Author Topic: Help me finding the timing!!  (Read 1176 times)

Offline glorfindel

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Help me finding the timing!!
« on: January 15, 2021, 05:21:40 PM »
Hi guys, i'm working on a 120cc flat 4 engine from Modelltechnik Jung plan.

Maybe it's a brain fart, but i cant figure out the timing from the plan.

I drew the cam, so it give me about 135 deg cam duration, The cams are 114° apart, about 42° overlapp.

From that drawing, what's the timing of the intake before TDC???

I dont mind putting my own cam design and timing, but i want to know what the designer did.

Thx.



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Offline Roger B

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Re: Help me finding the timing!!
« Reply #1 on: January 15, 2021, 05:29:58 PM »
To my simple thinking if the cams are symmetrical with 42° of overlap the inlet cam should start to open 21° BTDC. This is complicated by valve clearances  :headscratch:  If I was building the engine I would set the cam so that inlet and exhaust were equally open at TDC with the same valve clearances.
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Offline Admiral_dk

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Re: Help me finding the timing!!
« Reply #2 on: January 15, 2021, 08:15:50 PM »
I don't quite get it - should be simple to only use two lobes / cams per two opposing cylinders.
As the two are 180 degrees apart -> the two cylinders are firing 360 degrees apart ....

OK in a four this gives a firing order of 1 3 2 4 or 1 4 2 3 and it can be debated if this is the optimum for vibrations - old Beetles where 1 4 3 2 and they ran nicely.

So perhaps that is the reason why .... my idea works a lot better with a flat twin (BMW) or six (Porche) ....

Offline Admiral_dk

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Re: Help me finding the timing!!
« Reply #3 on: January 16, 2021, 11:50:53 AM »
I had a lot better look just now - with a pencil and paper - and it really makes no sense ....

I assume (hopefully not Ass-U-Me) that it follows the Classic Beetle layout, with the inlets in the centre off the head and an exhaust at each end of it. In that case it's a Big Bang engine, where cylinder 1 and 4 fires simultaneously and likewise cylinder 2 and 3 ....  :headscratch:

To me it looks like the camshaft 'needs to be cut in the middle' and the having the one half turned 180 degrees and put back together ....

Online cnr6400

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Re: Help me finding the timing!!
« Reply #4 on: January 16, 2021, 01:43:19 PM »
Just FYI, in most inline 4 cyl engines I have owned and worked on, many different makes and models, made in several countries, firing order is 1342 not 1324. There may be engines that use 1324 but I have not come across one as yet.  :cheers:

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #5 on: January 16, 2021, 04:11:27 PM »
I had a lot better look just now - with a pencil and paper - and it really makes no sense ....

I assume (hopefully not Ass-U-Me) that it follows the Classic Beetle layout, with the inlets in the centre off the head and an exhaust at each end of it. In that case it's a Big Bang engine, where cylinder 1 and 4 fires simultaneously and likewise cylinder 2 and 3 ....  :headscratch:

To me it looks like the camshaft 'needs to be cut in the middle' and the having the one half turned 180 degrees and put back together ....
There is a couple of videos on youtube of that engine running.

I emailed him...Still waiting for a reply...

It would have been so much easier if he had put a simple timing diagram....

Or i'll put the same cam desing/timing i got on my Nemmett based engine...

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Offline petertha

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Re: Help me finding the timing!!
« Reply #6 on: January 16, 2021, 05:29:08 PM »
Coincidentally I just got delivery of the same plans. I'll wait to hear of any communication response you can pass along.When I've emailed him a few times in the past, seems like eventually he does get to them.

Is it more the cam phasing you are wondering about or the individual timing parameters? I built myself a spreadsheet so I could digest this information (pertains to a glow radial) but eventually I could/will evaluate for this engine. I suspect, but don't know for sure, he sticks to similar recipe among his various engines.

Offline Admiral_dk

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Re: Help me finding the timing!!
« Reply #7 on: January 16, 2021, 06:25:25 PM »
A Flat Four is not the same as a Straight Four ...!

I agree on the firing order on a straight four - but the original question was for a flat four ....
This time I actually searched the page and found this :
https://www.cad-modelltechnik-jung.de/construction-plans-model-engines.html

One of the last drawings show the powertrain on this unik engine -> throwing ALL my assumptions down the drain  :-[
Not only are the inlet and exhaust positions not where I thought on the rear two cylinders - but the crank throws are with a single 'pin / big end' -> making the pistons go the same way - instead of opposite directions ....

I have never seen a full size engine with this layout - but it simplifies the build + make it more compact.

I conclude that the camshaft is shown (in the drawing) with the pistons at either TDC or BDC. I will look at the last post before this to (hopefully) verify.

Offline CHP

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Re: Help me finding the timing!!
« Reply #8 on: January 16, 2021, 08:58:45 PM »
Just FYI, in most inline 4 cyl engines I have owned and worked on, many different makes and models, made in several countries, firing order is 1342 not 1324. There may be engines that use 1324 but I have not come across one as yet.  :cheers:
1342 CW engine 1432 CCW engine
« Last Edit: January 16, 2021, 09:42:42 PM by CHP »
12x36 lathe,Seig7x10 lathe, Taig lathe
9x29 Mill, Emco 55 CNC mill.......

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #9 on: January 17, 2021, 04:29:50 PM »
A Flat Four is not the same as a Straight Four ...!

I agree on the firing order on a straight four - but the original question was for a flat four ....
This time I actually searched the page and found this :
https://www.cad-modelltechnik-jung.de/construction-plans-model-engines.html

One of the last drawings show the powertrain on this unik engine -> throwing ALL my assumptions down the drain  :-[
Not only are the inlet and exhaust positions not where I thought on the rear two cylinders - but the crank throws are with a single 'pin / big end' -> making the pistons go the same way - instead of opposite directions ....

I have never seen a full size engine with this layout - but it simplifies the build + make it more compact.

I conclude that the camshaft is shown (in the drawing) with the pistons at either TDC or BDC. I will look at the last post before this to (hopefully) verify.
Yes  it's a flat, v 180 engine, not a boxer engine.

Ferrari (flat 12)  and Porshe (flat 12) used that config.

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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #10 on: January 17, 2021, 05:18:48 PM »
3d model in progress. I'm doing it i  inchs so the 35mm (1.378) bore is now 1.375 "

All screws will be imperial, cam shaft is drill rod 6mm.

So far, i redesigned the back plate, not sure about the pushrod system, i like how i did my Edwards radial pushrods system, i'll probably copy that.



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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #11 on: January 17, 2021, 05:21:28 PM »
Coincidentally I just got delivery of the same plans. I'll wait to hear of any communication response you can pass along.When I've emailed him a few times in the past, seems like eventually he does get to them.

Is it more the cam phasing you are wondering about or the individual timing parameters? I built myself a spreadsheet so I could digest this information (pertains to a glow radial) but eventually I could/will evaluate for this engine. I suspect, but don't know for sure, he sticks to similar recipe among his various engines.
Same engine? Nice!!

I'll keep posting updates here.

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Offline petertha

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Re: Help me finding the timing!!
« Reply #12 on: January 17, 2021, 05:35:32 PM »
I'll be watching along glorfindel. I'm just starting the same cad exercise myself.... and not trying to get too distracted from my radial build.

- what is your rationale for changing the bore slightly from nominal metric to nominal imperial units by the little amount? Aren't the rings going to be sized based on resultant bore whatever it is (Trimble method), or do you have some other method in mind?

- what features of the Edwards pushrod system are different or better than this design in your opinion?

- not sure if you saw my inquiry post here on the forum about the Hirth coupling, but just wondering if you plan to adopt that feature on the crankshaft or have something else in mind.

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #13 on: January 17, 2021, 05:54:20 PM »


I'll be watching along glorfindel. I'm just starting the same cad exercise myself.... and not trying to get too distracted from my radial build.

- what is your rationale for changing the bore slightly from nominal metric to nominal imperial units by the little amount? Aren't the rings going to be sized based on resultant bore whatever it is (Trimble method), or do you have some other method in mind?

- what features of the Edwards pushrod system are different or better than this design in your opinion?

- not sure if you saw my inquiry post here on the forum about the Hirth coupling, but just wondering if you plan to adopt that feature on the crankshaft or have something else in mind.

I already have a 1-3/8 reamer ;-). I dont like how he make the rings. He seems to make an over sized ring... I will use my own piston design, with 2  0.050" square rings, and my own conrod design with bronzeBushing instead of a needle bearing.

I'm not fixed on the pushrod system yet...I will work on it today and post some updates.



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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #14 on: January 17, 2021, 05:59:46 PM »
I still.dont know what i will do with the crank too.


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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #15 on: January 17, 2021, 06:18:25 PM »


I'll be watching along glorfindel. I'm just starting the same cad exercise myself.... and not trying to get too distracted from my radial build.

- what is your rationale for changing the bore slightly from nominal metric to nominal imperial units by the little amount? Aren't the rings going to be sized based on resultant bore whatever it is (Trimble method), or do you have some other method in mind?

- what features of the Edwards pushrod system are different or better than this design in your opinion?

- not sure if you saw my inquiry post here on the forum about the Hirth coupling, but just wondering if you plan to adopt that feature on the crankshaft or have something else in mind.

I already have a 1-3/8 reamer ;-). I dont like how he make the rings. He seems to make an over sized ring... I will use my own piston design, with 2  0.050" square rings, and my own conrod design with bronzeBushing instead of a needle bearing.

I'm not fixed on the pushrod system yet...I will work on it today and post some updates.



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I did a search on Hirth coupling, but i ddint see your post. can you link me to it

Offline petertha

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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #17 on: January 17, 2021, 08:17:21 PM »
Is there a reason to not put the pushrods straight???

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Offline Charles Lamont

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Re: Help me finding the timing!!
« Reply #18 on: January 18, 2021, 09:20:31 AM »
I can't see any need for the push-rods to be angled. As far as I can see, the cam box could be altered so that the cams could be spaced to allow the push-rods to be square. On the other hand angled rods are not uncommon and that slight angle is not likely to be a problem, except that it will eventually cause the tappet holes to wear oval.

I don't like the skinny little tappets either. Are they supposed to have a slightly domed end, or are they flat?

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #19 on: January 18, 2021, 06:41:20 PM »
I can't see any need for the push-rods to be angled. As far as I can see, the cam box could be altered so that the cams could be spaced to allow the push-rods to be square. On the other hand angled rods are not uncommon and that slight angle is not likely to be a problem, except that it will eventually cause the tappet holes to wear oval.

I don't like the skinny little tappets either. Are they supposed to have a slightly domed end, or are they flat?
There is a radius. Pushrods are small too (2mm), but it should be ok, they will be made from drill rod.

Here i am so far. I got some minors interferences, but i'll sort it out soon.



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Offline petertha

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Re: Help me finding the timing!!
« Reply #20 on: January 19, 2021, 02:01:30 AM »
I haven't modeled it as far as you but I tend to agree, why not align the pushrods straight & adjust the cam lobe spacing accordingly. There appears to be room to extend the cam box housing & end bearings fore & aft to accommodate. I was also wondering to myself if maybe the rockers might be sitting at in a bit different position along the axle, but the general assembly shows as you have it - right adjacent to the upright supports. Sometimes things become more apparent as you get deeper into the design. And sometimes they don't haha.

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #21 on: January 19, 2021, 11:57:24 AM »
I haven't modeled it as far as you but I tend to agree, why not align the pushrods straight & adjust the cam lobe spacing accordingly. There appears to be room to extend the cam box housing & end bearings fore & aft to accommodate. I was also wondering to myself if maybe the rockers might be sitting at in a bit different position along the axle, but the general assembly shows as you have it - right adjacent to the upright supports. Sometimes things become more apparent as you get deeper into the design. And sometimes they don't haha.
The design is a little more compact with angled rods.

I still dont know what to do with the coupling.... I can use a graving tool to do the hirth coupling.

Do you have some pics of the "Schiling" way to do it ???

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Offline glorfindel

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Re: Help me finding the timing!!
« Reply #22 on: January 19, 2021, 02:56:28 PM »
Did some test with 60 deg graving tool and the link you provided for hirth calculation.

Looks good.

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Offline petertha

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Re: Help me finding the timing!!
« Reply #23 on: January 19, 2021, 07:48:21 PM »
I still dont know what to do with the coupling.... I can use a graving tool to do the hirth coupling.
Do you have some pics of the "Schiling" way to do it ???

go to post reply #14, there is a link to PDFs
https://www.modelenginemaker.com/index.php/topic,10107.0.html

His methods seem to vary by engine design, but from what I can see, various combinations of crank pin & axial retention bolt. Mike (Vixen) made a good point in the Hirth discussion that just joining the crank ends may not be sufficient. If I understood correctly, potentially the crankshaft assembly would be joined up but joint journals left oversize to be finish OD ground as a mated pair? Here I'm on uncharted waters. In some cases the pin OD surface is a sliding fit against say a bronze bushing of a connecting rod. In other cases they would be a presumably tighter fit to the ID of a hardened bearing inner race. Ohrndorf has (an even longer) V12 with built-up crankshaft, I'm going to look at that in more detail now. I think part of the design success depends on layout, spacing & accuracy of supporting bearings to minimize CS flex in any direction, but its just a hunch.
« Last Edit: January 19, 2021, 07:55:36 PM by petertha »

Offline petertha

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Re: Help me finding the timing!!
« Reply #24 on: January 26, 2021, 03:57:44 AM »
Re crank joining, there are 2 more references to ponder

A Bugatti on this forum (journal press fit into hole if I understand)
https://www.modelenginemaker.com/index.php/topic,6848.45.html

And coincidentally another Bugatti on the other forum (4 index pins & face to face joint if I understand)
https://www.homemodelenginemachinist.com/threads/bugatti-straight-8-cylinder-with-blower-design-3d-printed-molds-castings-machining-assembly.32045/page-3

The assembly & post finishing seems to be where the magic happens.

I'm sure I've seen more examples, I just never thought to bookmark them.

Offline glorfindel

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Re: Help me finding the timing!!
« Reply #25 on: February 23, 2021, 02:14:43 PM »
Coupling stuff was annoying me, so i did a flat twin lol!!!

I'll start fabricate it in 2 weeks!!!



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