Greg Rogers

I have a 70 Vista Cruiser with a 350 4bbl- all stock, which I bought about a year ago. I am just now getting it sorted out. I have been driving it some and I noticed slight spark knock on light acceleration. So I checked the timing and it was set at about zero or maybe even a degree or 2 after TDC!! So I set it up to 12 btdc and took it for a drive- spark knock big time! I also have a 71 Cutlass that I've owned for years. The 71 was set at 12 btdc but I found seems to run best at about 18 btdc. Both cars use 93 octane"premium" gas. I know the 71 has 8.5 compression and the 70 has 10.25, but could that make such a difference?? Also I believe the timing chain is quite loose on the 70, I think I can hear it. Or could the harmonic balancer slipped? Thanks for your thoughts, Greg.

MDchanic

Yup.


Could be. You'll never know 'till you check.

- Eric

oldcutlass

The harmonic balancer is easy enough to check, and the timing chain needs to be replaced.

Greg Rogers

After checking it out further I am quite sure it needs a chain, the timing mark jumps around on idle, so that will be done this winter(unless it quits before then). I'm not going to go too far from home until then...I kinda rescued this car from being a parts car so it is to be expected, I guess... but I may have to get a MAW helmet- I don't want to end up rebuilding this engine!

oldcutlass

Is your spark knock at very light throttle only? If it is check you vacuum advance canister, disconnect it and see if it goes away.

Greg Rogers

I'll try it. I checked everything out and the vac advance isn't leaking vacuum, in fact I didn't find any vacuum leaks except for some leakage at the carb throttle shaft. I will try it with the advance unhooked. Also I was thinking this old girl may have oil/carbon deposits- don't know how much oil it uses yet-has 176 (276?) thousand miles....