ESE's works engine tuner

[wobbly]

Re the Rotax big ends - the rods and bearings are reliable to 13000 all day for 1500KM as long as you realize one small issue.
For some very wierd reason Rotax do not match any of the parts in batches to get the clearances correct.
Every other manufacturer of racing engines measure the pin,rod bore, and needles, marking them and assembling a "kit" to get around 1 micron per pin mm dia total clearance.
ie with a 22mm pin you want around 22 microns clearance.
I used to buy 10 bearings at a time, and measure EVERY roller with a 4 figure digital mike - matching them in sets to with 1/2 micron.
Then measure the pin and bore and matching those with the rollers to get the correct clearance.
The rollers could be up to 2.5 microns different in diameter, thus the big one takes all the load and skids,shitting the cage instantly.
Needle diameter matching is the key to long life of the cranks - along with using the flat section cage shape.
RS250 cranks regularily do 2000Km with no issues as Honda match everything ,and dont trust anyone to rebuild them properly, so no parts are available ex factory for this reason.

[F5 Dave]

. . .
The short strokers would be reliable to over 15000rpm as long as the rod is physically well designed using the good cage design. . . .

My only point is that to be bucket legal these must be non competition parts. Sometimes you get lucky & there are road bikes that have good design cages in the sizes you want. Suzuki bearings don't seem to be that flash, at least on their older models. the MB bearing has been upgraded several times & is actually the same part as used on CR80s. However I am no expert on available sizes out there for common bikes.

But secrets aside - what we really want the beans spilt on is : What vegetable oil do you smear on pipes to make them make a nice clear skin? I've tried Soy & a cheap table oil, bit they all burn off the header.

[wobbly]

Mild steel pipes will always rust and or go black,the only way to help keep them looking OK is to use Castrol R.
You have to rub it on with a rag every time the bike is run, and eventually it will burn in like a wok surface preventing rust, but you cant stop the header going black.

All the common big end sizes are available in the newer flat cage design, as this type is used in all current road and race engines.
And who is going to say to you that your engine is illegal coz its got a modern cage design.

And re the step in a Honda exhaust duct.
When using a T port or a properly designed tripple port exhaust, the area just outside the port is way too big during the blowdown phase,and alot of velocity is lost.
I have found that a good rule of thumb is to gradually reduce the duct exit at the flange, to around 75% of the total chordal area.
This will often equal the area of just the main port in a tripple setup.
If you make the duct exit the width of the header, and then reduce the height, forming an oval to give the correct area, a heap of power is created, in part due to the much better flow from the outer parts of the port width of a T or the
aux ports in a tripple..
Steps work OK, but a CNC formed oval to round transition in the flange works best.
Note well, this technique DOES NOT work in a single Ex port engine, no matter how big it is.

[F5 Dave]

Thanks that is all very interesting.

Castrol R, bean oil. Not sure where the hell I'd get some of that this side of 1970

Re the 256 cages I'd heard of a chap boring the cranks & using Aprilia rods as were 2mm bigger. Perhaps the real improvement was the bearings were better made. Which is queer as Aprillia have a big tie up with Rotax & I'd always thought they had made their 2 stroke engines.

The duct info is very interesting & is making my head swim a bit.

[F5 Dave]

So after a brief foray to pick up my newly chromed pipe (don't panic its for my dirtbike where ease of cleaning is a serious prerequisite) I've been thinking.

So you are saying looking at the old RS ex port that this design is pretty big at the outlet. I always thought it looked huge, sadly I (15 years ago) welded a copycat flange onto the outside of an engine & with 2 sub ports added sort of extended it out to meet an RS125 pipe. The flange looks way too big for a 100.


Anyways so you are saying that the RS would have been better with a smaller pipe flange and a transition from the oval shape at the cylinder to a round at the flange of a smaller diameter. Of course this is hard to cast as the taper is the wrong way unless it was investment cast. So fitting a nozzle to adapt this to a smaller flange header is the way to go. Honda Band-aided this with the step.

Have I got this right? Makes sense.

This nozzle must get fairly hot not being a part of the barrel.

[jasonu]

Thanks that is all very interesting.

Castrol R, bean oil. Not sure where the hell I'd get some of that this side of 1970

Re the 256 cages I'd heard of a chap boring the cranks & using Aprilia rods as were 2mm bigger. Perhaps the real improvement was the bearings were better made. Which is queer as Aprillia have a big tie up with Rotax & I'd always thought they had made their 2 stroke engines.

The duct info is very interesting & is making my head swim a bit.

Blenzoil is a brand of castor oil comes in a yellow bottle. I used to put it my Maico 490. Smelt grrrrrrreat!!!

[wobbly]

The only connection between Rotax and Aprilia was that the race team used the 250 V twin cases from Rotax at the beginning of their attack on that class.
Very quickly they made their own cylinders, and later their own cases as well.
Then they got sick of the crap gearboxes and did their own, as the original design by Bombardier was for a 125, and this got used even on the 250cc single, with predictable results there as well.
The early Rotax had 20mm pins that were too small, and the later design had 22mm - when Hondas bulletproof cranks were 24 and 25mm.
So yes the uprated design you mentioned probably had some actual QC done on the parts, unlike the Rotax shit - they should have been shot very early on and prevented millions of dollars and grief being spent on broken engines for no good reason.

The nozzle is part of the Exhaust duct, you can weld the duct or counterbore it and press in a sleeve to be ground out to the right shape.
Honda use a cast oval to round transition male spigot flange in the A kit 125 engines, as well as some years of the 250 V twin design.
And yes the RS125 header size is way big for a 100 - but having the correct size oval shape in the duct would reduce its volume and increase velocity and power a heap.
The design I have just done for the RGV100 has an oval duct nozzle the area of a 31mm circle,that transitions out to a 36 diameter round header bore in the flange.
This matches an Ex port area capable of achieving an easy mid 30Hp number.

[Henk]

Castrol R, bean oil. Not sure where the hell I'd get some of that this side of 1970

Supercheap. The one in Westate has the stuff on the shelf.

[RMS eng]

Thanks that is all very interesting.

Castrol R, bean oil. Not sure where the hell I'd get some of that this side of 1970

Re the 256 cages I'd heard of a chap boring the cranks & using Aprilia rods as were 2mm bigger. Perhaps the real improvement was the bearings were better made. Which is queer as Aprillia have a big tie up with Rotax & I'd always thought they had made their 2 stroke engines.

The duct info is very interesting & is making my head swim a bit.

Dave i sell it $24.00 for 1L,or just go to super cheap.i use it in all my 125 MX bikes.

[F5 Dave]

The only connection between Rotax and Aprilia was that the race team used the 250 V twin cases from Rotax at the beginning of their attack on that class.
Very quickly they made their own cylinders, and later their own cases as well.
Then they got sick of the crap gearboxes and did their own, as the original design by Bombardier was for a 125, and this got used even on the 250cc single, with predictable results there as well.
The early Rotax had 20mm pins that were too small, and the later design had 22mm - when Hondas bulletproof cranks were 24 and 25mm.
So yes the uprated design you mentioned probably had some actual QC done on the parts, unlike the Rotax shit - they should have been shot very early on and prevented millions of dollars and grief being spent on broken engines for no good reason.

The nozzle is part of the Exhaust duct, you can weld the duct or counterbore it and press in a sleeve to be ground out to the right shape.
Honda use a cast oval to round transition male spigot flange in the A kit 125 engines, as well as some years of the 250 V twin design.
And yes the RS125 header size is way big for a 100 - but having the correct size oval shape in the duct would reduce its volume and increase velocity and power a heap.
The design I have just done for the RGV100 has an oval duct nozzle the area of a 31mm circle,that transitions out to a 36 diameter round header bore in the flange.
This matches an Ex port area capable of achieving an easy mid 30Hp number.

OK I'll have to make something similar if I keep with this barrel, -its a bit of an abortion until I get enough time to do another, but I can't seem to find that time with other commitments & projects. Thanks for the background, makes good reading.

Rotax's attitude seems to parallel Konigs if Hannah is to be believed.

[husaberg]

And re the step in a Honda exhaust duct.
When using a T port or a properly designed tripple port exhaust, the area just outside the port is way too big during the blowdown phase,and alot of velocity is lost.
I have found that a good rule of thumb is to gradually reduce the duct exit at the flange, to around 75% of the total chordal area.
This will often equal the area of just the main port in a tripple setup.
If you make the duct exit the width of the header, and then reduce the height, forming an oval to give the correct area, a heap of power is created, in part due to the much better flow from the outer parts of the port width of a T or the
aux ports in a tripple..
Steps work OK, but a CNC formed oval to round transition in the flange works best.
Note well, this technique DOES NOT work in a single Ex port engine, no matter how big it is.

Ok think I got that but what is the step in the pipe at the singer/baffle cone for? why does it cost hp to remove it .The restricting convex?

Ps isn't A747 castor based
Castrol r is available at any cmrr meeting for free if you don.t mind second hand find someone with a manx or G50 or 7r

[husaberg]

The only connection between Rotax and Aprilia was that the race team used the 250 V twin cases from Rotax at the beginning of their attack on that class.

They started with the tandam twin rotax didn't they?
Then I thought the v twin was mostly there work that how i recall it but it wouldn't be the first time i was wrong either.
I've got the step by step story of the engine devlopment somewhere buried if anyone is interested. its a bout 10 pages long in one of the gp autocorse books from when max first took the crown.

[husaberg]

My only point is that to be bucket legal these must be non competition parts. h

I thought parts were ok just weren't allowed to use gearbox or competion based engines.
I would have thought a big end bearing was ok?

[husaberg]

I thought parts were ok just weren't allowed to use gearbox or competion based engines.
I would have thought a big end bearing was ok?

busy night want a beer?
thought you would never ask.

[wobbly]

Removing the step from a Honda means you remove the oval nozzle restriction before the header, that increases duct velocity.
Bigger is certainly not better.
As an example when I did testing for the new Luyten 125 cylinders, I counterbored the duct and made inserts to change the oval size.
It started with 41 by 37, I dropped it to 41 by 35 then 41 by 32.The change was worth around 2Hp everywhere, but especially in overev.
Then I added a hand ground 41 by 32 oval, to 41 round, transition in the spigot - and picked up another 1.5 Hp, putting that cylinder over 50 RWHP for the first time.

The Rotax Tandem twin was the first 250 class engine, but it was way too long to get good chassis geometry, they then did the V twin for Aprilia, carrying on making the tandem for karting.

A747 is a synthetic hybrid with caster added, it doesnt work on pipes ( just as well at the price).Probably still the best 2T oil you can use.