924Board.org

[MikeJinCO]

On my race motor which is running quite well with strong acceleration, I can't get the timing right. First I have a block from a 1980T with unknown history. I believe we did measure its deck height but it did not appear to be an issue at the time as I recall, the S2 pistons come out flush to the deck. We had to cut valve pockets in the pistons to clear the valves on cam overlap. The motor he head is a NA and is from an equally unknown 1978, the motor was locked up when I bought the car and apparently had been so for 15 years. I don't think we measured the head height. This motor combination was NOT originally intended for this car. I was concerned when we first assembled the motor as Dan Becket's compression calculator had the pistons down bore a bit but I did the calcs and the compression ratio turned out correct.

When I get the crank and cam all lined up and the distributor lined up correctly I can't check the static timing due to the MSD ignition which doesn't work until the motor runs so I have to guess statically and set in while running. The distributor still has the mechanical advance Of about 14 degrees. I did put timing marks at about 15 degree(static)(Weber carbs and 2000m altitude) and 43 degrees on the front pulley.

When I try to set the timing it barely runs but If I turn the distributor full to the right so that the vacuum advance resevoir runs into the firewall, the timing comes back to about halfway between my 15 degree and 43 degree marks or maybe 30 degree on the front pulley at about 1500 rpm and it really runs well. Third gear acceleration at 4000 RPM is very good.

It has finally struck me that I probably have a combined deck height issue as I have reset the distributor multiple times and it always comes out the same.

I can't really get in to measure the C-C distance of the cam to crank with any accuracy. I'm beginning to assume that I'm basically one tooth short on the belt and it looks perfect. So the cam is advanced about 8.7 degrees.

Since it runs so well should I just leave it be or should I try to set the the cam back one tooth?? Or do something else?

Thoughts and or Suggestions please.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[RC]

Does this have stock mech/vac advance reluctor type dizzy, basic non programable MSD, or any adjustments? What about green dizzy connector wire?

You could try swapping polarity of pickup coil wires to MSD input. Yes, try this first, then reset timing.

With correct polarity on a good ignition unit, the firing point should be at the 0v cross over point when the reluctor and stator points align. Incorrect polarity could be triggering anywhere up to 45* out, but will vary offset with RPM. That`s how it usually works with most ignition units anyway.

You could also try removing the vac advance mechamism completely. Its unnecessary for a race motor, and will simplify tuning, simple 2D map: RPM-ADV.

Sounds OK though with 15* static + dist adv (14* x 2) = 43* total. That`s about right for Euro spec CR.
_________________
World`s quickest 924 2L slushbox