Vacuum advance needed for cam break in?

[xLURKxDOGx]

Thought this might be important but not entirely sure. Looking to get 34 total without vacuum and total 47 with. Thoughts and opinions much appreciated.

Thanks,
Jake

 

[yellow rose]

More timing is better on break in than less.

I'd rather see 47 than the 34. Get it retarded enough and it will stick exhaust valves, over heat and other crap.

Guys think retarding the timing is safe. It's not. It's a parts killer.

 

[xLURKxDOGx]

More timing is better on break in than less.

I'd rather see 47 than the 34. Get it retarded enough and it will stick exhaust valves, over heat and other crap.

Guys think retarding the timing is safe. It's not. It's a parts killer.

Thanks for the insight. It’s not something that I’ve seen discussed a lot and wondered if it was more important to the cooling side of break in than anything else since fuel economy is a non issue.

Jake

 

[RustyRatRod]

I never worry about "where" the vacuum can pulls timing. I just hook it all up and go. I've seen Rob (@crackedback ) say it time and again and it's the same way I do it. Soon as the engine busts off, run it up to "about" 3K "or so", grab the timing light and pull in about 35 "or so" degrees of timing. Break it in like that and you'll not have a problem.

 

[RustyRatRod]

Oh and my personal experience is to leave the vacuum advance disconnected during break in. That's just my personal preference.

 

[xLURKxDOGx]

Oh and my personal experience is to leave the vacuum advance disconnected during break in. That's just my personal preference.

That was the answer I was looking for. Like I said, I haven’t seen it discussed as of yet but didn’t dig into the catacombs of the forum.

Jake

 

[RustyRatRod]

That was the answer I was looking for. Like I said, I haven’t seen it discussed as of yet but didn’t dig into the catacombs of the forum.

Jake

Also, FWIW, I have never limited the vacuum advance can. I don't worry "how much" it pulls in. The MP engine book says 60* total is not uncommon. It's not how much, but when it pulls it in. Only at very light part throttle. That's to help clean up the combustion process so as not to have it "backing up" in the combustion chamber at very light throttle......if that makes sense. Since vacuum drops out on acceleration, you'll never see that much on accel anyway, so no danger of detonation.

 

[yellow rose]

I never worry about "where" the vacuum can pulls timing. I just hook it all up and go. I've seen Rob (@crackedback ) say it time and again and it's the same way I do it. Soon as the engine busts off, run it up to "about" 3K "or so", grab the timing light and pull in about 35 "or so" degrees of timing. Break it in like that and you'll not have a problem.

35 is pretty slow no load.

I also time the distributor while it's on the stand. If I want 40 or 45 or whatever I'm usually within a degree or two of that when it fires.

Never drop the distributor in timed at TDC. They sort hard and again, slow timing kills parts.

 

[RustyRatRod]

35 is pretty slow no load.

I also time the distributor while it's on the stand. If I want 40 or 45 or whatever I'm usually within a degree or two of that when it fires.

Never drop the distributor in timed at TDC. They sort hard and again, slow timing kills parts.

Maybe so, but I've never seen exhaust overheat at 35 "or so". I agree to try to drop the distributor in "a little" advanced. Usually, it'll pop right off.

 

[MopaR&D]

More timing is better on break in than less.

I'd rather see 47 than the 34. Get it retarded enough and it will stick exhaust valves, over heat and other crap.

Guys think retarding the timing is safe. It's not. It's a parts killer.

I always saw that mentioned in random places for engine break in, "set ignition advance on the conservative side" and no mention of vacuum advance... you want as much advance as it'll take since it's under no load. It'll probably work fine without vacuum advance but it won't hurt to hook it up and it will just help the engine run cooler. I'm willing to bet most of the time why engines get hot during break-in isn't as much because of the parts wearing in but more because there isn't enough ignition advance, or the idle mixture wasn't adjusted properly.

I put this in the same category as "run it rich to be safe"... might prevent detonation and overheating in the short term but you're just wasting gas and wearing out your rings and cylinders in the long term. And causing a bunch of carbon build-up in the chambers, fouled plugs etc.

 

[crackedback]

Get a bunch of timing on it. If the slowest speed you plan to run the engine is 2K get at least 35 on it there and let it go. Watch temps and leaks. No load, usually no issues with detonation

Unless you have a fast curve, all in at 2K, you may think you have a certain number of degrees on it because of the intended total number. If that total number isn't in until 3K, you aren't close to that number at 2K.

To me the vac adv is a potnetial variable. if you change throttle speeds and for some reason the vac drops below the can activation level, all that timing is dumped out. Make that stuff static, just twist the timing in. 40* is fine too.

Running rich is not good either as the unburned gases continue firing off in the exhaust port/system creating more heat.