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Big stroke 55 cc one cylinder ICE

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Niels Abildgaard:

--- Quote from: AlexS on March 27, 2025, 09:27:41 pm ---

After that connecting rod Titanium.



--- End quote ---

Titanium is NOT a good bearing material.

AlexS:
Agree Niels. Bearing material of both small and big end bearing would be (sintered) bronze. 1,5-2 mm thickness.

Added the photo's to previous post

Measured the clearance of piston and cylinder.

Piston skirt/cylinder wall clearance

Top 0,15 mm
Bottom 0,20mm

Piston ring slot width

Top 0,9 mm
Bottom 0,95 mm

Cylinder seems less taper. But ideal clearance between piston and cylinder would be around 0,05 mm with 0,5 mm piston ring slot width.

I am considering if I want to make a new cylinder, have already cast iron laying around.

Yesterday applied the given dimensions of the rings to the new piston. First manually shaped and reduced weight of the piston.

AlexS:
Valve guides overhaul

Maybe spring gives good mood!

Yesterday evening started with actual machining of the big overhaul of this engine.

Removed the valves. Also inlet shows residue of combustion. But it is a long time ago when I removed these valves and running quit a bit of time with current valve timing.

I think when the valve guides are ready, I would try to harden the valve seats (material is Silversteel also for the valves).

Well, I postioned the head in the vice and use a center to try to position to minimalize the concentric error with the valve seats.

Cut both 9,5mm drill and 10H7 reamer so it fitted in my mill.

Great after a long while to actually machining in the shop!

Next time machining new valve guides. Looked online, a press fit of t6 0,05-0,04 would be used for these bushes in aluminium cylinder head. Would use a propane burner to head the cylinder head before pressing in the valve guides.

Video of current valve / guide play of exhaust valve:

http://www.youtube.com/watch?v=O1wGC6mwSiw

AlexS:
3D printed X Turbolence Piston

Work in progress. Manually weight reduction. Previous 55 grams now 47.

First picture, red arrow, piston diameter 38,5mm according GY6 current piston.

Modified to dimensions of rings of GY6 piston.


Added cooling loop channel above top piston ring.

Added multiple channels exhaust valve squish zone.

Both channels 1mm diameter, smallest printable is 0.4, largest without supports 4mm.


Looked to thicken crankcase top plate from 3 to 6 mm. To able to use current connecting rod. It is possible. Only need a 560 instead of 550 timing belt.

But current connecting rod need more space around small end in piston. Because required wall thickness combustion chamber in piston crown!

AlexS:
Valve Guide Upgrade

Tonight machined one valve guide.
Quit easy to do on sintered bronze material. Reamed to 5H7. Valve stem shaft is 5h7.

Already have find a couple of small thickness (2.7mm) m5 nuts to fix the valve spring and retainer part to the valve. Normal pitch thread 0,8mm, 0,5 fine thread nuts expansive 4 euro each and need for a corresponding cut tool (already have a fine m5 tap by the batch tools I got from an old machinist).

Piston and Connecting Rod modification

No further engineering or modeling so far. Looked online for option to use a 10mm piston pin of puch or Peugeot instead of Honda's GY6 13mm.
Have already reamer for 10mm. Need to calculate to validate. Also smaller piston pen result in options to stoffen or reduce weight piston it self.

I am Thinking of using a guiding en pin in the piston pin that slide to cylinder wall. Rather than milling clips grooves. Option is to use PTFE als material or bronze.

More later!

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