New Help with Top Dead Center

[Billla]

It's not possible to set accurate timing "by ear". Yes, it "works" (the engine runs and drives) on a low-power engine, but in every case it will be far too advanced. Accurate timing is critical for performance, fuel economy and engine longevity.

[teejay65]

Usually I rotate my 350 engine to top dead center prior to installation and am careful to not lose the position even when bumping it around for transmission alignment. Lot easier for stabbing the distributor. This engine I bought from a friend, is highly modified-383 stroker, was sitting a while and so the valve springs were loosened up to prevent undue wear and the engine was not on top dead center. Its in my 65 truck now and was wonderig if someone has a procedure for finding top dead center involving adjusting valves. Usually I just put a compression guage on number one and wait until the compression comes up and align the mark on the harmonic balancer with the timing tab. With the value springs all backed off, this procedure is out. Any help would be appreciated.

TeeJay

[60-66 Nut]

Just turn the engine until #1 intake valve opens and closes, then as soon as the marks line up that will be #1 TDC. If the valves are real loose, you may have to hold in on the push rod end of the rocker arm to feel the lifter move.

60-66 Nut

[Billla]

See the SBC Timing FAQ link in my sig - starts with the process for verifying TDC. Never trust a TDC until you've verified it

[Chevysdominate]

I agree with Billla. I just built a 400sbc a few weeks ago and the 'stock' timing mark was at least 10 degrees off of TDC. I had to drill out the spot welds holding the timing tab to the cover and re-weld it in the correct position.

I'm not sure if this is mentioned in the link, but adjusting lifter pre-load on a highly modified engine should be done cylinder by cylinder. Don't adjust half at TDC compression and the rest at TDC exhaust. This could result in an improperly adjusted valve train.

Good luck

[60ratrod]

Originally Posted by Chevysdominate

I agree with Billla. I just built a 400sbc a few weeks ago and the 'stock' timing mark was at least 10 degrees off of TDC. I had to drill out the spot welds holding the timing tab to the cover and re-weld it in the correct position.

I'm not sure if this is mentioned in the link, but adjusting lifter pre-load on a highly modified engine should be done cylinder by cylinder. Don't adjust half at TDC compression and the rest at TDC exhaust. This could result in an improperly adjusted valve train.

Good luck

especially with a motor that is not running a stock cam. i know i had to go cyl by cyl when i changed to the crane energizer 272h grind cam

[hewlett2002000]

well the way i do it is i get a straw and take the #1 spark plug and valve cover off and i get someone to bump it till i feel the piston with the straw, and i take the valve cover off to verify that it is TDC.
good luck,
John

[Billla]

Originally Posted by hewlett2002000

well the way i do it is i get a straw and take the #1 spark plug and valve cover off and i get someone to bump it till i feel the piston with the straw, and i take the valve cover off to verify that it is TDC.

That's accurate to about +/- 15 degrees; essentially the only way to tell is both valves closed and that's for a BIG portion of the compression stroke.

The standard method is good to +/- 2 degrees...1 degree if you're very careful.

[60ratrod]

or you can take out the #1 plug and have a buddy put his finger over the plug hole while you turn the crank by hand while watching the timing mark on the balancer. its close to top dead when it puts pressure on your buddies finger

[Billla]

Originally Posted by 60ratrod

or you can take out the #1 plug and have a buddy put his finger over the plug hole while you turn the crank by hand while watching the timing mark on the balancer. its close to top dead when it puts pressure on your buddies finger

The assumption here is that the timing mark on the balancer and/or pointer is correct - this is not always the case and I find about 50% of the engines that I help tune to be off...sometimes WAY off. I always set this most carefully in my engine builds so it only needs to be done once

This is why I strongly encourage verifying TDC. The ONLY means to do this is with a piston stop using the process in my FAQ...unless the head is off

[hewlett2002000]

well i just use that to get it close then i set it by ear when i get it running. i know its not completely accurate but its not like any ive worked on are race engines or anything.
John

[teejay65]

Thanks guys. Appreciate your insight. Got some Christmas vacation I've saved up so this is on my to do list. Will let you know how this works out.

TeeJay