CMB 27GPX

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How many are interested in the new CMB 27cc engine?

  • prefer the AAC piston/liner ?

    Votes: 0 0.0%
  • prefer the ABC piston/liner w/ring ?

    Votes: 3 100.0%

  • Total voters
    3

David Bryant

Well-Known Member
Joined
Sep 7, 2011
Messages
2,256
Apparently CMB has released a new version of their 27cc gas (petrol) marine engine line- the “27GPX”.

Will be available in 2 to 3 weeks, as reported in a Facebook post by “Mr CMB” himself, Elisabetta Braghieri (on June 13, 2022).

From the minimal information provided in the single product image, the new engine appears to be an updated version of the 27cc Alpha-EVO.

The immediately noticeable updates are- what appears to be a new electronic ignition system, a new black coated crankcase. Also, more importantly, a new 6-bolt head/combustion chamber, and a new piston/liner assembly.

From the comments, it is confirmed that the new piston/liner assy is of AAC construction (billet Aluminum piston, w/Chromed Aluminum liner). No ring!

I’m curious if there is significant reduction in weight on this new engine.

PS:
I added images of the CMB 27cc Alpha-EVO2, the previous version of this engine, as a comparison to the 27GPX
 

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Last edited:

Wasted wages

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Joined
Jan 2, 2006
Messages
1,700
Never really liked AAC in nitro motors,,but I'm old school...in gas, I think the fit of an ABC with a ring will give a longer life.You gall up or overheat an AAC liner and piston..your done.

As long as they can SUPPLY PARTS, I'm good either way...but will watch on the sidelines before I jump in with both feet...
I suspect this motor will not be inexpensive...

BTW, Thanks for posting this up!!
 

Wasted wages

Well-Known Member
Joined
Jan 2, 2006
Messages
1,700
Also looks like a crank trigger, and possibly magnets inbeded into the flywheel on the other side that we can't see...needs to be some way to charge the coil...plus where's the plug wire ??
Maybe the coil assembly will mount separate from the motor....?
 

David Bryant

Well-Known Member
Joined
Sep 7, 2011
Messages
2,256
Never really liked AAC in nitro motors,,but I'm old school...in gas, I think the fit of an ABC with a ring will give a longer life.You gall up or overheat an AAC liner and piston..your done.

As long as they can SUPPLY PARTS, I'm good either way...but will watch on the sidelines before I jump in with both feet...
I suspect this motor will not be inexpensive...

BTW, Thanks for posting this up!!
yep, I will watch on the sidelines this time around. But I do expect that it performs well, as I’m sure there has been some significant testing.

I’ve never experienced an AAC based engine, so I couldn’t provide any insight. However, Ian Folkson, claims this configuration is better adapted to warm/hot climate, as the piston/liner fit is extremely tight and sensitive (to cold temps).

Moreover, Ian Folkson commented (quote):
"New 27cc available in ringed and AAC. With Standard ignition or no ignition so you can fit Powerspark ignition.
The AAC requires a very short run in time but is more sensitive to a lean mixture setting. It is important not to overcool the motor feeding in water to top of motor first and out at bottom of motor. Running in very cold weather is not recommended. If it gets too cold you can stick the piston.
The recommended oil is with castor like Castrol 747 at 10%"

So CMB will produce ABC and AAC versions of this new engine
 
Last edited:

Wasted wages

Well-Known Member
Joined
Jan 2, 2006
Messages
1,700
Agree,,, I now see in the comments, that it is a billet piston... so maybe they have the expansion rates under control and it will live in the AAC liner.. would be interesting to know what the recommended oil content per gallon will be as well as the type..
 

David Ashcroft

Well-Known Member
Joined
Jan 26, 2014
Messages
1,443
Never really liked AAC in nitro motors,,but I'm old school...in gas, I think the fit of an ABC with a ring will give a longer life.You gall up or overheat an AAC liner and piston..your done.

As long as they can SUPPLY PARTS, I'm good either way...but will watch on the sidelines before I jump in with both feet...
I suspect this motor will not be inexpensive...

BTW, Thanks for posting this up!!
AAC liner in my experience with the old 90 was shite...
CMB marketing...Different colour head etc
 

timwhalen

Well-Known Member
Joined
Oct 25, 2015
Messages
915
Apparently CMB has released a new version of their 27cc gas (petrol) marine engine line- the “27GPX”.

Will be available in 2 to 3 weeks, as reported in a Facebook post by “Mr CMB” himself, Elisabetta Braghieri (on June 13, 2022).

From the minimal information provided in the single product image, the new engine appears to be an updated version of the 27cc Alpha-EVO.

The immediately noticeable updates are- what appears to be a new electronic ignition system, a new black coated crankcase. Also, more importantly, a new 6-bolt head/combustion chamber, and a new piston/liner assembly.

From the comments, it is confirmed that the new piston/liner assy is of AAC construction (billet Aluminum piston, w/Chromed Aluminum liner). No ring!

I’m curious if there is significant reduction in weight on this new engine.

PS:
I added images of the CMB 27cc Alpha-EVO2, the previous version of this engine, as a comparison to the 27GPX

Dave, not to knit pick, but Elisabetta Braghieri is a 'she', and Mauro is her brother.

The GPX kit is also going to be available, supposedly in a week or so, for the 21 Beta EVO, 45 RS EVO, and the 91 RS EVO, as well. The kit is comprised of a new P&L and head button. Don't know any pricing or whether or not Stu is going to bring them in for domestic resale.
He did bring in a few of the M-1 kits for the 45 RS EVO, but I haven't had a chance to run mine since deburring and honing.
Spec wise, maybe Stu has some info.
 

timwhalen

Well-Known Member
Joined
Oct 25, 2015
Messages
915
thanks for correcting me.

Will the "GPX" imply AAC construction for the .21 Beta, and others as well?

Dave, we posted the photos CMB released regarding the 'GPX' options for 21, 45, and 91 over on Joe's 'Nitro Outlaw' group on FB... they appear to be of an ABC construct.
 

David Bryant

Well-Known Member
Joined
Sep 7, 2011
Messages
2,256
Dave, we posted the photos CMB released regarding the 'GPX' options for 21, 45, and 91 over on Joe's 'Nitro Outlaw' group on FB... they appear to be of an ABC construct.
yeah, it looks like the CMB 27cc "GPX" is the only model using ringless AAC construction. All nitro models are conventional ABC construction, only with updated porting?
 

RaceMechaniX

Well-Known Member
Joined
Apr 27, 2007
Messages
2,936
Is CMB recommending methanol and oil for the AAC spark engines instead of gasoline? That would make a lot of sense, but most of those engines go into endurance FSR hulls where I think they would run into issues having to carry 2x the amount of methanol over gasoline. The issue I know of with AAC and gasoline is the higher combustion temps lead to hotter piston temps. The piston grows beyond allowable fit and the oil film breaks down leading to scuffing. It does not help if we overcool the head which leads to more taper in the liner and tighter interference near TDC.

The aluminum sleeve expands more than brass over the temperature range trying to keep the taper and fit optimal, but it's tricky.
 

timwhalen

Well-Known Member
Joined
Oct 25, 2015
Messages
915
Is CMB recommending methanol and oil for the AAC spark engines instead of gasoline? That would make a lot of sense, but most of those engines go into endurance FSR hulls where I think they would run into issues having to carry 2x the amount of methanol over gasoline. The issue I know of with AAC and gasoline is the higher combustion temps lead to hotter piston temps. The piston grows beyond allowable fit and the oil film breaks down leading to scuffing. It does not help if we overcool the head which leads to more taper in the liner and tighter interference near TDC.

The aluminum sleeve expands more than brass over the temperature range trying to keep the taper and fit optimal, but it's tricky.

Aluminum also has a faster heat dissipating time, soooo...

Methanol does mix with certain synthetic lubricants available. The Klotz Techniplate line being one.
Red Line did produce one, too, but we're not sure of it's present availability status.

Modern synthetics and castors are impervious to the condition you mention related to heat.
If you look at the tribology specs on modern synthetics, they are virtually immune to the operating conditions our engines run in, even very high nitro %'s. Modern synthetics even out perform castors, and leave behind castors negative attributes.
 
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