New CMB 21 Rotor Assy

[DaveMarles]

I am running FSRV enduro boats where throttling is of utmost importance. It's faster with the bigger carb. CMB told me the engine did not like a big carb but thats not my experience.

Little OT, but can you explain your FSR-V fuel systems a bit? im interested in the float tank mainly.

also, whats the top speed you guys are seeing on the .21 FSR-V boats?

There is a good video here

There are strict rules regarding the rescue boat. You have to throttle when near it and if you don't, you get a stop and go or laps deducted. The race in the video was 12 boats. Sometimes we run 15 boats in a heat. Thats really hard work!

 

[Ray Sametz]

I am running FSRV enduro boats where throttling is of utmost importance. It's faster with the bigger carb. CMB told me the engine did not like a big carb but thats not my experience.

Little OT, but can you explain your FSR-V fuel systems a bit? im interested in the float tank mainly.

also, whats the top speed you guys are seeing on the .21 FSR-V boats?

There is a good video here

I'd be wearing a full face shield helmet and a flack jacket, them Bob the Builder hard hats don't cut it.

 

[carlnoki]

Bill Gibson;

You must dremel the channel tract up the transfer port located just above the new rotor assembly and possibly

champfer the case opening where the rotor assembly mates with the block so that the o-ring seal will fit properly.

All of my motors did not require the champfering at all. They all had it already.

Carl

you can go to www.iansboats.co.uk and yo uwill see the pictures of the case mods for the motor intake on the case.

 

[Bill Gibson]

Bill Gibson;

You must dremel the channel tract up the transfer port located just above the new rotor assembly and possibly

champfer the case opening where the rotor assembly mates with the block so that the o-ring seal will fit properly.

All of my motors did not require the champfering at all. They all had it already.

Carl

you can go to www.iansboats.co.uk and yo uwill see the pictures of the case mods for the motor intake on the case.

Thank you Carl....I will check it out!

 

[The Real Grim]

First off I would like to apologize to Stu for not making a post about the new 21 VAC engine.

The new 21 is completely new except the head button and the water jacket. The inside of the case now looks

like a shrunk down version of a 67/ 80 case.The tranfer ports are alittle narrower and the boost port is wider

than any of the other CMB 21 cases.It comes flowed for the new back plate.The exhaust port area is smaller

in volume than the last case, but not as small as the green head case.The lower part of the case is smaller

in volume also and combined with the new back plate assembly the torque of this engine is beyond any

21 I personaly have ever used.

The piston has a narrower and shallower dish, thus giving a slightly smaller total compression volume.

The sleeve ports are all different also. NO MORE TRI PORT EXHAUST.The width is the same as the

tri port but it is flat across the top of the port and the timing is 184.

The transfer ports are narrower to allow for the wider boost port. They are wider top to bottom to give them

the time area back and they have 130 degrees of timing.

The boost port is .408 wide verses .259 on the old sleeve.The time area is much larger and the timing is 129.

As you have seen the crankshaft is shaped differently and also has two bronze slugs to help with the balancing.

The motor is smoother than it's earlier versions.

The con-rod is larger and beefier at the bottom and has a V machined on the back of it.

The back plate assembly works so much better I could'nt believe the amount of torque gains that I got.

The timing on the rotor that I got is it opens 32 degrees abdc and closes at 61 degrees atdc.

One might think that it's alittle short on the opening side but you might want to try it in your boat stock

before you change it.

NOTE: Take set screw out and red lock tite it back in before you run it. I got lucky and noticed that it had backed

out before any damage had happened to the bushing or anything else.

The carb works great stock but the trick to it is open the low end needle out .I got it to work good if it just entered

the spray bar when it's about 3/4 closed. Stu wanted me to try it cut out to see if there was much of a differance so I did and I did'nt see much on the lowend but the top end was better.

I tested the engine bone stock with .008 deck with the CMB new 21 pipe in my rigger. I used 60% nitro and a Mc Coy

# 59 glow plug.

The first thing that we noticed was it left the beach so easy we quickly knew that we were going to need more prop.

We went from a H-10 with 3.75 to a 1450 cut to 48mm and pitched to 4.2 .

This was still too small of a prop so we started shortening the pipe. We cut off .500 and ran it with no header and then it started to really turn on the rpms. When all was said and done on the boat we were testing it in it was exiting the corners at 73 mph and was 76 mph in the straights.In my opinion that is pretty good for a bone stock 21.

It still has a good bump and compression after three gallons of fuel. The only thing that I have replaced is a set of bearing.

If you have any Question I will be glad to help any way I can.

Mark

 

[Luca Gray]

Hi Mark,

what pipe length where you running,

cheers Luca

 

[Nigtmare]

NOTE: Take set screw out and red lock tite it back in before you run it. I got lucky and noticed that it had backed

out before any damage had happened to the bushing or anything else.

Hey Mark where is this set screw :unsure: I got the engine apart and I don't see one?

Thanks. Nick

 

[BB Mods's]

Under the drum rotor

 

[Nigtmare]

Under the drum rotor

Thanks Tom...... Now I see it :lol: :lol: my eyes are bad I couldn't even see the hole with out my glasses :blink: (the set screw hole that is)

 

[BB Mods's]

No worries, as soon as I seen the set screw on mine I had the drum apart and Marty on the phone asking how to balance the thing

also, I cut my closing side of the rotor to allow 215* total intake duration, so far so good, same results as Grim, pulled up to 4.2" then ran out of prop

 

[Richard Dahlheimer]

No worries, as soon as I seen the set screw on mine I had the drum apart and Marty on the phone asking how to balance the thing

also, I cut my closing side of the rotor to allow 215* total intake duration, so far so good, same results as Grim, pulled up to 4.2" then ran out of prop

Thanks to all that have posted info on this topic. Mark, is the pipe you tested available from Stu now, or coming with the new motors? Could you post the rtr weight of the hydro used for the test? Richard D

 

[mtruex]

First off I would like to apologize to Stu for not making a post about the new 21 VAC engine.

The new 21 is completely new except the head button and the water jacket. The inside of the case now looks

like a shrunk down version of a 67/ 80 case.The tranfer ports are alittle narrower and the boost port is wider

than any of the other CMB 21 cases.It comes flowed for the new back plate.The exhaust port area is smaller

in volume than the last case, but not as small as the green head case.The lower part of the case is smaller

in volume also and combined with the new back plate assembly the torque of this engine is beyond any

21 I personaly have ever used.

The piston has a narrower and shallower dish, thus giving a slightly smaller total compression volume.

The sleeve ports are all different also. NO MORE TRI PORT EXHAUST.The width is the same as the

tri port but it is flat across the top of the port and the timing is 184.

The transfer ports are narrower to allow for the wider boost port. They are wider top to bottom to give them

the time area back and they have 130 degrees of timing.

The boost port is .408 wide verses .259 on the old sleeve.The time area is much larger and the timing is 129.

As you have seen the crankshaft is shaped differently and also has two bronze slugs to help with the balancing.

The motor is smoother than it's earlier versions.

The con-rod is larger and beefier at the bottom and has a V machined on the back of it.

The back plate assembly works so much better I could'nt believe the amount of torque gains that I got.

The timing on the rotor that I got is it opens 32 degrees abdc and closes at 61 degrees atdc.

One might think that it's alittle short on the opening side but you might want to try it in your boat stock

before you change it.

NOTE: Take set screw out and red lock tite it back in before you run it. I got lucky and noticed that it had backed

out before any damage had happened to the bushing or anything else.

The carb works great stock but the trick to it is open the low end needle out .I got it to work good if it just entered

the spray bar when it's about 3/4 closed. Stu wanted me to try it cut out to see if there was much of a differance so I did and I did'nt see much on the lowend but the top end was better.

I tested the engine bone stock with .008 deck with the CMB new 21 pipe in my rigger. I used 60% nitro and a Mc Coy

# 59 glow plug.

The first thing that we noticed was it left the beach so easy we quickly knew that we were going to need more prop.

We went from a H-10 with 3.75 to a 1450 cut to 48mm and pitched to 4.2 .

This was still too small of a prop so we started shortening the pipe. We cut off .500 and ran it with no header and then it started to really turn on the rpms. When all was said and done on the boat we were testing it in it was exiting the corners at 73 mph and was 76 mph in the straights.In my opinion that is pretty good for a bone stock 21.

It still has a good bump and compression after three gallons of fuel. The only thing that I have replaced is a set of bearing.

If you have any Question I will be glad to help any way I can.

Mark

interesting, my vac engine came with the standard mac/cmb type port arrangement, and tri port exhaust, it also has no weights in the crank <_<

it also doesnt seem to have a major torque advantage over my mac engine, i suppose the sleeve porting is part of the reason the motor has more torque, i will have to get the proper piston/sleeve and we will see...

 

[Luca Gray]

Martin,

where did you get your vac 21 from, as i heard someone else with the same piston/sleeve etc...

cheers Luca

 

[Richard Dahlheimer]

Martin,

where did you get your vac 21 from, as i heard someone else with the same piston/sleeve etc...

cheers Luca

From what i understand, the engine that Mark Grim is testing is a "pre-release" engine that is not available from Stu yet. The VAC-EVO that i have has the .21 RSV crankcase, piston and liner,head insert, rod and waterjacket. The crank is weighted and has the new inline induction. Just waiting for the water to warm up some before i test mine. Richard D

 

[Archie Stanton]

deleted...sorry it wasnt funny

 

[The Real Grim]

Luca

From the center of the case to the seem is 7 3/8"

Richard

It's the new 21 nitro pipe that I got from Stu over a year ago I dont know if he has them in stock.

The boat i was testing with weighs 3 3/4 pounds

Martin

That is not a VAC engine.There are three different motors in the last six months.The one you

have,then the next one that has the new backplate and crank, then the test VAC that I have.

Mark

 

[mtruex]

Luca

From the center of the case to the seem is 7 3/8"

Richard

It's the new 21 nitro pipe that I got from Stu over a year ago I dont know if he has them in stock.

The boat i was testing with weighs 3 3/4 pounds

Martin

That is not a VAC engine.There are three different motors in the last six months.The one you

have,then the next one that has the new backplate and crank, then the test VAC that I have.

Mark

the one i have has the new induction and carb assembly and has a v stamped in the rod, but obviously not the right crank or piston/liner..hopefully its the same case at least?

 

[DaveMarles]

Luca

From the center of the case to the seem is 7 3/8"

Richard

It's the new 21 nitro pipe that I got from Stu over a year ago I dont know if he has them in stock.

The boat i was testing with weighs 3 3/4 pounds

Martin

That is not a VAC engine.There are three different motors in the last six months.The one you

have,then the next one that has the new backplate and crank, then the test VAC that I have.

Mark

the one i have has the new induction and carb assembly and has a v stamped in the rod, but obviously not the right crank or piston/liner..hopefully its the same case at least?

Martin. The motor you have is probably the 21 EVO. It has the 3 port exhaust, the VAC rod and the new drum/backplate/carb assembly.

Dave

 

[mtruex]

Luca

From the center of the case to the seem is 7 3/8"

Richard

It's the new 21 nitro pipe that I got from Stu over a year ago I dont know if he has them in stock.

The boat i was testing with weighs 3 3/4 pounds

Martin

That is not a VAC engine.There are three different motors in the last six months.The one you

have,then the next one that has the new backplate and crank, then the test VAC that I have.

Mark

the one i have has the new induction and carb assembly and has a v stamped in the rod, but obviously not the right crank or piston/liner..hopefully its the same case at least?

Martin. The motor you have is probably the 21 EVO. It has the 3 port exhaust, the VAC rod and the new drum/backplate/carb assembly.

Dave

dave,

is the case the same? thanks Martin

 

[mtruex]

Luca

From the center of the case to the seem is 7 3/8"

Richard

It's the new 21 nitro pipe that I got from Stu over a year ago I dont know if he has them in stock.

The boat i was testing with weighs 3 3/4 pounds

Martin

That is not a VAC engine.There are three different motors in the last six months.The one you

have,then the next one that has the new backplate and crank, then the test VAC that I have.

Mark

the one i have has the new induction and carb assembly and has a v stamped in the rod, but obviously not the right crank or piston/liner..hopefully its the same case at least?

Martin. The motor you have is probably the 21 EVO. It has the 3 port exhaust, the VAC rod and the new drum/backplate/carb assembly.

Dave

dave,

is the case the same? thanks Martin