it comes down to trial and error as to what crank timings work for each engine. i have a fair success with the basic novarossi 21 7T motors. they can be very compettitive, and dont really lack that much anywhere on the track. i use a degree wheel on the crank, and a light through the back of the case to exactly measure crank open and close timings, as most of the guys who do work would have to use. its not guess work by any means. As for the balance of the cranks, well its a single cylinder engine, there is no way to make the crank balanced to any sort of precision. at higher RPM what you dont want is a counter weight trying to work against the movement of the piston. so in those terms, you can make the crank work after lightening it. it is done by removing more material from the other side of the counterweight for the turbo scoop area. if you have an old crank case with good bearings, then you can get the crank re balanced to what it was before. i heat up the case to free the bearings, and keep removing material till i spin up the crank till the piston pin centers just past TDC, about 4 deg. this prevents the weight being before TDC where the piston is coming down , and the weight of the crank is still coming up. this will stress the ROD and create unwanted vibrations at higher RPM. so it can be done, i have a few 21 -7t motors still flying around after a lot of fuel. but i am no Expert, i do this as a hobby, but the guys who have the engines i have done, they do really like them. and the cost of a 21 -7t isnt that expensive, for performace racing. the other battle is how they drive, and how they setup their cars. one of my modded motors made a top 10 at the AU Nationals last year. but great driving and setup ability, and talent all plays a part.

Gerberit, i dont change sleeve port timings. all timing changes i make are the crank open close timings. this is the best way to get easy reliable quick power.
all the R & D in sleeve design remains the same with what i do. but cranks are very conservative from the box.

Can you explain this in any scientific or engineering way?

If you have less material you have only les rotational mass and smaller inertial forces! But less material can handle less stress. Look, on witch branch can you sit on 20inch/cm diameter or 0.5inch/cm diameter. The power of a 2.11ccm engine is enormous regarding its displacement.

If this was so simple why didn’t the manufacturers come up with that idea!?

By

well unfortunately, the difference from a factory tuned consumer engine, and a Factory driver Engine, things have been lightened, timings changed to suit the track, conditions, and even runtime. where there is a will there is a way ;)

I know what you mean with the crank timing. And I see you have many experiences with the engines. I didn’t try to modify any engine yet but I’m considering buying a cheep one and giving it a try.

Tell me, what would you recommend when I buy a new engine. Should I tune it right away or should I run it in first and then tune?

Cheers

while you are learning on your own engines, run them in , race them , then do a little work at a time, so you know how the changes affect the performance.

Thanks for the useful information! I will give it a try this summer cause I like the technical stuff in this sport.

I hope we can chat about these things in the future.

Regards

I did even outperform a Mega ZX21 DSII (tuned) with a Nova Basic N21-3T just by copying all dimensions from a JP RX21 Kangaroo Teamspec 2003 and added a tiny bit more cranktiming.

As for messuring the timings I have a new toy:

http://www.debaanbrekers.com/ftp/timing9.jpg

that is nice Roelof. any tips where to get it from ? ;)

I've got it here: http://www.roeispul.nl/pitchmeter.php

But if you take a search on Ebay to a digital agle level meter you will find this model as well.

It is also handy for messuring camber if you have straight setup wheels.

THanks Roelof :nod:

Your right on one part, but wrong on another part.
Adding more material doesn't automatically makes for a stronger part.
Adding material in the right spot, makes a part stronger. Sometimes you could make a part stronger by removing material, because the material doesn't add anything to the structural integrity of the part and only weakens it because of the added weight, so more stress at high rpm.
I have a JP engine which has the intake side of the piston milled away from the bottom of the piston to the bottom of the piston pin.
Makes up for a much lighter piston, but it doesn't weaken it.
As a downside, the engine is much harder to tune and was worn out quickly (5 liters) because of the huge power and high revs.

The main thing to improve, especially for 2.1cc engines, are the bearings.
With the current high tuned engines they last 2-3 liters at most in high competition.
Another important thing is crankcase rigidity. You would be amazed how much the older crankcases flexed under high load.

Yes I agree with the excessive material in the wrong spots. So tell me I have a new Flash .12 and if I want to be on the safe side after how much fuel you would suggest to change the conrod? And how do you determine when to change the bearings?

Regards

Well basically I follow the same procedure with every engine and never had problems what so ever.
Break in, and the first race with the conrod the engine came with.
Mostly the engine is fully broken in after it's first race, at least in my case since I don't practice a lot.
After the first race I replace the conrod, and do a really good check up, clean up of the engine. With pretty much every engine I owned it wasn't needed to change the conrod a second time, because they were worn out before that point. My engines last around 10 liters after break in.

The bearings are really unpredictable, sometimes they become bad during break in already and sometimes they last 2 races.
When they start to feel different as when they were new, change them.
Don't wait until you see the (steel) balls become dull, then you have waited to long, and mostly you could see damage to the outside of your crank, it becomes hard to take it out.

When you change the bearings, put the crankcase in an oven, most of the time 45 min on 140C, then put the new ones in by using your crank to guide them in, and align them. I always immediately screw the flywheel on and rotate it. Since I have been doing it like this I feel the bearings last a little longer and the crank can spin more easily.
I wouldn't suggest using the cold-puller method, as this puts a lot of force on the components, and it's harder to properly align your bearings this way.

Woher bist Du denn? Sportkreis Süd?