Author Topic: Big stroke 55 cc one cylinder ICE  (Read 8315 times)

Offline Brian Rupnow

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Re: Big stroke 55 cc one cylinder ICE
« Reply #60 on: October 10, 2019, 01:43:50 PM »
I admire your support tower for the camshaft and how the rockers act directly on the valves. Nice design, nice engine.---Brian

Offline AlexS

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Re: Big stroke 55 cc one cylinder ICE
« Reply #61 on: October 14, 2019, 06:46:00 PM »
Thanks guys!

First try with oil was 300 ml ish. But this gave too much splashing oil in the crankcase. Such that at higher revs a reasonable amount of oil came out of the crankcase ventilation hole (no pcv valve/hose for now).
Get some oil out so there the crankshaft barely touch the oil bath. And modified valve timing (lobe degree) to compensate the very very unusual opening time of the exhaust valve. I think this caused 'some' pressure in the carter, because old timing openend the exhaust after bodem dead center ;)

The base circle of the exhaust cam should be the same as the intake. But with milling the profile I had milled off too much. So this also result to more exhaust valve clearance than intake. But valve clearance was easy to modified, by make the hole bigger  mounting block of the exhaust rocker assembly. Next time exhaust should be the same base circle as intake (15 mm instead of 13.16 mm).

Recently I have written down all notes and adjustments of the latest tests. This also applies to the valve timings and clearances.

Timing first starts with old camshaft axis.

- Intake
Valve Clearance: 0.6 mm
Valve lift: 4.1 mm (4.7 mm - 0.6 valve clearance)

Opening: 28 BTDC
Closing: 8 BBDC
Duration: 200 deg

- Exhaust
Valve Clearance: 0.5 mm
Valve lift: 3.83 mm (4.33 mm - 0.5 valve clearance should be 3.7-0.2)

Opening: 28 ABDC
Closing: 19 ATDC
Duration: 171 deg

Valve overlay: 47 deg

Lobe separation angle: 128.5 deg





Second timing. Goal to run with current cams but trying to get some early opening timing of both valves.

- Intake
Valve Clearance: 0.2 mm (minimum)
Valve lift: 4.5 mm (4.7 mm - 0.2 valve clearance)

Opening: 1 ATDC
Closing: 34 ABDC
Duration: 213 deg

- Exhaust
Valve Clearance: 0.3 mm
Valve lift: 4.03 mm (4.33 mm - 0.3 valve clearance should be 3.7-0.2)

Opening: 13 BBDC
Closing: 2 ATDC
Duration 195 deg

Valve overlay: 1 deg

Lobe separation angle: 100 deg



For next timing I will try to make an adjustment of the lobe degree to get a duration (with valve clearance in mind) for both cams around 220 deg. And opening intake and closing exhaust around 10 deg. Should be 20 deg valve overlap enough for low-mid rpm performance?

Compression test old camshaft and without oil in crankcase: 5 bar. Latest camshaft 9.77 bar.


« Last Edit: October 15, 2019, 04:48:00 PM by AlexS »

Offline Admiral_dk

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Re: Big stroke 55 cc one cylinder ICE
« Reply #62 on: October 15, 2019, 11:48:11 AM »
First, nice runner  :cheers:

You are right about the conrod only skimming the top of the oil is more that enough - just look at bearing tables, where the max RPM is a lot higher in a oil mist condition compared to oil bath.

I would had said that your first valve clearance values were much too high, as all my four-stroke bike over the years has between 0.08 and 0.15mm. in cold condition. Clearance in this area depends partly on materials and partly on dimentions, geometry and temperature range.

I'm no expert on this subject, but I would expect that the ideal clearance results in somewhere around 0.001-0.01mm. at max working temperature.

Offline AlexS

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Re: Big stroke 55 cc one cylinder ICE
« Reply #63 on: October 15, 2019, 04:50:47 PM »
Thanks for input Admiral. I would check what a reasonable valve clearance would be for this engine, I see no big expansions but be sure that valves not openend duo to not 100% round base circle of cams.

Offline Art K

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Re: Big stroke 55 cc one cylinder ICE
« Reply #64 on: October 15, 2019, 06:50:22 PM »
Alex,
I'm on vacation and just caught up on your build. Good job getting your own design running. :ThumbsUp: I saw the earlier video with the free standing cam with unsupported ends and made a mental note. I would have supported both ends but it obviously works quite well now that the cam is supported. My experience with crankcase splash lube is that to much oil without proper crankcase ventilation causes it to come out EVERYWHERE. Very messy.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline AlexS

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Re: Big stroke 55 cc one cylinder ICE
« Reply #65 on: October 15, 2019, 07:51:27 PM »
Thanks Art, I agree with the messy part of to much oil. The engine did get lubricated on the inside, but also on the outside.

Offline Art K

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Re: Big stroke 55 cc one cylinder ICE
« Reply #66 on: October 16, 2019, 01:56:49 AM »
Alex
I can laugh with you on that one! :lolb:
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King