TDC on a 12A?

[benracin]

My car came with a smaller pulley on the engine with 3 lines on it colored red, white, and black. I'm pretty sure red is TDC. John (the head wrench) and I are not certian that the pulley was put on correctly. Is there anyway to find TDC on a rotary without taking the thing apart? Thanks

Ben
ITA 33

[Mike Spencer]

Originally posted by benracin:
... Is there any way to find TDC on a rotary without taking the thing apart?...

I'll be the first to admit that while I love the rotary engine, I'm about as far as you'll get from an expert. I would like to ask for a clarification, though.

Before we try to "find" it, can we agree on what it is????

Top-Dead-Center is when the number 1 "PISTON" reaches the highest point of its' travel. AHEM... We don't got no stinking pistons!

So, is it the point where rotor #1 reaches highest compression? If so, the old screwdriver-in-the-spark-plug-hole should do the trick. OH! Which spark plug hole? I would guess "leading", but you'd probably do just as well flipping a coin.

And if that's not it, than I give up!


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Mike Spencer
NC Region
ITA/7 RX-7 almost In-Garage
1990 RX-7 Convertible In-Driveway

[wlfpkrcn]

Ben,

"TDC" can be found when the #1 rotor is at full compression. The easiast way is to pull both plugs on #1 rotor and rotate. you will see the apex seal come by, then the relief in the rotor. On either side of the relief is a machined surface. Once you are in the right vicinity the pulley indexing should be obvious.

Good luck,
Eric

[C. Ludwig]

The best procedure that will put you dead on TDC is as follows.

Pull both plugs from the rear rotor. Rotate the e-shaft clockwise until you see an apex seal in the trailing spark plug hole. With the motor in the car you'll need a small mirror and a flashlight to see in to the small hole. Once you have the seal in the trailing hole mark the pulley at the timing indicator. Now turn the e-shaft clockwise until you see the same apex seal in the leading hole. Mark the pulley. Use a dial caliper to measure the distance between the two marks and place another mark on the pulley half way between the two. This is TDC #1.

A degree wheel helps but is really un-neccesary.

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Chris Ludwig
08 ITS RX7 CenDiv

[This message has been edited by C. Ludwig (edited June 21, 2004).]

[Eagle7]

Where the heck does this guy learn all this stuff? Great info Chris.

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[lateapex911]

The rear rotor eh?

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[This message has been edited by lateapex911 (edited June 21, 2004).]

[Eagle7]

Originally posted by lateapex911:
The rear rotor eh?

With the rear out of phase with the front, the rear apex seal midway between the plugs would put the front "flat spot" midway between the plugs. Sounds right to me.

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[Speed Raycer]

Wow! I've been dealing with the same issue the past couple of weeks when I couldn't get my car to start. Only problem was that the car started and ran great before I burned up my MSD.

Not to jump on your thread Ben, now that I've got it running (love the ATF trick), I've got the 3rd line in time at 4K, and the first line lined up at idle... roughly correct???

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Scott Rhea
It's not what you build...
it's how you build it

Izzy's Custom Cages

[Quickshoe]

The pulley can only go on one way (indexed with keystock), the rotors will only go on one way, so you can't screw that part up.

I know it doesn't answer your question about what each mark means (20B, 10B, 0 or 10B, 0, 10A, or ????)

Anyone tell us with a 12A in front of them where the keyway is when the timing mark is at TDC?

[C. Ludwig]

ARRRRGGGG!!! I just read the other day where the keyway is always indexed in realtion to TDC but can't remember.

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Chris Ludwig
08 ITS RX7 CenDiv

[lateapex911]

Is it this pulley?

http://www.racingbeat.com/FRmazda1.htm

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[moto62]

Originally posted by benracin:
John (the head wrench) and I are not certian that the pulley was put on correctly. Is there anyway to find TDC on a rotary without taking the thing apart? Thanks
Ben
ITA33

To answer your original question, the pulley can only be installed one way over the keyway on the E shaft. There is no incorrect way to do it. Leave it alone.
Ray

[Speed Raycer]

Originally posted by lateapex911:
Is it this pulley?

http://www.racingbeat.com/FRmazda1.htm

This is the pulley on my car...

[Tak]

At TDC, the keyway on the eccentric shaft is rotated exactly 90 degrees from vertical.

Tak
#29 ITA
SFR SCCA

[Rex B]

"To answer your original question, the pulley can only be installed one way over the keyway on the E shaft. "

Actually, the hub that is keyed can go only one way. But the pulley with the timing marks can go 4 different ways, only one of which will give you usable timing marks. Unless you have the foresight to punch some marks on hub and pulley before disassembly, you can wind up clueless on disassembly.
Chris' explanantion is the first good one on how to resolve this common delimna.

[moto62]

Originally posted by Rex B:
[B
Actually, the hub that is keyed can go only one way. But the pulley with the timing marks can go 4 different ways, only one of which will give you usable timing marks. Unless you have the foresight to punch some marks on hub and pulley before disassembly, you can wind up clueless on disassembly.
Chris' explanantion is the first good one on how to resolve this common delimna.[/B]

Actually, you are right, if we were talking about a stock pulley but we're not. Ben described an aftermarket pulley (probably from Racing Beat) in his first post and those are a one piece design.
Ray

[jake7140]

I have this on my website under the tech section, but have never used it. Sound legit? (assuming everything is stock-ish I suppose)

"Date: Sun, 5 Nov 2000 16:39:34 EST
From: [email protected]
Subject: Re: (rx7-fb) timing and dist

OK. Heres a cool fact. look at the rear of the motor on the pass. side, remove the flywheel inspection plate, slowly turn the motor over. You will see a mark on the flywheel, and on the block it's a hash mark. Line up the lines and you are TDC."

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Steve
[email protected]
<A HREF="http://www.geocities.com/jake7140" TARGET=_blank>My racing page
</A><A HREF="http://www.geocities.com/elrss" TARGET=_blank>Elkhart Lake Racing_&_Sipping Society
</A>

[C. Ludwig]

It might be a 12A thing but there was nothing on the 13BT I have on the engine stand in the garage. IMO the flywheel isn't even close enough to the rear iron for you to align two marks.

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Chris Ludwig
08 ITS RX7 CenDiv

[Speed Raycer]

Originally posted by jake7140:
OK. Heres a cool fact. look at the rear of the motor on the pass. side, remove the flywheel inspection plate, slowly turn the motor over. You will see a mark on the flywheel, and on the block it's a hash mark. Line up the lines and you are TDC."

Ahhh crap! I just shoved all three of my spare 12a's flywheel first back into a deep dark shelf. DOH!



[This message has been edited by Speed Raycer (edited July 15, 2004).]

[weedracer94]

If you remove the front hub bolt, (DO NOT ALLOW THE HUB TO MOVE FORWARD!!!!), you can see the front keyway. When the keyway is in the 9:00 position the eccentric shaft will be in the TDC position for distributor installation and alignment. If the hub moves forward, it is likely that the needle bearings can fall out of place... OOPS. have to take off the front and make sure that they are OK.(experience).

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ITA 94
SFR SCCA