CMB 101 tuning issues

[Marty Davis]

Tom I would start by fattening up the needle and putting a bigger prop or same one with more pitch. Sounds like you might not be loading the motor enough and when you start squeezing the needle down to get it to clear out you wind up too lean.

I agree 100% with this. Saw it on Tommy Cordoza's mono. Put a larger prop on and it was perfect. That engine will NOT run well unless loaded a ton.

hi marty, is this also true for the cmb .91rs? thanks,mike.[/quote

Not sure about that. But it is in place on the older 91's and the 101's. I would assume that it is also true on the 91 RS, but not positive. All of these have the problem of sticking and transferrng piston aluminum to the sleeve and ruining the piston. The fixes below the exhaust ports seems to be effective.

I suspect the reason for the aluminum transfer is the cooling ring. You need to NEVER cool the engine below the head button. NEVER on the crankcase.

Marty, I think in the larger bore motors, as the piston speed gets high and due to the amount of surface area of the larger bores, the coefficient of friction goes up and heat then goes up and aluminum is left on the liner. We have found the only solution is to reduce the friction with lubrication using the sub exhaust port slits holes and groves. BTW the slit alone is not adequate, becasue we really twist the 91's and 101's up using 60% nitro. Gary

Gary:

I agree 100% with you on this!!!

 

[Tom Foley]

More progress , got the sleeve mod done for additional oiling of the exhaust side piston skirt . Today the head button and it's off to the lake . Also got the lower waiter cooling shut down with some 4- 40 stainless cap screws red loctited into the case . a couple of pics here .

I would like to see the trapped compression ratio and blowdown numbers. I have been watching a guy who knows a LOT about this stuff and have seen some big positive changes in performance by just messing with the head. Fun stuff

Norm Doerr

Timing is stock , just opening up the head volume , we'll see how she runs this weekend . running out of time ...big race next weekend . Norm , you ever gonna race again ???

 

[Joe Warren]

You need to cut more off the intake lower side(liner) if you want to let the fuel in? I would leave the disk alone & cut .020 off the closing side of the case. keep the Same angle the fac put there. should put your modified timing about 216 218 on intake timing.stk is 206-208 I have been up to 230 But thats too much & causes other problems. :blink: :blink: : Dont be SCARED...

 

[Tom Foley]

You need to cut more off the intake lower side(liner) if you want to let the fuel in? I would leave the disk alone & cut .020 off the closing side of the case. keep the Same angle the fac put there. should put your modified timing about 216 218 on intake timing.stk is 206-208 I have been up to 230 But thats too much & causes other problems. :blink: :blink: : Dont be SCARED...

Yeah , gonna clearance the sleeve more intake side , disc valve is just polished a bit from the rough blanchard ground surface is all . Thanks gain for all the help guys .

 

[Norm Doerr]

More progress , got the sleeve mod done for additional oiling of the exhaust side piston skirt . Today the head button and it's off to the lake . Also got the lower waiter cooling shut down with some 4- 40 stainless cap screws red loctited into the case . a couple of pics here .

I would like to see the trapped compression ratio and blowdown numbers. I have been watching a guy who knows a LOT about this stuff and have seen some big positive changes in performance by just messing with the head. Fun stuff

Norm Doerr

Timing is stock , just opening up the head volume , we'll see how she runs this weekend . running out of time ...big race next weekend . Norm , you ever gonna race again ???

Racing... yeah right, bench racing maybe. As soon as I quit playing "Boatclub" and get my #%@& together

 

[Tom Foley]

Finished the head button at work today , done working on it . Going to test a new pipe as well this weekend the Muck 15 CC pipe that I have had for some years now un-used . Also taking my daughter Carol ( 10 ) RC boating for the first time with the tried and true Seaducer 21 Mono . Hope she can deal with noise !!

 

[SayMikey]

Your pushing t close,maybe you need to borrow a bullet or a screaming MONSTA Frankie?

 

[Tom Foley]

HA ! What was funny was I'm in the lunch room at my shop going back and forth to the lathe and checking Volume with a syringe and a soda bottle cap of rubbing alcohol on the lunch table and a customer walks in !! DADADADADA anyway they understood after I explained my process of step by step metal removal and checking the volume in tenths of a CC . Funny stuff . :lol: :lol: :lol:

 

[SayMikey]

Dont show him the bolts in your neck! Or let him smell the nitro it might confuse him

 

[BigChuck]

Oh............FRANKEN-FOLEY, One last thing...............NONE..........NONE of the props mentioned are ENOUGH on that motor with a MUCK.............!!! Use the 15mac OBI WON!!

 

[Andy Greene]

I will make you a ONE TIME offer that is only for the Winter -Nats

If all doesnt work out- get with me and you can use the nasty Gold head I have

The stipulations are-

You cant take it apart and measure shzt

You kill it- fix it.

What time are you heading out to where to test btw ????

Oh yeah- your gonna need a muffler- LMAO

Andy

 

[shoboat]

Charles,

I sent him enough propeller today.

He just needs to know when to stop with the pipe length. :unsure:

Tom,

Just make sure it is short enough to win.

Have Fun Testing,

Mark Sholund

 

[dwilfong]

Tom

We are going to set up the lake tomorrow. All I can say is go "BIG"!!!!!!!

David

 

[BigChuck]

Good deal Mark!!.................I HOPE he can KEEP it on the WATER!!! :lol: :lol: :lol:

Foley.............If the boat dose some WEIRD stuff!!! E-mail me. You have crossed over to a ZONE that very few have had to trim for!!! TRUST ME!!! You will know what I mean!!!

And I can tell you because...........?????

 

[TUNLBOTR]

Tom

We are going to set up the lake tomorrow. All I can say is go "BIG"!!!!!!!

David

Got that right. Talked with Wayne earlier this week, good ole fashioned drag racin course. Keep the ramp close, we can have a freestyle competition...

 

[Tom Foley]

I will make you a ONE TIME offer that is only for the Winter -Nats

If all doesnt work out- get with me and you can use the nasty Gold head I have

The stipulations are-

You cant take it apart and measure shzt

You kill it- fix it.

What time are you heading out to where to test btw ????

Oh yeah- your gonna need a muffler- LMAO

Andy

NOT !!!! I'm bringing three spare bullets all set up the same way if this works !!! :lol: :lol: :lol:

 

[Jeff Lutz]

More progress ...after work I machined the backplate to get the desired disc clearance . Ended up with around .004 - .005 " measuring with a caliper . thanks to Stu Barr for his time on the phone last night and Mark Sholund as well with some info on these motors . More to come on the bowl volume when i get to that tomorrow or Thursday . Thanks again for all the tips guys .

BTW if you are wondering why i turned the inner surface it's because my lathe cut .012 " when I dialed .010" ...so I got paranoid about the disc being too tight and took a .0015 "skim cut on the face of the back plate to loosen it back up a tad ......**** nitro motors !! :lol: :lol:

Tom, Your lathe cut .012" because you dialed .012"! LOL!!!!! I modified Mark Sholund's engine and showed him this mod.In the future, it is much easier to build a simple fixture to bolt your crank case to,and cut the case to close the clearance. This prevents chucking and possibly damaging your backplate,also prevents you having to dial anything in, let alone dialing it 2 ways. P.S. All of the sleeve lub holes and slots below the exhaust ports are good, but, a Band-Aid for another problem----------Going lean on the top end.Jose is right, cmb use to put the cooling holes in the sleeve and should not have gotten away from it,but just keep the latter in mind. Jeff Lutz

 

[shoboat]

Jeff,

I have never even opened up that motor. I just told Tom

that the Muck 15 CC pipe was the way to go with a 101.

The motor that you did just sits in the box waiting for

another S.A.W. boat to be built. I cannot even tell you

what the motor looks like inside, all I know is that it

revs just like the 21 motor that you did for me.

Eric wants to try the motor in one of his new boats. :unsure:

I don't work on motors just propellers.

Thanks,

Mark Sholund

231.590.3023

 

[Tom Foley]

I am still waiting for Eric to come out of the wood work and run . I'm sure the shop is keeping him busy with family and 100 mph bass boat as well !!!!!

 

[Jeff Lutz]

Jeff,

I have never even opened up that motor. I just told Tom

that the Muck 15 CC pipe was the way to go with a 101.

The motor that you did just sits in the box waiting for

another S.A.W. boat to be built. I cannot even tell you

what the motor looks like inside, all I know is that it

revs just like the 21 motor that you did for me.

Eric wants to try the motor in one of his new boats. :unsure:

I don't work on motors just propellers.

Thanks,

Mark Sholund

231.590.3023

Mark, No worries there, disc clearance is no secret, its something that should be set proper out of the box.ON a heat race engine, like yours,being that the muck pipe is no longer made, the mac 15 is a great pipe as well.On a radar gun,heat race trim, very comparable. By the way,Did you go to huntsville? I was wondering if you brought all that cold weather with you!!!