# Master rod layout



## stevehuckss396 (Sep 30, 2011)

Does anybody know how to lay out the master rod for a 5 cylinder so that the cylinders are at TDC at the correct time. I know it is not as simple as a slave rod every 72 degrees.


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## kcmillin (Sep 30, 2011)

I can't help ya Steve, but I too am interested in how to do this, and I don't want to miss the answer. I might start a thread on cam designs for a radial. Awfully confusing, but I am sure it is simple.

Kel


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## mu38&Bg# (Sep 30, 2011)

I'm the books I've read they differences between cylinders is small, not enough to worry about. I don't think it can be fixed with position of the link rod journals anyhow. Only arrangements like the so called slipper rod actually fixes it. One reference had a chart which showed angular irregularity between cylinders. From memory, the maximum difference was 2.5°.


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## petertha (Sep 30, 2011)

Someone pointed me to a graphical solution (relatively easy in Cad) that will lay out component geometry to ensure the same TDC piston positions. This translates into equal compression ratio's, which for my project (glow ignition) was important. I believe the 'inputs' are:
- crankshaft throw
- master rod length
- diameter of linkrod bottom pins position located on MR
- cylinder angle (=72 deg on 5-cyl). 

When you do the layout, it 'yields' :
- a linkrod length suited to this configuration & geometry 
- a compensation angle on the MR pin circle. So instead of the LR pins being phased at the same 72 deg, they are staggered a bit, but still on the same diameter. If you simply do equal phasing (72 deg) you get different TDC's which requires an adjustment to either pistons or cylinders. 

This graphical method allows one to make make identical pistons, cylinders & LR's (which for me construction wise was preferred). But I seem to recall a necessary by-product is that you get slightly different BDC positions. If you fiddle with any other parameter, something else must give. Here is a screen cap of a similar project Ive been plunking away at. I will have to go back & refresh my memory as to the procedure. I wrote it down somewhere...

There is also a really good article by Carl Sorensen Jan-22-2008 called Kinematic Relations Between Master and Slave Cylinders in Radial Engines. I got it from the Yahoo R&R forum.


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## petertha (Sep 30, 2011)

petertha  said:
			
		

> There is also a really good article by Carl Sorensen Jan-22-2008 called Kinematic Relations Between Master and Slave Cylinders in Radial Engines. I got it from the Yahoo R&R forum.



Hopefully this upload works. Its a little math orientated, but it speaks to the interplay of variables. Once upon a time I wrote a spreadsheet that calculated this stuff. Anyway, the graphical method is easier  

View attachment master-slave.pdf


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## petertha (Sep 30, 2011)

I found some outputs from my spreadsheet that showed 2 glow engines I looked at:
- the Edwards 5 radial (at equal 72 deg LR position) 
- the JZ5 Kinner 5 (at compensated LR position) 
You can visually see the different CR on the radial graph. This difference was what I was trying to avoid. I think the Edwards had some sort of head shim compensation? (cant recall)

Originally with the spreadsheet I was diddling with the angles to get balanced CR. Then some nice person pointed me to the graphical solution. 

View attachment edwards kinemat.pdf


View attachment jz5 kinemat.pdf


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## petertha (Oct 1, 2011)

I took a crack at creating a step-by-step document. Give it a try & see if its delivering what its supposed to. If you spot any errors, I'll endeavour to fix them. 

View attachment MR layout equal TDC.pdf


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## stevehuckss396 (Oct 1, 2011)

I knew there was more to it. Thanks for taking the time to reply and dig up the info. I am working on another V8 and when completed, am considering a 5 or 9 cylinder radial.


Thanks again


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## 90LX_Notch (Oct 1, 2011)

petertha,

That deserves a Karma.

Bob


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## moconnor (Oct 1, 2011)

Hello Steve,

I think this topic was covered in some early issues of 'Strictly I.C.' magazine, maybe by Roderick Jenkins? I don't have quick access to them at the moment, so I can't check now. However, if you have the magazines and the indexes, it may be worth a look.

Regards,
Mike


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## stevehuckss396 (Oct 1, 2011)

moconnor  said:
			
		

> Hello Steve,
> 
> I think this topic was covered in some early issues of 'Strictly I.C.' magazine, maybe by Roderick Jenkins? I don't have quick access to them at the moment, so I can't check now. However, if you have the magazines and the indexes, it may be worth a look.
> 
> ...



Good to know! Thanks for the tip. I'll look right after i get done with the honey do list


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## GailInNM (Oct 1, 2011)

There are three articles listed under master rod design in this index for Strictly IC.
There may be others under other headings. 
Index is attached.
Gail in NM 

View attachment strictlyic_index.pdf


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## Lakc (Oct 1, 2011)

GailInNM  said:
			
		

> There are three articles listed under master rod design in this index for Strictly IC.
> There may be others under other headings.
> Index is attached.
> Gail in NM


I have the article from issue 28 in my collection, as I recall it was heavy on the math. 



			
				petertha  said:
			
		

> I think the Edwards had some sort of head shim compensation? (cant recall)


Yes, there is a note in the drawings stating to "trim cylinder height to obtain proper compression"


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## petertha (Oct 1, 2011)

stevehuckss396  said:
			
		

> ..when completed, am considering a 5 or 9 cylinder radial.


 Excellent news, I look forward to the build. Your constructions are very inspiring.


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## SKmetal7 (Oct 1, 2011)

Hey guys! I was the one who originally proposed the question at the CNCZONE, and Steve was kind enough to repost the question for me here.

Peter, that is exactly what I was looking for. Thanks thanks thanks!! I made a CAD drawing of the graphical solution. I need to keep playing with the numbers. I want to use a stroke length of about 1.000" with a piston diameter of .900"-.980". I can't have a large link rod diameter on the master rod due to a limit on the size of the crank case. I can't have a large crank case, since my lathe only has a 4" chuck, and the mill is about the same in the Y axis. 

I'm still messing around with all the dimensions, and it's still in it's eaaaaaarrrrlyyy stages of design, but this is what I'm trying to build. I'll start with 5 cylinders, and if I can hash that design out I'll try 10 cylinders.


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## petertha (Oct 1, 2011)

SKmetal7  said:
			
		

> I can't have a large link rod diameter on the master rod due to a limit on the size of the crank case. I can't have a large crank case, since my lathe only has a 4" chuck



Nice pics! Yes, seems like the unavoidable 'opposing design constraints' syndrome. 

From the bit of cad messing around I've done recently, the MR section is one issue for sure because its typically a fatter section relative to the LR's. But another thing to watch for is: as the crank throw become larger, you also see pretty dramatic LR angles that want to interfere with the crankcase ID in certain spots. Same goes for cylinder skirts that may require notching & similar fixes. It typically seems worse on the lower cylinders (#3,#4).. just the way the motion path works out. And yet cyl #1 where the fatter MR travels through may have lots of spare clearance & not indicate problems down below. 

The Kinner type engines, which seem to have larger proportionate strokes, are challenging in this way. Indeed the model builds I saw on the 1/4 scale & 1/5 scale engines showed the requirement to recess the case and/or notch the clinder skirts. It would be better to know this 'before-hand' IMO, vs the link rods unexpectantly go 'clank'. Makes me have a lot of respect for the pen & paper designers of the original engine vintage. I'm just getting up to speed on 3d cad modeling myself, but I was happy to at least simulate the interference issue. Now 'building' the thing is going to be a completely different matter! ???


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## stevehuckss396 (Oct 2, 2011)

SKmetal7  said:
			
		

> Hey guys! I was the one who originally proposed the question at the CNCZONE, and Steve was kind enough to repost the question for me here.




No problem SK. I was wondering the same thing myself. I was considering the Hodgson 9 cylinder for a future project and wanted to know how if i decide to alter the master rod.


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## MachineTom (Oct 2, 2011)

I do remember seeing my first radial engine apart, it was a 28 cylinder used in cargo planes at the local NG base where I lived. My auto shop teacher was a member, and they had just BLEW up an engine coming back from Greenland. It was as removed from the aircraft, with large holes where some cylinders used to be. the master rod was monsterous compared to the other rods, a bunch of parts spread accross tables. The spacing of the other connecting rods on the master hit me as odd, (I 16 years old) but, it wasn't until college that I knew why it was so. I think the pistons were about 7" and the stroke of 8".

The last part of the visit was there was a replacement engine bolted to a frame mounted on a large truck. driven to an area a distance from the hanger, tied down to the concrete and they started and ran the engine through a cycle of idle, mid, and full power, with a regular prop attached. Loudest think I ever heard run. Very cool it was.


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## SKmetal7 (Oct 2, 2011)

[ame]http://www.youtube.com/watch?v=BE6FhgO3u2Q[/ame]

A little more work, finally made an animation. Hopefully I won't change any more critical dimensions! Hammering out the cam, and gonna start designing the heads, valves, rockers, push rods, ect ect ect ect...........


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## Swede (Oct 4, 2011)

I compensated my master rod for this using the Strictly IC article. It was pretty straightforward math, but one thing to keep in mind... it is possible to create conflicts in the slave rods because they tend to become a bit more crowded near the 6 o'clock position, AND it is possible to have the slaves contact the cylinder skirts. 

In my case, it ended up working fine. I had to reduce the height of the cylinder skirts at the #4 and #5 cylinders, but it was only by maybe 0.005"

This picture shows it... note the spacing of the slave rod link holes on the master. They cluster a bit towards the 6 o'clock.


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## SKmetal7 (Oct 4, 2011)

[ame]http://www.youtube.com/watch?v=jY5ZzxdQXsY[/ame]
[ame]http://www.youtube.com/watch?v=-G0XYRx2O98[/ame]

Finally figured out the correct cam, and timing. It's really close, probably won't change it much. 3 lobes, rotating the same direction as the crank, at a 6:1 ratio. BDC isn't the same for all cylinders. Some will be on the way back up before the valve opens so they will probably 'pop' when the valve opens, I'm kind of concerned that this will cause unnecessary resistance, although not much; and I don't think there isn't really anything I can do about it.

What can I do about cylinder compression ratio? I'm thinking of making a spacer at the top of the cylinder under the head; but that will make it difficult to align the head with the crank case. Or maybe something between the cylinder and the crank case.

Learning a lot on how to use my CAD program, probably more in the past week than in the 6 years that I've had had it!


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