Is TDC a compression stroke?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

jvincig01

jvincig01

10 Year
Joined
May 4, 2011
Threads
297
Messages
1,465
Location
Sacramento, CA
I'm installing my first distributor and have a rookie question. I have my F engine/flywheel lined up perfectly at TC, dropped the disti in, everything is pointing where I think it should be. However, it occurred to me that I didn't check to see if TDC was in fact a compression stroke.

My question, is TDC on the flywheel a compression stroke? I know about checking the pressure with my thumb over the 1st cylinder but I need an extra set of hands.
 
TDC is accomplished on both the compression and exhaust strokes in a 4-stroke combustion engine. Pull the distributor cap off and validate that the coil tab is aligned with the #1 sparkplug cable on the cap.
 
When aligning the distributor you want #1 TDC on the compression stroke (both valves closed).

Make sure the distributor is fully seated before starting.
 
4-cycle = suck (intake) squeeze (compression) bang (ignition) blow (exhaust). Your either on TDC of the compression stroke (both valves closed) or TDC of the exhaust stroke (exhaust valve open - intake valve closed).
 
If you don't have an extra set of hands and you don't want to pull your valve cover. You can stuff some toilet paper in your #1 spark plug hole. It will go "pop" on compression stroke.

As mentioned above, make sure your dizzy is fully seated in your oil pump. The sure bet verification method I used was, spin off the oil pressure sending unit. Then crank engine over, Oil will squirt out that hole if dizzy is seated. I used a remote trigger to do this test solo.
 
A cheap remote starter button is your friend.
 
I discovered a 'poor mans' oil pressure gauge while helping a friend start up a 'used' 2F engine. He had dented the side of the oil filter while in the process of moving the engine around. I told him he should replace the filter, in case the crease caused a crack to form.

Nope, not wasting a new filter on an old engine.

We got it started, and the oil pressure pushed the dent out, so the filter was almost cylindrical again.
 
Nice. Have read about setting your dwell? Pretty sure 65swb45 has mentioned it as something to be aware of. I picked up a decent digital timing gun that also measures dwell. Kinda nice to see how points gap adjustments impact dwell. Best of luck:cheers:
 
5B872A8F-F988-4376-9ACD-73EBB7472E95.webp


Question: is #1 cylinder closest to radiator?

With valve cover off, how do I identify compression stroke?
 
Yes. #1 is front of rig.

You can watch the two rocker’s closest to valve cover. When they are both up the piston should be on compression stroke. Then shine light in spark plug hole. You can see piston when it’s at tdc. If you have a helper you can have them stick a screw driver in spark plug hole as you rotate engine by HAND. As piston rises they will need to slowly pull screw driver back so it doesn’t get bent.

My favorite trick when solo, which is all the time for me. Stuff some toilet paper in the spark plug hole, as you rotate engine the TP will pop out, making a cork gun sound. At that point feel where piston is and rock vehicle til piston reaches TDC.

Trick I learned from FJ40Jim, put tranny in high gear, not 1st. Rock vehicle forward to rotate engine. Works like a charm:cheers: you should have a TDC line on flywheel confirming TDC. You will see bb before TDC line. So if you see bb in viewing window you are almost at TDC.
 
If the valve cover's off, at TDC on compession you can easily rotate the push rods for # 1 with your thumb and forefinger. If your on the other stroke you can not.
I threw together a hand crank out of 1/2 pipe and works well for me. Once you find TDC and note the T-handle position you'll find it the next time much quicker.
The spark plug hole fitting I use for holding up the valves for a valve seal change is also good for determining TDC on compression stroke. I hook a short hose to it and blow. Get resistance, your on compression stroke. No resistance, you're not.

Hand Crank.webp

Hand Crank 2.webp

SprkPlgFtg.webp
 
Steamer said:
If the valve cover's off, at TDC on compession you can easily rotate the push rods for # 1 with your thumb and forefinger. If your on the other stroke you can not.
I threw together a hand crank out of 1/2 pipe and works well for me. Once you find TDC and note the T-handle position you'll find it the next time much quicker.
The spark plug hole fitting I use for holding up the valves for a valve seal change is also good for determining TDC on compression stroke. I hook a short hose to it and blow. Get resistance, your on compression stroke. No resistance, you're not.

View attachment 1653843
View attachment 1653847
View attachment 1653848
Click to expand...


I have a couple of the factory hand cranks but use another method. I've found pulling the coil wire off can use the starter to get close but not right on the pointer in the flywheel. Crank it with the starter and it will usually rocks forward or back once the starter stops because of the compression unless you pull all the plugs. If you want to get the distributor as close as possible you want the BB as close possible to the pointer on the bellhousing. The downside to the hand crank if you go just slightly past you can't go back, but have to rotate it two more times. I pull the cover on the bottom of the bellousing and use a 12" socket extension in a hole on the pressure plate to rotate. That way you can go back as well as forward to get the BB right on the pointer.
 
I stuck a screwdriver in #1 spark plug hole and sure enough I hit piston right away.

Funny thing is I originally thought rearward most cylinder was #1 . Is it possible #1 and #6 are at their compression stroke at same time?

Lastly, does my Dizzy appear to be in right spot?

B92216F8-4B25-4C38-9065-EC20AEB14F36.webp
630FFCD0-D145-45C6-90AE-B09203AF7E1B.webp
 
Iirc, 1 and 6 are companion cyldrs. When 1 is at TDC on the compression stroke 6 will be at TDC on the exhaust stroke.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom