Chris' Bucket photo thread - Bandwidth warning

[chrisc]

Go back one post to see the first post from this weekend

Glen O



Rick catching Henk out whilst he fiddled with something on the sled



Kel's new rocket. He was having a few issues with the bike on Saturday but when I was following him through the sweeper he really blasted off, it's fast! Good to see you out there again Kel



I also picked up some handlebars and cush drives for the GPRS125 from Kel, small steps. Thanks again Kel

[chrisc]

I just found this. So much reading to do, so little time.

Bert's link list

[chrisc]

Blasted the 'dummy' casings today, that I got from Tim. Came out quite nicely actually.



Picked up some devcon, a chunky carbide burr for the casings and a long shank ball end carbine burr for the cylinder. Devcon looks to have changed their packaging as I saw it in a few engineering shops with the same new packaging and the same product code as what I got from Rob.



I pulled the studs which surprisingly came out easily and scribed out the metal I need to remove from the casings. Tim made a template off one of the ESE casings which I borrowed. Looking back through old posts, the front clutch side (bottom left in the photo) looks to be far bigger than older engine photos. Is this a newer development Rob? Brendan on FXR150.co.nz hasn't cut deep into this area at all and I'm wondering if I should given my goal with this engine.



In went the Devcon to set overnight. I glued another bit on the ignition side that probably wasn't needed but oh well.



Filling in the tops.



Tomorrow I will start chewing into the casings with the nice big burr. My neighbours are going to love it

[TZ350]

Tim made a template off one of the ESE casings which I borrowed. Looking back through old posts, the front clutch side (bottom left in the photo) looks to be far bigger than older engine photos. Is this a newer development Rob? Brendan on FXR150.co.nz hasn't cut deep into this area at all and I'm wondering if I should given my goal with this engine.

Your casings are looking good. The template Tim got was one of Cullys and is a bit bigger than my first effort, I have used Cullys template on the new cylinder I am working on.



But I think we will have to be careful about how wide/deep we cut the cases.



The entry's to the rear transfer ports might need to be a bit compromised so as to avoid breaking through the cases.

[F5 Dave]

Asking for Devcon is like asking for Loctite, there are several formulation, I use the Fasmetal ally one which is close to the old 'f' I think.

[chrisc]

...the new cylinder I am working on.

Dang, so many ESE GP125 cylinder variations! I have that template that Tim made and I also nicked an ESE cylinder from him too which 'you went to far on the exhaust' on. The secondary transfers are really different in shape. The 'too far' cylinder is quite wide and buckety whilst the template is quite long like the one you are working on.

I'm keeping the below image in mind with the port angles. I am going to make some devcon dividers between the A and B transfer ducts but have them point to the rear of the cylinder like below.



I bought some cheap vernier calipers to sacrifice and I took a port rubbing of the 'too far' cylinder ports to compare to a rubbing of the stock ports. That exhaust really is massive! I'm surprised it didn't feast on rings too with quite flat top and bottoms.

Those carbine burrs were well worth the investment. Very smooth to use and it didn't take me long to remove most of the required material from the casings. I haven't gotten close to finishing them yet as I wanted to give the Devcon a long time to cure in the tops. After the casing photo below I took some more material out from the clutch side B transfer area.

I remember talking to you about inlet size and my goal of lower power with really good spread and you said to keep it smaller rather than go huge like suggested for the 30hp engines. I haven't taken much material from the inlet because of this but I might remove that corner that's still there.





Quite hard to tell what's happening in there with the black paint from factory but it's getting there. I haven't touched the outlets yet.



I bought some very nice handlebars from Kel last weekend and fitted them today. They fit like a glove.

[kel]

I'm keeping the below image in mind with the port angles. I am going to make some devcon dividers between the A and B transfer ducts but have them point to the rear of the cylinder like below.

Type 2 to both sides! The front edge (exhaust side) of the B port should exit square across the cylinder rather than angled to the rear. Try to make the near side duct wall as square and straight as possible. Have a good look at the RSA cylinder drawings, while you wont be able to match them they give a lot of info as to what shapes and areas work.

[chrisc]

Thanks Kel, yeah I wasn't going to go anywhere near the type 1 B transfers. I will look up the RSA drawings now

[chrisc]

Some pointers to myself

RSA125 cylinders

Inlet timing

Wobbly said it all. Closing the disc later than 88° aTDC costs top end power; closing it earlier would give more bottom and mid power, but with a 39 mm carb the engine would run out of breath too soon. Aprilia used 42 or 43 mm carbs (most riders preferred the 42) and a closure timing of about 85° aTDC.

Duct entry ratios

If you look at the old Rotax pic it has a duct entry to port ratio of about 1.4.
The base gasket dimensions are virtually identical to the late model cases.
The RSA/RSW has a ratio close to 1.2, so its still tapered down to the port exit but no where near as much.
If you look at the Delivery Ratio of a full on 2T engine, virtually all the volume that ends up in the cylinder, is actually sitting in the transfer ducts, NOT the case.
The smaller this volume is, the quicker it can be accelerated thru the duct into the cylinder.

Wobbly's thoughts towards sharp transfer dividers...

Sharpen the transfer septums and I will personally bend you over and do horrid things with your arse.
Sharp leading edges are used on supersonic aircraft, when your transfer flow goes supersonic then so will the bike.
Look at the fastest two stroke in the worlds septum, does that look sharp???

Frits on transfer ducts

The outer transfer duct radius is utterly unimportant; there the charge has no option but to go where the duct wall leads it. But the inner duct radius is very important: it should be as large as possible to avoid flow detachment. If you manage to keep the flow clinging to the inner surface (the Coanda effect), there will be less pressure-absorbing turbulence, so the flow will meet less resistance, transport more mass and deliver it where you want it to go.
The golden rule of flow: look for sharp inner edges and remove them. It always works.

The radii at the bottom bore edges, as visible in the picture above, yielded 1 HP; that's about 2% of the total power. The egdes where the transfer port windows cut the bore, should not be radiused; you do not want to promote inflow of waste gas into the transfer ducts. Here only the top and bottom edges should be chamfered lightly to make life easier for the piston ring.
There should be no widening just before the port exit; the duct cross-section area should gradually move from entry area to exit area. And with the inner curvature of the duct fixed, this more or less lays down the shape of the outer curvature.

Assuming that the flow in a duct will accelerate faster as a result of narrowing that duct is an ineradicable misconception. If it were true, it would mean that a duct narrowing to zero would yield an infinite flow velocity......
Flow velocity depends on the pressure difference between entry and exit of a duct, and in the case of an engine, where the flow constantly accelerates and decelerates, it also depends on the column length of the mass in the duct. It does not depend on the column's cross-area; twice the area would mean twice the mass per mm column length, but it also means that the cross-area exposed to the pressure difference is twice as big.
A smaller cross-area can have the effect that because of the reduced mass flow the pressure in the crankcase does not fall as quickly, which in turn may lead to a longer-lasting acceleration of the flow and thus a slightly higher top speed. But it will also mean less mass transport during the transfer phase.

The duct entry area of the Aprilia cylinder's B-ports is slightly smaller than their port exit area. This stems from the old obligation to develop cylinders that had to fit the existing crankcases of the Aprilia RSW engine, of which there are hundreds around. the RSA engine did not have this limitation, but simply enlarging the B-duct entries disturbed the scavenging, so the ducts were left as they were (and remember: while the B-ports' exit areas are only open part of the time, the entry areas are open all the time).
The transfer timing is 130° for the A-ports (they are really close to the auxiliary exhaust ports) and 132° for the B-ports and the C-port.

Aprilia drawings

I am willing allright, Myron; I am trying to promote two-stroke knowledge. But I'm short of time as it is.
Regarding testing: if you can think of anything at all, you can be sure it was tested.
Maybe the picture below will answer some of your questions. There is a lot more where this came from and I am willing to share, but you would have to convince your forum governor to allow uploading ZIP-files.

Interesting angles on this rotax compared to the RSA

Attachment 280014

[chrisc]

Taking inspiration from the best and brightest. So very thankful for this forum, pitlane and Frits, Jan, et al's contributions



p.s. all I can think/dream/wonder about is 2 stroke engines

[chrisc]

Ahhh, see now THERE's your problem!



I cut the end off of the street triple muffler I have been using on my FXR and found and big ass restriction in there. Man, no wonder it was stifling it so bad and why it lost so much power! The bit on the left of the photo is the inlet, the right, is where it enters the muffler.

Anyway I cut that out and welded it back up. It's a bit louder but not by much and hopefully I'll get back most of the 4hp I lost from it

Have done a bit on the GP engine but I need to get a small right angle head grinder to do the cylinder side of the transfer ports so I've kind of stalled on that

[chrisc]

Anyone else remember summer, that was nice wasn't it. Here's a quick edit of Brian doing a few tuning runs outside Steve's house before the Roys Hill round of the north island series.

[chrisc]

Brian and Mel's 'new' chair/suicide machine

Check out the third wheel on that first photo!

[chrisc]

[Pumba]

Great Photos Chris as always.