Author Topic: 4stroke multi cyl timing  (Read 3998 times)

Offline Cessna182

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4stroke multi cyl timing
« on: May 23, 2015, 10:52:03 PM »
Hi I am currently building a  four stroke glow boxer type engine ( 4 cyl  ) , the drawings I got from a guy in Germany, however I don't understand his language, using google translator is worse than trying to understand German. My question is on timing, I will use a four cyl glow driver. Where would I set the valves on number one cyl to open and close, top dead center, before or after? I understand setting timing on a spark system, but with glow plugs they are hot all the time ??
Thanks for any help you an offer.
Terry
Regards Terry

Offline Allen Smithee

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Re: 4stroke multi cyl timing
« Reply #1 on: May 24, 2015, 01:29:58 AM »
The valve timing for spark and glow engines are the same - the glowplug only ignites the mixture when it's compressed. In fact a way of confirming the compression ratio is correct for a spark-ignition engine on a specific fuel is to replace the spark plugs with glowplugs (this is usually done at some point in the development of serious automotive and aero engines).

AS
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Offline Admiral_dk

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Re: 4stroke multi cyl timing
« Reply #2 on: May 24, 2015, 10:47:48 AM »
Glow plugs are self regulating so to speak. On a light load it doesn't get so warm and therefore first ignite the gas close to TDC. So when you increase the revs and the load when using a prop, the plug gets hotter and therefore ignites the gas sooner on the compression stroke => automatic timing.

For this to work, you need to have the compression ratio, fuel mix and glow plug to match each other - this is one of the reasons that there are different glow plug ratings from "cold" to "hot". I would guess that the constructor has recommended a plug and mix for this engine, so try this first.

Offline gbritnell

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Re: 4stroke multi cyl timing
« Reply #3 on: May 24, 2015, 11:58:35 AM »
As I understand your question you're asking where to set the valve timing. Is this correct? If so then it depends on the design of the camshaft.
A camshaft has opening and closing timing. These points don't necessarily have to be symmetrical to TDC or BDC so that could affect the cam timing. Let's say that the cam had equal timing on both intake and exhaust.
For example. Intake opens 15 degrees before TDC and closes 30 after BDC. Exhaust opens 30 before BDC and closes 15 after TDC. To set the cam timing you would put the piston at TDC with the exhaust and intake open and equal amount. This would be equal overlap. The problem comes when the cam doesn't have the equal numbers. The proper way to do it, knowing the valve events is with a degree wheel on the crank and a dial indicator on the valve stem. In automotive practice this would be at .050 lift but naturally for a small engine you can't use that number so you would just have to adjust it when the valve starts to open.
Camshaft design numbers can vary greatly depending on the needed power range of the particular engine, torque at low rpm's, power at high rpm's, port flow etc.
When I design a cam I usually have equal numbers relative to TDC that way it's easy to set the timing.
gbritnell
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Offline Admiral_dk

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Re: 4stroke multi cyl timing
« Reply #4 on: May 25, 2015, 06:16:40 PM »
Ah - sorry, I oversaw that you asked both about ignition and valve timing.

There are several of us here that can translate German to English for you. You can't print the original text here because of copyright, but you could arrange with one of us to PM the original text and get another PM back with the answers, if this is what you're asking for. I will gladly help you with that - I'm admittedly dyslexic, but spellcheckers are a great help for me, so I'm sure you get the gist of what I'm trying to say  ;)

A Lycoming or Continental for instance has a firing order of 1-4-2-3 (cylinder 1 & 3 on one side and 2 & 4 in the other side). I know they write it differently for those two brands, but if you look at the pattern repeating itself - it's the same.

Offline petertha

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Re: 4stroke multi cyl timing
« Reply #5 on: May 25, 2015, 07:26:19 PM »
Hi I am currently building a  four stroke glow boxer type engine ( 4 cyl  ) , the drawings I got from a guy in Germany - Terry

Hi Terry. By chance is the engine design from Jung Cad Modelltechnik?
Would love to see your build pics one day in any event.

Offline Cessna182

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Re: 4stroke multi cyl timing
« Reply #6 on: May 27, 2015, 10:32:10 PM »
Thank you for your replies and the offer of translating, so far I have been able to bumble along using only the drawings, but may have to ask for help further along. The plans came from WTEngines. 
Terry
Regards Terry

Offline fumopuc

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Re: 4stroke multi cyl timing
« Reply #7 on: May 28, 2015, 05:37:33 AM »
Hi Terry, I do not know if it will really help, but I have seen at Wolfgangs (Wolgang Tr÷scher, WTEngines) home page the following data for this engine.
Inlet opening time 282 degree CS
Outlet opening time 300 degree CS 
Valve overlapp 30 + 10 Grad degree CS
CS means crankshaft
Kind Regards
Achim

Offline Cessna182

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Re: 4stroke multi cyl timing
« Reply #8 on: May 28, 2015, 06:09:03 AM »
Thanks Achim, i missed that.
Regards Terry

Offline Cessna182

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Re: 4stroke multi cyl timing
« Reply #9 on: June 01, 2015, 11:32:30 PM »
Hi Petertha, here are a couple of pictures so far, they show the block with cam in, the crankshaft, con rods, pistons with rings and cylinders. I will start making the heads, valves etc. next. With a lot of help from Admiral dk translating the text from the plans I can finally get it into my head how to go about it, the help was very much appreciated.
Terry
Regards Terry

Offline Admiral_dk

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Re: 4stroke multi cyl timing
« Reply #10 on: June 03, 2015, 08:06:11 PM »
The parts done so far look great - glad to help, though I can't guarantee that all I wrote is as the designer intended ....

Offline petertha

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Re: 4stroke multi cyl timing
« Reply #11 on: June 03, 2015, 11:15:33 PM »
Hi Terry, I do not know if it will really help, but I have seen at Wolfgangs (Wolgang Tr÷scher, WTEngines) home page the following data for this engine.
Inlet opening time 282 degree CS
Outlet opening time 300 degree CS 
Valve overlapp 30 + 10 Grad degree CS
CS means crankshaft

I'm not an expert on this subject & that is certainly useful information. But I wonder if it fully defines how the cams are laid out (phased). I built a spreadsheet to compare model engines & here is an example using Enya-60 glow 4S. Red numbers are inputs from manufacturers spec sheet. The second fictional example is a modified with altered inlet open & close positions in terms of BTDC & ABDC. What I'm trying to illustrate is you can achieve same 'duration' values (260-deg in this example) yet the cams are phased in different timing positions. So there might be more information required in terms of constructing the cams & setting relative to TDC. As others have mentioned, I'm not quite sure if this is what you are asking, but thought I'd throw it out FWIW.

ps - nice parts Terry!

Offline Cessna182

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Re: 4stroke multi cyl timing
« Reply #12 on: June 05, 2015, 08:22:05 PM »
Thanks Petertha I am going to try and post picture of this cam drawings, each cam lobe operates two valves.
Terry
Regards Terry

Online Roger B

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Re: 4stroke multi cyl timing
« Reply #13 on: June 06, 2015, 04:41:10 PM »
As I read it the information given is the operating angle of each can lobe and the overlap at Top Dead Centre. The inlet valve will open 10░ before TDC and the exhaust valve will close 30░ after TDC.

The drawing does not show the cam lobes themselves, but I guess that they have a grub screw opposite the lobe. If the flats are machined on the camshaft as shown on the drawing this should set the correct angular relationship between the various cams, you will then have to set the camshaft driving gears when you assemble the engine to get the correct overlap at TDC.

I hope this helps, if not please ask. (I can also read the German if necessary).
Best regards

Roger

Offline petertha

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Re: 4stroke multi cyl timing
« Reply #14 on: June 06, 2015, 07:39:40 PM »
Hmm... going to take a guess... Judging by the relative angles between the cam positioning flats & the finished engine pic, the cam lobes might go:
1=exhaust, serves front 2 cylinders
2=inlet, serves front 2 cylinders
3=inlet, serves rear 2  cylinders
4=exhaust, serves rear 2  cylinders

- position 3-2 = 339 - 249 deg = 90deg camshaft = 180 deg crankshaft at 2:1 ratio
- position 1 - 4 = 90 - 0 = 90deg camshaft = 180 deg crankshaft at 2:1 ratio

Does this guess make sense to any other parts labelling (ex- what is identified as inlet or exhaust valves/pushrods etc). Actually maybe I have the cam bass-akwards & its front to rear vs rear to front? Which end is the gear/pully on?

The other consideration is cam direction. Ie turning same direction like pulley/belt or idler gear vs. counter-crankshaft direction like direct gear to gear. Anyway, I suspect with this info you will get closer to back figuring your Inlet/Exhaust duration timing if that's of interest. One thing I image is critical to set up is TDC & corresponding cam position on a specific cylinder head (say #1 as reference). Thereafter, I think everything is kind of locked & follows along in terms of remaining cylinders if you build according to plans. Hopefully there is some verbiage on that that helps shed some light.