Should I check TDC?

[superhondaz50]

So I have my new GM crate 350, it came with a timing tab, I installed a new Dorman balancer on it. Can I trust the TDC line on the balancer to set my timing? Hopefully I can as I don't wanna have to take a bunch of stuff off (remove plugs, remove valve cover, remove#1 rockers, etc) to check TDC with my piston stop...

[Steeveedee]

Trust but verify. It's your money, bud.

[superhondaz50]

Ya true, guess I can't be lazy.

[Killer Bee]

assuming you balancer mark meets the scale 0 exactly at TDC, you still need to verify it on compression stroke to install distributor and static time it..

this is really easy.. there's a thousand videos but here's a quickie..

You Tube

and since all you need to do is pull #1 plug, might as well check TDC is 0 on yer scale while you're there

good luck!

[superhondaz50]

Ya, I followed a similar video to get TDC on the compression stroke to drop in my distributor. My concern is the accuracy of the balancer and the timing tab. I'm gonna use my piston stop to check the TDC mark on the balancer. Just extra work I was trying to avoid, but I guess it's preventative work haha

[RedRider]

3 years, 100,000 miles...throw caution to the wind!

[superhondaz50]

Originally Posted by RedRider

3 years, 100,000 miles...throw caution to the wind!

Haha very true

[Keystone_Hate]

Originally Posted by RedRider

3 years, 100,000 miles...throw caution to the wind!

More like 12 months and 12,000 miles. I just went through this with GM powertrain.

Also you can use a chop stick or a plastic straw to find TDC. Just slide it in the plug hole and watch for it to get all the way up.

[geezer#99]

Originally Posted by RedRider

3 years, 100,000 miles...throw caution to the wind!

Originally Posted by superhondaz50

So I have my new GM crate 350, it came with a timing tab, I installed a new Dorman balancer on it. Can I trust the TDC line on the balancer to set my timing? Hopefully I can as I don't wanna have to take a bunch of stuff off (remove plugs, remove valve cover, remove#1 rockers, etc) to check TDC with my piston stop...

You don’t need to pull anything off.
Just pull out #1 spark plug.
What are you using for a piston stop?

[superhondaz50]

Originally Posted by geezer#99

You don’t need to pull anything off.
Just pull out #1 spark plug.
What are you using for a piston stop?

I have a Summit brand stop. I believe I need to pull the #1 rockers off to use the stop so the valves don't hit it.

[jocko]

So, if you just replaced the balancer on a GM crate - was the line on the balancer in the same position under a number on the timing tab when you installed the new one? A GM crate is about the only one I WOULD trust to have an accurate mark/pointer - and if you’re new balancer line fell in the same spot, well, should be good. Having said all that - I too would still want to confirm.

[superhondaz50]

Originally Posted by jocko

So, if you just replaced the balancer on a GM crate - was the line on the balancer in the same position under a number on the timing tab when you installed the new one? A GM crate is about the only one I WOULD trust to have an accurate mark/pointer - and if you’re new balancer line fell in the same spot, well, should be good. Having said all that - I too would still want to confirm.

The engine didn't have any balancer, so nothing to compare to unfortunately.

[Killer Bee]

if you're only using this tool for this engine, I would suggest sending it back and saving your money..

use a small wooden dowel, pencil, pocket screwdriver, whatever..

bar the engine around rotation direction, on compression, and stop just before balancer lines up..

valves will be out of the way and nobody gets hurt.. stick something in the plug hole to gauge piston location, and slowly bar over to #1 highest point..

you'll be close enough to make whatever timing adjustments you're going to make on a cam driven distributor with a strobe..

good luck!

[superhondaz50]

So a pencil, stick, etc works? The tool was only $9, so no biggie. I just don't want to bash the valves with it. This is the first vehicle engine I've ever done so it's all foreign to me. I've done hundreds of motorcycles and jetskis, but have used a special dial indicator that screws into the plug hole to find TDC, but skis and bikes mostly have vertical plug holes, this horizontal Chevy stuff is weird to me haha. I just learned what a piston stop was yesterday and that the balancer mark could be wrong. I don't wanna grenade this engine, especially since it's gonna be a work truck and needs to be really reliable.

[Keystone_Hate]

Originally Posted by superhondaz50

So a pencil, stick, etc works? The tool was only $9, so no biggie. I just don't want to bash the valves with it. This is the first vehicle engine I've ever done so it's all foreign to me. I've done hundreds of motorcycles and jetskis, but have used a special dial indicator that screws into the plug hole to find TDC, but skis and bikes mostly have vertical plug holes, this horizontal Chevy stuff is weird to me haha. I just learned what a piston stop was yesterday and that the balancer mark could be wrong. I don't wanna grenade this engine, especially since it's gonna be a work truck and needs to be really reliable.

Yes they will work. I use a chop stick or a plastic straw. Don't use a pencil or anything metal, because if you do happen to lose something in there, a little sliver of bamboo or a piece of plastic will be spit out. A metal pencil eraser will be chewed up and banged around.

Its the same idea as a piston stop but you can go slower and watch the straw/chop stick rise to its highest point where you know it is at TDC. using a piston stop you are just relying on the stop being accurate to stop the piston at TDC.

[jocko]

Originally Posted by superhondaz50

The engine didn't have any balancer, so nothing to compare to unfortunately.

AH! Duh. Ok, got it now - thanks

[davepl]

I totally recommend this book for you:

https://www.amazon.com/Engine-Bluepr...e+blueprinting

Can you trust a new engine? Almost certainly. But now is a good time to develop your skills in checking/testing/measuring it because you know the answer you're supposed to get! That's way easier to learn than when you don't know where TDC is, for example... is your answer right or not?

[superhondaz50]

Originally Posted by davepl

I totally recommend this book for you:

https://www.amazon.com/Engine-Bluepr...e+blueprinting

Can you trust a new engine? Almost certainly. But now is a good time to develop your skills in checking/testing/measuring it because you know the answer you're supposed to get! That's way easier to learn than when you don't know where TDC is, for example... is your answer right or not?

I have that book actually, I need to find it, my ex girlfriends dad gave it to me prob 12-13 years ago haha

[Killer Bee]

yep, just like that quick video shows the guy baring it up on compression with his finger over the hole..

the valves will be closed and piston nearing the top when it starts hissing out the plug hole..

you can bar it with left hand and hold just about anything in your right hand to feel the piston crest..

I use a pocket screwdriver, I don't jam it in there, pry around the threads or anything silly..

just rest it on there gently in my hand the last inch or so of stroke to find the TDC and put it away..

no damage to anything, probably couldn't even find a witness mark on the piston if you pulled the head..

compare it to the balancer groove and the scale 0 and there you have it.. adjust/replace as necessary..

crank > timing chain > cam/dist gear > advance plate the pickup rides on, etc. are all going to have some degree of movement..

checking the piston topping out by hand is plenty accurate for 99% of the on-road performance level engines we're discussing here..

the scale numbers are there for your reference anyways.. you'll learn what timing values work for that engine and that's all you need..

and next to z e r o chance of breaking anything in the cylinder by following these simple steps..

now if you decide to crank it with the starter, bar the engine around randomly do-si-do, or whatever, you're on your own..

please post your results and good luck!

[geezer#99]

Hilarious stuff!
So, killer bee I got a question for you.

How many crankshaft degrees does the crankshaft turn when the piston is at tdc?

[Killer Bee]

Originally Posted by geezer#99

Hilarious stuff!
So, killer bee I got a question for you.

How many crankshaft degrees does the crankshaft turn when the piston is at tdc?

piston dwell isn't really necessary data for the OP's needs.. method I described is simple, it works, the end..

if he really needs to know the exact 0, splitting the beginning and end of dwell will yield the true 0.. and this is still easily done without any special tools, maybe add a sharpie to the list..

however, like I said, in a typical street engine, this level of precision is moot.. through various points of lost motion between the balancer and the trigger path that strobes the light on it, OP will likely not notice any difference..

and as I've mentioned several times, unless a factory assembled engine requires timing to a published spec, really makes little difference anyway..

performance timing an engine doesn't require any timing values from a book, only the timing values verified by drivability testing which can really be any numbers as long as they're on scale for base, advance, etc. comparisons..

so let me know when you guys get this thing into orbit, maybe I'll be able to see it from my house

[geezer#99]

You still haven’t answered the question.
Likely because you don’t know.

If you want to be off 10-20 degrees on your timing, so be it.
It’s only a few holes in pistons.
No biggie.
It’s not your dollar being spent.

[davepl]

Originally Posted by geezer#99

You still haven’t answered the question.
Likely because you don’t know.

If you want to be off 10-20 degrees on your timing, so be it.
It’s only a few holes in pistons.
No biggie.
It’s not your dollar being spent.

Your question made no sense. You said "How many crankshaft degrees does the crankshaft turn when the piston is at tdc?"

I don't even know what that means. I'd argue that the crankshaft turns 1:1 with the crankshaft.

If you meant cam, it's half the crank speed obviously. But by definition when something is at TDC it's not turning any degrees, it's sitting at TDC, so I still have no guess.

[superhondaz50]

Just gonna use the piston stop. Tracking says it's at my front door. If my wife falls asleep early tonight I'm gonna sneak out to the garage and have at it. Gonna rotate close to TDC, insert the tool, rotate to stop, make my mark on the balancer, take out the tool, rotate backwards about 340*, reinstall the tool, rotate till stopped, make my 2nd mark, pull tool. Shouldn't hit valves that way. TDC will be in the middle of my marks. I can then glue on my timing tape and be fairly precise. Sound correct?

[Keystone_Hate]

Sounds like a plan.