Changing valve seals using air chuck: If I have air leaks are the heads toast?

[thecatseye66]

I'm trying to change my valve seals while the engine is out of the truck, but without taking the heads off. I haven't noticed any performance problems, just some smoke at startup and some of the valve seals were in pieces laying on the head when I took off the valve covers. My truck only has 45,000 original miles on it ('68 396).

I've searched the threads on how to do this and I'm trying to do the air chuck method with a spring compressor. I haven't taken apart any of the springs yet because even when I get each cylinder to TDC and hook up the air at 90 psi in the spark plug hole I'm getting air blowing out the exhaust port and/or sometimes the intake.

Am I doing something wrong or are my heads toast?

[84_4x4]

to do a cylinder leakage test make sure its TDC of the compression stroke and then if it leaks out exhaust or intake you need new valves or new valve seats

[Sport/Truck]

A friend and I just started this yesterday. (see my post in the engine & trans)
Mine leaked some around the rings and at first it my exhaust valve was leaking. But using a small non-metallic hammer just give it a smack it will “pop” with the air in the cylinder. Mine sealed when I did it, but it clearly was leaking around the rings.
Hope this helps.
s/t

[Sport/Truck]

Originally Posted by 84_4x4

to do a cylinder leakage test make sure its TDC of the compression stroke and then if it leaks out exhaust or intake you need new valves or new valve seats

Anywhere on the compression stroke the valves will be closed.
s/t

[cdowns]

if the motor is out why not just remove the heads clean the carbon off the pistons and lap the valves

[thecatseye66]

Originally Posted by cdowns

if the motor is out why not just remove the heads clean the carbon off the pistons and lap the valves

What do you mean lap the valves?

[arkracing]

It's a normal occurance when you do valveseals that way.

I agree with the smacking the top of the valve with a hammer - just you can use a metal hammer - just don't go overboard. - plastic dead blow if you have it is best. Make sure you get a square hit so you don't chip the top of the valve or break it.
You'll hear it "Pop" as described - and should seal up - it you still hear "hissing" could be rings letting some into the crankcase.


"Lapping" the valves - basically you use a grit compund and spin the valve around in each of thier holes to clean up the valve and valve seat and give them a better seal.
its basically a "backyard rebuilding" technique

[fastwillie 696969]

did you get this motor real hot is so i would check the heads for cracks too

[arkracing]

Originally Posted by 70blowngmc

did you get this motor real hot is so i would check the heads for cracks too

He doesn't say anything about getting it hot or performance issues. 45k original miles -

Valve seals are dryed up and fell apart - normal for any engine of this age.

[thecatseye66]

Thanks for the help guys!
I put the spring compressor on the exhaust valve that was leaking and after tightening it up I spun it a quarter turn and it popped up tight with no leaks!

It's never overheated. The engine runs great.

But--now I can't get the concentric holders to release with the spring compressor on the valve/spring assembly.

Can I just tap the top of the retainers with a piece of wood?

I love this board.

[thecatseye66]

Tapped the retainer and it came loose--all is well!
Changed the first seal and I'm on to the rest!
Thanks much!

[Sport/Truck]

Use your tool to push down the spring and using a magnet (the type on a small screwdriver) to remover the keepers.
s/t

[piecesparts]

I agree, try tapping the valves with a hammer a couple of times to get them to seat, if they don't the heads will need to come off. It sounds like you may have driven a lot of city miles and carboned up the valves. However, even with the low miles, this would be an excellent time to tighten up the upper end of the motor and ensure the valves do not give you hell later. The motor is on the stand and you have some time(I hope) Go a step further and be satisfied that you did everything that you could do. BETTER Than having to take it apart after you have installed it in the next vehicle.

[WorkinLonghorn]

I agree with above. You probably don't want to hear this now that you've finished the seal job but I always hear (from machinists) that a motor with shot valve seals usually is in need of guide work anyway. If this was mine,I woulda taken the heads off and de-carboned etc.

[thecatseye66]

I finished up the seals about ten minutes ago. No problems at all once I learned to "seat" the valves by putting a block of wood against the valve spring assembly and give them a couple wacks before I took each one apart. I would just hook up the air after bringing each cylinder to TDC, then take off the rockers and give them a smack if there was air coming out of the exhaust or intake port. Once they seated I just tore them down and moved to the next.

I know a couple of you guys said I should do more teardown, but this motor is really clean. It is an original 45,000 mile 396 that came with a 2-barrel and was never driven hard. There is no sludge or carbon buildup anywhere--there were just a bunch of hardened and broken valve seals on the exhaust valves and it smoked a bit when I'd first start it up, but the compression is excellent. The motor had never even been out of the truck.

I'm putting in a new oil pump and I already put on a new timing chain and gears as well. I'm putting on an aluminum high-flow water pump and a quadrajet too. I picked up an original '68 q-jet high rise at a swap meet so it'll all look bone stock again when I'm done.

Thanks again for your input guys--

[Sport/Truck]

Did you do the rear main seal?
s/t

[thecatseye66]

Originally Posted by Sport/Truck

Did you do the rear main seal?
s/t

No, but now that you mention it maybe I should. Is there a better type of main seal I should use--like a Fel-pro or something? Should I do the front too?

I know you can remove the upper half without removing the crank by driving it out partway and grabbing the other end, but what is the best method to insert the new one?

[arkracing]

Originally Posted by thecatseye66

No, but now that you mention it maybe I should. Is there a better type of main seal I should use--like a Fel-pro or something? Should I do the front too?

I know you can remove the upper half without removing the crank by driving it out partway and grabbing the other end, but what is the best method to insert the new one?

The felpro's come with a little plastic tab to insert the new one (so you don't rip the back of it all up when installing) - just lube it up good and make sure you don't put it in backwards. You're going to have the pan off to do the oil pump so you might as well do the rear main - if the timing cover is still off I would do the front seal as well.

to get the "upper" half of the seal out (part that will be under the crank) - there is usually a little dowel pin where the rear main cap is (I know it is on the SBC's I can't remember it is on the BBC's or not) - I use this a fulcrom for a screwdriver and just move the seal out a little @ a time - it's really not that hard to do. You can also do it the way you said push it through a little grab it with some pliers or whatever - just be careful to not scratch the rear main journal.

Also you might want to "offset the rear main from the block - leave one side of the rear main sticking up past the block and then do the opposite with the cap. - just so the split in the rear main doesn't match the split of the cap to block. I don't think it will really make that much of a differance but have rear in a couple places that shops like to do that.