Peggy - my Holly Buddy remix - 2.5cc CI engine

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pat_pending

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Hi all,

after procrastinating for months and clearly overthinking the problem of how to make the crankshaft for a twin diesel I/C engine, I decided I needed to be making some swarf over Christmas to decompress from work. After poring over the MotorBoys plans for a while I ended up on Adrian's Model Aero Engines and found plans for a lovely simple little engine called the Holly Buddy (https://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=214). Nothing I haven't tackled before really apart from a front rotary valve in the crankshaft (my previous builds have all been RRV or sideport).

I've been beavering away on it for a couple of weeks so thought I'd share a few pics. This isn't a step-by-step thread as I just jumped in to the workshop and got cracking but if anyone has any questions on any of the parts shot an I'd be happy to share more pics.

The engine might be ready for a test run this weekend to the less time on my computer and more time at the lathe the higher the chances. I also want to have a go at anodising the prop spinner (any good tips on making prop spinners btw? info seems v scarce on the web) and cylinder muff so will share some more detail when I get to that.

Anyway, hope this is of some interest to someone out there in the 'engineverse' :) .

cheers,
Patrick

I use every build to improve my dodgy CAD skills too. I modelled this one to the point of being able to animate the turning crankshaft, piston, cylinder etc. Happy to share the files if someone wants a play.


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making the crank case. (BTW the camera is lying. The surface finish looks nice after the crud and oil has been cleaned off :D )




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Taking some metal off on the crank case making it look a bit more Nalon Viper style.

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Thought I'd go for an axial rather than a radial mount (partly for ease of slotting into my running mount later rather than screwing into a piece of wood)

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pat_pending

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Making the Venturi and NVA

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Reamer made from a bit of the same 1.56mm piano wire i used to make the needles.

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make sure there's an airtight fit between the NVA and the venturi.

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Dremel used to make up some needles @11degrees.

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Silver soldering makes me nervous no matter how many times I do it! This time i used some paste and it seemed to go ok.

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Bending that music wire is a pain! Actually cracked at the bend but you cant see unless you're really looking closely. Next time i think i need to apply some heat there.

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pat_pending

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A few pics making the crankshaft and cylinder liner.
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Hole drilled with a drill for most of the distance with a jobber drill and then cleaned up and the bottom flattened with a 4-flute endmill.
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I bought a slitting saw exactly the right size to make the exhaust ports. This seemingly simple operation ended up being a royal pain in the ****. Anything to hold the saw to the mandrel would foul the hole as it goes in pretty deep. In the end I had to silver solder it to the arbor. What a mess. I'll look for a one-piece t-slot cutter next time or try using a boring head as someone recommended to be last time.

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Crankshaft made out of a single piece of EN14.

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Polish crank pin to a close fit in the conrod.

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Finish off between centres and polish for the perfect fit into the ball bearing and reamed front housing.

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pat_pending

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Hi, bit more shed time today. I am ready for assembly and final fettling tomorrow after which I will strip off the cylinder muff and prop spinner to anodise.

All in all a good day in the workshop with some recovered near-misses narrowly avoiding the ever-growing scrap bucket. Some pics below.

Thanks,
Patrick



All the bits cleaned with thinners and then ultrasonic bath for 20 mins to make absolutely sure all the silicon carbide grit has been removed.

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Lapping the cylinder using an aluminium split lap and 320, 600, 1000 grit. The huge transfer ports on this cylinder interfered with the lap a little bit. Somehow I wasn't able to avoid some small circular scratches in the finished surface. I'm sure it will be fine.

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Machining the piston from cast iron bar. Messy stuff!
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I use the bottom of the piston as the reference to locate the gudgeon pin hole since the other surfaces haven't been finished to dimension yet.

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Piston and contra blank ready for finishing.
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Piston on a mandrel ready to finish.
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Piston turned till it will just enter the cylinder ready for lapping.
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Turning a prop spinner using a radius turning attachment.

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First time creating a spinner. Happy-ish with the result although it looks more like a christmas chocolate of some kind.


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pat_pending

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Partial success on a test run, but like all too often, need to take a step back before moving forward again.

Long story short, I made a mistake on the piston manufacture. I used 1000 grit emery paper on a parallel method to take off a tiny bit before moving to the lapping stage. This ended up making the piston a tiny bit out of round as evidenced by the surface during lapping. I could see clearly that the lap wasn't making proper contact all the way round. To remedy this I took a gamble on taking a fine cut at high RPM in the lathe and get back to lapping after. This meant that the piston was already part way up the cylinder when I went back to lapping and i couldn't really get a perfect surface finish as I had to stop lapping when the piston crossed the exhaust port as usual.

I thought I got away with it but the engine was difficult to start and the compression started to go after a few minutes of rich running in. Anyway, a valuable lesson learned about rushing/bodging things up. These small engines are unforgiving!

Plans for the weekend are to re-lap the cylinder and make a new piston + contrapiston. Dull work but at least end is in sight.

Good news is that I have ruled out other mistakes with port timing, the FRV and the venturi setup. The engine ran quite nicely with a decent bark and good manners on the compression screw. Hope to get her properly running this weekend.

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f2cf1g

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Rather than make new, why not try "cherry-bombing" the piston and contra to make swell a bit? Often works for me.
 

pat_pending

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Rather than make new, why not try "cherry-bombing" the piston and contra to make swell a bit? Often works for me.
Hi f2cf1g, I assume that is to heat red hot and cool a few times so the piston expands and then re-lap it? Any trouble with the gudgeon pin holes?

Patrick
 

f2cf1g

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Yes, but I only heat once and let it cool, then re-lap. I have never found any problem with the pin fit afterwards, though I suppose if it was retained with a light interference fit it might become noticeably looser which might have to be dealt with. Roy
 

pat_pending

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Hi, finally got her done!!!! :cool: :cool: :cool: 🤟 🤟 Runs great and happy with the finish. For a first time anodising aluminium it worked out pretty well too. Being picky, maybe got a bit too dark in the end. The video below is of the second breaking-in short run on a 8x4 prop and my phone app tells me 13k RPM. This means the engine is likely to get to 14K+ after breaking in and switching to a racing fuel. Strangely more power than my Vipers which confirms my suspicion that I made the transfer passages too small. I'll get the tachometer on her after 8 or so more short breaking in runs. Anyway Happy Camper! Thanks @edholly and Steve Jenkins for the plans.




Next stop: twin Diesel. STILL cant find plans so might go with the partial plans of the Sparey Twin (ken Croft) or do my own take on a twin Nalon Viper as I have the cutters and mandrels etc kicking about in the box.

Anyways, thanks for looking.

Patrick
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pat_pending

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Well done. Did you make a new piston?
Thanks. Yeah I re-lapped the cylinder, new piston and contra. Boring work good result in the end. I gave your cherrybombing technique a try but i'd lapped too much on the cylinder and the old piston just slid through.-P
 

edholly

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Hi Patrick - a wonderful build - congratulations.

Why not make a twin HB - will try to help you with plans if you wanted to ...

kind regards ... Ed
 

pat_pending

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Hi Patrick - a wonderful build - congratulations.

Why not make a twin HB - will try to help you with plans if you wanted to ...

kind regards ... Ed
Thanks Ed, I'd love to give that a go. I'll have a think about the crankshaft/crankcase/bearing setup and post on a new thread. If you have any fag packet sketches they would be gratefully received.

I was thinking opposed twin (simultaneous firing) rather than inline alternate firing twin as a first go.

Thanks,
Patrick
 

Olli-Matti

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Congrats! The engine looks absolutely beautiful and seems to run super nicely! Well done.

What substance did you use for lapping the cylinder? I see you referred to 320, 600, 1000 grit in the post when lapping with split alu mandrel.

Did you measure the taper of the cylinder?

I was supposed to take a little breather after last project but this one surely got my attention. I just love how your engine runs. If I could even come close to that that would be awesome. Love the racy Oliver Tiger like going of this one :)

Best regards
Olli-Matti


Oh and almost forgot: The changes you made to the crankcase are spot on! 👌
 

pat_pending

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Congrats! The engine looks absolutely beautiful and seems to run super nicely! Well done.

What substance did you use for lapping the cylinder? I see you referred to 320, 600, 1000 grit in the post when lapping with split alu mandrel.

Did you measure the taper of the cylinder?

I was supposed to take a little breather after last project but this one surely got my attention. I just love how your engine runs. If I could even come close to that that would be awesome. Love the racy Oliver Tiger like going of this one :)

Best regards
Olli-Matti


Oh and almost forgot: The changes you made to the crankcase are spot on! 👌
Thanks Oli-Matti. Much appreciated

On the lapping i used Silicone Carbide grit. Diamond grit (red) is recommended by some too but i always get worried that there is still some lingering about even after ultrasonic cleaning. Plus the carbide grit is super cheap so I will be sticking to that.

In terms of the taper: I do't measure (although now that you ask, its probably a good idea to ensure repeatability on future builds). I lap the whole cylinder straight with the 320 grit to get rid of any machining marks and start with a lovely smooth matt surface. I then switch to 600 (after thorough cleaning in thinners followed by a scrub in soapy hot water) and lap straight again. Only after the whole bore is smooth and shiny i start dwelling a bit more at the bottom of the cylinder on the up/down strokes of the lap.

I know the taper is done by feeling more than anything scientific when the cylinder catches the lap and tries to spin out of my hand just when it reaches past the exhaust port. I then clean anything up and lap the rest by inserting the cylinder in the bore (again clean) with the 1000 grit paste and lap it by hand with a smooth circular motion until it reaches just under TDC. Then again clean thoroughly and see where you are. Warning, after cleaning and a squirt of oil the cylinder goes in a tiny bit further so give yourself some room. You can always add some more paste and try again.

On a brand new engine, the piston should just about get stuck at TDC when rotating the prop. This loosens up quickly when it starts up and the final lapping is done during the breaking-in phases as evidenced by the black gunk that comes out after the first runs!

Some EPIC threads that I learned from and can explain a lot better than I can are pasted below. Looking forward to seeing your build thread! Happy making.

Patrick


 
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