273 Can't get too much timing - confused

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66fyssh

66fyssh

Don't Stop Believin'
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I have a 273 that won't ping or kick back the starter regardless of timing.

I just put a rebuilt distributor in it, but it was doing this before. The po said the cam is original but stronger valve springs were installed.

At this point I'm at 20* initial. Ground straps on the plugs are clean all the way to the bottom of the strap. But it's not pinging or kicking back on the starter. Should I back it off? Maybe the mufflers keep me from hearing the pinging??? Or, my dang bad ears. Drove it to work earlier this week up a good sized mountain and it pulled all the way up.

Any thoughts?
 
If the ground wire is clean to the shell you can bet you have a good bit of timing on it.

You don't always hear detonation.

You may have enough cam and low enough compression ratio that it won't detonate until the timing is high enough it puts the starter in the cheap seats.

I have a Pontiac 400 that's the same way. It has 46 total on it now and I can't make it rattle. I suspect the damper has moved, but I'm not even about to verify TDC. That turd need to come apart and be rebuilt.
 
What are the specs of your rebuilt distributor? SB’s like total timing of 32 to 36 degrees on todays pee pee fuel. If ya had it rebuilt to have 12 to 16 degrees of mechanical advance you are good at 20 initial. If ya just put a repop/stock spec distributor in you are not.
 
Lol. I would like to get through the summer and pull it this winter for a rebuild. I may back off a little.
 
Distributor was done by @chargerjoe68 who did a great job on it. It's right at 36 total timing.

Thing that gets me is the plug ground straps and the starter not kicking back after being heat soaked.
 
When did you figure out it likes 20°?
 
stock 273 damper? Have you checked TDC with a piston stop to the TDC line on the damper?
 
Checked TDC with a piston stop. After rebuilt distributor I started with 16, then bumped it up to 20 when it didn't ping or kick back the starter.

Then after a 70 mile round trip to work, I pulled some plugs and see the entire ground strap is clean. Runs great! Much better with the rebuilt distributor.

I'm just concerned about getting detonation. Wish I had a scope to see the pistons. Think I'll back it off a couple degrees.
 
I've had a low compression race engine that needed 30 degrees of added timing to get it to detonate... 7.6 SCR and in the upper 5's for DCR LOL. The distributor got whacked around in a hard race, and put around 40 degrees added initial in it, and it finally destroyed a forged piston. So low compression will be a LOT more forgiving.

Yes, your bad ears might be a factor.
 
Ok let me get this straight. You started with 16° for a total of 32°. You bumped it to 20° for a total of 36°. Did you tell Chargerjoe how many degrees initial works best for you so he could limit the total? Do you have a limit plate in it so you can change it as needed?
 
It's a Commando engine but I'm not sure if the heads we're ever pulled and can't say what current compression is.

Yes TMM, you are correct. Joe built it for 36 total. At 36 total...if my timing light is good...the plugs look like it's getting much more. Can't remember what plugs I have in it now, but they are fairly new. I can pull one when I get home.

Oh, and I have a limit plate, but didn't put it back in the rebuilt distributor.
 
If you set it at 20* at idle, that doesn't mean an awful lot. At 650 rpm or 1100 rpm could be a big difference.
Check the timing at rpm. At the slowest rpm, then when it starts advancing. Then get at least 3 or 4 more rpm and timing measurements up to 3000 or 4000 rpm.
Do this with the hose ( for vac advance) plugged. Then we'll have some idea what's going on.
Its not going to ping under light load. You may hear it ping at part throttle moderate load esp with vac advance and too fast of a curve. But you could burn a piston at full load or close to it if its bad enough. That's when you've got to get out of the gas immediately if you hear it ping.
 
66fyssh said:
It's a Commando engine but I'm not sure if the heads we're ever pulled and can't say what current compression is.

Yes TMM, you are correct. Joe built it for 36 total. At 36 total...if my timing light is good...the plugs look like it's getting much more. Can't remember what plugs I have in it now, but they are fairly new. I can pull one when I get home.

Oh, and I have a limit plate, but didn't put it back in the rebuilt distributor.
Click to expand...


If he built it for 36 total and 20 initial gets you there without starter kickback or detonation you should be good to go. When you connect the vacuum advance and give it some rpm you may get 50 or so. No ping, you're good.
 
66fyssh said:
Thanks Mattax. I'll check it out after church tomorrow.
Click to expand...
Take cylinder compression readings..... that will give us some idea of the dynamic compression ratio. BTW, be aware that when you went up in altitude on that mountain, the air is thinner and the effective dynamic compression ratio went down and the tendency to detonate also went down. Where are you near? Dawsonville or Helen?
 
It was Taylor's Ridge near Summerville GA. Not too high, about 1600 feet. But high compared to Rome, lol.
I'll need to borrow a compression tester from a parts store. I don't think the engine has ever been apart and it's somewhat tired.
I backed the timing down to about 17* after church this afternoon. I'll check the plugs again after I put some miles on it.

Thanks!!
 
OK, then elevation was not that much of a factor... just a minor one. I have seen an engine more prone to knock a bit when going from 1000' to sea level, but that was a high compression engine.
 
I backed it down to 17* and put probably 15 miles on it. Checked the plugs and they are clean now to just below the curve. I feel much better myself and it runs just as good.

I was surprised the starter never kicked and I never heard pinging. But like you mentioned, it could be that the compression is not high enough. Hopefully it will get rebuilt this winter...
 
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