Go Back  RCU Forums > RC Boats > Speed - RC Nitro Boats
Reload this Page >

CMB .67 piston position

Notices
Speed - RC Nitro Boats For all your rc nitro fuel burning boating needs.

CMB .67 piston position

Old 07-23-2007, 07:19 PM
  #1  
rosecrafts
Member
Thread Starter
 
Join Date: Mar 2007
Location: Sun City, AZ
Posts: 54
Likes: 0
Received 0 Likes on 0 Posts
Default CMB .67 piston position

Just got a CMB green head. I was told told to break it in manually. I did that but I did not notice if the low end of the piston goes toward exhaust port or the carb . It is a CMB .67
Old 07-24-2007, 07:40 AM
  #2  
f16man
 
Join Date: Nov 2005
Location: MANTECA, CA
Posts: 1,264
Likes: 0
Received 1 Like on 1 Post
Default RE: CMB .67 piston position

Low end should go on ex. side but I will check on that for sure and get back to ya.
Old 07-24-2007, 08:20 AM
  #3  
Square Nozzle
My Feedback: (1)
 
Join Date: May 2003
Location: Vernon, CT
Posts: 1,953
Likes: 0
Received 1 Like on 1 Post
Default RE: CMB .67 piston position

I would think you are correct F16. It seems logical that the piston skirt needs to cover the exhaust port when the piston is at TDC. Otherwise you will loose the crankcase fuel charge through the opened port. It may also be that the piston skirt has to be short on the front side to miss the crankshaft counterweight when the piston is at BDC.
Old 07-25-2007, 08:42 AM
  #4  
f16man
 
Join Date: Nov 2005
Location: MANTECA, CA
Posts: 1,264
Likes: 0
Received 1 Like on 1 Post
Default RE: CMB .67 piston position

Yep I checked it out that is correct, thanks John.
Old 07-26-2007, 08:04 AM
  #5  
rosecrafts
Member
Thread Starter
 
Join Date: Mar 2007
Location: Sun City, AZ
Posts: 54
Likes: 0
Received 0 Likes on 0 Posts
Default RE: CMB .67 piston position

F16 thank you for the info. I wonder could you help me. I bought this CMB be with a remote. When I hook up the fuel line to the carb it leaks around the cap on the the carb. Is there suppose to be a needle mixture valve any where or is the remote the needle? The guy I bought it from claims the motor is almost new and Cmb's don't leak. Mine does unless I am hooking it up wrong and the carb is getting to much pressure? Can you help?
Old 07-26-2007, 08:20 AM
  #6  
Ron Olson
My Feedback: (1)
 
Ron Olson's Avatar
 
Join Date: May 2002
Location: Kalamazoo, MI
Posts: 18,688
Likes: 0
Received 20 Likes on 17 Posts
Default RE: CMB .67 piston position

CMB's and MAC's all come from the same factory and use a remote needle. Andy Brown at www.cmdracing.com sells the Kalistratov remote needle for them. You need the one with the coarse threads and have to use large fuel line on them.
The carb may be siphoning fuel from the tank.
Old 07-26-2007, 08:53 AM
  #7  
rosecrafts
Member
Thread Starter
 
Join Date: Mar 2007
Location: Sun City, AZ
Posts: 54
Likes: 0
Received 0 Likes on 0 Posts
Default RE: CMB .67 piston position

Ron , I am not familiar with remotes so I will discribe the one I have. It has an arm just like a rotory carb. It is in a case that looks like a small carb body. It does have large fuel tubing. The carb leaks not through the throte but around the cap where the fuel line connects opposite the the throttle arm. I have taken the cap off and turned it to try and give it a better seal to no avail.
Old 08-03-2007, 06:52 AM
  #8  
towchief
Junior Member
 
Join Date: Feb 2004
Location: Tickfaw, LA
Posts: 7
Likes: 0
Received 0 Likes on 0 Posts
Default RE: CMB .67 piston position

Ron, are all MAC 67 parts interchangeable on the CMB 67? I have an older purple head CMB hydro 67. Only useing 30% nitro, still has good compression. HELP!
Old 08-03-2007, 09:09 AM
  #9  
Ron Olson
My Feedback: (1)
 
Ron Olson's Avatar
 
Join Date: May 2002
Location: Kalamazoo, MI
Posts: 18,688
Likes: 0
Received 20 Likes on 17 Posts
Default RE: CMB .67 piston position

The MAC engines do have a few parts that are interchangable with some other engines. The needle bearings from a Kalistratrov. 67 will work in a MAC .67 .
Again, call the ladies at CMD. If they don't know the answer they can always ask Andy. The problem can occur with engine models as they may make changes from one to another as the engines are updated.
Old 08-08-2007, 07:17 AM
  #10  
f16man
 
Join Date: Nov 2005
Location: MANTECA, CA
Posts: 1,264
Likes: 0
Received 1 Like on 1 Post
Default RE: CMB .67 piston position

That carb leak fixed? there should be an o-ring to seal the cap.
Old 06-06-2009, 03:26 PM
  #11  
apcud7
 
Join Date: Feb 2008
Location: Allen Park, MI
Posts: 23
Likes: 0
Received 0 Likes on 0 Posts
Default RE: CMB .67 piston position

I'm taking apart a new CMB .67 Greenhead. First CMB I've ever had and Itoo was told to go through it before cranking it over. What is the trick to getting the head off after the water jacket has been removed?The head is on extremely tight and I'm not sure how to get it off.

Thanks Guys
Old 06-19-2009, 11:05 AM
  #12  
HendricX
Senior Member
 
HendricX's Avatar
 
Join Date: Jan 2009
Location: Rotterdam - NL
Posts: 686
Likes: 0
Received 1 Like on 1 Post
Default RE: CMB .67 piston position

Pull head with old damaged plug in it in a vice-grip.

There's a chance the liner comes with it ... that's OK.

Then you can tap out the head with a wooden dowel.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Manage Preferences - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.