MK1 crank pulley questions

[hunter85]

Ok I put this MK1 pulley on and it starts runs and idles 200% better than with the wiggly one I can also tighten my alternator/water belt finnaly . For funsies I checked the timing {put a new mark on the mk1 pulley exactly where the stock pulley mark was} It was at 6btdc and now it rests at 10btdc without advance and when I started it with advance line still on it was off the scale completely I guess 18-20 btdc. It runs fine and I think the mk1 pulley was slightly bigger {underdrive} which would explain why it is so off or did I do something wrong and should throw it back in perfect time thanks in advance Travis

 

PS these pulleys look awesome and perform good but I got to thinking how long can a alluminum pulley last without warping I hope almost 30 years like the stock one

Edited November 9, 2014 by hunter85

[scott87star]

The correct way would be to use a piston stop to find exact TDC and mark that, then time it per FSM. There is no guaranty the old TDC mark was correct.

[techboy]

I didn't think the MK1's were meant to be underdrive. My understanding was that they were a stock replacement. Do you compare by mating them together? Was one bigger? Did you use a different size belt other than the OEM belt?

[mikec]

Testing ignition timing:

1: engine must be warmed up. If you live at high altitude (above 2000 feet or so) use the two-prong terminal hanging unplugged & hopefully capped shut between the air filter canister and fender to force the car into low altitude mode.

 

2: connecting the distributor vacuum advancer hose should NOT alter timing at idle RPMs. If it does the vac hose connections are wrong. The distributor should be getting "ported" vacuum which is not the same as "manifold" vacuum. At idle, ported vacuum should be pretty much zero; as the throttle plates open the vacuum will build up a bit... as the throttle plates open futher the vacuum will once again drop and then transistion into whatever boost pressure is present.

 

The diameter of the crank pulley does not affect timing unless you are viewing the timing mark from a bad angle. Imagine drawing a line from the center of the crankshaft (the rotation axis) up through the "T" mark on the front of the engine. Keep extending that line. Ideally your timing light and eyeballs are on that line. If you look from some other point, then parallax issues may cause you to mis-read the timing especially when the crank pulley is something other than the stock diameter - i.e. when the distance between the timing mark on the pulley and the "T" on the engine is larger than stock. The bigger this distance the more sensitive the timing error will be to having your eyeballs not on that extended line.

 

mike c.

[questtuner82]

Off the subject, but an underdrive pulley "crank" would be smaller not bigger. The waterpump pulley would be bigger and crank pulley would be smaller. The "drive pulley" ie crank pulley would have to be smaller. " hence the term underdrive"

[importwarrior]

the mookeeh is supposed to be the same as a stock size pulley diameter.

[TexasQuest]

They are not underdriven, they are oem size billet aluminum replacement. Question to the OP, why would swapping a crank pulley affect your timing? Your outside the timing cover, simply replacing the crank pulley. One way on, one way off.