A new nitro engine coming soon (some say I am mad for doing this!)

Intlwaters

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David Bryant

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Sep 7, 2011
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2,278
How is that ring pin held in ?
yeah, if you zoom-in on this image, you will notice a notch within the ring slot (it’s actually a very small pin, pressed into, through the top edge of the piston- see bottom image)
Anatoly_BilletPiston-CMB27AlphaEVO_June2021_02.jpeg

The split in the ring has a machined internal surface (shape) that will match, and lay over this notch, which locks the ring in place.

Anatoly_BilletPiston-CMB27AlphaEVO_June2021_01.jpeg
(you can see small pin pressed into place, outer circumference of piston)
 
Last edited:

Wasted wages

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Jan 2, 2006
Messages
1,840
I understand all of that fully...my concern is the pin coming loose and falling out when the piston gets hot.

Seems like the aluminum around the top of the pin should be peened over the pin to lock it in place.

My brother had a ring rotate in a Mercury 150EXP outboard, at about 6000 rpm, caught a port and exploded the power head... wasn't pretty.
 

Charles Perdue

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Oct 8, 2005
Messages
2,177
Some use splined pins and some use a split roll pin.
This one looks like maybe a splined pin, I do not see the hole in the middle of the pin for the split roll pin.
 

dwilfong

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Jul 1, 2008
Messages
5,894
On the outboard eng thy top pin them then put a spot of weld on it to keep it in place.
 

Ricky Neal

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Dec 5, 2020
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143
Hi All,

Sorry for the lack of updates on this project. Things have been progressing slowly in the background. Due to a combination of being very busy running my main business and struggling with a few technical challenges progress has been a lot slower than I hoped but I have a small update for you.

We had some issues with the 3D printed cases, dimensionally they seemed to be warped. it's hard to show this but in certain areas, the cases tended to sag. Round features were the worst affected, becoming oval but also flat features like the mounts, were not dimensionally accurate enough adding a lot of additional complications to the case machining. The biggest challenge was that this sagging/warping was not consistent across all the cases we had 3D printed.

In addition, the material was prooving somewhat brittle and liable to cracking in thin areas. There are limited material options when printing aluminum.

Not all was lost though, as I have tried to make clear, we are developing this engine and unless we can make it competitive and reliable we won't bring it to market so we expect these challenges and that there would be iterations and changes as we developed this engine.

The early tests showed some areas that needed some design alterations, I will list them below

1. Additional material for head screws (Pretty self-explanatory, they are only 2.5mm cap heads and we stripped a few so have added some additional material. Additionally, we may look at changing this to something like a UNC thread or something with a courser thread than 2.5mm. (We are about to test some options)

2. We changed the exhaust outlet design. The design we had worked well but meant there was almost no ability to tweak the angle of the exhaust. We soon realised that not everyone has a model designed with a perfectly straight line for the pipe to follow and it's fairly normal to have a couple of degrees of movement. We basically copied the Novarossi design. It's proven and it works well and everyone seems to have Novarossi Exhaust rubbers. (Why reinvent the wheel?) - We did decide to keep the spring clip mounts though as it is by far the best way to secure a pipe/manifold to the engine.

3. Some alterations to the front motor mounts - This was mostly from feedback from some of the tether hydro guys as they direct mount the engine to the sides of the hull. Squaring them off enables a more secure mounting.

4. Some small geometry changes to the internals of the case. This is to smooth out and improve flow to the ports

To solve the issues related to 3D printing we are now using a new process where the mold and core are 3D printed and then the cases are cast in a more conventional way. This is a more expensive process for prototyping but should be more cost-effective when we get to production quantities.

This new process is much more dimensionally accurate and has solved all the warping/sagging issues as far as we can tell. In addition, this has allowed us to use more tried and tested materials for casting. We have opted for a heat-treated LM25 - This is a nice easy machining aluminum but pretty much offers the best in terms of strength and is typically used by companies such as Cosworth for engine case and head castings.

See the pictures below for comparisons. In the future, castings will be sand/glass/bead blasted to give a more uniform matt textured finish. We will see what works best but for the prototypes, we will test them as is

IMG_7896.jpg

IMG_7897.jpg

IMG_7898.jpg

One of the areas that we could really benefit from some help with is advice on low volume crankshaft grinding. We have farmed some out but are getting some very inconsistent results so we are looking to bring it in-house.

I want to avoid doing it on a lathe with a tool post grinder if possible and would be more interested in buying a cylindrical grinder and setting it up for this job specifically. If anyone has any experience of a setup like this I would love some advice.

We have also made some alterations to the induction system but they are all very minor to help smooth the flow path as well as add some additional material where we think we may need it. We have also tweaked things to improve manufacturability that should lead to slightly fast and more cost-effective production

Once we have the crankshaft issues solved we hope to have some engines running - I will post some videos as soon as I can.

Thanks for sticking with us on this journey.

Ricky
 

Grimracer

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Dec 27, 2001
Messages
8,867
We have a grinder on here. his name is Matt Krieger.. He is a real nice dude and might be be able to provide some insight.

Grim
 

LohringMiller

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Jan 25, 2017
Messages
732
Unfortunately, Jim Allen's gallery has been lost. I have some of his information on crankshafts. See below:

The sample dog bone crankshaft pictured definitely makes less hp. than the full disc crank used at the present. The full hard O-1 tool steel front end uses ceramic bearings with the crankshaft fastened to both inner races. This front end type runs faster & longer than any aluminum set up! The 2024 T-351 aluminum crankcase is one piece with 5 transfer ports cut from the inside. All parts are machined to less than .0001 tolerance & squareness. Many types of tool steels were tested for both crank pins & wrist pins. The final material used for both is full hard (Rc-63 to 65) AISI M-2 tool steel. These parts have very high wear resistance & have never failed at any time.

From left to right; the first two one piece crankshafts (.375X.500) made of 8620 tool steel had their .281 diameter crank pins sheared off during dyno runs. The next three crankshafts (.375X.500) made of 9310 tool steel through hardened failed when their .3125 diameter crank pins were pressed in with a heavy press fit (.0013). The last two crankshafts (.3937X.5906) made of AISI S-7 tool steel through hardened, with .3281 diameter crank pins at .0013 to.0015 press fit, have never failed on any dyno run or lake testing.

AISI S-7 tool steel that is through hardened & tempered at 600 deg F is used for crankshafts. The crank pin hole is carefully ground to give a .0013 interference fit. The sleeves are made of full hard AISI O-1, are not ground on the OD or ID, but are ground with both ends square to each other. Crankpins are full hard M-2 steel reamer blanks.



This dedicated fixture is used to grind crank pin holes in through hardened crankshafts. The crank pins used are full hard M-2 steel & are a .0012 to .0014 press fit. The press fitting operation is done with a fixture to insure alignment when starting the crank pin in the ground hole. The crankshafts are made of AISI S-7 shock resisting tool steel; tensile strength is 285,00 psi; yield strength is 220,000 psi; hardness is 53 Rc; with a Charpy impact value of 219 ft lbs. This fixture could also be used to grind a one piece crankshafts crank pin; including the induction valve driver. The crank throw of this fixture is fixed at .9020. A fixture like this assures that every crank is exactly the same!
Crankshaft & Front End.jpg Crankshaft fixture 1.jpg Crankshaft fixture.jpg Crankshafts 1.jpg Crankshafts.jpg
 

Ricky Neal

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Joined
Dec 5, 2020
Messages
143
Unfortunately, Jim Allen's gallery has been lost. I have some of his information on crankshafts. See below:

The sample dog bone crankshaft pictured definitely makes less hp. than the full disc crank used at the present. The full hard O-1 tool steel front end uses ceramic bearings with the crankshaft fastened to both inner races. This front end type runs faster & longer than any aluminum set up! The 2024 T-351 aluminum crankcase is one piece with 5 transfer ports cut from the inside. All parts are machined to less than .0001 tolerance & squareness. Many types of tool steels were tested for both crank pins & wrist pins. The final material used for both is full hard (Rc-63 to 65) AISI M-2 tool steel. These parts have very high wear resistance & have never failed at any time.

From left to right; the first two one piece crankshafts (.375X.500) made of 8620 tool steel had their .281 diameter crank pins sheared off during dyno runs. The next three crankshafts (.375X.500) made of 9310 tool steel through hardened failed when their .3125 diameter crank pins were pressed in with a heavy press fit (.0013). The last two crankshafts (.3937X.5906) made of AISI S-7 tool steel through hardened, with .3281 diameter crank pins at .0013 to.0015 press fit, have never failed on any dyno run or lake testing.

AISI S-7 tool steel that is through hardened & tempered at 600 deg F is used for crankshafts. The crank pin hole is carefully ground to give a .0013 interference fit. The sleeves are made of full hard AISI O-1, are not ground on the OD or ID, but are ground with both ends square to each other. Crankpins are full hard M-2 steel reamer blanks.



This dedicated fixture is used to grind crank pin holes in through hardened crankshafts. The crank pins used are full hard M-2 steel & are a .0012 to .0014 press fit. The press fitting operation is done with a fixture to insure alignment when starting the crank pin in the ground hole. The crankshafts are made of AISI S-7 shock resisting tool steel; tensile strength is 285,00 psi; yield strength is 220,000 psi; hardness is 53 Rc; with a Charpy impact value of 219 ft lbs. This fixture could also be used to grind a one piece crankshafts crank pin; including the induction valve driver. The crank throw of this fixture is fixed at .9020. A fixture like this assures that every crank is exactly the same!
View attachment 296171 View attachment 296172 View attachment 296173 View attachment 296174 View attachment 296175

Thanks Lohring. Some intersting info there.

We have opted for a case hardening steel with an integrated pin, this is is for a few reasons but mainly because we can get 62-64 HRC surface while maintaining a relatively ductile core.

What's the theory behind why a full circle crank makes more power?
 

Terry Keeley

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Jul 24, 2002
Messages
6,782
Unfortunately, Jim Allen's gallery has been lost. I have some of his information on crankshafts. See below:

Found Jim's stuff here: Media added by Jim Allen

I'm always amazed at the tolerances required to build our ABC nitro motors these days, some specs need to be in the 1 micron (1/2 a tenth or 50 millionths of an inch) range.

What material did you settle on? I'd think S7 (shock resistant tool steel) would be an excellent choice, I've made some parts from it and it gets very hard yet is tough and very stable in heat treat.

I would definitely stay away from a pressed in pin, seen too many issues with that.
 

Ricky Neal

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Dec 5, 2020
Messages
143
Found Jim's stuff here: Media added by Jim Allen

I'm always amazed at the tolerances required to build our ABC nitro motors these days, some specs need to be in the 1 micron (1/2 a tenth or 50 millionths of an inch) range.

What material did you settle on? I'd think S7 (shock resistant tool steel) would be an excellent choice, I've made some parts from it and it gets very hard yet is tough and very stable in heat treat.

I would definitely stay away from a pressed in pin, seen too many issues with that.
After speaking to Peter Halman (of Halman special F2A fame) we settled on EN36 steel. This is a UK spec case hardening steel. Peter said there were issues with using through-hardened steels as it can lead to brittle shafts that can break, especially of the smaller engines where the material thickness is much less.
 

dwilfong

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Jul 1, 2008
Messages
5,894
Would be nice to sodium/cyanide heat treat the crank when done if you are going with a aluminum rod and bushing.
That EN30B would take to that very nice.
 

LohringMiller

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Joined
Jan 25, 2017
Messages
732
Terry, thanks for finding Jim's gallery. There's a lot of valuable information there. I'm not sure why Jim found more power with a full circle crank disk. Our testng on gasoline engines showed no difference. A long time ago we dyno tested an RC car 4 port cylinder on an RC car crankcase with a full circle crankshaft and a normal PUM crankcase with the dogbone crankshaft. There was no measurable power difference. The pipe should do most of the pumping work so crankcase compression is only good for starting these days. More crankcase volume may improve power to a point, but there is probably an optimum crankcase volume for each setup.

Jim used a two piece crankshaft so he could run a very hard crank pin for a needle bearing surface and a tough steel for the rest of the crankshaft. You can buy hardened and precision ground M-2 steel reamer blanks from McMaster Carr. That makes one off manufacturing easier. Early runs of K&B's last outboard engine suffered from crankshaft fractures at the port window. Better heat treatment and careful deburring solved the problem.

Lohring Miller
 

Ricky Neal

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Dec 5, 2020
Messages
143
Would be nice to sodium/cyanide heat treat the crank when done if you are going with a aluminum rod and bushing.
That EN30B would take to that very nice.

In addition, we are looking at DLC coating the crankshaft for wear resistance and friction benefits - still to be tested of course
 

Ricky Neal

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Dec 5, 2020
Messages
143
Been awhile since the last update,
Is this still going, or no?
We REALLY need this!

Yeah, still slowly making progress. I haven't updated for a while for a few reasons (Mainly just too busy) but we had a real issue with the last lot of cases we had cast and we are getting another batch done now. I am sorry for the slow progress but I feel I definitely underestimated the technical challenges and I have had to do a lot of very expensive learning.

An update will be coming soon though
 

FloridaScaleBoater

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Oct 2, 2005
Messages
6,866
Yeah, still slowly making progress. I haven't updated for a while for a few reasons (Mainly just too busy) but we had a real issue with the last lot of cases we had cast and we are getting another batch done now. I am sorry for the slow progress but I feel I definitely underestimated the technical challenges and I have had to do a lot of very expensive learning.

An update will be coming soon though

Thank you,
Looking forward to something new.
 
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