timing, stock 283

[bobbybelair]

I think I need to fiddle with the timing on my stock 283. I get a bit of rattle sound when I get on it just before shifting into second. Too much advance on the timing? Another clue is sometimes when it is hot and I have stopped for gas, when I turn the key the engine will turn a bit, basically go dead stop, then fire up. Too much advance in general?

I'm going to unplug the vac advance - do you plug the vac going to the distributor or the carb? Also, set the advance to 36 at 2500 revs (don't have a tach so will have to guess revs, I'll get a timing tape and glue it on as Rick_L suggests), then check what the advance is at idle for reference, with the vac plugged back in. No distributor genius here, I assure you, so any help appreciated.

[bobbybelair]

Just cracked the manual, and it calls for 4 degrees at 1000 rpm. Assuming the distributor is still in decent shape, I guess I should start there. Not having a tach handy, I will probably end up setting it by drive and feel anyway.

[Rick_L]

When you say it's "rattling" on the 1-2 shift, is that with your foot on the floor, or some other driving condition?

The initial timing spec of 4* was recommended back in the days when gasoline wasn't as good as now. You may be able to use more.

Don't worry about not having a tach, it's not really required. What you want to do when checking at rpm's above idling is just to slowly increase the speed until the timing quits increasing. This with the vacuum advance hose removed and plugged at the carb or manifold.

Tuning by feel and by ear (listening for pinging) is fine, but you want to use a timing light to know where you stand once you get it right. And you must isolate the vacuum advance from the mechanical advance to understand how both are working.

You have a good start and must have read some other posts.

[bobbybelair]

This rattle has elicited a a different opinion on what it is from a few observers. It occurs when I get into it pretty good (doesn't have to be wide open) from a stop and becomes noticeable just before the Powerglide shifts into second, say between 35 to 40 mph. Quite a mechanical sounding clatter, mostly from the right passenger side in my opinion. It can occur in second at higher speeds if I get on it but not as noticeable.

Another point, but not sure if this is relevant - linkage needs adjusting because it doesn't kick down from 2nd to 1st at speeds that it should, say 35 mph. Or any speed where it should.

I figure taking a good shot at setting the timing one more time to eliminate it as a reason.

My old time mechanic friend says he thinks a cam lobe is somewhat wiped. Says it reminds him of the good living he made off replacing cams and lifters on the early 305s (and maybe 267s?) which had a bad grind and didn't rotate the lifters properly. That's possible too. I could pull the valve covers and watch the rockers to know for sure

[chevynut]

Your symptoms sound just like a friend's 62 Impala did years ago...rattling, then hard starting after stopping at a gas station for gas. We never tried to figure out what it was. I'd back off timing and see if it goes away.

I guess I don't understand what a cam lobe would have to do with it. It's either pre-ignition or detonation, imo. What is your CR? Have you tried using higher octane fuel?

back in the days when gasoline wasn't as good as now.

That's funny....lots of guys claim gas isn't as good as it used to be. LOL

[Rick_L]

Certainly the hard starting when hot is usually an indication of too much initial timing. So that's what should be diagnosed and fixed first if needed.

If you have a bad cam lobe then that's another situation altogether. It's also possible to have a burnt exhaust valve seat.

A compression test can isolate these kind of problems, as will using a vacuum gauge.

Both the cam lobe and burnt exhaust seat will get worse pretty quickly.

But bobby don't let us discourage you into panicking, work through diagnosing all this.

[bobbybelair]

No panic here, I've been nursing this old 283 since I pulled it a long time ago and did some backyard work on it. I sent the heads out to be done a couple years ago and put them back on after I broke 3 pushrods if you recall. I'm gonna pull it again someday and see if it can be saved. It's already 30 possibly 40 over I think. I won't rebuild it without a sonic test though - I'll be asking questions about that later.

It runs ok, and it is not hard starting, it always starts easy, just sometimes when I start it hot it turns briefly, does a quick interruption stop, then starts right up. All on the same key turn, it's a brief pause is all but it starts immediately. But I will do the timing and let you guys know.

[chevynut]

To me your hard starting when hot problem sounds like it might be heat soaking of the starter solenoid. Have you tried to address that with a remote solenoid? It may not even be related to your timing, especially if it doesn't do it cold.

[bobbybelair]

Anything is possible with this old boat, cnut. I'll tinker with the timing but don't think it is the problem.

[Rick_L]

About 95% of the time or more, this "heat soak" problem is either timing related, or a bad starter. battery, or connections. The heat soak deal is overrated.