ESE's works engine tuner

[ken seeber]

Where's Ken. Get him out of Bed.

Better get up I guess. Well, up already as we were casting this morning.

Side holes. For our anti rotation pins, we put the hole in prior to the ring groove. This does mean an interrupted cut, however there is a subtlety. After drilling the hole, we make a first pass cut, using a 0.9 mm diamond tipped tool, Interrupted, but seems to be no bother. Then we do a second cut, to finish off the seat, in our case for a 1.0 mm groove, we move the tool down on the Z axis and repeat, making it a 0.1 depth cut. Then instead of withdrawing the tool directly we come away in a 45 deg angle, by around 0.05 from the seat. This removes and possibility of having scrolling or a spiralled groove as the tool withdraws.

Have a squiz at http://www.strikeproducts.com.au/features.asp. Somewhere in this is a feature we did ages ago on how we make pistons. Quite a few changes since then though.

In reality, there are tons of ways to do the side holes, whether they be for anti-rotation pins or gas holes and I know of some that are done in a separate operation after the groove and skirt are done. Clearly though, one needs very rigid tools and/or guide bushes to prevent deflection if cutting down the side of a groove.

We also don't cut the groove into the piston side in a square fashion. When one considers the running temperature gradient, there might be a 200 deg temp difference between the skirt and ring groove area. So, when a cold piston heats up, presumably to a nominal parallel and round shape, from a cold machined "tapered" and cam shape, a square cut groove has a tendency to be angled or coned downwards, albeit by a very, very tiny amount. So, we cut the groove in on a very, very slight angle. We called it RLTC, Ring Land Tilt Compensation. Wouldn't know if it makes any difference, but it is very simple on an NC to programme it in.

Kevin Cameron. My scribe heroes were the man KC, Gordon Jennings (early Cycle World) and Vic Willoughby in the UK "Motor Cycle Weekly". This used to have absolutely beautiful engine cutaways drawings, well before 3D CAD was even thought of. This dates me.

[peewee]

hey guys heres my first ever attempt at using a tig welder on alloy. its pretty ugly but after 30min i was doing alittle better. ill get alot more practice over the weekend . will probly order a pyrex setup as that should allow me to see whats going on alittle better. any of you welders have some pointers ? i been watching alot of youtube videos so i can get headed in the right direction

[TZ350]

https://www.youtube.com/watch?t=22&v=Vaa96_WVdEE
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Mt Wellington from the air.

[ken seeber]

It's just so green. Do you guys have rain over there?

[seattle smitty]

I havnt asked Wossner about the machining process, but I would imagine that the 1/2 moons are machined after the groove is done, as trying to keep the
groove surface finish high when bouncing thru radial drilled holes would be nigh on impossible.

Yeah, which would indicate they make the half-hole with a little endmill; I was wondering how they might sequence the machining so as to leave the smallest amount of burring to deal with.

[F5 Dave]

Wow who owns the drone?

[twotempi]

It's just so green. Do you guys have rain over there?

Yes - Don't you ????

Oh sorry - hadn't noticed that you were from Perth !!

[speedpro]

Wow who owns the drone?

For a day there bucket racing at Mt Wgtn was pretty flash. Apart from the usual real time lap scoring and lap times available via WiFi in the pits we had overhead coverage via drone mounted camera.

[AndreasL]

Rule of thumb ex-port size maxed out thoughts.

Lets assume a single ex-port taken as wide as can be done between the thight studs and still not up to the "% of bore" you like to have.
Crappy old 2 port transfers with way to high duration for the intended use.
Maybe we can get a reed and old style boost in there as wobbly already suggested.

Still, not enough blowdown STA to match up to the rest of the engine. Transfer duration…

Lets, for the sake of the argument, say that no welding/adding of material is doable to put things straight. Shiming the bottom of the barrel will not work either due to perfect match of piston timing edge and lower edge of transfer port.

To the point.
With the ex-port/header area at approx 90% of the effective port already, would it still be advasible to rise the duration to gain blowdown STA even if this gives a "higher ex duration then desirable"? (I'm aware this is the single most important number to make power so…) I guess it is but at the cost of a narrower power band. Or maybe the impact may not be that big even if aiming at the same rpm as for the lower duration concept.

Better run some EngMod sims but think I have answered my self already.
The question about the theory behind it all still interests me though.
It worked at the RSA, but that was a racebike. Mines not.

[AndreasL]

Thanks Frits!

Played around with your guidelines on ex-ports in my CAD model. It certainly makes sense.

Hear what you say about the 70% and stud spacing. My biggest problem in reality is a to thin ex-port wall. For this one I was thinking to do the most of it without any welding etc.
Managed to up the % a fair bit after analyzing the casting more carefully and following your guidelines.

Yes, I really hope my engines follow the same rules of physics as the RSA.
My concern for adding to much duration is to end up in a useless rpm range. Your Power Range feature will be a great help hear I think. Finding the best compromise will get us a winner.

Really appreciate the point of increased blowdown (may) reduce the transfer blowback and what that does to temps. Very helpful.

[wobbly]

The max Ex port width is dependent upon the bore size as well. when dealing with small pistons like 50cc or similar.
You can safely go out to 75% as the bore to supported ring section ratio is skewed in the small pistons favor.
This is a proven safe width in many small engines, but at the end of the day you will be limited by the worst STA number.
If this is the transfer ports, then over spec'ing the blowdown will simply make the thing peaky and hard to tune.
The actual Ex STA is pretty much irrelevant, except to match its effective area to the outlet size.

[lodgernz]

The max Ex port width is dependent upon the bore size as well. when dealing with small pistons like 50cc or similar.
You can safely go out to 75% as the bore to supported ring section ratio is skewed in the small pistons favor.
This is a proven safe width in many small engines, but at the end of the day you will be limited by the worst STA number.

True. The Honda NSR50 engine as standard has a single port whose width is 77% of the 39mm bore, and they can be and are thrashed mercilously with total reliability

[Frits Overmars]

OK, let's assume the studs are in a square, so close to each other that they are almost touching the bore. Even then you could fit in a 70% wide exhaust port, which is the optimum width anyway. That single exhaust port may not give you sufficient blowdown angle.area, but widening it will not help either because wider ports require bigger corner radii to keep the piston ring happy, and those bigger corner radii would eat into the upper part of the port area, where it counts.

I never said 70% is the maximum width. Metal permitting you can make it much wider than 70%; it just won't do the blowdown angle.area much good.

[peewee]

i practiced on some junk cylinders i had. alittle more practice and i should be ready to weld on the good cylinders

[F5 Dave]

For a day there bucket racing at Mt Wgtn was pretty flash. Apart from the usual real time lap scoring and lap times available via WiFi in the pits we had overhead coverage via drone mounted camera.

Actually there was a drone camera chap at Kaitoki yesterday, had a quick look at it, pretty cool.