First 4 Stroke First V twin.

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c_mario

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Hi
Started building V Twin 4 Stroke 35CC Engine from Plans from Germany. This is the same model Ghosty has built.
Started with Crankcase In December Last year 2021.
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Built various pieces in an order I thought was appropriate for my skill level.


The next images in in a bit of a random order.

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These were my first attempts at bending stainless steal tube for the manifold and exhaust
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Then I built a Mandrel bender from photos I found on this site.
Bends much nicer now.
 
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c_mario

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Better Bends
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Cylinder head
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Completed model.
I haven't run it yet I didn't have a setup to run two glow plugs at once so have to work on that now.
The OS carb is from an Engine I purchased 40 years ago. That engine still runs, well it did when it had the carby.

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gbritnell

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Very nice work! Great looking engine!
 

c_mario

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Mario,
It sounds lean, also are you using plenty of oil(20%)
Cheers
Andrew
i was thinking about that. When I was attempting to start it for the first time , while it was cranking and not firing I quickly covered the carby intake with my finger for a second or less and it would fire. Started to make it richer bit by bit, so I will continue to do that . The fuel is purchased premixed and it does not specify the oil content.
 
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I run a MOT GUZZI V50 motorcycle. With twin carbs.Twin carbs are necessary, because the "dwell" between intake suck is different for each cylinder. SO, with twin carbs it tries to run as 2 singles... but then 2 follows closely behind 1, but 1 lags behind 2.... This means the idle running is lumpy, as the uneven dwell means 2 is running faster than 1 for the intake stroke. The only way to balance this is with vacuum gauges. 1 on each intake.
You can "cheat" by setting idle with it running as a single first cylinder 1 then cylinder 2. (Moto G manual says do this.. Ha! Ha!). But that isn't as accurate due to the dwell induced lumpiness when both cylinders are working.
But if your ears are the same, you can listen to the 2 exhausts - or fit exhaust pressure gauges, or microphones, to balance the noise levels at idle. From 1/4 throttle upwards, set carb slides at the identical height of lift.
If using CV carbs, you must set with vacuum gauges at idle, and butterflies at identical opening from 1/4 throttle to WOT.
Good game!
K2
 
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Excellent work making it and getting it to run! Thinking about the way it slowed as you disconnected one glow plug, then stopped when you disconnected the second plug, it does seem like there is insufficient Temperature in the engine to keep the glow plugs hot enough to trigger combustion. possibly the compression is too low? Is the a way you can make a fitting (1/4" ME thread?) to replace the glow plugs and put a pressure gauge onto the fitting to get a good impression of actual compression as it cranks - with wide-open-throttle? It may be a simple matter of valve clearances, (open the tappets by just a thou and see if that improves compression), or running -in of the rings, or something else? What is the compression supposed to be according to the design?
I'm not following the "Lean mixture" trail, as others are already on that one. Just thinking of "why?" the glow plugs don't stay hot enough for constant running. Incidentally, a higher real compression can run a leaner mixture effectively.
K2
 

c_mario

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Thanks Steamchick, I already had a fitting to connect a dial gauge to the glow plug hole to find top dead centre so I could do the valve timing.
however I would not have an idea of what a pressure gauge should read as good compression. The design does not say what the compression should be.
 
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Hi Mario. It was just a thought, based on the video, where it looked like the first glow plug disconnect caused it to appear to slow, then the second one caused it to stop.
Model aero engines have high compression if running "diesel" mode with 30% ether in the fuel.I guess this is over10:1 which would show over150psi on a gauge. but glow fuel runs at lower compression - the red hot platinum wire starts the combustion as the pressure gets over 5 bar (a Guess) or whatever, so compression is similar to spark ignition engines of 5 to 10:1. 75 ~150 psi on a gauge.
But these are my guesses. So you need a "proper guy" who knows these fuels and stuff to tell you the real answers. I have only dabbled with a bit of guesswork on one single cylinder engine 2.5cc.
When you find the "Proper Guy", do tell us where? My misses wants to get one to do all the jobs I don't do properly.
K2
 

gddecker

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Beautiful piece of work! Looking forward to seeing you getting it tuned a little better. Nice work!!
 

c_mario

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I adjusted the tappets and fiddled with the mixture and locked the throttle at half open.
In this video the engine runs after removing glow leads until I had to stop it as a mounting bolt was coming loose.
Some observations. It seemed as if it was running on one cylinder only since I could see smoke from the right exhaust but not the left.
I stopped it and was able to start it on the left cylinder only, after which i reconnected the right glow lead and the engine revs increased so both cylinders must have been firing.
Also there seems to be a lot of fuel being blasted out of the carburetor intake.
Any thoughts on smoke and fuel from intake?
 

minh-thanh

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Hi !
Make sure your engine runs with 2 cylinders.!!
Because it is possible that the intake valve of one cylinder is not airtight
If you are sure both cylinders are running, then check the timing of the intake cam
 
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Hi Mario, immediately, I remembered highly tuned camshafts on racing single cylinder motorcycles in the 1970s... The cams with "too much overlap for low revs" simply caused exhaust back pressure from the late closing exhaust valve to push gas out of the intake before the exhaust valve closed and the engine could suck-in the intake mixture. But these cams allowed higher revs - and power - for racing. On the road they soaked a trouser leg with fuel while riding through the city...
So I guess you have a late closing exhaust valve, due to cam timing? (Grinding of the cam lobes).
Modern cars alter cam timing (with independent intake and exhaust cams) so it is more suited to torque - and no intake blow-back - at below 3000rpm-ish - then fully set for higher revs over that speed. It helps both emissions, fuel consumption and drivable of your family bus...
For an aero- engine, I would live with it and put a large intake box on the air intake, to collect most of the blow-back and it will be taken in after the exhaust valve closes. At higher revs the cam should be well suited without blow-back problems.
Just my ideas though.
K2
 
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Hmmm. On smoke from one cylinder, on a single carb V-twin, with intake blow-back issues....? I don't know, but my hypothesis: left cylinder blows-back, then suck in some of that mixture, before the intake valve closes, Then the right cylinder blows-back, before sucking-in the mixture, including the residue from left cylinder blow-back, and the cycle continues. If the cylinder timing was at 180degrees, both cylinders would see the same conditions of blow-back and residue from the other cylinder's blow-back, so would have the same mixture. BUT a V-twin has an irregular timing of cylinders, and maybe the right cylinder gets a lot more of the blown-back fuel from the left cylinder than the other way around? That, compounded with the natural variation of carburation conditions (left-suck, dwell, right-suck, dwell, etc.) again due to the uneven timing of suck of fuel, (short dwell, long dwell, etc.) should give a different mixture in the 2 cylinders.
Draw a circle, representing cam rotation and valve timing, a look at which cylinder could get more blow-back fuel? This should match the real condition you are witnessing. Does it clean-up at higher revs when the blow-back dissapears?
Enjoy the study!
K2
 
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Mechanicboy

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It spits a mist of fuel mixture out of the carburetor = too high overlap or too late closing of intake valve in valve timing. You will probably need to make a new camshaft with the right timing.
 

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