Hi, I’m replacing my valve springs in my LT1. I have my engine lifted up about 1.5” and I will not be able to remove spark plugs to check with something like a stop. I’m trying to figure out the easiest way to check if a piston is at TDC before I pull the springs off so I don’t drop a valve. Intake/valve covers removed. I do not want to remove the heads and do it out of the car.

 

both valves on #1 closed then #1 is TDC. With any cylinder piston at top the valve only drops about 1/4"

With #1 cyl at TDC, you can do both valve springs on #1 & 6 cyl
Rotate engine 90 degrees, do cylinders 5 & 8
Rotate engine 90 degrees, do cylinders 7 & 4
Rotate engine 90 degrees, do cylinders 3 & 2.

Now do valve lash EOIC method

 

No. The piston can still be close to BDC on the compression stroke. It's still a good idea to figure out how to get those plugs out to find out what position the piston is in before starting. I've always used nylon rope instead of air or whatever other method there is. After the intake valve closes I then stuff as much rope into the cylinder as possible via the plug hole and then turn the crank by hand until the piston stops. Works like a charm.

 

Thanks for the replies. I’ll probably do the “head work” portion of it once I get the new cam in, and can lower the engine back to its original spot. I’ll use the rope method since I’ll be able to remove the spark plugs once it’s lowered.

 

I have done both methods, rope and the method I described several times. Both work.

If you have a motor with heads off....doing the #1 TDC then turn in 90 degree increments, you will see both pistons are at top in the order I described. Of course, various valves are open doing it that way so it's only good to replace springs, do valve lash after per EOIC method

I have found using air can be problematic if compressor is set to high...it pushes piston down and the fing noise of compressor running all the time sucks

OP, replace valve stem seals also when replacing springs. IMHO check installed spring height for new springs and use shims if needed

 

What method did you describe? Just because both valves are closed does not mean the piston is at TDC. You know this. Do better.

 

Several articles suggest a different procedure, which is apparently needed when you have an aggressive cam and want to make sure you are on the base circle during adjustment. Set #1 to TDC and adjust #1, move the crank 90 degrees and adjust #8 valves, and so on through the 1-8-4-3-6-5-7-2 firing order, moving the crank 90 degrees each time. Thre is always two cylinders that are at TDC at a given time. 1-6, 5-8,7-4, 3-2

 

I (OP), was able to remove spark plugs and used a 1/4” ID hose to stick in the spark plug holes.

 

The method I "described", post 2.

If you have ever spun a motor by hand with heads off you will see 2 pistons are at top as I noted...and post 7 says.

This is a way to replace valve springs without air or rope as the valve will only drop about 1/4". Not the way to set valve lash.

 

Regardless of using that method you still need to know where actual piston position is, and you can't do that just by seeing that both valves are closed. With the heads on you need a physical reference, and we all know you can't rely on a damper unless it's been keyed. C'mon, man.

 

Not saying you don't need to know where piston is....FSM describes rotating engine watching valves close on #1 to determine if its #1 TDC or # 6.. Me, I have a real damper, keyed with timing marks.

Just using a zip tie in plug hole you can feel when pistons reaches top. For those of us who do our own engine work this is all SOP. Using a piston stop tool is also the way to find it...if you know how to use one.

Point is if you know wtf you are doing, there are several ways to find TDC and swapping valve springs with heads on without needing any air hose connection or using rope through plug hole.

For those of us with built motors who do drag race, valve springs are a wear item and changed when needed.

 

That's what it sure read like when you first were only referencing valves closed and TDC, my guy. Thanks for finally clearing up whatever it was you were trying to say.

 

when motor is #1 at TDC, both intake and exhaust valves are closed.on that cyl. What I said in my 1st post.

Sorry you are having such a hard time understanding SBC 101.

 

I assume when you say "when motor is..." you mean when the piston is at TDC, right? Regardless that is not what you said in your first statement. Let's go to the tape:
These two statements are different. Word salad all you want, but your original statement is inaccurate and needed clarification.

 

guess reading was never your best subject SS RRR, as the 2nd highlighted statement in my 1st post could not be clearer if you could not grasp the meaning of the first sentence. Also just like post 7 says, BTW he gets it, that "There is always two cylinders that are at TDC at a given time. 1-6, 5-8,7-4, 3-2"....the point is you can replace valve springs on 2 cylinders at the same time as any time a piston is at TDC, there is another corresponding cyl with piston up as I noted in my first post and post #7 also states that. Yes, when cyl 1 is a TDC "compression" stroke, cyl 6 is "top" as both intake and exhaust valves are overlapping. For the purpose of changing valve springs (read not setting valve lash) those 2 cylinders have a piston up top so both intake and exhaust valve springs on both cylinders can be changed without using air or rope method.

OP, hope you are good with a way to swap your springs. There are a few ways to do it, pick what is easiest for you.

 

Without the ability to remove the spark plug and no mark on the damper or balancer indicating TDC for No.1 you will need to pay attention to the valve events to determine when you are at or near TDC on a given cylinder. If changing valve springs you're going to have to send rope or air into the cylinder regardless. Removing the valve springs without pulling spark plugs to put air or rope in there first is not something I'd do. You're much braver than I.

 

That's all fine and good, my guy, but TDC of the piston, whether one starts with 1, 3, 5, 2 or 19, still needs to be determined by some sort of physical reference, and intake/exhaust springs closed is not a good indicator.

 

I to was WTF when I read about swapping springs without air or rope on the LT1. I have a spare motor with heads off and could see at any one time when a piston is up top, there is also a corresponding one also up top. I put a head on and pulled the keepers out of a spring while that piston was up. While the valve seal did hold it, I pushed it down and it only dropped about 1/4" before hitting piston. Since then I have used this method 4 times swapping springs on my LT1 using method I described.

The Crane valve spring tool #99473-1 allows both intake and exhaust springs to be pulled/installed at same time. It was well worth the $100 when I bought it many years ago. Its extinct now but there are similar tools available

No argument using some form of feeler, piston stop tool, etc to confirm when a piston is up top especially using a stock damper non keyed which "may" have been off before and not installed back where it was when engine was built. Watching cyl one valves closing on exhaust and as you continue rotating as the piston on #1 comes back up and intake valve stays closed, than both valves are closed on that cyl for "compression" stroke. With both #1 valves closed and piston ontop, #6 rockers would be uneven (not closed) as those valves are passing each other. The piston however is up top in #6 when #1 is also up.