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150cc Radial Engine - A restoration or new build...

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Michael Checkley02/12/2017 18:01:56
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109 forum posts
65 photos

I have been working on a 5 cylinder radial engine for a couple of months now and the project has reached a stage where I have something to show for my efforts. As an introduction this is how I came about starting this project...

My interest in model engineering came through making bits for model aircraft, a hobby which I have been involved with for about 20years flying most weekends and visiting most of the big shows throughout the year. Those that also enjoy this hobby and visit the shows will have seen Ray Slack flying a variety of large scale model aircraft some of which had his very own design and built radial engines! Ray flew in a model flying club not far from me and he often used to visit my club to display his aircraft giving me the opportunity to chat about model engineering type things.

Sadly Ray passed away and like a lot of model engineers his equipment was divided up and dispersed. It was a few years later that I stumbled across his 5 cylinder engine in an aeromodellers shed. The engine had run for a couple of years since finding its new home but had reached a point of needing new parts and then eventually finding its way to becoming a boxed up collection of parts. As the new owner knew that I was a keen model engineer I was lucky enough to be given the engine for rework. Upon examination it was clear that new parts had been attempted and was now in need of a serious makeover.

Ray based the engine around laser engine cylinder heads, valve gear, pistons and what looks like some kind of agricultural crank shaft. I couldn't identify the crankshaft and some of the laser engine parts needed replacing which when multiplied by 5 started to look costly.

At this stage I decided to take a step back and 'draw up' the complete engine in CAD and then remake all the parts apart from (for now) the cylinder heads and valves. The plan is to split the project up in to stages ultimately replacing all the commercial parts (apart from the obvious like bearings) with machined from stock items making a complete home built engine. If my engine performs half as well as Ray`s original did then I will be doing well.

The engine is ~150cc with a 34mm bore. I have changed the bore diameter a small amount to be able to use Zenoah piston rings as I didn't fancy making rings at this stage. This then meant moving away from the laser pistons and making my own. I have changed the bearing arrangement slightly to be more inline with my working life experience. Its a glow engine but in time I would like to have a go at a petrol conversion. Petrol radial engines are common place on the show circuit now so getting the bits should not be a problem.

And some photos of the manufactured parts plus an original....

Michael Checkley02/12/2017 18:08:58
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109 forum posts
65 photos

Set2Cylinders and LinersOriginal Engine

Michael Checkley02/12/2017 18:15:28
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109 forum posts
65 photos

Liners are cast iron and aluminium parts are a mixture of 7075 and 6082. The plan so far is to use EN24T for the crankshaft which will be a little more substantial than the original to take a bit more abuse.

I have used a few plans and books as reference but found that very few include a tolerance for critical dimensions, I guess most are made as a one off to fit the mating part. For this project I have chosen to go for a tolerance on all the critical features to enable me to make each part individually much like a more commercial/industrial item. So far so good and the fit of the parts is good, perhaps a little more in the scrap bin though!

Next job is to finish off the pistons and make some gudgeon pins.

Neil Wyatt02/12/2017 19:02:55
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16562 forum posts
687 photos
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I look forward to hearing more, Mike.

Neil

Chris Evans 604/12/2017 09:39:04
1476 forum posts

Nice neat work and a challenge for the brain. Keep the article updated for us to admire.

Michael Checkley10/12/2017 17:27:49
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109 forum posts
65 photos

Yesterday I wrote the program to mill the the inside of the pistons and following a few iterations committed to the actual 5 pistons which resulted in a few more iterations to the program. It seems that even after 3 practice runs there was still a lot to learn!

Today I drilled and reamed one of the test pistons for the shoulder bolt soon to be gudgeon pin. The original plan was to use a dowel pin for the gudgeon pin but I wanted to hollow it out and didn’t think this would work out well. The 12.9 shoulder bolt fits well enough.

Milled Pistons

ChrisH10/12/2017 20:26:31
827 forum posts
12 photos

Looks a very interesting build, and lovely machining so far. Keep on with the updates please - I will enjoy following this one!

Chris

DrDave11/12/2017 14:47:37
164 forum posts
32 photos

Michael,

This looks like it will be an interesting build: I am looking forward to your progress. Your use of 12.9 shoulder bolts for the gudgeon pins is interesting. I was going to use silver steel for the engine that I am making but a quick Google showed that I can buy suitable 12.9 bolts off the shelf, which will be far superior.

Dave

Michael Checkley17/12/2017 17:43:01
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109 forum posts
65 photos

Hi Dave,

I’m not sure how well the shoulder bolts will do the job but worth a go. The original plan was to use rollers from roller bearings, readily available and quite cheap but only available solid and I want to keep the mass down on the moving bits!

Pistons have all been milled and drilled and the bolts cut down and hollowed out to make the pins. Rapidly running out of 5 off parts to make smiley

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Jon Harper 119/12/2017 09:33:58
1 forum posts

Hi Michael

I believe the crankshaft in the engine is from a zenoah 62. Neil Tidey and i were discussing it some time ago as i would very much like to offer a Laser radial.

i hope you are able to get this one running again

thaiguzzi24/12/2017 04:07:09
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571 forum posts
130 photos
Posted by Michael Checkley on 17/12/2017 17:43:01:

Hi Dave,

I’m not sure how well the shoulder bolts will do the job but worth a go. The original plan was to use rollers from roller bearings, readily available and quite cheap but only available solid and I want to keep the mass down on the moving bits!

Pistons have all been milled and drilled and the bolts cut down and hollowed out to make the pins. Rapidly running out of 5 off parts to make smiley

0723a1f6-55cc-4c0a-b0bb-66fbec2c5bce.jpeg

Very nice work! Cylinder barrels are beautiful.

Michael Checkley24/12/2017 20:05:41
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109 forum posts
65 photos

The new 16mm milling cutter from Greenwood tools made short work of roughing out the conrod, only trouble is I didn’t leave enough height to get the slitting saw in so it’s either start again with new blanks or make a low profile slitting saw arbor. I think the arbor may come in handy for future jobs.....

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Michael Checkley24/12/2017 20:56:31
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109 forum posts
65 photos

Hi Jon,

I looked at the zenoah crank and there are a couple of differences and after searching the chainsaw/scooter market I eventually gave up and decided to make one from scratch.

From what I heard Neil has the original Corsair with an equivalent 150cc engine. It would seem like a good engine to add to the range given the interest in radials at the moment. I think it will only be the cylinder heads that fly again from the original engine given the rework that would have been required and replacement of a few missing bits.

Edited By Michael Checkley on 24/12/2017 20:57:01

Neil Lickfold29/12/2017 11:30:28
568 forum posts
102 photos

A2 tool steel makes for great wrist pins/gudgeon pins. Harden and double temper to 58 to 60 Rc. H13 hardened to 50Rc and Nirided also works quite well, but A2 would be my 1st choice. Not sure if you are going for the press fit to the pistons or the fully floating set up. You want less than 0.01mm diameter clearance for a floating wrist pin and piston fit. For the retaining circlips and pin length, ideally you want no mare than 0.03mm of total end float between the pin and the circlips.

Nice project and thanks for sharing.

Neil

Michael Checkley29/12/2017 22:31:53
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109 forum posts
65 photos

Hi Neil,

Thanks for info on the pins. I have used the shoulder screws so far but not completely sold on the idea as the tolerance on the shoulder was wider than expected. Can you provide some more details for the tool steel please? Is that grade available in various diameters? I have had a quick look online and not found much.

Neil Lickfold30/12/2017 11:17:59
568 forum posts
102 photos

McMaster Carr sell the drill rod stock. Here is a link https://www.mcmaster.com/#tool-steel/=1awo5pi

A2 tool steel should be available or the equivelent, but not sure what that number is from any tool room supply company. Most commercial places that do the air hardening of the A2 steel do son in a controlled atmosphere and so it comes out looking a nice purple sort of hue. Normally it will be centreless ground after but can be cylindrically ground and if there are centre's can be hard turned between centres. So lots of options. For hard turning, Cermaic inserts work very well in the 0.4mm radius range and so does CBN inserts in 0.2mm radius range. The CBN actually has a slightly higher cutting force over a Ceramic insert, but a 0.2mm radius CBN is slightly less cutting force than a 0.4mm Ceramic. I have not seen for sale 0.2mm radius ceramic inserts, or else I would be buying them. You can heat treat the A2 tool steel yourself quite easily at home with an Oxy Acetylene torch and some compressed air to quench from very bright cherry red. But not Orange. Then temper 2x at about 160c should bring them back to the 60Rc temper range. 180C is getting on the hot side and 150C is on the cold side. Polished before tempering and free from oil, they will be a very light straw colour. Light brown colour is on the softer side.

Neil

Michael Checkley01/01/2018 18:57:03
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109 forum posts
65 photos

I think the pins need a bit more thought and I’ll see what I can achieve with the heat treatment kit that I have in the workshop. The plan is to have floating pins with PTFE plugs which seems to be the most common approach with model aero engines.

Low profile slitting saw finished and ready to slice off the conrod from the blank.

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Michael Checkley02/01/2018 18:48:56
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109 forum posts
65 photos

Slitting saw works ok. A fixture to machine the newly cut face is required next.

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Edited By Michael Checkley on 02/01/2018 18:49:57

DrDave02/01/2018 19:10:57
164 forum posts
32 photos
Posted by Neil Lickfold on 29/12/2017 11:30:28:

A2 tool steel makes for great wrist pins/gudgeon pins. Harden and double temper to 58 to 60 Rc.

Neil,

Is tool steel suitable for gudeon pins? If it needs to be hardened & tempered, would not a H&T structural steel such as 4340 (or European equivalent) be a better choice? Am I right in thinking that either would need professional heat treatment, or can this be done at home and would this require a decent furnace rather than a propane torch?

Dave

Neil Lickfold02/01/2018 21:12:07
568 forum posts
102 photos

A2 is preferred because it is a dimensionally a very stable steel . I use oxy acetylene for the hardening and a home oven for the tempering on fanbake. Small parts may be heated with a propane torch.just not sure, it needs to get to bright red heat to a very dull orange at the very hottest. With A2 as soon as you have it heated, keep it at temp for a minute or 2 then take the toch away and blow down cool with compressed air. With A2 steel you can drill it heat treat and then lap to size if required. 4340 and other steels are not as stable, so will require turning between centres or grinding. Some people use O1 or silver steel, some also use case hardening steels like EN36A or EN39B. Case hardening is a little more difficult to do at home. O1 and silversteel and 4340 can all be used at home. My 1st choice is A2, 2nd will be O1 steel, both double tempered. Silversteel is way down on my list with 4340 or 4130.

To get a really good service life, the pin needs to be micro polished as well. So it will look very shiny with no scratches , so will look like a needle roller bearing.

Drilled out Needle roller bearing needles also make good gudgeon pins as well, but need carbide drills.

Neil

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