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If you want to use O-rings This is how I used to measure the cylinder bore to see if it was ok with the O-ring OD I was using. It also gave me the groove diameter for the O-ring on the piston An amateur way ;).

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I use it regularly - But it has another problem: you have to have experience to know that the compression is good enough to make the engine run.

And it is not necessary for other engines, unless you are working with smaller sizes. No need for this engine, can do it with 2nd engine if you want - maybe...you will learn something ;) If the measurements are the same then : Great 👍👍👍👍 Which lapping method did you use ?

Hi Brian ! I intend to say more... But in conclusion: Read what everyone has suggested People are not trying to prove anything, just giving information and hope it will give you a different view on how to make a model engine and tune it... Everyone has their own way but the end result is a...

Maybe: The timing overlap of the lobe is too much so the fuel suction ability of the engine is not much, you change the Cab to make the engine easier to suck fuel only solves the tip of the problem - For example, with a compression ratio of 6-1, the timing overlap is too much --> engine only...

Just cover your finger on the suction port if you feel the suction "pulse" when the engine is running you will know the lobe timing is ok If there is none or just blowing out then check the lobe timing again *** That only ensures if your engine is airtight.

Hi All My next game: Gears 32DP - - helical gear

I was a little busy this morning. So, Hello again Don't worry about questions, all questions are welcome !!

Edit : changed image .

Here :

Hi @Danuzzo ! My experience: I would choose Ramon's method. Always start lapping from BDC -->TDC. Why: Ramon's method? Because when the lapping ring is expanded, it will "expand relatively evenly" in diameter and that is good for cylinder lapping. Why: Always start lapping from BDC -->TDC...

Maybe because they are not completely clean, a little oil... so the loctile glue does not work much. Personally I would not use that glue for that position, O-rings or make a copper ring (machined from sheet or cut a copper ), it only takes a little time instead of having to fix the spark plug...

Hi All Gears 35-70 DP40 or 35-70 module 0.635 or module 0.6 or 0.7 I don't know but it's pretty smooth :D

Great ! 👍👍👍 .

Hard to answer. It depends on the tool marks, big or small, deep or shallow ..on the surface Try with 600, if you find the abrasive process is too long then reduce to 400. If the process is ok for you then you start at 600

just a simple way to see if the cylinder surface needs lapping. @Jasonb has given a lot of information about lapping ( 👍 ), watch and practice As I read you are not using rings so you don't need a certain exact diameter , if 25mm diameter is not good then lapping to 25.05 or 25.08 .. and...

I've said it a few times...and I probably understand how you want to cast and also the plan of the engine you design - it's only for those who buy the big casting set Of course deciding what to do, how to do it, big or small.....that's each person's choice.... Good luck !!!

I quite agree. For me, a model engine needs to be relatively easy to move, I can take it anywhere, I can put it on shelves, cabinets, tables... I see quite a few engines from 1 to V12... they are quite small and I can lift it with just one arm A cylinder diameter of about 25 mm is fine (30 mm is...

Here is a picture I took at x4 magnification on my phone, 19.7mm diameter cylinder 60mm long with a 2x10 mm HSS tool bar With a "straight" cylinder you will see they are almost touching everywhere "Straight" : in quotes because I am not sure if they are 100% straight but good enough . If there...