Has anyone experienced spark scatter on a sbc caused by the oil pump?  I've heard that the sb pump (w/ 7 teeth) is not as "smooth" as the bb (w/ 12 teeth) and this can cause spark scatter.  Personally, I don't know if that's fact or fiction.

Here's my gig:  Sbc with a solid tappet cam, Cloyes chain and Mallory Electronic Breakerless (mechanical) distributor.  The engine has 15 passes on it and 500 miles of street driving.  While setting the timing at 38* (all in at 3,000rpm) the timing jumps back and forth from 36* to 40* (about a 4* swing).  It does this all the way up to +6,000rpms.  I originally thought I had a bum distributor and installed another Mallory.  Yet, I ended up with the same problem.  It's not a faulty timing light either, because I've used three of them all with the same result.

At first I thought the cam was "walking," but it's a flat tappet stick.  Then I thought the chain might be stretched, but it has less than 1,000 miles on it and there certainly was no slack when insalled.  Mallory's help desk told me to check the distributor ground.  I did, and it's grounded.

Could this be the oil pump?  I have a Melling sbc high volume pump, and use Red Line 10/40 synthetic. 

On the Prestage.com board, someone suggested checking the end play of the distributor shaft - which I'm going to do today.

Any other suggestions?    

* The engine runs very strong, no visible warnings while reading the plugs, etc.  Frankly, without seeing this with the light I'd never know it existed.

When I worked at NAPA my co worker installed a timming set on his astro van with a 4.3 and  180 k on the factory one . After about 35k more the new chain was found to be stretched and causing the same thing . With the computer disconnected and timming souposed to be staying at base it was jumping all over. I called clevelite tech line. I was told the chain should be soaked in a heavy oil overnight before instalation. I asked my friend and he said he just put it on out of the box. Next one he soaked in gear oil. I think the only oil supply is splash or a little gets picked up from the crank sproket . The damage is done in the first few minuits if dry installed. I never thought about this and makes me wonder about all the ones I changed in the past?  Aftre that last one I did I  Put pretty much a whle bottle of thick red stuff all over it ,the same stuff I coated the cam and lifters with . You surley dont have many mes on it but incresed valve spring preasure could increese the wear. Another place to look is what springs are on the centrifigal advance. I have had problems with the lightest ones before. Sometimes I run two different springs on either weight to cure this. Also the pickup module in your distrubitors could be damaged from shipping . Had this problem ith a dord  this spring . I allmost put a chain and gears on it but found the distrubtor I had put in last fall to have the pickup cracked where it mounts . Napa tech line told me to check this first  (it happens in shipping if it gets dropped once or the truck hits a good bump). It must of ben cracked half way cause it ran good till next spring then I put a timming light on it. I am so glad i did not do the chain because it is a 90 E150 and vans can be a pain.  

Could be the distributor is jumping around, the oil pump could be the source of this. The cam could also be changing time because of a sloppy chain, lots of reasons for this from a loose/early failing chain to the cam and crank bores being too close to each other (a factory machining error) and the chain can't be made tight enough. It could be the timing light, sometimes the electronic circuit is inconsistent in its data processing time.

Bogie