Four cylinder scale engine

[ThomasM]

Hello everyone,

It has been a while since my last update but i had to do a few things at the house. I now have a paved yard and driveway and we are able to walk from the car to the house without the need of rubber boots which is very useful.... Also the nice weather is often calling for other open air activities.

So here is the next update and i hope you are still interested.

Pic. 1:
I have made the next set of castings which are the cylinder head and the housing for the camshaft gear drive.
This parts are not machined yet but maybe i will work on them today.

Pic. 2:
I tried to make some pistons the way i usually do which means i turn the outside diameter and the inside from the rod material and parting the pistons of after that. This time something went wrong because after  i milled the slots for the conrods the pistons where not round anymore and not usable. Maybe there was internal stress in the rod material ? So i decided to make the tool you see in the picture ( #2 ). With this tool i am able to machine the whole piston oversize with all the holes, slots and so on and turn the outside and top to finished size without having to clamp the piston on the chuck. The tool simply pulls the piston trough the piston pin hole against the tool when the screw on the backside is tightened.

Pic. 3:
Milling the slots for the conrods. The piston is still oversize so i had no worry damage it when clamping it tight.

Pic.4:
Turning the outside diameter and the length of the piston with the described holder. The pistons are 23,95 mm diameter.
Also the slots for the rings where machined now. I machined them very carefully because the surfaces on the side of the slots are sealing surfaces an they will not brake in because there is no movement there when the engine is running. In the past i had many times problems with my rings not sealing properly because i did not consider this fact. There is a chance that a piston ring which is not perfectly round on the outside and therefore is leaking between the cylinder wall and its outside diameter will break in during operation. But there is no chance it will break in when the leaking is between the surfaces of the slots in the piston and the ring itself.

Pic.5:
Turning the grooves for the piston pin retainers with the help of a mandrel (?) which holds the piston through the opposite piston pin hole.

Pic.6:
Lapping the surfaces of the piston rings top and bottom for sealing against the grooves. The ring compressed in the holder. There is only a very small ring gap because the rings are split by breaking them.

Pic.7:
Finished pistons whith pins and rings. One piston already jumped into the engine.
There are holes in the reduced diameter below the second piston ring. I hope this will help the second piston ring to scratch off the oil from the cylinder wall and bringing it down to the sump when the piston moves down. The disadvantage of this holes is that compression will only take place when the rings are working from the beginning. A good fit of the piston in the cylinder will not compensate leaking piston rings with this holes.

Pic.8:
I pinched of the piston ring retainers from a spring and bent it a bit for better installation.

That is all for now. I hope you stay tuned.

Best regards,
Thomas

[william johnson]

still watching like it a lot

[fumopuc]

Hi Thomas,  I am following each part of your build log. Good to see any progress.

[ThomasM]

Hello everyone,

To keep my thread up to date here a few pictures about my recent work.

1.1 - 1.4 : A few of the steps of how i machined the casting of the camshaft gear housing. I placed the sprue of the casting on the backside so it was usable to clamp it in the vise to machine the inside of the housing and also to clamp it in the bandsaw to part the front section off wich becomes the cover.

2. : Milling the cylinder head casting flat but not to finished size to have a surface to clamp on the milling table
3. : The sprue and the riser of the casting are very useful for clamping it to the milling table. On the upper side of the casting i only had to drill the holes for the head screws at this point.
4. : Machining of the combustion chambers and drilling of the spark plug holes (1/4 x 32).
5. : Finished combustion chambers with the sealing surface milled to size.
6. : Engine with pistons
7. : Mounted cylinder head without gasket to check if all holes are on the right place.

The engine more and more looks like it should. I think i am half way gone but there are many difficult details ahead.....

Best regards,
Thomas

[Ye-Ole Steam Dude]

Following your build with great interest.

[b.lindsey]

I have been checking in from time to time also Thomas. You are making some fine progress..it's really coming together nicely!!

Bill

[Roger B]

Excellent progress  I'm still following along in the background 

[Brendon M]

Fantastic work, Thomas

I'm glad to see the idea of casting parts from 3d printed molds works. I attend a makerspace that has 3d printers and I had ultimately wanted to try it out.

Do you need to finish the surface at all or are the molds usable straight away?

[ThomasM]

Hello Brendon,

Im sorry for the late answer. I have seen one video on youtube ( myfordboy ) and he has used a pattern of a flywheel right of the printer successfully. I dont know exactly why but my patterns are not usable without filling, priming and grinding. Maybe there is to less draft angle on then or the texture my printer creates on the patterns is to rough.

But filling and grinding them is no big deal since i have learned not to print the whole pattern as one part. It is better to print multiple smaller parts that are more easy to finish. The surfaces are more accessible and after finishing all of the surfaces i glue them together. I print with PLA fillament.

I am currently working on the shape and the pattern for the exhaust manifold. Maybe i will give the lost PLA method a try but i am not sure if it would be possible to burn all the plastics out of the pattern before casting....

Best regards,
Thomas

[Brendon M]

Ah, I suspected that some finishing work would be required (*depending on the printer of course). Thank you for taking the time to explain

[ThomasM]

Hello everybody,

It is about time for the next update. I split this update into two posts.

Post #1 will contain thing i did right which is not much this time.

Post #2 will contain my countless, frustrating and demoralizing fails while trying to cast the exhaust manifold.

Picture 1 : machining of the backplate which will be bolted to the crankcase to hold the gearbox. At the original engine this is a part of the crankcase.

Picture 2 - 4 : The casting and machining of the gearbox. It looks large, especially in comparison to the rest of the engine but it is the right size.

Picture 5 : Drilling of the coolant passage in the cylinder head. My milling machine has not enogh clearance on the z - axis to do this and i dont want to rotate the milling head because it is time consuming to set it back to zero degrees exactly. So i used the late for this. The drill bit in the picture is a masonry drill which i grinded to cut aluminium. I dont have and was not able to get such a long drill in 7 mm diameter.

Picture 6 : The machined blanks for the camshaft drive. They are 50 /25 teeth M1. I machined them longer to be able to make a few more gears out of them.

Picture 7 + 8 : The engine with the still not painted gearbox hosing and the assembled camshaft drive. The camshaft drive will also act as an oil pump wich will bring oil up to the valve gallery to lubricate the valve tappets. The oil line for this will be bolted on the hollow screw beside the crankshaft.

Post # 2 will follow....

[ThomasM]

Here is Post #2 wich is the proof that the most difficult and time consuming part of an engine is the exhaust manifold. 

Here is the story: Of course the manifold has to look as close as possible to the original. So the way to go is to cast this part. The outher shape is not a big deal but it is not possible to make a two pieced model of because there is no possible parting line on it. So i wanted ( and still wanting ) to use the lost wax method on this part and burn out the PLA - printing material out of the mould before casting.

While trying this i ran into a few problems which i was not able to solve until now :

 1. The core ( which forms the gas passage ) can not be machined after the part has cast so the mould has to inklude a core.
     This core is very thin ( 8mm ) and long because it goes trough the whole manifold .

 2. The right material to make this core would be sodium silicate bonded sand but it is not possible to to use it on this shape.
     The reason is i was not able to fill the sand in the plastic model and compress it because there are to much corners and the sand is not
     liquid enough to squirt it in. So the only way is to make the core out of plaster of paris and use a injection sqirt to fill the model.

 3. The plaster of paris made core is to fragile.
     I tried to support the core with short pieces of steel wire to prevent it from falling to the bottom of the mould but i failed because of a
     different reason.

 4. The heat treatment of the mould to burn out the lost model is also a problem. While trying to cast the part as a one piced part the whole
     mould would be a large block of plaster of paris. It lasts a very long time to bring the heat to the inside of the block to vaporize the
     embedded plastics. This time is so long that the whole block will become cracks and beginns to become unusable.
     The heat resistance of the plaster of paris investment material is not high enough. Maybe one mould out of ten would be usable.

Conclusion : As you can see in the pictures i tryed many times to make a one pieced casting of the manifold and every time i tried the reason for the failure was different. Yesterday was my last attempt and the problem was that there was still plastics left in the mould when i filled it with molten aluminium.

New plan :

I give up and will try something different. I will cast smaller sections of the manifold wich will include only one corner in the gas passage so i will we able to use sodium silicate sand for the core and maybe also for the outer investment material. Many of my problems are caused by the plaster of paris material so i have to ged rid of this material at least for the core section.

I will use brass to cast the sections to be able to hard solder them together when i have all of them. My first try will take place today.

Here a few pictures of my failed attempts. No comment.

[Ye-Ole Steam Dude]

I admire and respect your dedication and effort to create a "true" scale replica for this engine.

Thank you for sharing,
Thomas

[Ian S C]

I don't know if it is of any use, and I don't have all the details, but I have heard of a method for making such items. A model is made of the interior of the manifold in engineering wax, and this is coated with graphite,  this is electroplated with copper to the thickness required. Once finished the wax is melted out, and flanges etc., silver soldered on.
Ian S C

[Vixen]

Hello Thomas,

I have been quietly following this build from the beginning. I have enjoyed reading every post, until I read about your problems with the lost wax (lost PLA) casting for the exhaust system. That part was not so good.

In the past I had similar problems with ordinary Plaster of Paris. I was advised to buy the correct investment powder that the jewelry trade use for casting precious metal. Their investment is a mix of different refractory materials and plaster and much more resistant to cracking during burn out. Unfortunately the shipping costs can be more than the cost of the investment powder unless you have a jewelry maker near you. You can also find "investment powder" in e-bay.

What are you using for the burn out? That can also be a problem due to the amount of time (12 hours) required. An electric burn out furnace is preferred over fuel fired.

Good luck with your project, keep trying

Mike