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So I had my carb dialed in and then over time it started to run poorly and I couldn't figure out how a well dialed system would just go to crap so I figured its not the carb...checked a bunch of stuff and was looking for a vac leak because vac was low as well...Finally checked timing and found it at zero....I was sure I had it set to 12 okay fine roll in 12deg and it runs killer for a day then its back to zero...WTF? set it back to 12 and make sure the hold down its RFT...runs great 3 days its back to zero.
Place a witness mark on the dizzy flange roll in 12 deg and its fine for a few weeks now tonight the mark appears to be where I left it but its back to zero......!
1) Why does it never end up at a neg value? it will only retard a far as zero. It might retard 12 in a day but stop at zero for weeks?
2) how could it retard 12 deg in a day without physically twisting the dizzy housing?
3) the dizzy gear is steel and im running a roller cam the gear has 30k+ has a noticeable wear pattern there is some slop but isnt knifed edged and doesnt look like "new cam time" pattern....if a gear could wear 12deg in a day im pretty sure it would be dead long ago. I daily drive the thing.
4) This is an MSD E curve system there are no counter weights its all digital...Im wondering if this is perhaps a digital issue.... Everything else seems to operate proper with that system. It operates a bit odd as it can only retard timing not advance it so you set total timing then add a curve that retards that value to give you base and vac...I do not know if my issue is something that could be caused by a firmware issue or not. Im not that well versed in its digital logic.
did the ring on the balancer slip? this is common and will appear to make timing change, but in reality its just the mark on the crank moving. inspect it, if the rubber between the 2 pieces seems odd, get a new balancer and compare the position of the marks
I doubt it...its a pretty decent quality balancer plus I can see the physical effects ( poor throttle response, low vac, low idle, off idle hesitation....)
-Gun
ok then, the msd distributor is solid state with no weights, but a quick check turns up more than a few customer complaints of dizzy failure with that e curve setup. if i was you i would pull it out and swap in a pro billet with a digital 6 box. appears much more reliable
I turns out it was the gear actually slipping on the shaft.
I have no idea how that even happens (have you tried to actually pull a gear off a dizzy shaft??) It also broke the roll pin the goes through the shaft and gear..
A nice 2nd gear pull at 6,200 rpm pin pointed the issue.
just read through this- dizzy gear is steel? swap to the bronze. Just a bit softer, takes out some of the vibration. I'd also look at how deep the gear is setting into the cam. If its too deep in then it might be making a lot of friction/binding.
The gear falls within spec for position on the dizzy shaft. Bronze is significantly softer than steel...that seems like a good option if I wanted gold sparkly oil. I dont recall anyone recommending bronze for use on a roller cam. Is there a reference you can link to or further explanation?
The gear literately just slides on on the shaft with no effort it was that way when they installed it. Ive tried to remove gears from MSD shafts before you need a legit die and press I'm nearly certain they are pressed on with a 1000+ pounds.
There is no galling or indication of significant friction on the shaft.
08-27-2016, 12:20 AM
How the hell does base timing just evaporate?
