# 120 cc 7 cylinder radial



## Pat1311 (Dec 28, 2017)

Hello all,

This is going to be  my first build log on this forum  and my 5th attempt on building a ic engine.
I've build 2 one cylinder two strokes a one cylinder four stroke and a  flat twin four stroke.

4 of them ran the first try and only the first engine,a two stroke design from Jan Ridders never ran properly.

I always was interested in radials and always wanted to build one but I didn't feel that my machining skills were up to it and most of the plans I found on the internet were imperial and  that would make things even more complicated. 

After finding metric radial plans and hopefully having somewhat more machining skills i started machining on the crankcase about a month ago.

I first started with sawing off a slice of  120 mm 2007 alu for the crankcase to be.

Drilling a pilothole to make room for my most stable  boringbar.
Slowly progressing to the the required depth and diameter,2007 alu machines very nicely even on my little chinese hobby lathe.

After turning the outside to the required diameter the alu lump was transferred to the rotary table.


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## Pat1311 (Dec 28, 2017)

After dialing in every axis i started to mill out the flats.
Being a 7 cylinder there is no whole degree division so I had to use the dividing plates,this was the first i ever used them so i was a little nervous making a mistake and having to start all over again.

90 turns on the handwheel for 360 degrees so 90 divided through 7 makes 12 6/7  so 12 turns and skipping 18 holes  on the 21 plate.

This worked out fine and after that i made all  threads and the holes for the cylinders.
I broke a tap in one of the m4 holes but i luckily got it out.

Next step was turning an arbor or plate to get the locating spigot for the crankcase frontpart concentric with the bearing seat in the crankcase and milling the 3 slots.
After this step this part was done for now.


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## camm-1 (Dec 28, 2017)

Nice start!
But what motordrawing is it??
Ove


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## Pat1311 (Dec 28, 2017)

camm-1 said:


> Nice start!
> But what motordrawing is it??
> Ove



Ah yes,
 The design of the engine is by Volker Jung, a german engineer and the plans can be bought through his website.
The 60 cc flat twin i build was also his design.

Ok,
Next part to make was the crankcase frontcover which also houses the second crankshaft bearing and the camdisks and gears.

First another piece of alu under the bandsaw.
I decided to do the inside first because otherwise  it would not be easy to chuck up for machining the other side .

For the outside i turned up a plate withe a spigot to get everything concentric again.
I made the curve on the outside handholding a piece of sharpened hss.

Last thing to do in this setup was machining the front bearing seat.
It took me some time to get all the holes and threads for the cam followers in the right place but finally got there.

Also made the sliding bushes for the cam followers.


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## Pat1311 (Dec 28, 2017)

Ok,

Next part I made was the crankshaft ,I've finished it just last week together with the master conrod.

According to the plans the crankshaft had to be made in one piece but turning a lump of 90mm round 200 mm long C45 excentric with an interrupted cut down to 17 mm would have been the end of my little lathe.

I made the crankshaft of my 60cc flat twin in one piece and 50 mm round  with  a stroke of 30mm was allready very scary en frankly too much.

So,I decided do make up a compound shaft and press/shrink them together  and just see if it is going to be strong enough.
I use shrinkfits very often at work and they are very strong so it's worth a try.

I started making the web/counterweight.
I bored the shaft and pin hole and mounted it on an arbor to turn the crankpin spigot and the recess that is concentric with the crankpin.

Then to the milling machine to cut the shape of the counterweight before starting on the shaft.

3 steps of 17,15 and 12 mm and a length of M12 thread.
I still have to cut a slot for a key in it.

Last part was the crankpin itself which I hardened.
Heated it to just over 800 degrees Celsius and then quenched in water.

I heated the counterweight to 400 degrees and the shaft just slid in.
The pin was pressed in in the vise.

All feels very solid but that doesn't say much of course but we will see.


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## Pat1311 (Dec 28, 2017)

Last part I made was the master con rod.

I made this out of 7075 alu,very nice to machine and very strong.
Unfortunately it is not easy to get in flat stock so I had to machine it out of a slice.

First milling some squareness to it and reducing the thickness to 15 mm for the big end.
I then bored the hole for the needle bearing and drilled and reamed the holes for the  slave rods and piston pin.


On with milling down the rod and the small end to 7 and 10 mm before milling out the shape of the rod.
I then turned an arbor to mount it on so I could turn the 45 degree chamfer on the big end.

Back to the rotary table to mill the 7mm slot where the big ends of the slave rods will fall into.

This is as far as I got to date, I'm now working on the camring,C45 that has to be hardened.


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## petertha (Dec 28, 2017)

Very nice! I'll be following along.


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## petertha (Dec 28, 2017)

I know I'm getting ahead & you will get to the pistons & rings eventually, but I noticed you also built the Jung 60cc four stroke flat twin. Nice runner on YouTube! 
Did you make your own rings? Does Jung suggest the 'heat set' on a specific pin diameter (Trimble method) or something else?


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## ShopShoe (Dec 29, 2017)

Pat1311,

Your parts look beautiful so far. I'm impressed. I'll be following along.

--ShopShoe


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## Herbiev (Dec 29, 2017)

Looking good so far. I'll be following along too


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## Pat1311 (Dec 29, 2017)

petertha said:


> I know I'm getting ahead & you will get to the pistons & rings eventually, but I noticed you also built the Jung 60cc four stroke flat twin. Nice runner on YouTube!
> Did you make your own rings? Does Jung suggest the 'heat set' on a specific pin diameter (Trimble method) or something else?



Right,

Yes,eventually the rings will come up,better said they just popped up when I read your question.

First I didn't know what the Trimble method was  but after searching a bit I stumbled over an article on modelenginenews.
This was somehow how I made my rings before.

Jungs method takes another approach.
The plans say making the rings over sized and removing a calculated part of the ring so when it compresses it's the exact diameter of the liner bore.
So no heat treatment there.

Plans also say to make the rings out of C45(don't know what your equivalent is but it's a carbon steel suitable for hardening)in cast iron liners but I'm leaning more to cast iron rings.


I'm not sure if I will follow the plans on this one.
I have a little lab oven connected to a cheap chinese PID controller so I can control pretty accurate any  heat treatment and just go for the Trimble method.  

Maybe I try them both


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## petertha (Dec 30, 2017)

Pat1311 said:


> Jungs method takes another approach.
> The plans say making the rings over sized and removing a calculated part of the ring so when it compresses it's the exact diameter of the liner bore.
> So no heat treatment there.


 
That's why I was curious. I have a different set of Jung plans & noticed that. Yet the videos, including yours, demonstrate that they obviously run fine. From the reading I've done on this forum & others, the ^^ method described does not result in equal radial stress. But maybe 'close enough is good enough', who knows. The Trimble sizing equations are relatively straightforward but FYI I made a spreadsheet, happy to share when the time comes. I'm approaching this stage on my own (Ohrndorf) radial, that's the main reason why I was asking.

OK, sorry for the interruption. Back to regular scheduled 7-cylinder radial construction by the author!


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## Pat1311 (Dec 31, 2017)

petertha said:


> The Trimble sizing equations are relatively straightforward but FYI I made a spreadsheet, happy to share when the time comes. I'm approaching this stage on my own (Ohrndorf) radial, that's the main reason why I was asking.



Great to hear you are building a radial too,and not the least also.

The Ohrdorf engines are very very nice engines,nicer in design then the Jung versions but also require a higher skill level I think.

Which one are you building and do you have a buildlog?
Really want to see some pics of it.

And that spreadsheet would be more then welcome,could you send it to me?


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## petertha (Dec 31, 2017)

PM'd you about the spreadsheet. Mostly it was for my own purpose so hopefully not too confusing. There are other references on this forum but you might have to do a search, I didn't keep links. Here is another useful link that elaborates on Trimble method & related information. Look for the MS-word doc summary at bottom of post.
http://www.modelenginemaker.com/index.php?topic=3794.msg68928#msg68928

I'm building Ohrdorf 5-cyl radial. Its a 'mostly similar' reduction of his original 9-cyl. The only thing is you have to buy both sets of plans (9&5) so you have complete parts listing to make the 5. I have made a complete cylinder assembly & the crankcase. Was just working on the crankshaft spring-2017 when my lathe developed problem. That was a loooong, painful lapse but hopefully finally resolved now so I can continue with engine building now.
https://www.****************.com/threads/14x40-lathe-power-feed-improvement.64907/#post-540705

Don't want to plug up your build post. Hopefully this was helpful.


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## Pat1311 (Jan 1, 2018)

That's looking sweet!

That valve cover looks very nice,how did you make that?


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## petertha (Jan 1, 2018)

Valve cover made from block of 6061 aluminum. I think the operation went like:
- size block to dimensions
- drill topside M2? bolt holes & c/bore
- outer fillet using radius round over tool
- mill inside cavity away. I think I ultimately tweaked the plans a bit experimenting because plan design necessitated ball end mills to make the 'shell' but these weren't great for deeper hogging. Maybe my particular tool or method? So I think I slightly adjusted height  to accommodate rocker movement & use conventional flat bottom end mill & leave a bit more material remaining. Its a fiddly operation & has to fit nicely over rocker perch.
- hand file corners to blend 3 fillets


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## Pat1311 (Jan 1, 2018)

Wow,

Handfiling the corners,I love the dedication this hobby takes

I did some work on the exhaust cam disk.

Had to be made out of carbon steel so it could be hardened,designer suggests C45 which hardens quiet easy when heated just over 800 C and the quenched in oil or water depending on  how hard you need the part to be.

Started out with a slice of C45.
chucking it up and give it a face cut

moved on drilling and the boring the bearing seat to just under bearing size for a press fit.
I then turned a mandrel to chuck it up concentric to turn the outside and the spigot.

Moved the part to the mill to  drill the mounting holes for the intake ring and giving shape to the outside including the actual cams.

And a try fit on the crankshaft just to see how it all fits together.


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## petertha (Jan 1, 2018)

Nice. Are the cam lobes based on a circular/arc profile or a funky coordinates shape for valve lift? I didn't see a rotary table setup like: rotate X degrees increment, in-feed Y amount, rotate/repeat etc. around the lobe..

Very interested to see your hardening procedure.


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## Brian Rupnow (Jan 1, 2018)

Very nice craftsmanship.---Brian


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## Pat1311 (Jan 4, 2018)

petertha said:


> Nice. Are the cam lobes based on a circular/arc profile or a funky coordinates shape for valve lift? I didn't see a rotary table setup like: rotate X degrees increment, in-feed Y amount, rotate/repeat etc. around the lobe..
> 
> Very interested to see your hardening procedure.



 No,
No lift diagram or coordinates,not yet anyway.
Last year I converted a small(only 60KG) benchtop mill where I had no use for anymore to cnc.
Bought some chinese steppers,drives and 3 little ballscrews and then I had a litlle cnc machine in my garage.

Unfortunately,it's not very accurate  (0.05 to 0.10 mm)and I use it only for non critical dimensions like outside contours of conrods.
Everything that has to be spot on is made on the manual mill with the DRO.

I tried it on the camdisk and measured it and the bearing seat was about 0.25 mm out of centre,this is way too much.

Don't know if the disk moved during milling or maybe I did'nt dial it in properly or maybe my homebrew machine just isn't accurate enough.

I ran out of C45 of the correct diameter so I ordered some,checked backlash on the machine and going to give it another try.

If it's still not good enough I'll make it with the rotary table
Allready made a lift diagram with a polar array in autocad with steps of 0.5 degrees angular separation.

The hardening process is pretty easy for C45,just heat up to over 800 degrees C then quench in oil or water depending on how hard you need it to be.

You can then temper it between 500 and 600 degrees and let it cool in air to make it tougher.

It helps if you can controll the temperature of course,I have a 15 dollar chinese PID controller on a cheap old lab oven  doing that.


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## Pat1311 (Jan 20, 2018)

Because I didn't have any C45 in the right diameter to give the cam disk another try I made a start on the cylinders.

The start of making 7 or even 14 of the same parts.

I also made a fixture  to mill out the conrods,took me 2 hours but it will shorten the time being spend on the  6 conrods by a lot more.

I made the cylinders out of 65 round 2007 aluminium,the plans say to make it out of square stock because of the square flange on the bottom but I find it easier to start with round stock,there's a bit more wasted but I don't like the interrupted cut involved turning square stock.


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## Pat1311 (Jan 20, 2018)

And a quick mock up and test fit just to see how it looks.

Next will be the conrods and then another try on the camdisk and the rest of the gears.
I decided to make the gears myself,I ordered a set of module 1 gearcutters,see how that goes.


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## Pat1311 (Feb 4, 2018)

Next  parts to make are the con rods.

Not very complicated but the holes for the big and small ends have to at the right distance and the bores have to be exactly 7 mm in my case.

I ordered some flat stock 7075 alu,this was a bit hard to find so I had to order it in Germany,a bit expensive but it saves a lot time not having it to make out of round stock.


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## Pat1311 (Feb 4, 2018)

Next were the big end pins and 2 cover plates that secure the pins.
I also had to make 3 bronze washers.


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## Pat1311 (Feb 4, 2018)

The pins fit very nicely,the rods can rotate freely and there is no play at all.

Next to make were the gears and a bush where the gear shaft runs in ,but first I had to make an arbor for my new bought  module 1 gear cutters.

I needed 1 10 tooth gear on a shaft and 2 25 tooth gears.

The 10 tooth was easy on the rotary table,just 9 complete rotations per tooth.
The 25 gear was 3 rotations and 12 holes skipping  on the 20 hole dividing circle.


Everything fits very nicely.

next to do is the second attempt on the cam disk


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## Cogsy (Feb 4, 2018)

Great work so far. Radials just look so 'pretty' inside. I'm almost tempted to seek out a set of plans but I think I've got enough on my list for now.


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## petertha (Feb 4, 2018)

Coming along nicely!

So looks like neither big or little ends of the connecting rods have bronze bushings in them, right? Just the aluminum itself? That's the same I see on comparable designs, some have, some don't. Some guys put them in on their own even if plans don't call for. But I think the amount of remaining stock material is already pretty skinny.

Getting back to your crankshaft, maybe I missed but are you cross-pinning the  counterweight/crankpin assembly to the shaft itself? I'm making my 5-cyl crank now, also out of solid. Not as large as yours but still lots of material to remove. Was thinking out loud about an assembled crankshaft vs. solid. I might even make one for the heck of it so was wondering.


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## Pat1311 (Feb 4, 2018)

No,there's no pin in there.

I thought about pinning the shaft but was advised not to because the shaft is a shrink fit in the counterweight and it would only weaken things.

And there's allready not much "flesh" around the shaft.

I'm by no means sure if it is going to be strong enough but the alternative was making it out a lump of 90 mm round C45 turning it excentric with an interrupted cut and I don't think my little lathe is up to that.

My thought was just to try first the easy way and if it fails I can allways go and try the hard way.


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## petertha (Feb 4, 2018)

Food for thought. A keyway method & cross pin method.

http://modelicengine.la.coocan.jp/k070601.htm

http://modelicengine.la.coocan.jp/h9090903.htm

I know, I've been thinking about same issue. A shrunk joint or glue (locktite) joint hopefully would 'fail' with crankping/counterweight spinning around shaft & (hopefully) minimal internal damage to engine. Pins coming loose would be more dramatic. OTOH, maybe designed not to fail?

The way I look at it is the crank pin itself is a pretty hefty diameter, supposedly sized not to shear under cylinder firing. Maybe its over designed, who knows. Anyway, the crankshaft 'joint' we are talking about should be somewhere around that same strength? 

Maybe you could make a simple test piece using same size, material, interference method & apply torque with torque wrench. If value meets expectation of engine rating, will give you much more confidence. If it breaks, saves you an ugly problem down the road?


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