ESE's works engine tuner

[guyhockley]

Some pictures of the 250 engine.


Think Rotax built a V twin as a one off for Cotton before the tandems came along.
Presumably the engines had more and more Aprilia built parts as time went on.
I saw an article in an Italian magazine about the development of the 250 and (I think!) it said that power slowly increased over the years but the biggest jump was the introduction of crankcase cooling.
Was that similar to the 125?

[guyhockley]

Found this

[Tim Ey]

The shim package of the 250 Garelli was about 1mm.

Jan, did you ever thought about using bearings with steel cover discs instead of a labyrinth seal?
(6204-z-c3 would be an example)
so you may use two bearings right next to each other without the need of any extra parts.

the question is where to place the covered side.
1. covers at the crank webs with an oil feeding hole between them
pro: crankcase volume does not differ
con: might get full of oil


2. covers facing each other, feeding hole in the middle
con: probably not enough oil supply

3. using only one closed bearing with feeding hole in the middle
pro: more vented bearings than 1.
con: crankcase volume of one gets higher than the other

[Fabio15]

Can one find reasonably powerfull(up to date) 50 ccm cylinders,pistons and exhausts without silly money and where?

Malossi, Polini and Roost make very good cylinders for the 50cc piaggio engines.

[jamathi]

Thanks for the insight, Jan!

do you remember the difference between both of the A-port variations from the picture? Which was better, version A or version B?
Attachment 330106

And did you ever have the pin come loose on the pistons? I guess not, buit it does look brave to me.
Attachment 330105

Version A was the best.
The pin never came loose.

[ken seeber]

Jan,
In all your time at Aprilia and others, when you wanted to try a different port or passage shape, did you actually reshape the sand cores yourself (eg by rubbing, filing or even building up with more sand) or was the new design formally designed/drawn up and new coreboxes made?
Otherwise this is a great unfolding of the history, even though you’re not writing a book, I’m sure the likes of Husa will compile something.

[jamathi]

I often modified sand cores by filing
We also used to 'cast' ducts in some resin, and modified these.
After that we made new core boxes, using the modified resin cores.
Our core boxes were really very nice, I shame I never made some pictures of them!
We mostly did those things by ourselves, without involving the technical office.
When we had arrived at the best transfer ducts the whole sand core was put on design.
So a one-piece cylinder core could be printed.
Also a study was made to improve cooling, especially the hot spots, as were the bridges in the exhaust duct.
A cooling channel through the inside wall of the transfer ducts brought an additional 0,5HP
The result of this was the APF cylinder.

[jamathi]

Some pictures of the 250 engine.


Think Rotax built a V twin as a one off for Cotton before the tandems came along.
Presumably the engines had more and more Aprilia built parts as time went on.
I saw an article in an Italian magazine about the development of the 250 and (I think!) it said that power slowly increased over the years but the biggest jump was the introduction of crankcase cooling.
Was that similar to the 125?

I don't know when water cooled crankcases were introduced at Aprilia.
When I started working there in 1995 all engines already had water cooled crankcases.
I made my first 50cc with water cooled crankcase in 1972.

[jamathi]

The cooling channels at the inside wall of the transfers.

[lodgernz]

I do not understand .If the dome bends inward compression ratio go down and that is less power?

Yes...I think so.

And maybe because the depressed dome pushed the crown outwards a smidgen causing more friction?

[breezy]

I don't know when water cooled crankcases were introduced at Aprilia.
When I started working there in 1995 all engines already had water cooled crankcases.
I made my first 50cc with water cooled crankcase in 1972.

Jan, which area of the cylinder would you say water cooling has the greatest effect on improving power? does the cooling have to bring the temps down really low to have the best effect? would having that area benefit from having its own dedicated cooling circuit and radiator rather than being part of the a general cooling circuit?

regards, nigel.

[Niels Abildgaard]

Hello Jan

It strange that You could see 0.5 horsepower differences on dyno and be able to decide if it was a good or bad change.
How much running in was nessecary to get reliable data?How often did You compensate for air pressure,humidity and temperature?

[F5 Dave]

Whoa, this Bs look bigger than any other picture I've seen of them before. A lot bigger.

[jamathi]

Jan, which area of the cylinder would you say water cooling has the greatest effect on improving power? does the cooling have to bring the temps down really low to have the best effect? would having that area benefit from having its own dedicated cooling circuit and radiator rather than being part of the a general cooling circuit?

regards, nigel.

The lower the water temperature was the more power there was!
40° was the lowest we tried, each 5° more giving a power loss of about 0,4-0,5HP.
On the dyno we normally used 50°
The exhaust duct had to be cooled really well, especially the bridges in it.
In the beginning we had some trouble with holed pistons, caused by auto-ignition.
But bringing the water closer to the spark plug cured this completely!
We also found out that the quicker the water circulated the better.
An electric water pump was insufficient!!

[jamathi]

Hello Jan

It strange that You could see 0.5 horsepower differences on dyno and be able to decide if it was a good or bad change.
How much running in was nessecary to get reliable data?How often did You compensate for air pressure,humidity and temperature?

Our computerized testing program was fully automatic and very precise.
There was, of course, automatic compensation for temperature, humidity and air pressure.
You could choose the cooling water temperature you wanted, and it was kept constant.
Also the dyno room was air conditioned, with constant temperature and humidity.
You could be sure that if you saw a 0,1HP gain that it was 100% true!!
And I repeated every modification at least 3 times....
A test went as follows: The engine was started and put at 10.000 rpm to warm up, full throttle.
When the desired temperature was reached you had to push a button.
Then the test was executed fully automatically, say from 9000 until 14500rpm
When maximum revs was reached you had to stop the engine.
Tests were 99,9 % repeatable