NMPRA

Now on to the degree wheel.

This part will throw the "using liner shim by the numbers" and motor measurements right under the bus. I.e. why does this motor run good but this other motor "set up identically" runs completely different. Well let's start by matching the exhaust port timing and see what happens. As mentioned before not all liners are crated equal. Not knowing what the degrees of exhaust timing is, is like pissing in the wind and, if you piss long enough you might find a combo that works for "that" motor. First, get a timing wheel. You can tell this wheel has been in use especially for FAI. Buy one with the small hole, I think it's 1/4 inch but I'm prolly wrong. Either way, this one is 5/8 hole. It fits the 15mm FAI stuff better. Just tap the small hole to fit the 5/16 crank. Affix the wheel using a prop and prop nut. Finger tight is ok. Using a head bolt, a nut that the head bolt goes through wrap a piece of wire around the bolt and tighten down. now, looking at the exhaust port on an angel like the pic move the piston until that little light gap disappears. . Next, making very sure the top of the piston has just caused that light gap to dissappear make sure it don't move, position the indicator wire on 0. adjust the wheel to accommodate the wire, or vice versa. it doesn't have to be straight up and down.

Once your convinced the light is gone, the wire is at 0, rotate the crank the opposite direction NOT UP but down all the way around until the light gap disappears again. Look at the indicator, this is your degrees of exhaust timing. in the case of the blue too sweet it's 197 degrees with no cylinder shims. If you rotate 180 degrees from 0 to 0 then add the 17 hash marks you get 197.

Now, and only now can you match one motors exhaust timing to another motor.

Blue two sweet fits.

The piston dry fit is .245 extremely loose. The prop was a 6 two exhaust gaskets.

Exhaust timing and shims.

Once you measure your motor, a mathematical certainty, every 1 degrees of exhaust timing is. 003 shim. If your best running motor is set up at 195 and 19. Pull the shims and measure it. "If" it measured 197 degrees with no shims and your TDC was 189 like the blue too sweet when you put .006 under your liner to get to 195 .006 is 2 degrees of exhaust timing, so, your exhaust timing would be 199. if your other motor set up at 195 and 19 has a different exhaust timing say 201 degrees then you would need to come down 2 degrees or .006

The reason I used the blue too sweets motor was to show the setup it was running. Also to show another trash can motor that went real well. The setup is mixed in the thread. To answer the messages its..

.245 dry fit piston depth. You will need to have a piston fitted to achieve this.
The exhaust timing is 197 degrees.

So, to match the setup, 197 exhaust and .020 clearance what ever shims you need to get that setup.

Another answer, yes lots of motors run higher timing. I don't know what their exact numbers are only what I've heard. If you measure your motor with out shims and you know what your base exhaust timing is when you hear a conversation about motor setups you can do some simple math in your head based on the 1 degree of timing per .003 of shims.

The biggest variable is case, cylinder and crank stroke. there can be as much as a degree or more in just the crank throw but usually less than that. This is based on .789 throw which is what mike shoots for.

Cool stuff Ray.

Nothing to contribute, just letting you know I'm paying attention and thanks!

Tim

I agree this has been great

Thanks Tim and dwyane. I really enjoy the cudos.

A better way..

While playing with the motor with holes in the case I found a new and improved way to measure exhaust timing. I've been doing FAI motors so long it was second nature to do it from the front. Turning the wheel around makes it tons easier for side exhaust. That being said let's check the numbers. .This motor is the CA to fill the cracks motor from the thread that almost got tim a new nelson. The same setup with no liner shims it's exhaust timing is 198. That's .003 different from the motor before which was 197. The BDC measurement was 980, less the stroke of 791 gives a TDC of 189. . To match the exhaust timing of 197 on the motor a few post before this is not possible, we can't go down only up. I would need to add a .003. To the 197 motor to get it to 198. This would mean one motor is at 189 and one at 191 to get them the same.

wouldn't adding a .003 shim take you from 198 to 199 on the timing? You'd have to lower the port to reduce the exhaust duration.

Yeah, I just changed it. A customer was talking to me while I was typing.

Ray is a Multi Tasker


Great thread Ray

What I meant by "we can't go down only up" was these motors have liner shims. So in my case it's as low as it will go now so only up with liner shims.

Rocket,

I really do appreciate all the information and pictures you have posted on Q40 motors.

Thanks for all the effort!!

This kind of information exchange is exactly what NMPRA and this forum should be about. Great work, Rocket Ray!