# Merlin V12



## JRR

[ame]https://youtube.com/watch?v=_uyvY0tDU4M[/ame]


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## Herbiev

Nice build JRR. Where did you get the plans. How long did it take you to build it?


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## JRR

G'day Herbie
I bought all the castings and drawings from USA. I had it running 20 months later. Thanks for your nice comment.
I should have completed my address by adding Australia to it! 
    John


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## mayhugh1

JRR,
My hat is off to anyone who has finished one of these. Your twenty month build time is really impressive. Are you using a spark ignition or glow plug? Is your supercharger functional and building boost? - Terry


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## JRR

G' day Terry
I started building the oil pump first in March 2013 while waiting for the castings to arrive.It ran for the first time in November 2014. It is spark ignition and as for the supercharger it is turning at 30000 rpm but I cannot be sure if it is contributing any thing to the performance as I am not sure how to measure it, I suspect not much as it is too slow. I used the casting that was avaible for the crankshaft, that saved a bit of time.
I have to dismantle it soon to fix the water leaks from around the bottom of the sleeves and the last time I ran it , it passed a lot oil out from the exhaust pipes  
I've had much enjoyment in that time but I am not expecting as much I this next phase!
                    John


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## JRR

Terry I will try to down load some pictures


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## kvom

Guess that's how it runs down under.


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## mayhugh1

JRR
Do you suspect the double o-ring seal design isn't adequate or do you recall any problems during fabrication? I'm concerned about all the coolant passages between the head and the cylinder block. Have you had leaks up there as well? Any tips or things you would have done differently if you were starting over? Thanks, - Terry


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## mu38&Bg#

JRR said:


> .... as for the supercharger it is turning at 30000 rpm but I cannot be sure if it is contributing any thing to the performance as I am not sure how to measure it, I suspect not much as it is too slow.



What is the OD of the compressor wheel roughly?

Greg


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## JRR

Greg, the compressor wheel or impeller is 3" in diam. 
  John


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## JRR

mayhugh1 said:


> JRR
> Do you suspect the double o-ring seal design isn't adequate or do you recall any problems during fabrication? I'm concerned about all the coolant passages between the head and the cylinder block. Have you had leaks up there as well? Any tips or things you would have done differently if you were starting over? Thanks, - Terry
> The answer to your first question is yes.If you check the drawing ( 2161a) you will see that the size of the o ring 028 is to big in in section so I used some made from 1 mm cord glued ends. I suspect that they have come apart
> There appears to be no leaks from the heads.
> I changed gear ratio on the prop drive from 48T/21T to 40T/ 29T as the prop revs was much to slow.
> It's good to have someone to converse with on this project ,I suspect there are not many of us .    John


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## kvom

Curious as to why prop speed matters on a model not mounted on an aircraft.


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## mu38&Bg#

kvom said:


> Curious as to why prop speed matters on a model not mounted on an aircraft.



The slower the prop turns, the larger is has to be to absorb the power.

Greg


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## mu38&Bg#

A 76mm radial flow compressor spinning 30,000 RPM will develop very little pressure. Compressor maps of the KKK K27 76mm compressor suggest it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is 0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the compressor is very near the surge line for sure. The compressor might make ~0.1bar (1.5psi) of pressure.

Greg


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## rythmnbls

> A 76mm radial flow compressor spinning 30,000 RPM will develop very  little pressure. Compressor maps of the KKK K27 76mm compressor suggest  it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is  0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the  compressor is very near the surge line for sure. The compressor might  make ~0.1bar (1.5psi) of pressure.


Yep, and while making about 1.1 bar of pressure it will absorb approximately 1-2 hp. Not good for overall efficiency.

Steve.


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## JRR

kvom said:


> Curious as to why prop speed matters on a model not mounted on an aircraft.


To satisfy your curiousity I need air flow through the radiator. A 3 blade prop would be the way to go but I have no information as how to build one.
I made a copy of the one I made for my 18 cyl Hodgson which moves a lot of air at 3000 rpm. It's diameter and pitch is 32" x 16". With the original gearing this only give me 1315rpm @ 3000. With the 40T/ 29T teeth I can get 2175 rpm.
Can you advise me as to what would be a suitable  diameter and pitch for a 2 blade prop if I reinstall the original gearing?
      John.


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## JRR

dieselpilot said:


> A 76mm radial flow compressor spinning 30,000 RPM will develop very little pressure. Compressor maps of the KKK K27 76mm compressor suggest it has a pressure ratio of 1.1 at 30kRPM and it's surge limit is 0.02m^3/s. At 3600 RPM flow through the engine is <0.013m^3/s so the compressor is very near the surge line for sure. The compressor might make ~0.1bar (1.5psi) of pressure.
> 
> Greg


r
I never held out much hope that a supercharger would serve any use at this size, I think it's only there so we can say " yes it has a supercharger" but it was interesting to make.
     John


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## mu38&Bg#

Are those RPM figures wide open throttle? With the 32x16 prop at 2175RPM that's only ~830W(1.1HP). The website was suggesting 16HP.

Greg


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## mayhugh1

JRR,
Could you please tell me what you used for a carburetor? If I hadn't just completed the prop gear over the weekend I might have changed my reduction ratio. Do you think the overheating problem would be solved by a small electric fan blowing air through a small radiator tucked away under the engine? That's what I've been planning for mine when I get to that point. I think I read that some of the planes that used this engine had to have an auxiliary radiator (no fan) under the plane to control engine temperature during long idling times on the runway. - Terry


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## JRR

dieselpilot said:


> Are those RPM figures wide open throttle? With the 32x16 prop at 2175RPM that's only ~830W(1.1HP). The website was suggesting 16HP.
> 
> Greg


Yes , Wide open . How do you arrive at that figure? I'm out of my depth when it comes to the mathamatical part of this hobby.
    John


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## mu38&Bg#

There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.

Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?

Greg


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## mayhugh1

Greg,
Here is a link to a static thrust calculator that I used to sele t tbe prop for my 18 cylinder radial:

http://personal.osi.hu/fuzesisz/strc_eng/

Terry


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## JRR

dieselpilot said:


> There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.
> 
> Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?
> 
> Greg




The Venturi diameter  is .406". 
            John


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## JRR

dieselpilot said:


> There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.
> 
> Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?
> 
> Greg




The Venturi diameter  is .406". 
            John


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## JRR

dieselpilot said:


> There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.
> 
> Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?
> 
> Greg




The Venturi  diameter is .406"
     John


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## JRR

dieselpilot said:


> There is a formula to calculate propeller power. A google search for prop power calculator will turn up a few apps and calculations.
> 
> Thinking about the power the site quoted, 16HP isn't out of the question, but I expect much more than 800W from this engine, at least 8kW. What is the diameter of carb venturi?
> 
> Greg




The Venturi diameter is.406"


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## mayhugh1

Greg,
Are you using a commercial carb? If so, what have you tried?
Terry


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## mu38&Bg#

JRR said:


> The Venturi diameter is.406"



While that is at least half the required area to make full power it shouldn't be so restrictive as to limit power to what you're seeing. Of course, I haven't looked at this design closely and don't know what other factors may be limiting power output.

Greg


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## JRR

mayhugh1 said:


> JRR,
> Could you please tell me what you used for a carburetor? If I hadn't just completed the prop gear over the weekend I might have changed my reduction ratio. Do you think the overheating problem would be solved by a small electric fan blowing air through a small radiator tucked away under the engine? That's what I've been planning for mine when I get to that point. I think I read that some of the planes that used this engine had to have an auxiliary radiator (no fan) under the plane to control engine temperature during long idling times on the runway. - Terry




Terry
I removed the carby,witch was Jerry Howells 2 jet throttle from my 18 cyl and attached it to the inlet manifold and it ran.I then made an adaptor to fix it in correct place,but it didn't look correct.I wanted to use the castings (the one with the 2 vertical tubes) so I blocked up one and built the concept of Jerrys design in to it.If you like I could send a picture of the parts and what it looks like.
I expect there are many opportunities  here to improve things but not being an expert in carburation I don't know what they are.
I would have though an idling prop would provide more air than a small fan, but that's just my opinion .In my case I think I should move the radiators to the front which will mean a lot work.
John


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## mayhugh1

John,
Yes, I would be interested in any pictures you could provide of your carburetor set-up.
Air flow through a radiator can be disappointing at times. If, in your photo, the black box at the rear of the engine is the radiator there may not be much air actually flowing through it. If you place your hand behind the radiator with the engine running, do you feel feel much hot air coming through it? I've seen lots of model multicylinder engines with the engine's fan blade behind a front mounted radiator, but without a shroud I'll bet most of the air is being pulled from behind the radiator rather than through it. Jerry Howell's V-4 was the best example I've seen of doing it the right way using a shroud. If you have a way of measuring the coolant temperature it would be interesting and easy to put one of those larger size computer fans right up against the radiator to see if you can measure a temperature drop in the coolant. In a radial, the engine heads are pretty efficient radiators, and prop is right up aginst them, and so that system works pretty well. In enclosed engines like the Merlin, we get little benefit from the prop wash.
By the way, it sounds like you've built several engines. I sure many of us would like to see more pictures of your work, if possible. - Terry


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## mu38&Bg#

John, it looks like this is your engine? http://www.homemodelenginemachinist.com/showpost.php?p=261990&postcount=7

If the radiator is at the back like that, a few small brushless fans would make a big improvement. They are available in a large range of sizes and flow ratings.

Greg


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## JRR

mayhugh1 said:


> John,
> Yes, I would be interested in any pictures you could provide of your carburetor set-up.
> Air flow through a radiator can be disappointing at times. If, in your photo, the black box at the rear of the engine is the radiator there may not be much air actually flowing through it. If you place your hand behind the radiator with the engine running, do you feel feel much hot air coming through it? I've seen lots of model multicylinder engines with the engine's fan blade behind a front mounted radiator, but without a shroud I'll bet most of the air is being pulled from behind the radiator rather than through it. Jerry Howell's V-4 was the best example I've seen of doing it the right way using a shroud. If you have a way of measuring the coolant temperature it would be interesting and easy to put one of those larger size computer fans right up against the radiator to see if you can measure a temperature drop in the coolant. In a radial, the engine heads are pretty efficient radiators, and prop is right up aginst them, and so that system works pretty well. In enclosed engines like the Merlin, we get little benefit from the prop wash.
> By the way, it sounds like you've built several engines. I sure many of us would like to see more pictures of your work, if possible. - Terry




Terry
I've taken on boarded all what you say, it all makes a lot of sense . I had though of making some changes to the position of the radiators so I think I will have to remove it from the "to hard basket " and change things around.
I would love show you some picture of my engines ( I wouldn't have done so unless you had asked) .As you will see I am able to do that but when it comes to download pictures you might have to wait awhile !
John


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## JRR

dieselpilot said:


> John, it looks like this is your engine? http://www.homemodelenginemachinist.com/showpost.php?p=261990&postcount=7
> 
> If the radiator is at the back like that, a few small brushless fans would make a big improvement. They are available in a large range of sizes and flow ratings.
> 
> Greg



Greg 
Yes this my engine.It was posted by a friend of mine.I didn't know he had sent it until he introduced me to HMEM. I am very pleased he did.
John


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## ZAPJACK

Hi John,
i'm alsoo busy with the V12 Merlin.
But I don't see (or understand) witch the link between cranckshaft and supercharger gear.
LeZap


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## mayhugh1

Zapjack,
I'd love to follow your build if you're posting again.
Terry


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## JRR

mayhugh1 said:


> JRR,
> Could you please tell me what you used for a carburetor? If I hadn't just completed the prop gear over the weekend I might have changed my reduction ratio. Do you think the overheating problem would be solved by a small electric fan blowing air through a small radiator tucked away under the engine? That's what I've been planning for mine when I get to that point. I think I read that some of the planes that used this engine had to have an auxiliary radiator (no fan) under the plane to control engine temperature during long idling times on the runway. - Terry



Hi Terry
This was my solution to the carby on the Merlin and my alteration to the slip clutch.
I have put some pictures of my engines in photos.
  John


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## mayhugh1

John,
Thanks for the photos. They should be very helpful when I get to that point. 
I'm soon going to start on the cam, and so I'm beginning to plan for the valves and seats. The drawings show a 30 degree angle on the seat and a 45 degree angle on the valve. Did you seal your valves this way, and did you install separate seats or did you cut the seats directly in the head as the notes are encouraging? 
Over time I've developed a techinque for making and sealing valves that has worked well for me, but I'm not going to be able to apply it to these castings. This extreme angle mis-match may work fine, but I have no experience with it nor have seen it used before. Since I'll only get one chance to get it right with these castings, I'd appreciate an opinion from someone who has already been successfully through it. - Terry


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## JRR

Terry,
I put the valve seat directly into the head and I think I used the 30/45 angles,it makes a lot of sense when you think about it because it will give a very narrow seat. I have made a tool using a round India stone dressed with an angle of 45 bonded to a length of .125  drill rod about 2 inches long with spigot to fit the valve guide ,used between finger and thumb to put on a very small seat ,works for me !
I will be very interested to hear how you go with the camshafts. I found this to be the hardest part and made a few before I got a  pair ok 
John


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## gbritnell

Terry,
I have never heard of anything like you have mentioned on cutting and matching valves and seats. The common practice is to cut the valve and seat at 45 degrees. In full sized practice there is what's known as a 3 angle valve job. That is where the seat is cut at 45degrees and the angle above is cut at 60 degrees and below the seat is cut at 30 degrees. With this method the seat width can be adjusted. 
Naturally on small engines it would be really hard to do this but the method I have adopted over the years has worked quite well on my engines. The works whether you're machining into the head or machining valve seat inserts.
Make up a tool like I have attached. It is similar to full sized seat cutting where the cutter is aligned by the pilot. I make mine from drill rod and only use it by hand, no power. I lightly turn the tool until it knocks the corner off of the port. Once complete I lap lightly with some very fine grinding compound. 
gbritnell 

View attachment VALVE SEAT CUTTER INSTRUCTIONS.pdf


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## petertha

I've seen the 3-angle seat method referenced on Brian Perkins Hydra valve cages in Yahoo Groups R&R forum. Attached screen grab of Cad sketch (in Bristol Hydra folder, Files section). Possibly he describes this method somewhere in the posts, not sure though. Holy teeny-tiny angles. 

https://groups.yahoo.com/neo/groups/R_and_R_engines/files/Bristol Hydra/


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## JRR

Hi Terry 
I see that you are going to start on the camshafts . Might I suggest that you mill a hexagon on the end of each shaft ,it will make it easier to set the timing as you need to rotate the shaft before you lock up the screws on the sprockets. 
     John


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## mayhugh1

Great idea John. Thank you. 
I'm trying to decide whether to make the cams from single pieces of steel or to build them up. I was thinking about making 'spools' that would consist of an intake lobe and an exhaust lobe on either side of a bearing. Six spools would be needed for each camshaft and they would be bored to slip over a central rod and be Loctited. I'm still trying to figure a way to insure I get the phasing between the spools done quickly and accurately during assembly before the Loctite sets up which will happen almost immediately. I might be able to delay the curing by chilling the Loctite before use. The lobes on the spools would be easy to machine on the mill, but I would also introduce another thousandth or so run out in the bearings with the build-up. But the result might be better than trying to make them from single lengths of steel. What to you think? - By the way, it's OK to post your comments or recommendations  in my thread if you like. - Terry


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## JRR

mayhugh1 said:


> Great idea John. Thank you.
> I'm trying to decide whether to make the cams from single pieces of steel or to build them up. I was thinking about making 'spools' that would consist of an intake lobe and an exhaust lobe on either side of a bearing. Six spools would be needed for each camshaft and they would be bored to slip over a central rod and be Loctited. I'm still trying to figure a way to insure I get the phasing between the spools done quickly and accurately during assembly before the Loctite sets up which will happen almost immediately. I might be able to delay the curing by chilling the Loctite before use. The lobes on the spools would be easy to machine on the mill, but I would also introduce another thousandth or so run out in the bearings with the build-up. But the result might be better than trying to make them from single lengths of steel. What to you think? - By the way, it's OK to post your comments or recommendations  in my thread if you like. - Terry




Hi Terry 
I am pleased you liked the hex on the camshaft, you won't regret doing it . Just make it a little bit longer.
As for the camshafts, I think you should make them in one piece, although I can understand your reluctance to milling them on a conventional dividing head as the chances of a stuff up are very high. I have a dividing head on which I am able to index individual  degrees which makes it a lot safer. When you have all the degrees worked out for each and all the cams it was quite  straight forward. I did a test run first on some free cutting mild steel,when I was happy with that I carried on with drill rod and left  it soft as it has roller followers.
Silly question, how do I post to your threads?
John


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## JRR

mayhugh1 said:


> Great idea John. Thank you.
> I'm trying to decide whether to make the cams from single pieces of steel or to build them up. I was thinking about making 'spools' that would consist of an intake lobe and an exhaust lobe on either side of a bearing. Six spools would be needed for each camshaft and they would be bored to slip over a central rod and be Loctited. I'm still trying to figure a way to insure I get the phasing between the spools done quickly and accurately during assembly before the Loctite sets up which will happen almost immediately. I might be able to delay the curing by chilling the Loctite before use. The lobes on the spools would be easy to machine on the mill, but I would also introduce another thousandth or so run out in the bearings with the build-up. But the result might be better than trying to make them from single lengths of steel. What to you think? - By the way, it's OK to post your comments or recommendations  in my thread if you like. - Terry




Hi Terry 
I am pleased you liked the hex on the camshaft, you won't regret doing it . Just make it a little bit longer.
As for the camshafts, I think you should make them in one piece, although I can understand your reluctance to milling them on a conventional dividing head as the chances of a stuff up are very high. I have a dividing head on which I am able to index individual  degrees which makes it a lot safer. When you have all the degrees worked out for each and all the cams it was quite  straight forward. I did a test run first on some free cutting mild steel,when I was happy with that I carried on with drill rod and left  it soft as it has roller followers.
Silly question, how do I post to your threads?
John


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## mayhugh1

John,
Thanks for the reply. I'm still trying to make up my mind, but I highly value your input. I've just completed a successful cam blank turned from a single piece of steel, and so I feel more comfortable now. 
You can post in my thread in exactly the same way that you post in your own thread. The forum is set up so that you can post comments or questions in anyone's thread. Just use the reply button at the bottom of the last post in any thread that you want to comment on and then type in your comment just as you have been doing in your own thread. - Again, thanks - Terry


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## mayhugh1

John,
Can you tell me what you did for valve springs. I don't find anything in my documentation about them.

Best Regards,
Terry


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## JRR

Hi Terry  You are quite right I  have no details of the valve springs , so I wound mine up out of .035 dia wire with a pitch of .1 & a length .625, it worked for me.
That was a challenge  making the timing change cover ,even more so when you come to thread in the chain with a length of string!
You might like to consider fitting ball bearings to the magnetos as it will solve a lubrication problem an remove any load on the gears.
Kind regards John


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## mayhugh1

John,
Thanks once more for you insight and invaluable help. Don't be shy if you think of anything else. - Terry


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