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!


Cox.049 timing change Babe_b10
Log in

I forgot my password

Search
 
 

Display results as :
 


Rechercher Advanced Search

Cox Engine of The Month
September-2019
Levent Suberk's

CEF Magazine cover featuring the Ex Model Engines Harpy Eagle .049



PAST WINNERS
CEF Traveling Engine

Win This Engine!
The Traveling Prop
Gallery


Cox.049 timing change Empty
World of Aviation

Cox.049 timing change

Go down

Cox.049 timing change Empty Cox.049 timing change

Post  F4D Phantom II on Mon Apr 08, 2019 9:08 pm

. I have  lowered the cilinder in the cranckase of my .049 surestart to change the timinig in hope to increase the torque to use a prop bigger than the 6/3 . I thought that that by lowering the cilinder and adding head gaskets to avoid over compressing the the engine I would have more volume of air and fuel inside the cilinder increasing torque.I`m using the diesel crank and TD hi comp head also will be trying .051 cilinder and piston with a galbreath Head with nelson plug.  I`m not looking for speed but a lower RPM steady run with bigger prop for sport an stunt. Has anybody tried this before ? I have given the engine a few runs to heatcycle it but have not tried a bigger prop yet.All advice appreciated.
                                                                                                                            Juan
F4D Phantom II
F4D Phantom II
Bronze Member
Bronze Member

Posts : 39
Join date : 2019-04-08

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  Levent Suberk on Tue Apr 09, 2019 3:08 am

Add %10 nitro to fuel for one head gasket.
Levent Suberk
Levent Suberk
Gold Member
Gold Member

Posts : 404
Join date : 2017-12-24
Location : Turkey

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  Surfer_kris on Tue Apr 09, 2019 4:01 am

I have never lowered the cylinder, only raised it to reduce the amount of SPI. The effect on the timing itself is rather small and you are also changing both the transfer and exhaust timings at the same time.

In order to use a larger prop, take a look at the texaco engine for inspiration, or simply get a texaco engine I guess. I don't think they change anything to the cylinders, compared to the regular engines, only reduce the intake diameter and improved the cooling of the head.

As is obvious with diesel engines, a larger prop needs a lower compression ratio. A glow engine acts the same, try a few different numbers of shims and write down the needle settings and rpms, that way you can find the optimum compression setting. Then use one more shim than optimum in order to stay on safe side.
Surfer_kris
Surfer_kris
Diamond Member
Diamond Member

Posts : 1593
Join date : 2010-11-20
Location : Sweden

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  F4D Phantom II on Thu Apr 11, 2019 10:49 am


Thanks for replying guy`s .
Juan
F4D Phantom II
F4D Phantom II
Bronze Member
Bronze Member

Posts : 39
Join date : 2019-04-08

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  wmazz on Sat Apr 13, 2019 10:35 pm

F4D Phantom II wrote:I have  lowered the cylinder in the crankcase of my .049 surestart to change the timing in hope to
increase the torque to use a prop bigger than the 6/3 .

I`m using the diesel crank and TD hi comp head also will be trying .051 cylinder and piston with a galbreath Head with nelson plug.  
I`m not looking for speed but a lower RPM steady run with bigger prop

That sounded like a good idea, lowering the cylinder and increasing the
power stroke. I have not tried it on a Cox, but it is common practice
for other 2 stroke engines.

You might try the Texaco cylinder, I don't see the need for large exhaust
and transfer ports of a TD cylinder. Someone else will know if the Texaco
cylinder uses SPI or not? If not, you might pick up some torque from SPI
if can you lower the cylinder enough.


Bill M.
wmazz
wmazz
Bronze Member
Bronze Member

Posts : 40
Join date : 2018-12-31
Location : Riverside CA.

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  F4D Phantom II on Sun Apr 14, 2019 9:37 am

Hello Bill
I`m using a TD .051 cilinder and piston on my engine I still want the bigger ports and I have always heard that there is nothing like cubic inches. I`m working on a little P-40 plane at this time and haven`t worked on the engine idea. I will start with about 6 head gaskets and work from there. I will make sure my exhaust ports face fore and aft because I want my intake ports to be to the sides of the crankcase for better mixture flow. I will see how it handles a 7 x 4 Master airscrew, I have been looking for a cox 7 x 3.5 with no luck.
Juan
F4D Phantom II
F4D Phantom II
Bronze Member
Bronze Member

Posts : 39
Join date : 2019-04-08

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  Dave P. on Sun Apr 14, 2019 9:43 am

I got some parts from an old 1/2A speed freak's estate some time ago and one of the TD cases had been shaved to lower the cylinder.  I can't really tell how much, maybe .010 or so.  I haven't tried it and I've been curious about it.  It doesn't appear that it was run very much.  Anybody know if this was anything of a standard kind of mod, or was it a one-off experiment that didn't work so well?

The old adage "There ain't no replacement for displacement" still applies as far as I know, Juan.
Dave P.
Dave P.
Gold Member
Gold Member

Posts : 218
Join date : 2017-07-31
Age : 62
Location : Durham, NC

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  wmazz on Sun Apr 14, 2019 2:10 pm

F4D Phantom II wrote:
I`m using a TD .051 cylinder and piston on my engine I still want the bigger ports

The TD cylinder has SPI, and by lowering the cylinder, you are increasing the
SPI. There will be a point where too much SPI will cause problems.

I assume the TD has a larger exhaust port than other cylinders, and they
have a lot of transfer port area. That extra transfer port area is useful for
supporting hi rpm.

IMO a cylinder with partially blocked exhaust (2 slits/side) with no SPI is a
better choice.

I recommend you look at "Iceberg's" threads on his Texaco engines and his
quest for a 5 minute run time with 8 x 4 propeller.


Bill M.
wmazz
wmazz
Bronze Member
Bronze Member

Posts : 40
Join date : 2018-12-31
Location : Riverside CA.

View user profile

Back to top Go down

Cox.049 timing change Empty Re: Cox.049 timing change

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

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