Locating TDC : dumb questions

[trinitrona]

Also keep in mind that a four stroke engine has two TDC per cylinder, hence the suggestion mentioned early on in this thread to take the dist cap off so you can figure out if you are at TDC exhaust stroke (i.e. exhaust valve closing, intake valve opening) or TDC compression stroke (i.e. intake valve closing, spark about to fire).

It's good practice to keep in mind which TDC you are trying to reference. What I do to find TDC compression stroke is take the spark plug out of #1, put a piece of tissue in the spark plug hole (enough that it doesn't fall in of course!) and when the tissue blows out while rotating the motor, you know you're on the compression stroke. Then a screw driver or fancy dial feeler gauge will get you to TDC. If you're looking for TDC exhaust stroke, then of course you go round one more time. Then you can verify that your cam belt and distributor rotor are on correctly.

Maybe it's overthinking it a bit on a SOHC engine...I'm used to working on quad cam V-6's

[Bukowski]

Originally Posted by trinitrona

...[trim]... Then you can verify that your ... distributor rotor is on correctly.

Interesting comments - I thought the rotor comes off/on only one way or something like that - IOW ignorance is bliss for replacing the rotor?

@sausagehacker : I'll have to understand those bolts first before I drizzle.

[Arizona_928]

Originally Posted by trinitrona

Also keep in mind that a four stroke engine has two TDC per cylinder, hence the suggestion mentioned early on in this thread to take the dist cap off so you can figure out if you are at TDC exhaust stroke (i.e. exhaust valve closing, intake valve opening) or TDC compression stroke (i.e. intake valve closing, spark about to fire).

It's good practice to keep in mind which TDC you are trying to reference. What I do to find TDC compression stroke is take the spark plug out of #1, put a piece of tissue in the spark plug hole (enough that it doesn't fall in of course!) and when the tissue blows out while rotating the motor, you know you're on the compression stroke. Then a screw driver or fancy dial feeler gauge will get you to TDC. If you're looking for TDC exhaust stroke, then of course you go round one more time. Then you can verify that your cam belt and distributor rotor are on correctly.

Maybe it's overthinking it a bit on a SOHC engine...I'm used to working on quad cam V-6's

I'm confused by that post. lol
Simple rule, cam goes twice as fast as the crank.

[trinitrona]

@ Bukowski: You're correct of course, the pin is slotted, so the rotor only goes on one way. Apologies for the confusion. Again, I'm more familiar with engines where the distributor is geared off the cam, or for added fun, off an auxiliary shaft. In that type of arrangement, knowing which TDC you are at in the engine stroke is important because it is very easy to install the distributor 180 degrees wrong. Anyhow, let's just say working on a 944 8V NA motor has been pleasant compared to a Maserati V-6 with about 6 feet of timing chain: http://tinyurl.com/hbk5ju7

[edredas]

Originally Posted by AZ_porschekid

I'm confused by that post. lol
Simple rule, cam goes twice as fast as the crank.

The cam rotates half as fast as the crank. So every 360* of the crank, the cam only moves 180*.

He is saying that if you use the mark on the flywheel you may be on the exhaust stroke with the cam 180* out. You will then need to rotate the crank another 360* to get the engine to TDC.

[sausagehacker]

Originally Posted by Bukowski

@sausagehacker : I'll have to understand those bolts first before I drizzle.

there are 6 plugs, 8mm allen head. Go slow and be careful, they strip. Happened to me twice now. now, just pour some oil in each hole (they're just access holes, the inner cavity only contains the cam and its journals/bracing). You want to have some oil present on the cam lobes and lifter faces as you turn it, ideally.