Author Topic: 1909 Mercedes Aero Engine  (Read 45747 times)

Offline Old Bill

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Re: 1909 Mercedes Aero Engine
« Reply #105 on: January 28, 2019, 09:44:22 PM »
If you plan to start the engine with a drill or RC starter go to 140 (280 crankshaft) degrees with a 110 degree lobe seperation

Thanks for the advice Steve but I am afraid that I don't quite understand! The exhaust and inlet cams are 110° apart so that is fine but I am not sure about the 140°. Could you explain a bit more please? I plan to start it by swinging the prop so I will set the position of that so that the engine compresses as I push the prop down.

My biggest concern is the tip radius of the cam. Please may I have your thoughts on what it should be? I have never made one before and I just don't have a feel for what is right!

Many thanks,

Steve   :) 

Offline stevehuckss396

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Re: 1909 Mercedes Aero Engine
« Reply #106 on: January 28, 2019, 10:48:18 PM »
You may know a lot of this but i'm going to give you the full version.

140 degrees is the amount of rotation of the cam that the valve is open. All cam manufactures cite cam specs in crankshaft rotation so 140 cam degrees is equal to 280 crankshaft degrees. Cam rotates 1/2 the speed of the crankshaft. That is known as "duration". 280 degrees duration blah blah. The more duration the cam lobe has the wider the nose will be at a given base circle and flank radius.

So at 110 degrees separation, the more the 2 valves are open at the same time known as overlap. As the exhaust closes and the intake begins to open the exiting exhaust can cause a vacuum and help to fill the cylinder with fresh fuel in the higher rpm range. Problem with that is you don't begin to compress gas until both valves are closed so you lose compression. That can be compensated by running higher compression pistons. More overlap can make it harder to start an engine by hand. SO!

If you want a hit miss engine that you can start with a flip of the flywheel, reducing overlap is a good idea. To keep duration at a minimum you might have to go to a flat flank with a lifter that has a radius on the bottom of the lifter. That will allow you to keep some kind of nose radius. Flat flank isn't a big concern because the operating RPM is low and so are the forces on the cam and lifters.

If you want a V8 engine that is going to be started by a drill of RC starter then overlap wont hurt. More overlap will allow you to have larger nose radius and flank radius. You need that to reduce forces on the lifter and allow the cam to push the lifter open and closed nice and smooth. Flat flank in a high rpm engine is like opening the valves with a ping pong paddle slapping them open and dropping them closed.

Camshaft theory is one of those things that if you ask 10 people you get 10 different answers. This is what i live by and i have received many complements on how my engines sound but none of mine will start with a flip of the flywheel. If you have any specific questions about any part of this vague answer just ask.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Offline Old Bill

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Re: 1909 Mercedes Aero Engine
« Reply #107 on: January 29, 2019, 09:39:31 PM »
Thanks Steve. That is a perfect explanation!

So my 120° cams set at 110° have a 10° overlap. Looking at my drawing, this looks like it is fairly insignificant as the movement is tiny and will probably be absorbed by the tappet clearance. However, I do want to be able to start it by hand so I might be better increasing the flank radius to 12mm to give a 0.4mm nose radius. The followers are the mushroom type so I don't want the flanks to be flat as the opening will then be brutal rather than a smooth continuous movement.

Thanks Steve! That has made it very clear!

Steve    :)

Online Roger B

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Re: 1909 Mercedes Aero Engine
« Reply #108 on: February 01, 2019, 07:21:39 AM »
A radiused flank and a flat follower will also give a smooth opening. I played around a lot with the MEN programme to get a sensible nose radius and reasonable accelerations.
Best regards

Roger

Offline Old Bill

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Re: 1909 Mercedes Aero Engine
« Reply #109 on: February 01, 2019, 05:29:36 PM »
Very many thanks for your assistance, gentlemen.

Roger has given me a spreadsheet to calculate the cam height at any position and Steve has very kindly laid out various profiles for me. They have given me plenty of food for thought and been a great education. You have made all the difference!

Whilst thinking about the cam profiles, I have made up the tray for the bottom of the sump so that the big end dippers have a profile to follow. I started off by trying a piece of aluminium to get the length right.



Once that was confirmed, I cut my brass.



It is very thin so I could easily have curved it by hand but it just so happens that I made George Thomas's bending rolls some years ago so it was a good excuse to get them out and blow the dust off!



Some silver solder.



A night in the pickle.



I drilled a level hole and overflow hole as shown in the drawing and also screwed it into the bottom of the sump.



It all looks very nice but it is a slightly odd arrangement. The divider between the two halves of the crank case means that I could fill one end without filling the other. Also, there is no way of telling how much oil is in the engine. It needs a dipstick or level plug but I shall ponder that some more before I do anything about it.

Incidentally, can anyone tell me who invented the dipstick or when? It is one of those things we take for granted but someone must have done it! We have a collection of vehicles from the Great War era and none of them have a dipstick. They either have level cocks or floats which are much more effort to manufacture. I should be interested to hear your thoughts!

Camshaft tomorrow!

Steve   :) 


Online Vixen

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Re: 1909 Mercedes Aero Engine
« Reply #110 on: February 01, 2019, 05:35:51 PM »
Steve you have a PM

Mike
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Sometimes, it can be a long and winding road

Offline Old Bill

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Re: 1909 Mercedes Aero Engine
« Reply #111 on: February 02, 2019, 09:04:42 PM »
Well, I have finally decided how my camshaft should look and have spent today cutting cams. I set up with the dividing head and a steady made from a piece of plate.



I used Roger's Excel to generate the cutting tables and made sure that I had a large copy next to me whilst cutting!





It all went quite well in the end although there were 130 cuts per cam and eight cams so it did get a bit tedious. I don't think the mill has run for so long in many a year. The result is satisfactory but not perfect as the base circles vary a bit in diameter. I put this down to my steady not properly supporting the shaft so the next time I cut cams, I will make a proper one.



The question now is should I harden it and, if so, how should I do it so that it doesn't come out like a banana? I have a propane torch as a heat source and could use the domestic oven for tempering.

Many thanks for all of the help that has got me this far.   :ThumbsUp:

Steve    :D


Online Kim

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Re: 1909 Mercedes Aero Engine
« Reply #112 on: February 02, 2019, 09:14:13 PM »
Great looking cams!  130 cuts per cam?  That's 2.769o per cut which seems a bit odd?  Or did you do uneven rotations for some cuts?  Very nice results regardless.
Kim
« Last Edit: February 03, 2019, 05:48:51 AM by Kim »

Offline Old Bill

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Re: 1909 Mercedes Aero Engine
« Reply #113 on: February 02, 2019, 09:37:39 PM »
Yes! Ten further passes to get to the base diameter before incrementing in 3° steps!

Steve   :)

Online Vixen

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Re: 1909 Mercedes Aero Engine
« Reply #114 on: February 02, 2019, 11:03:34 PM »
Hello Steve,

That's what I call a good days work. Nice camshaft. :ThumbsUp: :ThumbsUp: :ThumbsUp:

Any blisters on your fingers from all that handwheel cranking?

What you now need is a nice little Emco F1 CNC mill. There is one going dirt cheep in Havant, Hampshire. Have a look in the Model engineer website classified adverts.

Cheers

Mike
It is the journey that matters, not the destination

Sometimes, it can be a long and winding road

Offline stevehuckss396

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Re: 1909 Mercedes Aero Engine
« Reply #115 on: February 03, 2019, 12:33:47 AM »
I make my camshafts out of O-1 drill rod and the lifters from 12L14. The lifters are the softer material and would wear before the camshaft. The camshafts are unhardened.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Online steamer

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Re: 1909 Mercedes Aero Engine
« Reply #116 on: February 03, 2019, 12:35:03 AM »
I make my camshafts out of O-1 drill rod and the lifters from 12L14. The lifters are the softer material and would wear before the camshaft. The camshafts are unhardened.

Is that working for you Steve?

Dave
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Damned ijjit!

Offline stevehuckss396

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Re: 1909 Mercedes Aero Engine
« Reply #117 on: February 03, 2019, 01:47:49 AM »
Peewee has been running sense 2010 with no trouble.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Online steamer

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Re: 1909 Mercedes Aero Engine
« Reply #118 on: February 03, 2019, 01:49:54 AM »
Awesome
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Damned ijjit!

Online Roger B

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Re: 1909 Mercedes Aero Engine
« Reply #119 on: February 03, 2019, 07:57:55 AM »
Excellent  :praise2:  :praise2: I always tick off each cut on the Excel table as I make it just in case I get disturbed/distracted.

I think it will be difficult to harden a cam of that length without a proper oven/furnace. If you are just going to run the engine from time to time to show people leave it as it is.
Best regards

Roger

 

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