Cox Engines Forum
You are not logged in! Please login or register! Guests are limited to posting in the "General Questions (Guest Posting Allowed)" section only. Becoming a member is fast, easy and FREE!


Search
 
 

Display results as :
 


Rechercher Advanced Search

Latest topics
» CEF speed contest Design Discussions
by getback Today at 6:35 pm

» Genius.....
by RknRusty Today at 5:05 pm

» Why won't my tee 049 run properly
by SuperDave Today at 11:16 am

» Cox Sandblaster parts needed
by jsesere Yesterday at 7:19 pm

» O.S. Max 10 FP
by fit90 Yesterday at 6:56 pm

» Control line hints and tips for beginners.
by pkrankow Yesterday at 5:19 pm

» Super Custom 46 AII ABC R/C
by ian1954 Yesterday at 5:10 pm

» Wanted A free flight Glider for an .049 engine
by Blue Eyes Yesterday at 4:36 pm

Cox Engine of The Month
April-2014
John Goddard's

Family of Space Hoppers



PAST WINNERS
CEF Traveling Engine

Tach Race 2014
Its time for Tach Race 2014!
Profile Scale Reed Speed Contest
Gallery


Win This Engine!
The Traveling Prop

bad compression.. how to fix it

Page 1 of 2 1, 2  Next

View previous topic View next topic Go down

bad compression.. how to fix it

Post  casalejuan on Sat Feb 18, 2012 4:20 pm

Hello,

I bought 3 Pee Wee 0.20 engines Babe Bee .049 but only one of them works Sad . Before start, I changed all the venturi gasket, and little parts like needles, etc.
I saw that the engine that works, has a good compression and the others has not a good compression Huh... . Somebody can tell me how can I fix this problem? all the engines are new and they came in unopened blisters. So never were started.

I wait for your answers Reading

Thanks!!

Juan.

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  WingingIt74 on Sat Feb 18, 2012 4:22 pm

your prop is a little big I believe. How many head gaskets do you have installed?

_________________
-Travis
HorizonRcFlyers.com - A Forum Dedicated to "YOUR" RC Aircraft

Winging It! with Travis & Jeremy
On FaceBook & YouTube

WingingIt74
Moderator

Trusted Seller
Posts: 2968
Join date: 2011-08-11
Age: 39
Location: Waterloo, IL

View user profile Http://www.HorizonRcFlyers.com

Back to top Go down

Re: bad compression.. how to fix it

Post  nitroairplane on Sat Feb 18, 2012 4:47 pm

I have had pee wees swing 7x5 props .
Well one thing I did for a low on compression pee wee was to remove the piston and bake it in the kiln for about 30 mins, this swells it somewhat giving a tighter fit. After this the engine had to be run in again.
Indra

nitroairplane
Top Poster
Top Poster

Posts: 6956
Join date: 2011-04-11
Location: London

View user profile http://modeldieselengines.forumstopic.com/

Back to top Go down

bad compression- how do you fix it

Post  proctor on Sat Feb 18, 2012 4:52 pm

If they are new engines the piston cylinder fit should be OK.
I would look at whether the cylinder is properly screwed down
into crankcase and remove head and make sure just one gasket
fitted. Check the glow then screw head down carefully and make
sure it is snugged down properly.
The engine should then at least fire on the prime.
Not one of the more expert member but I have wasted a lot of
flying time trying to start a peewee with a head that had slackened off
after a flight.
John

proctor
Gold Member
Gold Member

Posts: 198
Join date: 2012-01-31
Location: Scottish Highlands

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Cribbs74 on Sat Feb 18, 2012 5:01 pm

I only can add one thing to the comment above.

Lap the head on some very fine grit sandpaper to ensure it is level. Install a new gasket or flip the one already there if you don't have spares. I have corrected many compression issues doing this.


_________________
Someone sent the promised land
And I grabbed it with both hands
Now I'm the man on the inside looking out.

-Pink Floyd-

Cribbs74
Moderator

Trusted Seller
Posts: 6890
Join date: 2011-10-24
Age: 40
Location: Tuttle, OK

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Surfer_kris on Sat Feb 18, 2012 5:02 pm

Check where they leak first. Put a bit of detergent around the head and turn the engine over slowly and check for bubbles. Some heads have a poor sealing surface, use fine grinding paper in a flat surface, like a piece of glass. If that is not enough you might have to lap the head to the cylinder, remove the washer and lap with fine grinding paste.

If there are bubbles around the piston there is nothing you can do (I've never had any success with growing piston using heat). But the oil they come with is very thin and they can seal better once they are running on full castor fuel.

Surfer_kris
Platinum Member
Platinum Member

Posts: 667
Join date: 2010-11-20
Location: Sweden

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  casalejuan on Sat Feb 18, 2012 7:15 pm

WingingIt74 wrote:your prop is a little big I believe. How many head gaskets do you have installed?

Hi, the prop is not the problem. I have a lot of props and is the same thing. I have one gasket installed in the head.

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Cribbs74 on Sat Feb 18, 2012 7:18 pm

Yeah, the prop is not the problem.

All the suggestions above are good ones. How's the compression now?

_________________
Someone sent the promised land
And I grabbed it with both hands
Now I'm the man on the inside looking out.

-Pink Floyd-

Cribbs74
Moderator

Trusted Seller
Posts: 6890
Join date: 2011-10-24
Age: 40
Location: Tuttle, OK

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  casalejuan on Sat Feb 18, 2012 7:26 pm

Surfer_kris wrote:Check where they leak first. Put a bit of detergent around the head and turn the engine over slowly and check for bubbles. Some heads have a poor sealing surface, use fine grinding paper in a flat surface, like a piece of glass. If that is not enough you might have to lap the head to the cylinder, remove the washer and lap with fine grinding paste.

If there are bubbles around the piston there is nothing you can do (I've never had any success with growing piston using heat). But the oil they come with is very thin and they can seal better once they are running on full castor fuel.

Hi! I┬┤m going to try this first. Mabe that┬┤s the problem and is a simple way to check it.

Thanks!

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  casalejuan on Sat Feb 18, 2012 7:29 pm

cribbs74 wrote:Yeah, the prop is not the problem.

All the suggestions above are good ones. How's the compression now?

Compression is very slight. however one of the two engines that does not work occasionally makes an explosion but does not start at all.

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  John Goddard on Sat Feb 18, 2012 7:44 pm

If it's firing but not running it's not getting fuel.
If it were me because its a new engine I'd start looking at the reed valve first. Has
It stuck or is there some dirt underneath it.
I've several new in boxes that don't seem to have a lot of compression
Whilst others of the same type and age do. I was so concerned with
A late 1960's 010 that I took it from box (because I thought it was a dud)
And fired it up, I ran it in as per instructions and it seems to have
A bit more comp now but it runs like a champ.
What's your glow like is it bright yellow orange or dull orange?

John Goddard
Diamond Member
Diamond Member

Trusted Seller
Posts: 2447
Join date: 2011-11-24
Age: 49
Location: Leyton North East London

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Mike1484 on Sat Feb 18, 2012 8:27 pm

Maybe your problem is sticking your nice motor in a vise . A complete lack of respect for any motor.

Mike1484

Mike1484
Moderate Poster
Moderate Poster

Posts: 26
Join date: 2011-10-28
Location: Northern Ohio

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  andrew on Sat Feb 18, 2012 8:32 pm

nitroairplane wrote:Well one thing I did for a low on compression pee wee was to remove the piston and bake it in the kiln for about 30 mins, this swells it somewhat giving a tighter fit.

Indra --

I've heard for some time that heat soaking a piston can cause it to swell, but I've never tried it. What kind of temperatures are we talking about here?

andrew

andrew
Platinum Member
Platinum Member

Posts: 1016
Join date: 2011-08-11
Age: 66
Location: Western Kentucky

View user profile http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Back to top Go down

bad compression- how do you fix it

Post  proctor on Sun Feb 19, 2012 6:55 am

Hi, back in the day we Brits had a technique called ' Cherry Bombing'
which entailed heating your piston to red heat and dropping into
brake fluid. This did work but entailed lapping piston to cylinder to
get our wee diesels working again. Mostly practiced by the team
race people. Most of us never used our engines enough to have
to resort to this fairly desperate measure.
john
ps cast iron pistons of course, running in a steel liner.

proctor
Gold Member
Gold Member

Posts: 198
Join date: 2012-01-31
Location: Scottish Highlands

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  nitroairplane on Sun Feb 19, 2012 6:59 am

proctor wrote:Hi, back in the day we Brits had a technique called ' Cherry Bombing'
which entailed heating your piston to red heat and dropping into
brake fluid. This did work but entailed lapping piston to cylinder to
get our wee diesels working again. Mostly practiced by the team
race people. Most of us never used our engines enough to have
to resort to this fairly desperate measure.
john

You wanna see a really wee diesel?

Thats piston thing is what I was talking about but I never used the break fluid I must try that one day!

nitroairplane
Top Poster
Top Poster

Posts: 6956
Join date: 2011-04-11
Location: London

View user profile http://modeldieselengines.forumstopic.com/

Back to top Go down

Re: bad compression.. how to fix it

Post  casalejuan on Sun Feb 19, 2012 7:12 am

Mike1484 wrote:Maybe your problem is sticking your nice motor in a vise . A complete lack of respect for any motor.

Mike1484

Sorry Mike but that's not the problem. One of the three engines work well and they were all initiated in the vise. But your observation is good because if I adjust the vise incorrectly, I can break the tank. Sorry! I┬┤m new in the Babe Bee .049 Small Cox Logo world.

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  casalejuan on Sun Feb 19, 2012 7:23 am

ultimately, you think it would be a good measure to buy a new kit that includes a cylinder, a piston and a glow head? I saw that in E bay we can find those parts.

casalejuan
Bronze Member
Bronze Member

Posts: 45
Join date: 2011-11-29
Age: 32
Location: Ciudad Autonoma de Buenos Aires, Agentina

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  GermanBeez on Sun Feb 19, 2012 7:55 am

juan, pleeease put that engine out of the vise...it's not good for the engine. Neutral
screw it onto a block of wood and put THAT into the vise. Wink

GermanBeez
Platinum Member
Platinum Member

Posts: 1167
Join date: 2011-06-15
Location: Bavaria, Germany

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Cribbs74 on Sun Feb 19, 2012 8:08 am

casalejuan wrote:
cribbs74 wrote:Yeah, the prop is not the problem.

All the suggestions above are good ones. How's the compression now?

Compression is very slight. however one of the two engines that does not work occasionally makes an explosion but does not start at all.

Perhaps compression is not the issue. Are all these engines new and never run? You say some were in blister packs. If that is the case did you disassemble them and clean them?

I am going to have to agree that mounting engines directly in a vice is a bad idea. It's not safe and it will marr the finish and distort the steel. You probably spent a lot of money to obtain these engines. You should protect your investment and pick up a correct bench mount from Cox International. Or at least use a block of wood.


_________________
Someone sent the promised land
And I grabbed it with both hands
Now I'm the man on the inside looking out.

-Pink Floyd-

Cribbs74
Moderator

Trusted Seller
Posts: 6890
Join date: 2011-10-24
Age: 40
Location: Tuttle, OK

View user profile

Back to top Go down

Re: bad compression.. how to fix it

Post  Surfer_kris on Sun Feb 19, 2012 8:31 am

If they have never been run before I cannot imagine that the piston to cylinder fit would be so bad that they cannot run, that just doesn't sound like a cox engine...

Check the head to cylinder fit, you might have a leak there. Other sources of problems are the tank to case fit and the tank-backplate to ventuiry seal, it is a really tiny o-ring.

I once tried the heating method on the piston of an old Veco .19 engine, didn't work one bit. Biggest change was the loss of the castor build-up, hence giving an even looser fit.

Surfer_kris
Platinum Member
Platinum Member

Posts: 667
Join date: 2010-11-20
Location: Sweden

View user profile

Back to top Go down

Page 1 of 2 1, 2  Next

View previous topic View next topic Back to top

- Similar topics

Permissions in this forum:
You cannot reply to topics in this forum