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

[Ricky Neal]

Hello Ricky, first of all good luck with this venture. We do not know each other but I have some very old connection with the Metkemijer brothers and we all share the same passion.
I have read this post with interest and would like to share with you some of my findings and let you guess the rest...
To prevent the bearings from rotating in the crankcase we need to make a press-fit for the bearings. As you probably know there is always a working tolerance for the bearing fit in the crankcase as there is a tolerance for the outside and inside diameter of the bearing itself.
So there will be a situation where the combination of both the fit is very tight or less tight.
This is one of the reasons why we use bearings with more internal play(C3), just to compensate and to have a free bearing once the bearing is in place. A bearing with not enough play will prevent the engine from performing and also fail prematurely.

Thanks Rody,
I appreciate your input. I admire what the Metkemijer brothers have done with their engines. they are very clever.

Re - the bearing clearance, I am aware of the bearing fits and clearances but we were confused as to why CMB uses a loose fit for their bearing to the shafts. It seems very common to have inner races spinning on the shaft. See the picture below. I was guessing as to why this may be the case as it seems unique to CMB engines - what do you think may be the reason?

 

[LohringMiller]

It looks like the engine has potential. One thing I noticed is that you don't need the huge exhaust port at the bottom. It doesn't even need to go all the way to bottom dead center. If you have enough time area between the exhaust opening and the transfers opening, the cylinder pressure will be around the same as the transfer pressure. The smaller exhaust port reduces short circuiting from the transfers, increases the outflow velocity to the pipe, and reduces the exhaust duct volume.

See examples of port and duct design below.

Lohring Miller

 

[Ricky Neal]

It looks like the engine has potential. One thing I noticed is that you don't need the huge exhaust port at the bottom. It doesn't even need to go all the way to bottom dead center. If you have enough time area between the exhaust opening and the transfers opening, the cylinder pressure will be around the same as the transfer pressure. The smaller exhaust port reduces short circuiting from the transfers, increases the outflow velocity to the pipe, and reduces the exhaust duct volume.

See examples of port and duct design below.

Lohring Miller


View attachment 288234View attachment 288235

You have touched on something that we will be testing. The CAD drawings above are not the most up to date but they were already saved so easy to share for the forum but you can see on the above that the bottom of the exhaust port is already higher than the top of the piston at BDC but we also have 2 other variations with a port designed much like you have shown.

 

[Terry Keeley]

Hello Ricky, first of all good luck with this venture. We do not know each other but I have some very old connection with the Metkemijer brothers and we all share the same passion.
I have read this post with interest and would like to share with you some of my findings and let you guess the rest...
To prevent the bearings from rotating in the crankcase we need to make a press-fit for the bearings. As you probably know there is always a working tolerance for the bearing fit in the crankcase as there is a tolerance for the outside and inside diameter of the bearing itself.
So there will be a situation where the combination of both the fit is very tight or less tight.
This is one of the reasons why we use bearings with more internal play(C3), just to compensate and to have a free bearing once the bearing is in place. A bearing with not enough play will prevent the engine from performing and also fail prematurely.

Pretty sure Henry Nelson went to C4 clearance because of this. I tried C4's in my bigger motors and found them too sloppy, rod was rubbing etc.

I'm now re-fitting WIB cages with Cerbec grade 5 balls to get the high side of a C3 fit which is 0.0004" - 0.001" (11 - 25 microns) for bearings with 10 - 18 mm bore (our 6000, 6001, 6002's). C4 is 0.0007" - 0.0013" (7 - 13 microns).

Not sure if you're planning to use hybrid ceramic bearings but I think from the small bit of testing I've done and talking to others they might be worth it. I'll soon try some on the dyno to see it there's a performance gain.

 

[Ron Zaker Jr]

Fantastic! You are very brave to go down this path, may before you have tried and failed.

I think you should re-consider a needle bearing bottom end like the CMB's, it's a fantastic improvement over a bushing. I have many, many gallons through their motors and the wear on the rod bores and cranks pins are negligible, just keep an eye on the needles and when they get a couple tenths worn replace them. Would be fantastic to have that system in a 3.5, especially with the rpm's they turn.

I didn't know Profi made the MB40, very impressive. Here's some video of one doing 225+ mph in the straights:

Love it!

 

[Wasted wages]

I have a question..... what type of metal are our little engine crankshafts cut from ?

ie: are they Billet steel? 4340 ?

Is there another proprietary metal that could be used that would hold a better final tolerance for the main bearing or crank pin surface?

better heat treatment final processes ?

 

[dave roach]

I use 4140 peheat treat.

 

[Rody Roem]

Re - the bearing clearance, I am aware of the bearing fits and clearances but we were confused as to why CMB uses a loose fit for their bearing to the shafts. It seems very common to have inner races spinning on the shaft. See the picture below. I was guessing as to why this may be the case as it seems unique to CMB engines - what do you think may be the reason?

If you look at the tolerances(outside and inside diameter) given by bearing manufacturers, you will notice that they are quite big compared to the tolerances used rectifying the crankshaft itself.
So in a production it is very hard to get the perfect fit and even more difficult to assure the spare-parts aftersales after. If you work with too close tolerances you can find yourself sometimes in a situation that you cannot fit the bearing on the crankshaft anymore and so you need to widen the tolerances to avoid this possible situation.
I guess CMB plays it safe in this way like most of the other manufacturers in their production.

Also since the bearings are press-fitted in the crankcase you want the crankshaft to be able to move free on the inner ring of the main-bearing, otherwise the crankshaft makes the bearings bind with the different temperatures.
The front-bearing is the one which gives the position of the crankshaft in the engine since this is where you fix the flywheel.

For me the ideal situation would be that the main-bearing is press-fitted on the crankshaft and the outer ring would move free in the crankcase. Or what Profi has done with the crankshaft on their pylon engine is very nice but also very expensive.

 

[Ricky Neal]

If you look at the tolerances(outside and inside diameter) given by bearing manufacturers, you will notice that they are quite big compared to the tolerances used rectifying the crankshaft itself.
So in a production it is very hard to get the perfect fit and even more difficult to assure the spare-parts aftersales after. If you work with too close tolerances you can find yourself sometimes in a situation that you cannot fit the bearing on the crankshaft anymore and so you need to widen the tolerances to avoid this possible situation.
I guess CMB plays it safe in this way like most of the other manufacturers in their production.

Also since the bearings are press-fitted in the crankcase you want the crankshaft to be able to move free on the inner ring of the main-bearing, otherwise the crankshaft makes the bearings bind with the different temperatures.
The front-bearing is the one which gives the position of the crankshaft in the engine since this is where you fix the flywheel.

For me the ideal situation would be that the main-bearing is press-fitted on the crankshaft and the outer ring would move free in the crankcase. Or what Profi has done with the crankshaft on their pylon engine is very nice but also very expensive.

Thanks for your input, the more I have got into this project the more I have realised how difficult details like this are to perfect,. This was one of the main reasons to work with a company like Profi - Experience is impossible to replicate.

I also, just want to reiterate a point I made in previous posts, I am not trying to question the quality of CMB products, In fact, I think their engines are first class. they are great. It was more me trying to understand why as I suspect they know something I do not.

 

[Ricky Neal]

I have a question..... what type of metal are our little engine crankshafts cut from ?

ie: are they Billet steel? 4340 ?

Is there another proprietary metal that could be used that would hold a better final tolerance for the main bearing or crank pin surface?

better heat treatment final processes ?

Various manufacturers use different materials but. Some are through-hardened and some are case hardened.

Also, there are different material grades from country to country, the European standards are different from US standards and we even have different grades in the UK.

On the cranks I have made myself, I try to use EN40b, this is a UK spec material similar to 4340 and is excellent.

I don't think final tolerances are really an issue now with modern manufacturing but wear still can be, for this, there are now developments of surface coatings for wear parts.

This has been done with model engines, mostly high-performance RC car engines, they now tend to DLC coat the crankshaft, including the crank pin. There are different kinds of DLC coating but in general, they provide a much harder wearing surface than a polished, hardened steel crankpin (regardless of the exact material), and they also reduce localized friction.

This coating theoretically enables much longer component life, less heat and friction, and so improved performance. It seems to work well in RC car engines

This technology was developed in F1 engines and is now used on many parts of the reciprocating component, Crankshaft, camshafts, piston pins, piston rings, valves stems, etc, etc - In effect, any part that has ant friction wear surfaces.

Here is a picture of an F1 camshaft that I own, this is from a CA-V8 F1 engine, this engine has a rev ceiling of 20k RPM, low friction technology was key to enabling this high RPM.



Also, here's a TJ-V10 F1 engine Titanium connecting rod, the small end is DLC coated so as to reduce friction from rod to piston interference.



Here is a Cosworth XG V8 IndyCar engine connecting rod and DLC coated gudgeon pin



As you can see this technology is nothing new but we will be testing coatings in our engine to take advantage of any benefit.

 

[dwilfong]

I have had great success with full complement ceramic hybrid bearings.
I have them built with between .0008 and .001 clearance.
Thy will handle much more load than ones with retainers.
Thy last twice as long and will rev higher than any bearing.
Greg Settle built the first test sets for me. After his passing I had to find a new source for them.
Check this place out thy make them to order to you specs and are no more than off the shelf bearings.
Thy do take some time to get done depending on there work load.
But if making a large order could be done with plenty of lead time I am sure.



Just some thing to think about if you are building from the ground up.

 

[Ray Sametz]

Boy, they got some balls!! CHM

 

[dwilfong]

This is the link
Each bearing is made by hand and set to your specs.
The ones I had made where if I remember $45 for the full complement and the good balls.
https://www.ortechceramics.com/

 

[dwilfong]

Boy, they got some balls!! CHM

You need lots of balls to run a billet 1.01 piston in a VAC .91..........

 

[ids987]

This is a superb thread, and a superb initiative. I take my hat off to you Ricky, for what you’re doing here, and the effort - not to mention resources which you’re putting in. Cant wait to see the end result.
Some superb info and knowledge sharing - by everyone in the thread too.

 

[Ricky Neal]

This is the link
Each bearing is made by hand and set to your specs.
The ones I had made where if I remember $45 for the full complement and the good balls.
https://www.ortechceramics.com/

Thanks David, I have actually used Ortech before, I use their hybrid ceramic bearings with a Peek cage in my Soluev .21 engine, they are very good quality. I have not tried full complement bearings though - Definitely something to add to the test regime.

 

[LohringMiller]

Model turbine engines run full complement ball bearings a lot faster but probably at lower loads. Boca has a few limited sizes in 8 and 10 mm ID. They look more expensive.

Lohring Miller

 

[dwilfong]

Model turbine engines run full complement ball bearings a lot faster but probably at lower loads. Boca has a few limited sizes in 8 and 10 mm ID. They look more expensive.

Lohring Miller

That is what got me thinking about using them.
Thy rev them to the moon in the Turbine eng.
I had many bearing failures with my VAC 1.05 eng build up.
Went with this full complement and that all went away.
Many tanks of fuel and piston changed still run the same bearing.
Same with my CMB 1.01.

 

[dwilfong]

I have not had any inner races spin on me after going with the full complement bearings set at the proper clearance.
Think about why would the inner race spin?
It would have to have rotational drag on it ?
Think there is more to it than the inner race fit to the crank.
The balls would have to bind to spin the inner race.
Greg opened my mind up to what makes a bearing fail.

 

[Richard Dahlheimer]

Hello Ricky, any thought on glow plugs? Cone lock or conventional? Good luck with your venture. Richard