bikeordie092

iTrader: (2)

ok, so a crank angle wheel, but how do i find tdc?? lol

diabolical1

iTrader: (3)

you basically position the front rotor in such a way that the chamber is at it's smallest volume in the compression/ignition stroke, with the eccentric shaft keyway at 9 o'clock. look at the first photo Karack posted and match that with the photo Ghooble posted in this thread: https://www.rx7club.com/1st-generati...iming-1037182/

RotaryEvolution

iTrader: (30)

i found exact TDC by doing just that, measuring rotor clearances in the pockets to the rotor housing so that each spacing was equal.

this gave a perfect TDC baseline, since the FC pulleys were inaccurate i had to set up that jig to find 5/20ATDC to check each engine with. some pulley sets were upwards of 30 degrees off in some odd combinations. once TDC was found i drilled and set the degree wheel to the hub. this allows me to slide the degree wheel on, set the engine to 5*ATDC and then switch out the original FC pulley and verify if it wasn't botched by another rebuilder(throwing random hub and pulley combinations together).


i had tried the method that some people suggested using the tip of each apex seal in each plug hole and split the difference, the result was a ballpark TDC but ballpark blows turbo engines. how far off was TDC with that method? 30-40 degrees depending on the engine series. yes, it is a horrible ballpark... because the spark plug holes are nowhere near the center of the compression pockets in the housings.

bikeordie092

iTrader: (2)

hey thats a good idea. i believe i can get tdc that way. one more question lol... what do you use to reference your degree wheel on the block? im going to get a degree wheel, but i am unsure of what size to get cuz idk what ill use to reference the degrees.

RotaryEvolution

iTrader: (30)

you can use the factory pointer on the front cover or make a plate to bolt to the bottom deck of the engine with a pointer attached to that.

bikeordie092

iTrader: (2)

i was just thinking the factory pointer would be behind the wheel.. its like right on the pulley as it is...

Ghooble

iTrader: (1)

Oh mah gerd. I got cited as a source

diabolical1

iTrader: (3)

well, what can I say? it was a great illustration. it was fresh in my mind at the time and you posted it. no chip here.


oh ... and for my red face moment. I just realized that I said Karack in my post, and not RotaryEvolution. so while I was technically still correct, I just wanted to make sure he and everyone else knows there was no disrespect meant. just in case ...

bikeordie092

iTrader: (2)

lol nice... well it looks like im pulling the motor here in just a few minutes, since the "rain" outside is soo pretty lol

diabolical1

iTrader: (3)

I screwed up with this response ....

smallest volume is correct and keyway at 9 o'clock is correct. however, the rotor is against the side with the ports, not the plugs.

sorry Ghooble ... you photo is not correct. nor was I.

in my defense though, I haven't touched my wheel since I last messed with my semi-pp, so that's about 4 years ago.

sorry for any confusion I caused.

there's a better link in post #9 of this thread
https://www.rx7club.com/general-rota.../#post11498631

bikeordie092

iTrader: (2)

there is also a very informative picture in post 8 of that thread. thats how i figured out the rotor being on the opposite side lol...

so TDC for port timing is the opposite of TDC for ignition, from what i understand lol

bikeordie092

iTrader: (2)

wait! i get it! lol.. there are "technically" 3 strokes in the rotary: intake, combustion, and exhaust.

intake and combustion both have their own respective TDC. intake port opening references the intake stroke's TDC. intake port closing references the intake stroke's BDC.

exhaust port opening references the combustion stroke's BDC. exhaust port timing references the INTAKE stroke's TDC.

omg. im pretty sure i just blew my own mind. i feel awesome lol

j9fd3s

iTrader: (3)

lmao! you're right, except there are 4 strokes, intake, its goes from small to big, compression, it goes from big to small, power! the important one, goes from small to big, and then exhaust,big to small again.

so as you've noticed the power stroke is a bit short, which is one of the reasons the rotary isn't *** efficient as a piston engine and why the Rx8 exhaust port actually opens later.

good job! you put it better than i would have

bikeordie092

iTrader: (2)

well, i kinda combined compression and combustion. lol thats where i made it "three strokes"