One cylinder has web other doesn't

[DickyArt]

Hi Pedro (have we spoken through e-mail?)
I plan on matching all the ports.
I made some patterns to check the differences.




Only found out today my local suzi dealer can get +1.5mm Pistons and have ordered everything I need at good prices! I do get discount from them also. But thanks for the info and nice to know you can get parts if I'm stuck.
I like the TR cafe tank you do, so maybe after one in the next month or so (need to spread the spending!)
Cheers

[pedro]

If thats the pattern you are using to match the ports I would have a re-think as you have clearly removed the pattern and put it back into another barrel to do the individual ports, you have no datum reference point for the port timing.

Not wishing to be rude but if I were you I would leave the dremel in the box as obviously from the questions and the pattern shown you seem to have missed the concept of port timing, ie you are matching port size but clearly not position which is THE most critical part of a two stroke barrel.

[DickyArt]

No you're not rude! Just missed the fact that there are 2 patterns overlayed to see the differences using the back lit window These are "patterns" for comparison, so I could see how they differed.

I understand the timing issues and I also can see (both patterns have same datum points on respective bores) that the port widths, heights and positions laterally differ on some.

I've made and measured all sorts of things throughout my jobs as Tool Maker Fitter/Turner and Quality Inspector, using all kinds of equipment, so matching the ports won't be a problem. We used to use Microset http://www.microset.co.uk/media/background.html replication polymer for taking casts to measure using Optical Comparitors to tolerances of tens of microns, so a couple of thou is nowt to worry about

I take your point on timing of ports being important with 2 strokes though with them not having valves etc to regulate inlet and exhaust volume and speed.

[pedro]

Hi, nope I did not miss the overlay as anyone with half a eyeball can see it!

OK, you have measured many things, so could you explain to me how and where you have taken datums from? considering the ports on you pattern(s) are in completely the wrong positions

quote"I take your point on timing of ports being important with 2 strokes though with them not having valves etc to regulate inlet and exhaust volume and speed."

With the above comment from yourself I actually can't make my mind up if you are being facetious or as said before have missed the port timing concept, the evidence points to the latter.

[DickyArt]

I'm starting to think I've offended you some how!
What's facetious?

Timing?
Port duration in degrees of crankshaft rotation divided by the time the port is open in seconds, multiplied by the average port area.

Big ports pass a lot of mixture at high RPM, but may make less power at moderate revs. Raising ports to make them open longer will make them larger. Might make the engine become unusable. Ports can be made wider, to give increased flow due to increased area but NOT increase their duration. Increasing the time area - more flow/volume in the same amount of time due to an increase in the port width. A balance of time and area designed to give power and delivery for either normal everyday riding or top end power. That’s where experience tells! I understand but have little experience.

There are equations that I don’t profess on knowing or using! To compare against proven dimensions that are tabulated.

The patterns show that one cylinder has wider, shorter small transfer port. So the timing differs there. But the flow may be the same! The large transfer port on the earlier barrel sleeve is slightly smaller but has same timing/duration (same height position and dimension but 1mm each side narrower) so the flow will differ there. The inlet ports on the earlier barrel has longer duration (higher) with the same width.

I've read tuners widening exhaust port by 10mm raising by 2.5mm. Lowering inlet by 2.5mm, increasing width by 15mm!
http://www.ozebook.com/compendium/t5005.htm

I know ideally a matched set of barrels would be best but how much 1 mm in any direction would make I don’t know. Not sure the passages are similar size either.

4 strokes increase flow/mixture/exhaust by the camshaft (cam lobe size and profile give lift of the valve and duration of lift and speed/acceleration of valve opening and shutting) also valve size, profile and seat profile, passageways/ports size. Polishing port bores has very little effect. In fact smoothing them, then adding a few dents/bumps just below the valve heads to disrupt flow increases turbulence when entering the cylinder to improve burn. These valves obviously are in the cylinder head. These bores are port free.

Anyone would think we are talking rocket science here! It's a 2 stroke! I'm not starting from scratch, only altering ports by 1 mm or 2

[pedro]

No mate not offended, I just get fed up with people who come on forums asking for advice and then can't be arsed to listen to people who do it for a living.

you clearly have read a couple of books but your knowledge is limited (4 strokes aswell) your datums for the ports should have been taken from the top of the barrel and clearly were not from you patterns.

so I am not going to bother trying further, but as an aside to your you TIMING assesment is incorrect as a whole as you have mixed timing with mean port area and average port area, and large ports do not always flow more, two or four stroke.

cheers

[DickyArt]

sorry to have waisted your time



Obviously time for me to......

[DickyArt]

Not any more! Web gone. A little more to come out and clean up.
Next port matching after a bit of more accurate measurement!


Piston kits arrived with a few other bits!