Cox Venom Piston Rod Reset Question

The Venom will need to be tuned to get over 20K, the folks that blew the pistons were probably running very hot fuels and small props.
35% nitro and a 5" prop, play with head shims a bit should get more RPM. The last Mouse I sent to Kim was a Venom, I broke it in on the bench then tuned it with a Galbreath head
and Nelson plug. It came in 4th place at 22350K, I probably had it over compressed. No reason you can't tighten up the rod, carefully.

Sorry, I am the owner of the engine and it is only hitting about 14,500 with a 6x3 but I also have a tank extension on it. Not sure if that is restricting airflow in. The fuel I am running in it now is Power Master 20/20. This is supposed to be 20% oil with half of that being castor. I have a bottle of Sig castor as well as I want to run a little more. The plug I am using is the stock plug. I will look into one of those glow heads as they seem to have boosted RPM over the high compression head on my Tee Dee by over 1500. Hard to believe that there would be so much difference just on a glow plug. I guess "ignition is not ignition". This motor will be used for RC applications in a plane called a Cloud Ranger. Prop diameter might be critical to get it outside the fuselage area. I will try a 5x3 to see how it spins up later.

I am curious about the concept of 'Growning the Piston'. Does high rpm stretch the crown out? Is there copper/brass in the piston socket? I ask this since you referenced work hardening.


Background on this engine:
I purchased the engine new in 1996 when they first came out and ran it on a flying wing that my club was racing aat the time. Not sure I ran good fuel through it as I was really more familiar with .40-.90 sized motors. Compression seems ok but fades a little as it warms up.

Thank you for your time with this matter.

Based on the description of what you are going to use the engine(Venom) for,you might want to consider looking at a Cox Texaco type .049.You can use the tank extension with this engine and it will swing a 7X4 prop.That's what I currently have on one of my 2 channel R/C planes.

I did pick one of those up too. I am such a hoarder! I hear that they turn just under 10,000. I can see if that will be enough to pull the plane as I have quite a few engines to test with. I am just trying to evaluate the health of all of my candidates and I was curious about this piston growing process too.

Which 7x4 are you using?

Couple questions, how long has it been since you have replaced the reed and gaskets? How long has it sat without being used?

A piston reset may be required, but it won't help your rpm's much if any. Depending on how sloppy the ball and socket is it may actually decrease your SPI. I would still reset it though.

Ron

I replaced the gaskets yesterday. Reed is original. Prior to that, it has been 15+ years since the motor has been run.

rscarawa wrote:I replaced the gaskets yesterday.  Reed is original.  Prior to that, it has been 15+ years since the motor has been run.

Get a new reed. It may look good, but you would be surprised how a small flaw can affect performance.

If you haven't already, break it down and clean everything, concentrate most of your effort on the backplate.

Does it run steady?

It runs steady. I cannot say that for my BW, but that is another issue.

I will look into getting another reed. Do you have a preferred reed type?

rscarawa wrote:It runs steady.  I cannot say that for my BW, but that is another issue.

I will look into getting another reed.  Do you have a preferred reed type?

That's a loaded question... lot's of opinions on that. I like the stainless steel ones, but the original plastic ones work well also.

Cribbs74 wrote:Couple questions, how long has it been since you have replaced the reed and gaskets? How long has it sat without being used?

A piston reset may be required, but it won't help your rpm's much if any. Depending on how sloppy the ball and socket is it may actually decrease your SPI. I would still reset it though.

Ron

 Ron if you reset the ball socket that will bring the SPI more were it was to start with (reason for reset) That and blowing up !! And on the reed I use Mylar Reeds i think it's 0.005 " ,,, you can buy or may have a clear mylar page separator the are cheap and cut your own !! Or go Here a good start to get the pattern...  http://coxengines.ca/home.php?cat=29

Possibly Eric, but not always. If the rod had been pounding the bottom of the piston a good while it creates excess space, In that case the reset will lessen or completely remove the SPI.

Is it a Herr cloud ranger? That is a great plane. But, it might be asking a bit much of that engine. The plane is a bit big, heavy and draggy for an .049 that was made for speed. I love both the plane and engine but have found that the cloud ranger does best with a little bigger engine that produces more thrust.

Cribbs74 wrote:Possibly Eric, but not always. If the rod had been pounding the bottom of the piston a good while it creates excess space, In that case the reset will lessen or completely remove the SPI.

If that is the case, I should be able to measure from the top of the piston to the bottom of the rod to get an idea how sunk in that rod is. Does such a dimension exist to compare against?

fit90 wrote:Is it a Herr cloud ranger? That is a great plane. But, it might be asking a bit much of that engine. The plane is a bit big, heavy and draggy for an .049 that was made for speed. I love both the plane and engine but have found that the cloud ranger does best with a little bigger engine that produces more thrust.

Correct. I do have a couple Aces up my sleeve if needed. I have some Tee Dee 051 motors, an 09 in Tee Dee and Medallion form and I have two Norvel 074 motors. One of these will do the job. If they do not, I will electrify if needed.

getback wrote:

Cribbs74 wrote:Couple questions, how long has it been since you have replaced the reed and gaskets? How long has it sat without being used?

A piston reset may be required, but it won't help your rpm's much if any. Depending on how sloppy the ball and socket is it may actually decrease your SPI. I would still reset it though.

Ron

 Ron if you reset the ball socket that will bring the SPI more were it was to start with (reason for reset) That and blowing up !! And on the reed I use Mylar Reeds i think it's 0.005 " ,,, you can buy or may have a clear mylar page separator the are cheap and cut your own !! Or go Here a good start to get the pattern...  http://coxengines.ca/home.php?cat=29

Do you have a special tool to punch them out yourself or do you cut them out?

rscarawa wrote:

fit90 wrote:Is it a Herr cloud ranger? That is a great plane. But, it might be asking a bit much of that engine. The plane is a bit big, heavy and draggy for an .049 that was made for speed. I love both the plane and engine but have found that the cloud ranger does best with a little bigger engine that produces more thrust.

Correct.  I do  have a couple Aces up my sleeve if needed.  I have some Tee Dee 051 motors, an 09 in Tee Dee and Medallion form and I have two Norvel 074 motors.  One of these will do the job.    If they do not, I will electrify if needed.

Sounds like you have plenty of great options. If you replace some of the kit's heavy wood with lighter stuff and keep the weight down you could still come up with a good flyer for the Venom. Please start a build thread and keep us all posted. There are a lot of guys here who can offer some great tips. Good luck with it!

fit90 wrote:

rscarawa wrote:

fit90 wrote:Is it a Herr cloud ranger? That is a great plane. But, it might be asking a bit much of that engine. The plane is a bit big, heavy and draggy for an .049 that was made for speed. I love both the plane and engine but have found that the cloud ranger does best with a little bigger engine that produces more thrust.

Correct.  I do  have a couple Aces up my sleeve if needed.  I have some Tee Dee 051 motors, an 09 in Tee Dee and Medallion form and I have two Norvel 074 motors.  One of these will do the job.    If they do not, I will electrify if needed.

Sounds like you have plenty of great options. If you replace some of the kit's heavy wood with lighter stuff and keep the weight down you could still come up with a good flyer for the Venom. Please start a build thread and keep us all posted. There are a lot of guys here who can offer some great tips. Good luck with it!

I am partially into the build already. I suppose kits vary but the wood in my kit is ridiculously light. With the exception of where I put the wrong fire wall in, all wood (balsa) feels like contest grade. There are some issues with the instructions which caused the mix up. I am documenting the errors and omissions. One omission was with a step on assembling the fuselage. They tell you to put the bulk heads in via one step. The next step is to glue the firewall in. Problem is the firewall will not fit in if the glue from the previous step sets up. So a bit of a panic resulted in me using the wrong firewall so this plane will have two of them. One laminated ontop of the other. The firewall insertion should have been in the same step as the bulk head insertions. My wing panels are in a holding pattern while my servos arrive. Was not aware this was a dual servo wing. Thought it was a single servo with torque rod style.

Also, my phone died so I am waiting on HTC to send a replacement. I will get some pics up as soon as my new phone comes in.

Take care.

Well this went off the grid , i cut them out by hand for the reeds ( use the punch out for a template after purchasing some in bulk from Cox Inter. Sounds like you have a lot more going on than i realized with engines and planes COOL !! I dont know if the measurement is available for the pis/rod assy. Have you taken the engine down to ck the play in the ball? Sounds like if you don't reset it it will do itself, so i would go with it carefully , light tapping and rotating the assy in the jig every time , check often for tightness .

getback wrote:Well this went off the grid , i cut them out by hand for the reeds ( use the punch out for a template after purchasing some in bulk from Cox Inter. Sounds like you have a lot more going on than i realized with engines and planes COOL !! I dont know if the measurement is available for the pis/rod assy. Have you taken the engine down to ck the play in the ball? Sounds like if you don't reset it it will do itself, so i would go with it carefully , light tapping and rotating the assy in the jig every time , check often for tightness .

I have not done a measurement on the Venom yet.  It still has some SPI but all my engines with SPI seem to have varying amounts of gap.  I will check that out today.

I have another motor that I purchased in the late 80s that I thought was a BW but may not be after all.  It came with a Craft Air kit.  it has no SPI that I can see and the gap measured in at .011.  SOunds like a lot but I did get one engine off ebay that came in at .037.  I reset my motor and one other without destroying the piston so far so I might give this one a shot in the next could of days.


I am intrigued about this piston growing concept.  Is this nothing more than getting it hot in the motor for a couple of minutes and then lapping it?  Anyone else do this on their motors?  I am reasonably certain my motors never ran real hot in their lives at all since I was flying RC.  I typically used 6x3 props with low nitro (10%).  I wonder if this option is still open to me on this and other motors.  How does this heat cycling affect the piston socket?  Is the piston all steel or is it two pieces pressed together where one is a non-steel part?

Piston rod play is .013".

Just reset the fit and it is around .001" now. Piston does not appear damaged and fits in liner. Will run later.

That sounds Great Scot , i was going to say 1-.002 would bee good for a reset , Have you got any higher nitro with good castor content to try maybe with a 5 or 4 " Prop? to see if you can't get some more Rs out of it .

getback wrote:That sounds Great Scot , i was going to say 1-.002 would bee good for a reset , Have you got any higher nitro with good castor content to try maybe with a 5 or 4 " Prop? to see if you can't get some more Rs out of it .

I do not have higher nitro at this time.

As for props, I have a 4.75x4 but no spacer for it. I ordered a bunch of different APC props in the 5-7" range just now for bench testing. They should be here in a few days. I need to order a spacer to work with these props to see if I can get the RPM up. It might be that the Venom needs to spin faster to build the power it was meant for. I will try the Texaco route too. Can a BW be converted to Texaco or is there something difference about the motor for turning lower RPM?