Originally Posted by
Geberit
Hey Pattojnr,
You are right regarding the timing. I would be interested exactly what did you do and how did you know how much to change the ports in the sleeve?
Regarding the Crank I wouldn’t touch it, because the last action in the production process is balancing. So if you modifying it you can ruin the balance of the crank. The result can be shorter life time of the bearings or worse breaking of the bearings.
But anyway always when you tune an engine (assuming you are doing it right) you shorten its life time because you expose it to greater stress.
The power of engines in these days is way over what materials can handle! In the future the manufacturers don’t have many options to get more power. If they increase power with existing materials the life times of engines will be shorter and shorter. So the main point is to focus on stronger materials that are able to withstand more stress. But this will mean more costly engines for us.
By
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.