Timing problem - Help!

[Mark57]

1986 Corolla 4AC Auto 2bbl - Head gasket blew out between #3 and #4. Removed head and found that #4 was taking on water from 2 small pits in nearby coolant ports. Had the head tig welded and surfaced. A .020 shim was added below the head gasket to compensate for the machining (2X). This brought the distance between crank and cam to stock and the timing belt went on perfectly with the crank and cam marks “right on”. Valves are adjusted and manifold vacuum is 18-19lb.
Here is my problem – timing! No matter what I do, I can’t get any better than 0 degrees BTC, 10 degrees with vacuum advance connected. I need 3/13. I have the distributor cranked all the way to the right (advanced) just to get this. If I jump a tooth it just goes more advanced than I need. Seems that one tooth gets me 0 degrees and below and the other tooth gets me 20 degrees and above. I can’t find anything between 0 and 20.
I don’t know what the timing was set at before the head went, but I do believe it had a little more power then. When I took the timing belt off I did notice that the cam may have been to the right of the alignment mark from a prior repair by another owner. Also, my Haynes shows 3 “marks” on the valve cover, with the center mark being TDC. Is this correct?
When accelerating, there is a place where letting off a bit on the gas seems to give me move power than holding position or applying more gas. I don’t know if this is related to the timing or not.

Thanks for any help.
Mark

[spawn7037]

Mark, the center mark on the cam cover is tdc to my knowledge, I have the exact same problem with my 83' corolla after a rebuild, I get a weird lag that I have to rev past, a guy told me to advance timing 5 degrees but I haven't had the chance to try it. Not sure what to tell you about not being able to get the right advance tho, sorry bud.

[Mark57]

Thanks for the response above. I may have stumbled onto the problem solution this evening. With my brothers encouragement I went to the shop to remove the distributor and drill out the adjustment slot to allow for the remaining 3 degrees. Well as most of you know the aluminum slot is braced at each end with right angles cast in the housing. So there would be no way to lengthen the slot. I had already checked for play in the shaft -zero. I did twist the rotor alittle harder than I ever had and found it would turn on the shaft. Played alittle with it right and left until I found a sweet spot that got me to 15 degrees BTC. Not the 13 I need, but better than the 10. The engine seems to be much more responsive now and I'll drive it tomorrow after work.
Does anyone want to respond to the issue of leaving it at 15 degrees BTC and what negative affects if any will it have on the engine?

[spawn7037]

If you are detonating too soon you could get engine knock which isn't great for the motor. People worry more about it on turbo's more than anything.

[nbm077]

puts flame suit on---preignition or detonation during initial throttle transitions from idle position will cause lots of damage.

from my very limited knowledge, i would think that doing some kind of alterations to the distributor will change the degree's allowed from 0 to 25 degrees. (change some of the components in there around? i have no clue what? springs? levers? gears? cogs? thicker wire? more current?)



edit:

When accelerating, there is a place where letting off a bit on the gas seems to give me move power than holding position or applying more gas. I don’t know if this is related to the timing or not.

Thanks for any help.
Mark

I think this has to do with a Rich environment, especially if you have part damage. does the engine smoke alot? Also the power band could have been affected as parts wear over time. this might not be noticeable in a heavier/clunkier/more common coupe, but in the hachi-back i can notice shifts in power band due to small changes in engine wear etc.

[Mark57]

Just to let everyone know. I have now driven the Corolla nearly 100 miles with the timing set at 15 degrees (13 factory) and I notice no preignition or detonation. In fact, the little 4 door seems to have found new life in the old motor (152K). I'm am very happy with both the sound of the motor and its performance at all rpms. When I have time and we get out of this deep freeze here, I may play some more with the rotor position and the distributor in a attempt to dial-in exactly 13 degrees.

Thanks, Mark