CMB 101

[Marty Davis]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

 

[steve wood]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

 

[carlnoki]

I do something a bit different on the inside of the sleeve.

At TDC I make 2 marks aprox. 1/16" blow the piston skirt on the inside

of the sleeve aprox 1/16" apart. (running across the sleeve under the exhaust area)

I then take a dremel and ball mill tip and carefully make a grove

the length of the lines I drew on the inside of the sleeve.

This catches the fuel mix and lubes the hot spot on the piston

in the exhaust portion of the piston area. Works good for me.

I have not had one stick in the umpteen years I have been running the big blocks.

Hope this helps.

Carl

 

[Marty Davis]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

How big are the holes?

 

[Joe Warren]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

I have seen Steve`s liner mod. is located correctly & done very nicely. When you open up the head & get the head volume correct. Your engine will be Fuelie....... Consider the application to get the cooling water correct. Mono`s run full loop cooling. Hydro`s you can plug the holes in the inner ring & just run water across the top of the head. You will want the engine to make a lit heat. if not you will have to needle it down to make heat.....(Not Good). Also deburr the intake disk. it has many sharp edges that will destroy the case & intake hsg. intake closing 65atdc is nice...215-216 total. Pipe selection is 15cc mac`s open nitro pipe will an add-on.11 1/2 from the plug to the middle of the band & a unrestrictive header....Note the engine sold before 2010 seem to have the case cut deeper & we ran .015 shim to raise all ports up. This is Good it helps take some of the taper in the liner up & the piston dont block as hard. The 2010 101`s the case is cut higher liner location & we have done away with the shim..& you have to be aware of the piston / liner blocking fit. Dont even think about putting in on a high piston speed needle untill about 8-10 tanks goes thru.If you do you will regret it.... the engine begins to free up @ 11-12 tanks. Great engine if you get them broke in Properly

 

[steve wood]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

How big are the holes?

.078

 

[steve wood]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

How big are the holes?

you will find the rotor clearance to be anywhere from .010 to.025. face off the back of the case to get about .004 = much better running motor,more torque and easier to find a needle

.078

 

[Marty Davis]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

Steve:

What head volume and clearance have you found works best?

 

[Piston1]

Marty you can not go wrong with the 101because it has so much HP. It revs. higher than the 91. Open your head volume to adjust to the % you are running. Tighten up the rotor. It takes time and a lot of fuel to break them in. If you find the correct hone let me know, I am still looking for it. B)

 

[John Knight]

Marty you can not go run with the 101because it has so much HP. It revs. higher than the 91. Open your head volume to adjust to the % you are running. Tighten up the rotor. It takes time and a lot of fuel to break them in. If you find the correct hone let me know, I am still looking for it. B)

Jose,

Not to hijack Marty's thread, but educate me. How does the 101 run higher rpm than the 91 or the 90?

 

[Piston1]

Marty you can not go run with the 101because it has so much HP. It revs. higher than the 91. Open your head volume to adjust to the % you are running. Tighten up the rotor. It takes time and a lot of fuel to break them in. If you find the correct hone let me know, I am still looking for it. B)

Jose,

Not to hijack Marty's thread, but educate me. How does the 101 run higher rpm than the 91 or the 90?

John I don't need to educate you. I know you are a seasoned CMB racer. I have no datalogger and / or dyno that I can quote from, but from my experience running the 101 and all other 90, 91CMBs the RPM sound difference is obvious both in riggers and monos. No, I do not have a calibrated ear but you can tell. Would you believe me if I tell you that a 91RS revs higher than a 90 EVO. John in my opinion the slight piston mass difference between the engines appears to be negligible. I am not talking theory here. I understand a lighter mass piston is capable of reving higher, but in my estimation the 101 engines rev higher than the 91s under my applications (Twin rigger and Mono). John, I have a pair of 101s that scream props that bog down my 91s.

 

[BigChuck]

And I have the same motors and think different..................So it is what it is.

Also john I will say this I have not yet Cut a 91 or 101 as hard as I have cut the 90/1.0.

But now that a new batch of P/S have arrved I will be looking to "swiss" one very soon.

 

[Mark Bullard]

Marty you can not go run with the 101because it has so much HP. It revs. higher than the 91. Open your head volume to adjust to the % you are running. Tighten up the rotor. It takes time and a lot of fuel to break them in. If you find the correct hone let me know, I am still looking for it. B)

Jose,

Not to hijack Marty's thread, but educate me. How does the 101 run higher rpm than the 91 or the 90?

It is because the motor is over squared. The bore is greater than the stroke. This makes the motor rev more but moves the lower torque curve to a higher rpm.

Marty, the numbers that Steve quoted is what I have been running for years on the 101. The cut under the sleeve is what I did to make the K 90 live. I have just carried it over to the CMB.

 

[John Knight]

Jose, Chuck & Mark,

Thanks guys for the info. I can clearly hear the difference between the newer RS engines from the older EVO's and even older GP's. Each were improvement over the prior one. The power and rpm advances are quite evident. Mark hit the real reason and turned on the light for me about the bore/stroke difference in the 101. I will pay very close attention at the Fall Nationals to the very big blocks.

I ran my 90 EVO2 on Saturday for the first time in a while and it was a thrill again as always. Unreal the power it generates.

 

[steve wood]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

Steve:

What head volume and clearance have you found works best?

.9 cc head volume,.014 clearance

 

[Marty Davis]

I am working on a CMB 101 for a friend and know nothing about the engine. What kind of head volume and clearance are people finding work well on this engine?

I have seen a lot of them stick when running and wonder if people have found a good solution.

i open up the head to .90cc,with .014 to .015 clearance.also have been putting 5 holes below the exhaust port,20° apart,and milling .030 deep slots up from the bottom of the liner, to the holes,to cool and lube the hot area around the exhaust port

Steve:

What head volume and clearance have you found works best?

.9 cc head volume,.014 clearance

Steve:

Is this WITH the volume of the Piston or WITHOUT?

Thanks,