Top dead center compression stroke Help!

Messages
56
Location
Under MI thumb
A few weeks ago I blew a head gasket in my blazer. Due to lack of funds I have undertaken the job of rebuilding the top half of my vortec v-6. I am nearing the stage of installing the distributor and the shop manual says I need to position the crank so I am at top dead center on the compression stroke of cylinder #1. Are there any mechanics in the family that can tell me how I determine this position? Can somebody help me turn my garage back into a woodshop?
 
A few weeks ago I blew a head gasket in my blazer. Due to lack of funds I have undertaken the job of rebuilding the top half of my vortec v-6. I am nearing the stage of installing the distributor and the shop manual says I need to position the crank so I am at top dead center on the compression stroke of cylinder #1. Are there any mechanics in the family that can tell me how I determine this position? Can somebody help me turn my garage back into a woodshop?

Sorry Vic I can not help you. It's been to many years sense auto shop class in HS.
 
TDC

Look for timing marks on the front end of the crankshaft.

Should be a mark and a tab for TDC and maybe some timing marks with +- 5/10/15 degrees
 
I believe with the valve cover off the drivers side, and spark plugs removed, you should see the intake valve close and then feel the piston top out on the stroke for cylinder #1, this should be Top dead center.

A good place that I use is for vortec advice is: http://www.chevytalk.org/fusionbb/showforum.php?fid/78/fp/1/

The guys on that site are always very helpful.

Additional info: There are two TDC, compression stroke and exhaust stroke, this is where I mentioned that the intake valve should just be closing and then the piston will be coming up for it's compression stroke. You can also use a straw or dowel and mark it as it comes up to determine where it reached the top at. Just don't use something that will break off in the cylinder.
 
Last edited:
Darren is right on, with the valve cover off, you can see the pushrods/lifters. On top dead center of compression stroke the piston is compressing the fuel air mixture in the cylinder, at TDC the plug fires igniting the mix pushing the piston down (power stroke now). Next time up is exhaust stroke because the exhaust valve is open and the upward motion of the piston is pushing the burnt fuel/air mixture out. At TDC then the exhaust valve closes and intake valve opens, piston goes down sucking in (kind of like inhaling hence intake) the new fuel/air mixture, at bottom dead center the intake valve closes (exhaust valve is still closed) compression stroke is beginning, at TDC the mixture gets ignited again. Thus you need to identify which cylinder is #1, find both valves for that cylinder and when the piston is at the top of its stroke and both valves are closed, you are at TDC on compression stroke. By the way, that is the four strokes of a four cycle engine! Good luck, can be an intimidating task, but man will it make you feel good when it is done and you saved all that money! Hope this helps.
 
What Pete, Darren and Jonathan said is right on the money :thumb:

One more point, take the spark plugs out when you do this, MUCH easier to turn the motor over by hand with them out ;) :D
 
I look forward to seeing how all goes for you. I just had the upper intake off of mine to change the fuel regulator, boy what a pain. Had to literally remove the upper wiring harness to get the thing off. Still have my main issue with it cutting out, but it did fix one of the symptoms I was having. I only had 53 lbs of pressure when it was suppose to be 55 - 65, at least it's back in that range.

Good luck! :wave:
 
Align the TDC mark. Then using a piece of hose or something that will fit into the sparkplug hole blow some air in. TDC on the compression stroke will build up pressure. Your lungs can detect this. If TDC is on the exhaust stroke it will allow the air to freely pass on to the exhaust.

I have several old spark plugs I have modified fro this as well as some commercial adapters for compression testers.

I use the same items with a homemade leak down tester which I find most useful for checking things out before a tear down. I have discovered the leakdown tester is much better at telling me what is wrong than a compression test alone. Still do the compression first.

I'll Try and post some pictures later...
 
before car engines got all of the smog equipment added on I would remove the number-one spark plug and stick a finger tip over the hole,the compression can be felt
 
before car engines got all of the smog equipment added on I would remove the number-one spark plug and stick a finger tip over the hole,the compression can be felt

Ray
Actually that still works but I never tell anyone about it because I fear they will stick their finger in the hole and bring the piston up against especially if they have help. You can also still find a whistle to screw into the spark plug hole that will let you know when you are on the compression stroke.

Of course if you pay attention as you are putting everything back to gather there is nothing to find you set it up right from the beginning.

Thats what I do.. Sure it is....:rofl:
 
Ray
Actually that still works but I never tell anyone about it because I fear they will stick their finger in the hole and bring the piston up against especially if they have help. You can also still find a whistle to screw into the spark plug hole that will let you know when you are on the compression stroke.

Of course if you pay attention as you are putting everything back to gather there is nothing to find you set it up right from the beginning.

Thats what I do.. Sure it is....:rofl:

That what I was going to say.:rofl::rofl::rofl::rofl:
 
Thanks again everybody! Truly we got ourselves a good family here. I found the timing mark on the torsional damper and lined it up with the mark on the timing cover. That was too simple! So just to be sure I took a piece of foam caulking backer and stuffed it into the spark plug hole and spun the crank. That made a very satisfying pop as the marks lined up. Had loads of fun getting the oil pump lined up with the distributor. Taped a flashlight to a screwdriver and used a mirror. Oh my aching back!

Anyway, I got the engine back together. Still need to put everything on the front of the motor but it's all downhill from here.

Thanks again guys!
 
Ray
Actually that still works but I never tell anyone about it because I fear they will stick their finger in the hole and bring the piston up against especially if they have help. You can also still find a whistle to screw into the spark plug hole that will let you know when you are on the compression stroke.

Of course if you pay attention as you are putting everything back to gather there is nothing to find you set it up right from the beginning.

Thats what I do.. Sure it is....:rofl:

WARNING, do not stick your small finger into the chamber,if your finger tip will not cover the spark plug hole then find a different method--GARRY , thank you for catching my mistake
 
Top