interchangable OS parts (+ 3rd part items that may fit) and so on?

​Cause I would be more than happy to share info I have, I`m also constantly searching for the same info, however it is kind of expensive when you have to buy all material just to check measurements.

Hi Joern,

I am not really searcing for anything, however I am always intrigued by wat people discover and create.

Most of my R&D for the last few years has been around the 21xm.

If there is ever any info I may be able to help with, lmk.

yeah, even OS parts are expensive now.

 

[Joern Markset]

The OS 21 RX engine has the same measurements as the 21 XM. You may use crankshaft from the XM engine in your RX, and the PTO housing will fit directly as well.
​Then you can have your choice of cooling head, air or water. Put on a 21D carb and you will have a nice engine.
​If you are not racing you may put in a CMB 21 RS crankshaft, it will stroke your engine to 3,614 cc. You will have to put a 0,40 mm shim under the liner flange. Also recomend using a CMB conrod. You will need to slightly grind of some material in your crankcase to prevent the conrod from touching the wall.

​The numbers for the 21 RX-R engine:
Exhaust - 168​​ deg.
Transfer - 118 deg.

Boost - 114 deg.
​Front induction - 201 deg. opens 41deg. ABDC and closes 62 deg. ATDC
Blowndown - 25 deg.

 

[Joern Markset]

Here is my new built OS .21 RX-R Outboard.
​I have used stock parts, no modifications needed.
OS RX crankcase
OS RX-R piston / liner
​OS XM crankshaft, conrod, flywheel, PTO housing and carburetor
​OS XM VII head
​All parts are new

 

[BradSpencer]

That's awesome what you have come up with Joern,

Thanks for sharing your engine build and detailed info.

Did you measure the opening times for the exh/b/t ports on that R sleeve?

It would be great to see more engine builds on this forum. Both stock and modified. I will find time to run through what I do in a modified 21xm build

 

[Joern Markset]

That's awesome what you have come up with Joern,

Thanks for sharing your engine build and detailed info.

Did you measure the opening times for the exh/b/t ports on that R sleeve?

It would be great to see more engine builds on this forum. Both stock and modified. I will find time to run through what I do in a modified 21xm build

Yes I did, Brad, the numbers for the R sleeve are mentioned in my previous post above.

 

[BradSpencer]

Ah, yes you did

I did read that. Brain fart.

Slightly higher on the exh, and slightly lower on the intake ports compared to the 21xm. Perfect starting figures for liner shims

 

[Joern Markset]

I have some plans together with my team mate to convert the OS .46 AXII engine to outboard.

​That means a new CWR crankshaft has to be made, first drawing is finished. Then a new PTO housing. PTO shaft will be taken from K&B 45 and the bearings from CMB 45 HR (front bearings) Probably flywheel from K&B

Our concern is the crankshaft as we don`t have experience in doing the correct hardening, will be learning by doing ;-)

​Planing to use the original muffler for testing and also a wrap around Pitts style muffler.

​Now I guess you are asking "why convert a lazy engine like this"... The answer is that we wish to recruit more tunnelracers. We don`t have many tunnelracers in Norway. We are not allowed more than 25% nitro, OS is a supernice engine to deal with, and if we start at this point most of the guys will probably reach the finish line. Both because the engine is reliable and also because the speed is not over the limit (yet)

 

[BradSpencer]

Wow, what a great project you have taken on. Just what outboard racing needs. A low cost, mild performance 45 for a stock like class.

A Nova 46 setup is at least $1k in engine hanging off the back. Certainly not a great starting point for beginners.

With your iginuity and enthusiasm, your coming with really great projects. Staying tuned.....

 

[Alan Elzer]

I have some plans together with my team mate to convert the OS .46 AXII engine to outboard.

​That means a new CWR crankshaft has to be made, first drawing is finished. Then a new PTO housing. PTO shaft will be taken from K&B 45 and the bearings from CMB 45 HR (front bearings) Probably flywheel from K&B

Our concern is the crankshaft as we don`t have experience in doing the correct hardening, will be learning by doing ;-)

​Planing to use the original muffler for testing and also a wrap around Pitts style muffler.

​Now I guess you are asking "why convert a lazy engine like this"... The answer is that we wish to recruit more tunnelracers. We don`t have many tunnelracers in Norway. We are not allowed more than 25% nitro, OS is a supernice engine to deal with, and if we start at this point most of the guys will probably reach the finish line. Both because the engine is reliable and also because the speed is not over the limit (yet)

Joern. many years ago I was constantly breaking the old 45 outb cranks. A machinist buddy made 2 for me. He used stress relived 4140 leaves a smooth finish. He ground a dial pin to correct rod size, heated crank & froze the pin, then pressed it in. It was a full circle crank. I still have them & can send you pictures next week. PS: plain 4140 is hard to machine a smooth finish cause it's so tuff it tares..

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[Kris Flynn]

pretty sure EN36A is what others have used with great success for cranks. you do not want them too hard though! The last batch of Precision racing nova cranks had issues with hardness.

lights cranks seemed to be pretty good for hardness

 

[Joern Markset]

Lets see how it goes, it does not matter if we break some parts, the parts for this engine is pretty cheap anyway

Ive ordered a new OS 21 XZ-B spec 3 that I will convert to outboard and see if it performs ok

 

[Joern Markset]

OS .21 XZ-B Spec III Outboard

 

[Alan Elzer]

Joern what did you use for the crankshaft? XM OUTB? What bore & stroke of that motor

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[Joern Markset]

This was a very easy build as I got the crankshaft and PTO housing from Rody Roem. His VS PTO outboard is based on the XZ crankcase.

Bore is 16,27 and stroke is 16,80

 

[Alan Elzer]

This was a very easy build as I got the crankshaft and PTO housing from Rody Roem. His VS PTO outboard is based on the XZ crankcase.

Bore is 16,27 and stroke is 16,80

Thnx
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[Alan Elzer]

Have you ran your 45 cmb conversion yet

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[LarryConrad]

Brad, any updates on your testing? The local club in my area held the first race of the season today. Servos for my M-13 Dragon

 

[user 115]

I have a couple of these for some reason. I believe we were going to try and put them in the OS Max 21 O/B as they were a direct fit.

https://www.propshophobbies.com/ProductDetails.asp?ProductCode=OSMP23703000

Not sure if these are what you are using but if you need them, make an offer. I have one BNIB, the other is new as well but not in the original bag. I have no use for them anymore.

Thanks,

Charley