Crank Timing vs. Port Timing
 

I posted a question on the IMDRA forum related to "crank timing", and a member responded stating, essentially, that "crank timing" and "port timing" are not the same thing. Can someone please explain to me how and why they are different, or was the guy simply poking fun?

port timing is the timing of the ports in the sleeve. Crank timing is the timing of the induction port in the crankshaft. Basically the same thing as rotor timing on a traditional rotary valve engine.

Okay, so what can be done to "port timing" to increase power, other than the usual fanging?

Port timing refers to when the piston opens and closes the ports, and for how long(in degrees). Nobody is going to tell you what to do. The people that truely know what they're doing will lose money, and the ones that think they know what they're doing will only help you ruin engines.

LOL!! I understand completely! Thanks anyway. However, I have managed to create some very quick motors through adding a little duration to the opening and closing sides of the crank (more on the closing side), fanging the sleeves and a few other tweaks here and there. I have a trick TZ-18 with a 9mm carb on it that is absolutely amazing. I guess the biggest problem I've had is not watching the motors close enough, because I have blown up a few! Absolute screamers though!

The basics is nothing more than every kid on the corner of the street is doing to his 50cc 2-stroke motocicle :rolleyes: And what is wrong with learning and doing it yourself? Take some old engines and experiment on them.

Here an interesting link all about 2-stroke engines: http://edj.net/2stroke/jennings/

that book is great. i recommend all rc racers read it. it's motorcycle engine based but all info is still applicable as it is 2 stroke.

Wow! Damn good information. Thanks, and with that information I'm sure I can improve on what I have been doing to these little engines. I have a question though; I notice that most of the top engine modifiers are putting this "red putty" (or something) in the crankshaft to better distribute fuel into the crankcase. How can I do that and what material are they using? Thanks.

It gas several functions but with all of them they are maybe slight noticeable. I have a N21-5T and it has that hole in the crankschaft without the putty and that engine is running awesome.

The main reason is weight and the ease of production. They drill out the crankshaft and drill it a bit deeper to the front bearing. It saves weight and for adding the flow they put in the putty. There is a topic on ths forum of what people are using. Most of them are using Permatex high-temp RTV silicone or ThreeBond 1211 silicone liquid gasket.

But be aware the visable tuning like flowing, teardrops etc does not add much more power to an engine, it can make the engine run more smoother. Changing timings will make the huge improvements.

Roelof:

I have always simply trimmed (knife-edged) the opening and closing sides of the crankshaft. Very little on the open and quite a bit on the closing. Is that the wrong way to increase duration, or is it better to cut the recommended 2mm from the closing side only? Also, if you don't mind, what else can I do to these engines for maximum horsepower for drag racing?

Port timing and Crank timing go hand and hand. You can't have one
without the other, you have to have some form of both. :nod:...:lol:

Care to provide a bit more information? How do you change "port" timing, and what is the best proven method?

Knife edging is no change of timing, the moment of opening and closing will be the same.

I do not think crank and poortiming are that much related to each other, I have messured a lot of engines and have seen a lot of combinations with timing. The funny Thing with most Novarossi (based) engines is that the intake is always @65 degrees (130 in total opening)

On most onroad engines I always do add 2 or 3 degrees at the closing moment of the crankshaft and making the exhaust a little bit wider and higher (0,2mm).

A simple calculation:

- Krankshaft 14mm
- 1 full turn (360 degrees) is 14 x PI = 43.98mm
- 1 degree = 43.98/360 = 0.122mm

A stock Novarossi 14mm crankshaft is 10mm in diameter messured on the crank opening.
When grinding one side and messuring on the crank opening you must think in half the size so taking away 0.122mm at one side is making 9.939mm messured on the crank opening you have changed it almost 1 degree.

In the drawing you can see the explenation why thinking half the size

And if you want to do more with engines you make a tool to messure timings.
http://www.modelbouwforum.nl/forums/...-en-tunen.html

Roelof:

It is amazing how much I "don't" know about these little engines. The above information is good stuff. Unfortunately, I was not able to translate the information found within the link you provided. Obviously, my computer is missing something. However, I have another question; in the drawing, are the "red" sections on the crank the area "where" and "how" I should be cutting the crank? Also, is the OS TZ-18 a Novarossi based engine? Your knowledge is amazing! I have learned more about these engines through you today than I have in the last 20 years! Thank you for sharing it with me.

The red part is indeed the part to grind away.

The result of this mod is that the engine will rev up much quicker and does reach a tiny bit more RPM. If you go to far the LSN setting can be a lot tricky, the further you go the smaller the window of the LSN will get.

With ,26 and larger monstertruck engines a 4 to 6 degree can make it an all time wheely monster ;)

That link is in Dutch, I have got a same topic here as wel:
http://www.rctech.net/forum/onroad-n...e-timings.html
(had to look for it)

By the way, this is how I do it, others do other things.....

On this page you can see some stock and modded engines to see what are the differences,
http://www.first-racing.eu/html/steuerzeiten.html