I want to build my first engine

[Makintrax73]

Some work on the carburetor

 

[Makintrax73]

The Owen Mate project is nearing the end. I made a serious rookie error in ignoring the instructions. I used a commercial 3/8 bearing rather than fitting the carburetor FIRST then boring a bearing from bronze. Why this is important might not be immediately obvious unless you've done this type of engine before. The carburetor body needs to seal against the crankshaft in order to properly time the opening of the intake port. If it doesn't seal the timing opens way too early and closes late. The troglodyte method used to fix this is probably better left unsaid. In any case to crank bore is slightly worse for wear, but may do the job for a while.....




A fuel tank needs fabbed, fuel mixed, final cleaning and assembly, and test stand rigged. God willing it may just run but I'm not getting my hopes too high ....

 

[Makintrax73]

Well, it's an "engine" in as much as it looks like an engine, turns over smoothly, and makes compression.



I'm waiting on some John Deere 80% ether. I tried to get it to "pop" by priming the carb....no joy. But also no idea what % ether the cheap hardware store starting fluid might be.

Turning it over slowly I find a flaw in my lapping. It makes great compression a few degrees past the intake ports, then slacks off slightly so I can hear compression leaking past the piston. Slowly but it does hiss past. Probably .0001" looser if i had to guess. Whether it is to much idk, but I suspect it is since I can't get so much as a puff of smoke even on a squirt of straight starting fluid. I may be going back to remake the cylinder and piston idk.

 

[Ben17484]

That looks really cool. Nice job. You’ve inspired me to find and download the plans for this. I’m not ready to start and engine yet as I’ve plenty of skills to learn first, but when I’m ready I’ll try and build this myself.


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[Ghosty]

I'm waiting on some John Deere 80% ether. I tried to get it to "pop" by priming the carb....no joy. But also no idea what % ether the cheap hardware store

Most of the cheep starter fluids you buy at the hardware store are lucky if they have 30% ether
Great work on the engine
Cheers
Andrew

 

[Makintrax73]

Most of the cheep starter fluids you buy at the hardware store are lucky if they have 30% ether
Great work on the engine
Cheers
Andrew

I had forgotten that most companies post MSDS sheets online, and they usually contain ingredient data.....the starter fluid I used states "20-30%" ether. Hopefully the JD80% ether will get me enough boost to get it running.

I coated the piston with spindle oil and the compression was near perfect....oh so close.

 

[Ghosty]

I have been able to get a supply of ether, not easy to get,6 hr round trip. Then just mix my own fuel.
When machining the crankcase, The first thing I do after marking out the base block, is drill the engine mount holes. Makes it easer that drilling after.
Cheers
Andrew

 

[Makintrax73]

I haven't given up, but this is really a struggle. I scrapped the original cylinder. Machined a complete new one w/ .002" smaller bore. The old one just would not fire and I could feel compression just wasn't holding.

As you can see I did a rather nicer job on the new one in general. My taper was corrected, and I didn't snap an end mill in the exhaust port. :-/



I have lapped the cylinder and relapped the piston down around .001" to fit the new bore.



It doesn't exactly drag going in but it probably takes more force than I think is quite right. The piston jams just past the exhaust ports, which I believe is right.

At this point I'm pretty unsure. Reading articles is all well and good but IDK what the correct feeling is. I'm not sure it will turn smoothly once assembled as it might be a smigde tight. But if I go another tenth and it doesn't hold compression I get to start over again.

 

[Olli-Matti]

Good work Makintrax73 Perseverance pays off in the end surely!

I have been there where you are at the moment. You are 100% right that you can only feel the correct fit by experience and impossible to have that when making the first one. Rest assure I have made too tight pistons. A little too tight is not a bad problem as well oiled it will usually turn and even ignite a ok. Ofcourse if it really is too tight then it will give you problems and you propably notice that when making final assemblies.

When you have all the parts done and you are making the final fits and assemblies you can try the piston fit with different oils. I use the ATF oil and with that even a tight piston will turn over TDC relatively easy when you start the engine you see some scoring marks along the piston and you can lap the piston and bore a bit and usually it gets better. With experience and tachometer you can find and the optimum fit but to start I like to be a bit on the snug side first and then work from there.

I am although using the diamond lapping method so not 100% sure if all this applies here.

Good luck and keep up the good work!

-Olli

 

[Ghosty]

Here is an article on mixing you own fuel, also has a section on using starter fluid in the mix and how to adjust the ratio's

AdriansModelAeroEngines.com :: Fuels for variable-compression diesels

Cheers
Andrew