The Stovebolt Site Forums The Shop Area Engine Shop 228 GMC engine timing problem

Friend has a newly rebuilt 228 engine. Vac advance was not working, wo he pulled the dist and fitted a new vac advance. Its not 180 out of time. New points set at .016. The distributor that came with the engine is a 1112360. The book sais it should have a 1112390 however I do not know the difference. Here is the problem. With the vac hooked up the only way to stop engine knock is to retard the octane selector 3 clicks or 6 degrees??? Whats going on here? The initial advance is set nuts on the mark on the flywheel. However when adding in 2-3 clicks advance on the octane selector it starts to knock. Again the only way to get it to stop is to dial in 3 click or 6 degrees retarded? This has got me stumped? Could this be too strong a vac advance, we may have to limit the vac advance arm movement? Maybe it the wrong vac advance? Any and all ideas welcome.

Do you have the advance hooked up to ported vacuum?

Yhep it screwed right on the side of the Carter W1 carb in the stock location.

Tim, I have a Delco Remy book that lists a bunch of distributor applications..

An 1112360 lists as fitting a 1950 and 51 GMC 228, 248, 270.

An 1112390 lists as fitting a 1953 228. An 1112391 fits the 248, 270 and 302 of the same year.

The 1112360 has a contact set listed as requiring a D100P or 1944374 and a condensor number D201 or 1900272.

The 1112390 calls for a different numbered contact set, D105P or 1944375 as well as a different condensor, D203 or 1928111.

The cap and rotor part #'s are different as well..

I am not a real student of ignition timing or octane selectors but perhaps you have the wrong set of points in your distributor ??

The D105P could have superceded the D100P and they are one in the same ? Or they could be different parts..

If you want a scan or a fax of these pages, drop me an E mail and let me know.

I am not sure if any of this helps but it's all I got, lol..

Bill,
Thanks for the reply. We will bump your info up against what he has installed and go from there. Thanks again.

Tim, if the truck runs well down the road, then it should be allright no matter what the timing say. There are minor difference in the advance curves with the different distributer #'s, but by the later on GM carried only the 1112403 distributer as a replacement,even for early models.The D105P or 1944375 is the point set used with the taller cap distributers.

Thanks Tony,
We can get it to run down the road under load without it pinging but only if the octane selector in the retard setting as described. Where we have the timing set starts it good and the vac is 21. It just didn't make sense.

Tim

Problem solved by drilling out the new vac advance arm and pinning to limit the travel. Some trial and error determined travel. Octane selector set at 2 clicks or 4 degrees now and initial timing on flywheel somewhat retarded.