Big stroke 55 cc one cylinder ICE

I am almost ready to start making the camshafts.

Does anyone have hits tips to make these on a milling machine with an indexing table? I was thinking to do it like shown in the first picture (blue square is the cutter)

The camshafts are mounted on an axle. The pics shows the intake and exhaust dimension. For the intake I want a duration of +- 200 degrees. This due to run the engine at low rpm. But as you can see in the first picture, with this geometry there is a duration of 272 degrees (136 *2). And for the exhaust the duration is 238 degrees (119*2). The third picture shows the valve timing. Here you can see that for the intake a late closing angle is chosen (for a small valve overlap with the exhaust).

What is the best way to reduce this duration (especially for the intake)? Increase the diameter of the circular arc to lets say 10-12 mm? Or applying a ridge with hollow flanks?

I have milled my camshafts using a table of lifts at 6° intervals. The tables were generated using the cam calculator on the Model Engine News website:

http://modelenginenews.org/

Go to Resources and then Design Centre. I'm not sure how compatible this is with the latest operating systems. Others on this site have also written similar programs which they are willing to share.

The cam blank was held in a simple fixture with a 60 tooth gear for indexing. The lift values were set using a DTI under the milling head. I have attached the table I used for the camshaft on my horizontal engine.

Alex,
My suggestion would be to use this program.
http://www.modelenginenews.org/design/CamTable.html
You use an end mill and a rotary table. You zero the Z axis on the base diameter of the cam, mill across the Y axis then move the table up and down as the table tells you. Just fill out the parameters and it gives you a Z height for every degree increment. I did mine in 2 degree and it was ready to run that way, that also means 180 passes for each cam lobe. But there is no filing sanding ect.
Art

Roger and Art. Thanks for your information and explanation!  Tonight or tomorrow I look after this.

Hello guys, it has been a while since I gave an update. But in the meantime, the engine has already made a few plops! I had some 'problems' (challenges ) with sealing the valves for example (Now 5 bar pressure when turning the engine, had to say that the theoretical compression ratio has been increased duo to thinner Head gasket, so 1:6->7). But I am currently having a question about the crankshaft.

The crankshaft is currently split up. The cheeks are made of aluminum. This was a guess as to whether this went well with the drive shafts and pigtail pen of C45. I have found out that this is a bit of a success. Provided you turn a smaller diameter on the shaft for 'searching' the hole during pressing. But the squareness I did only afterwards. The squareness of the holes for the drive shafts are not good. Both drive shafts do not run in each other's center line. In other words, no straight crankshaft. You also notice this when you mount the block and turn around. It is a little more difficult with some strokes and you can see the drive axles swinging a little bit.
All in all, I think this is enough to start him.
But in addition, I have found out, as soon as he tries to start, that the drive shaft is rotated in the axle. This was fixed with a reasonable fixed fit. This can of course be remedied by the use of glue / or the installation of locking pins.

I am thinking to tackle the total crank cheek problem. So I want to make the cheeks of steel. At the moment I have a leftover cast iron. I wonder if this is strong enough? Given that the material is brittle. However, the material is easy to machine. And I'm probably going to use glue as a deposit (locktite 4xx, I do not know my number).
Or is it advisable to use another type of steel such as C45?

Soon I would upload some more pics and talk. Greetz Alex

First picture of the first test. It was pointed and quite messy in the R & D section! Here I found out that the engine contains too little compression.

The second photo is recently after disassembling the second test session.

Today do some bit of math!  Cast iron can not handle the theoretical bending forces. Gas force is 4.8 Kn (ideal situation of combustion 100% VE). The safety factor is 0.7 ish (compared with 1.3 for aluminum and 2.3 for C45) with taking into account the jump load factor.
Cast iron GG25 is weaker than 2020. C45 would be ideal. But, you will not end up balancing the weight of the crank (rotating balance). It is possible, but then it is necessary to build a steel connecting rod. Maybe for another time.

Now I want to adjust the current crankshaft. The insertion of fitting sleeves to improve the squareness of the fitting of the respective shafts in the crank cheeks.
The new confiscation can be seen in the image below.

The bending forces on an IC engine crankshaft are quite high. I have made my bigger ones from C45k with the balance weights bolted on. I think that getting a good bond between steel shafts and aluminium webs will be quite difficult. RC in Luxembourg do some useful sizes of C45k

https://www.rc-machines.com/en/materials/steel/flat/c45k

Your engine is big enough to get into trouble with the distance between crank webs and the bearings ....
Since it looks like the bearings are in separate holders (might be problematic too) I hope that you just can turn them 180 degrees or swap left with right side and get the bearings almost flush with the webs - this should stiffen the crank quite a bit ....

I got absolutely no experience nor ever seen a crank with alu webs, so my next comment might not be worth much, but ..:
Removing material from alu webs will not give you much, but putting heavy metal into the opposite position should be enough to balance the crank.

Best wishes

Per

Thank you gentlemen for your reactions! Meanwhile I have been busy fixing the aluminum handle cheeks on the crankshaft.
For me it was also questionable whether it would work. You can take a gamble anyway! The main reason was that I had no experience of milling harder metals. In addition, the use of aluminum ensures less oscillating vibrations. With an aluminum crankshaft and connecting rod it was possible to balance the crankshaft (rotating balance).

But! Last Monday the engine ran a few minutes !! And still pretty neatly stationary.
But unfortunately the locking(pins) of the cranks has been released. I doesn't have put some fitting sleeves in the crank. Now I intend to make the crutches, and possibly the connecting rod, of C45. I collected this material yesterday at a local machining shop.

First, before I go into detail, I chronologically upload the progress of the past months.

In the month of March the components were made for the rocker arm / camshaft assembly.

The first series of images are the assembly and adjustment blocks of the tumblers. Now the valve clearance can be adjusted per valve. The axes on which the tumblers rotate are currently glued(locktite 402). But this can be replaced by a threaded rod by mounting both blocks. The valve stem lengths are almost identical. And the valve stem caps can be adjusted to the play (added later).

The tumblers are equipped with rollers. These are admittedly of softer steel than the silver-steel cams. For now the use of ball bearing grease for lubrication is sufficient.

Hi AlexS,

Beautiful design engine, will follow along.

Have a great day,
Thomas

Time to make some tools! A mounting block for fixing a three claw on the index table. The indextable is mainly used for milling the cams.

The three-claw is fixed with the 3 original bolts of my lathe. Given that you can only mount bolts on one side. Did I use three imbus bolts as centering on the indextable side. In addition, the whole is mounted by means of a threaded rod that you tighten through the middle.

The whole has done a nice job. However, the span was large. For the milling of the cams it was advisable to also manufacture a countercenter. This naturally resulted in fewer vibrations.
I like to make some useful tools.

Thank you Thomas! I appreciate it.

Some nice work there    I am not sure that the aluminium crankshaft webs will work due to the different stiffness (Youngs Modulus). The webs will less stiff than the shafts which will tend to make the holes in the webs barrel shaped.