2nd try at a head button

[Sean Bowf]

Here is my second try at making a head button. It is too tight in the cylinder, and the chamber is not as large as I was shooting for. The stock one has a .11 CC chamber. To get the clearance right, and get the CR down to 10 to 1 or lower, I was shooting for .21 CC. Wound up at .17 CC.

Sean

 

[Harald1966]

Sean

What do you mean, 21 vs 17? I don't understand?

 

[Sean Bowf]

The engine I am fooling around with to learn from, is a GO engine. The "bowl" in the head button has a volume of .11 in the stock head button.


The stock head clearance of the engine is .022. This is way too big.

The stock compression ratio is 10.4 to one. This is already a little high, and if I got the head clearance where it should be, it would be over 15 to 1, which is WAY too high.

So, to set the head clearance correctly, I need to make a new button for the engine with a larger bowl volume, so the compression ratio will be closer to where it should be.

More or less, I am kind of just fooling around right now to learn from it. The metal I am using is 6061, which from what I have been told is not the best metal to make head buttons from. I have the correct metal on order, but it won't be here till Monday. The button in the picture above actually popped out of the lathe chuck while I was working on it, and that screwed it up. So I turned it down a little more to clean it up. I still have over 2.5 feet of the aluminum rod...so got a lot more chances to learn .

Sean

 

[Harald1966]

OK, I see!

Is this for the Miss Vegas?

How is your Speedmaster boat doing? Did you make it run well last season?

Meeting next week?

Keep us posted Sean!

 

[Martin Hamilton]

Sean are you sure the stock bowl is .11cc, As ive never sean a stock button on any 21 size motor any where near that small. Also the button that you made the tool radius looks to big, Thats what stops you getting a larger volume in the bowl. I use a tool with 5-6mm radius on .21 motors. Depending on bore size, squish width, bowl depth and volume im looking for. Regards Martin.

 

[dwilfong]

Sean

Looks like you are having fun. Try using a ball end mill in the tail stock. This will give you a round bowl. This way you can make the diameter of the bowl smaller and have more squash. Use a 2 flute and turn slow less chatter cleaner cut. Also get a tool holder for inserts. There many different grades of inserts. Some for finishing and some for aluminum. You will get much better results.

David

 

[Terry Keeley]

Looks good, you're well on your way to having one of the fastest Miss Vegas' around!

I like a 3/8" ball end mill for 21 heads and actually 0.17cc isn't a bad number, 0.21 will work but be on the big side IMHO.

As suggested it looks like you need a smaller radius tool, the squish band should end up being about 60% of the total surface area of the bore, I finish it 1/2 flat, 1/2 at 5*. h34r:

6061 will work OK but is gummy to cut and tap, I like 7075. Whatcha gonna use?

ps: If you hold the head by the glow plug in a vise it'll be easier to measure.

 

[Sean Bowf]

OK, I see!

Is this for the Miss Vegas?

How is your Speedmaster boat doing? Did you make it run well last season?

Meeting next week?

Keep us posted Sean!

Yes Harald, I am running the GO in a MV. A friend of mine asked me to try out the GO engine and give him feedback on it. I was not real happy with the GO engine. It was pretty much on par with a stock AQ engine. I took it apart and found that it looked like the ports, rod, carb, etc, was better set up than the AQ engine...which left the top of the engine...which is what I am trying to figure out. The engine turns a larger prop than my CVRM, but will not push the boat as fast.

The best I have got my speedmaster is a little under 55 MPH. I am really at a loss with tuning the hardware to get better results. I think I am going to need to add some more weight to it. It just gets too flighty when it gets up to those speeds. I think the engine I am using is capable of pushing it faster...I just can't keep the wet side down and the pointy end forward.

Norm mentioned the meeting...not sure if I will make it or not. Hard to justify the 4 hour round trip for a 1 hour meeting. If it wasn't so freakin cold and we could run a little, it would be easier to justify. Where you out of town for the club dinner?? Had a good crowd there, but thought it would be more.

Sean

Sean are you sure the stock bowl is .11cc, As ive never sean a stock button on any 21 size motor any where near that small. Also the button that you made the tool radius looks to big, Thats what stops you getting a larger volume in the bowl. I use a tool with 5-6mm radius on .21 motors. Depending on bore size, squish width, bowl depth and volume im looking for. Regards Martin.

Martin, attached is a pic of the Go head button next to an OS CVRM button (GO on right, CVRM on left). Pretty big difference in volumes... I think the head button volume is what led to a lot of the other problems on the top of the engine. The volume is too small, so they made the head clearance too large to compensate for the CR being too high. If they would have made a better button for the head instead, I think the engine would have done a lot better. Pretty sure it is pretty much just a buggy engine with a marine cooler on it though...like most .18 engines...

I agree that a smaller tool radius would allow me to fix the button. All I have right now is a 3/8 ball end mill I am using. I get the feeling I might be better off by buying some HSS blanks, or bits, and making them into what I want on the grinder. 12mm diameter is pretty small compared to what I am using. That is about 1/10th the size of what I am using. Do your bowls have a flat top and very little rounded edge to them?

Sean

Looks like you are having fun. Try using a ball end mill in the tail stock. This will give you a round bowl. This way you can make the diameter of the bowl smaller and have more squash. Use a 2 flute and turn slow less chatter cleaner cut. Also get a tool holder for inserts. There many different grades of inserts. Some for finishing and some for aluminum. You will get much better results.

David

David, I did try the ball end mill held in the tailstock. I ordered the wrong one (4 flute) and was getting a lot of chatter from it (did not look smooth). I then put the mill in my tool holder and used just one of the flutes like a lathe bit. That seemed to work a lot better.

Been looking at tool holders a lot. Especially the quick change tool holders. Just having a hard time pulling the trigger on the $100 price tag. I know I will either get tired of the lathe, or want a better one some day...so didn't want to dump a bunch of money into things that will only be able to be used on this lathe. HF sells a QCTH for about $90. I think it has an allen head screw you need to tighten to hold the tool holder. I like the levers better. I am sure I could find a 20% off coupon on the web some place for HF though... A2Z has a nice looking one. I would probably prefer it.

Looks good, you're well on your way to having one of the fastest Miss Vegas' around!

I like a 3/8" ball end mill for 21 heads and actually 0.17cc isn't a bad number, 0.21 will work but be on the big side IMHO.

As suggested it looks like you need a smaller radius tool, the squish band should end up being about 60% of the total surface area of the bore, I finish it 1/2 flat, 1/2 at 5*. h34r:

6061 will work OK but is gummy to cut and tap, I like 7075. Whatcha gonna use?

ps: If you hold the head by the glow plug in a vise it'll be easier to measure.

Terry, what CR do you shoot for?? Most of these .18 engines have a CR of 7.5 to 8.5 out of the box. I was shooting for some place between 9 and 10 to 1.

I had the squish half flat, and half at 1.5 degrees...but wound up taking a lot of the 1.5 degree area away as I tried to make the bowl wider to gain volume. I read the 1.5 degree angle some place. Is the 5 degree angle better? I think it needs a deeper bowl to get the volume. I am at around 50% squish ratio now.

6061 is the only thing they had local. I ordered some 2011 but it won't be here till monday, and I wanted to fool around with the lathe this weekend.

 

[Terry Keeley]

Terry, what CR do you shoot for?? Most of these .18 engines have a CR of 7.5 to 8.5 out of the box. I was shooting for some place between 9 and 10 to 1.

I had the squish half flat, and half at 1.5 degrees...but wound up taking a lot of the 1.5 degree area away as I tried to make the bowl wider to gain volume. I read the 1.5 degree angle some place. Is the 5 degree angle better? I think it needs a deeper bowl to get the volume. I am at around 50% squish ratio now.

6061 is the only thing they had local. I ordered some 2011 but it won't be here till monday, and I wanted to fool around with the lathe this weekend.

I did a lot of "cut and try" with my RS21 in my little Speedmaster mono, went from 0.1cc to .2, found a happy medium at about .17 with 60% nitro. Think it works out to about 10:1 trapped C/R but I don't worry about that number as much as some, think the pipe, fuel, plug, head temp., etc effect the outcome too.

Think the 1/2 and 1/2 is a good compromise, totally flat seems to make more grunt but is hard on plugs. I like at least some flat so it's easier to measure the squish clnc.

Did you use the 3/8" end mill set up on center? Seems like a wide bowl in the pix...

ps: little motors like to turn up, try to prop it to turn fast then bring the pipe in to make it happen!

pss: what about just opening up the GO button a little?

 

[Martin Hamilton]

Sean dont know why but i assumed you were refering to .21 motors but in your later post you mention .18 motors, This will have a bearing on the size radius you need over a .21 motor. The Go .18 motor is also a very large bore and very short stroke motor. Regards Martin.

 

[Glenn Gates]

High speed blanks may be the way to go. 1/4"-cheap and you could grind whatever radius you like on it(up to 1/4"). Set the compound @ 5 degrees to cut the squish band. Use a coffee can full of water to keep from overheating the blank as you grind it. Grizley Engr. had some small indexing tool posts for around $35.00 years ago. remember to shim the tools if nec. to keep them on center.

Glenn

 

[Sean Bowf]

I did a lot of "cut and try" with my RS21 in my little Speedmaster mono, went from 0.1cc to .2, found a happy medium at about .17 with 60% nitro. Think it works out to about 10:1 trapped C/R but I don't worry about that number as much as some, think the pipe, fuel, plug, head temp., etc effect the outcome too.

Think the 1/2 and 1/2 is a good compromise, totally flat seems to make more grunt but is hard on plugs. I like at least some flat so it's easier to measure the squish clnc.

Did you use the 3/8" end mill set up on center? Seems like a wide bowl in the pix...

ps: little motors like to turn up, try to prop it to turn fast then bring the pipe in to make it happen!

pss: what about just opening up the GO button a little?

Knowing what a good CR to shoot for would get me in the ball park of where to start trying stuff. EAP seems to recommend 8.1 to 8.5. The stock engines I like seem to be lower. Another person(s) "in the know" told me 10 to 1.

I did use the 3/8 ball mill on center, then measured the volume and found it too small. I then mounted it in the tool holder and started widening the bowl to try to add volume. I can see now that some things should be done in a certain order to allow for more adjustment. I had left the button kind of tall with the plan being to shorten it to whatever makes the plug sit in it right after I got the bowl volume set, but when I pulled the button out of the lathe with a tool, I had to take more off it to clean it up...and didnt have enough metal left to make the bowl deeper.

This (too shallow button) is the problem with opening up the go button. Unless I run it with a bunch of washers under the plug, there is not enough meat in the stock GO button to make the bowl deeper. I think I could make it larger by making the bowl wider, but I don't think I will be able to get the volume I need to take .014 out of the head clearance (at .022 now). Attached is the button I made next to the stock one. You can see how much taller the one I made is compared to the OEM one. I think it needs to be even taller to get the volume out of it. The .21 CC volume I was trying for would get me a CR in the 9s AFTER adjusting the exhaust timing. So for a stock timing, it would need to be even larger to get it below 10-1.

Sean

 

[Terry Keeley]

See what you mean now about the stock button, you'd have to use a smaller radius tool (maybe 1/4" end mill) and open up the top corners, leaving you with a more flat-topped or "bathtub" chamber. I've heard that will give a little more top rpm but less mid-range, can't say I've tested it myself. Anyway you're having way too much fun making your own!

When I quoted the 0.017cc head volume that worked for me (stock is 0.19cc for 8.6:1) I didn't include the squish volume or the 0.01cc dish in the piston, just the chamber. The trapped C/R with 0.010" squish it works out to about 9.4:1, so that 10:1 figure might be about right. Here's specs on the RS21, maybe you could run it through your EAP to check my math? :unsure:

https://www.intlwaters.com/gallery/albums/userpics/10068/2006_CMB_RS_21.xls

If your interested, here's the formula for a "sperical segment", you can calculate how deep to plunge your tool to get the volume you want:

http://www.engineersedge.com/volume_calc/spherical_segment.htm

If you want to include the glow plug, here's "spherical zone":

http://www.engineersedge.com/volume_calc/spherical_zone.htm

I figure a number to plunge to, get close then check it while still on the lathe. :unsure:

Yup, best to cut the chamber first, drill and tap the plug hole, then turn it around and finish the top side.

Just curious, why the 2011?

 

[steve wood]

to clone a nova rossi 21 head bowl, use a 5 mm ball end mill,move out from dead center .080 and plunge in .140. to get .19 cc (what we run on all novas) plunge in .115. all numbers will vary,depending on squish band angle,and dia. it can take many tries to get it where you want it.i always drill and tap,before i plunge in the ball mill,to eliminate the burr that the tap makes. i use a 1/8 in spacer plate to set up from and add the 1/8 to my final depth. i have made dozens this way

 

[tnrcboatracer]

I agree that a smaller tool radius would allow me to fix the button. All I have right now is a 3/8 ball end mill I am using. I get the feeling I might be better off by buying some HSS blanks, or bits, and making them into what I want on the grinder. 12mm diameter is pretty small compared to what I am using. That is about 1/10th the size of what I am using. Do your bowls have a flat top and very little rounded edge to them?

12mm diameter is bigger than 3/8" diameter (only about 0.028 under 1/2").

You an also use both 3/8" and 1/2" ball end mills to make a "double bubble" combustion chamber.

I have a ground HSS tool for the OPS90 chamber, as well.

 

[tnrcboatracer]

Been looking at tool holders a lot. Especially the quick change tool holders. Just having a hard time pulling the trigger on the $100 price tag. I know I will either get tired of the lathe, or want a better one some day...so didn't want to dump a bunch of money into things that will only be able to be used on this lathe. HF sells a QCTH for about $90. I think it has an allen head screw you need to tighten to hold the tool holder. I like the levers better. I am sure I could find a 20% off coupon on the web some place for HF though... A2Z has a nice looking one. I would probably prefer it.

If you get a QC tool holder, go with the wedge type, not the plunger. The wedge types are typically much more repeatable and rigid that the plunger type. In this case, you do get what you pay for.

 

[Sean Bowf]

Just curious, why the 2011?

Terry, I won't pretend to know anything about making buttons. I just read that this is what an engine modder uses (Steve Wood).

If you have any other inputs, I would love to hear them.

Sean