absolute timing

dingo · Post by **dingo** » Fri Sep 22, 2006 10:24 am

OK...what is the absolutre bulletproof way to find TDC ? I have this 1700 motor (914) with history unknown. With the 914 fan/pulley, i look down the rabbithole and there are TWO distinct markings...which one is TDC?

I DO have a timing scale, but the Bus fan/pulley i have is beat up and no discernable markings.

The offset half-moon on the dizzy driveshaft points to mystery spot and does not match the picxture in Wilson book(which is vague enough as it is)

I tried putting a pencil down the #1 pluig hole..it may work for T1, but all i get is a crunched up pencil..obviously the angle of piston in T4 is not compliant

My dad says to watch the valves while turning the pulley..i find this method confusing and tedious...

thanks, dingo

spiffy · Post by **spiffy** » Fri Sep 22, 2006 10:36 am

Hard to go off of the dizzy because some PO may have put the drive pinion in 180* off....if you know it to be put in right, it helps tremendously! I have heard of the finger in the SP hole but can't remember from who ar how to do it....I would go with watching the valve train...after you find #1 you will then have a reference point on your dizzy (make a mark with a felt pen or something, the notches aren't always right on) and you can make a mark on your fan to match up to the timing scale.

Adventurewagen · Post by **Adventurewagen** » Fri Sep 22, 2006 11:04 am

Here is some good info from Richards Site along with links to other articles on timing and marks.

http://www.ratwell.com/technical/FindTimingMark.html

If I had a TypeIV engine I'd try to help more, but I dont'. sorry.

Post by **Sluggo** » Fri Sep 22, 2006 11:10 am

Adventurewagen wrote:Here is some good info from Richards Site along with links to other articles on timing and marks.

http://www.ratwell.com/technical/FindTimingMark.html

If I had a TypeIV engine I'd try to help more, but I dont'. sorry.

Good info. But do not take the fan apart. They are balanced at the factory and taking it appart can throw this off. Since it's connected directly to the Crank Shaft, this can cause bearings to wear and (over time) extra endplay. I've made this mistake.

Post by **Amskeptic** » Fri Sep 22, 2006 11:14 am

dingo wrote:OK...what is the absolutre bulletproof way to find TDC ? My dad says to watch the valves while turning the pulley..i find this method confusing and tedious...

Rotate engine clockwise with adjustable wrench on alt pulley and yes! listen to dad! look at #3's valves. When exhaust rocker starts coming back up (closing) look for intake to just start going down (open). That overlap point is subtle and it is #1 TDC for power stroke.
Colin

dingo · Post by **dingo** » Fri Sep 22, 2006 11:16 am

thanks..im half-way there. I have the same fan as in the ratwell pic. D-Jet with a '0' (hidden beneath dirt and rust). So ive lined up the '0' with crack, notch etc

so now i just need to find the firing stroke...so i can set the valves on the correct stroke.

...one false assumption, and things go awry pretty quick !

chitwnvw · Post by **chitwnvw** » Fri Sep 22, 2006 8:57 pm

If both valves are closed that's your firing stroke.

dingo · Post by **dingo** » Fri Sep 22, 2006 9:59 pm

Rotate engine clockwise with adjustable wrench on alt pulley and yes! listen to dad! look at #3's valves. When exhaust rocker starts coming back up (closing) look for intake to just start going down (open). That overlap point is subtle and it is #1 TDC for power stroke.
Colin

Ok thanks.., i think i will give it a whirl in the morning...see if i can find the subtle overlAp

dingo · Post by **dingo** » Sun Sep 24, 2006 1:16 pm

look at #3's valves. When exhaust rocker starts coming back up (closing) look for intake to just start going down (open). That overlap point is subtle and it is #1 TDC for power stroke.

..so when exhaust rocker is closing..that means exhaust valve is opening ?
intake rocker opening = intake valve closing ?
...so #3 has exhaust valve open and intake valve closed....releasing exhaust ?

also Wilson book talks about 12 deg between dizz drive notch and centerline. When my pulley is at exact '0', i get more like 15-25 deg between d-d notch and centerline. does this really matter ? so long as rotor points to #1 tower ?

Post by **Amskeptic** » Sun Sep 24, 2006 5:02 pm

dingo wrote:
look at #3's valves. When exhaust rocker starts coming back up (closing) look for intake to just start going down (open). That overlap point is subtle and it is #1 TDC for power stroke.

..so when exhaust rocker is closing..that means exhaust valve is opening ?
intake rocker opening = intake valve closing?

#3 piston is going up on the exhaust stroke, shortly to go down on the intake stroke.
At the same time, it's opposing pair cylinder (#1) is going up on the compression stroke shortly to go down on the power stroke.

You are looking for the #3 exhaust valve to be closing and the #3 intake valve to just start opening.
Colin

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absolute timing

absolute timing

Re: absolute timing