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change valve springs with engine in the car?

6K views 32 replies 11 participants last post by  -SS454- 
#1 ·
I've been thinking of maybe replacing my valve springs, but I am not in a position to pull the engine. I seen a video of a guy pushing compressed air into the cylinder and using a funky tool to pop them out, so it seems doable. But how much of a PITA is it?

I'm thinking of this because of my dyno results. It's a Comp 280H cam that should hold better to 6000 IMO.

First time I dynoed the car I had a torn vacuum secondary diaphragm so it's not truely accurate, but it sure looks like valve float above 5500.



Second dyno test I didn't run it much past 5500.



Thoughts? Is it even worth it?
 
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#2 ·
IMO, I really don't see that cam peaking much higher (if any) than 5500 rpm in a 454. What is the rest of the combo?
 
#4 ·
We did this here ; Mark J provided me the all new stiffer springs , shims and micrometer . I bought the tool from Summit - We used a plug wire to keep the valves up ( no compressor needed ) all the new spring were measured and installed at correct height . It was a fun job i did all the measuring , my friend the mechanic did the rest - it took about 4 hours :) slowly but surely !






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#8 ·
Yes, after measuring every valve height, the springs need to be measured for height at full valve lift to have the correct pounds as per the cam specs. Adding shims of different thicknesses lets you attain that. Then every spring needs to go to the valve for that height.

And I'll tell ya, doing them in a big block car with air conditioning, with 620 pounds at full lift is no easy task.

 
#9 ·
Yes, after measuring every valve height, the springs need to be measured for height at full valve lift to have the correct pounds as per the cam specs. Adding shims of different thicknesses lets you attain that. Then every spring needs to go to the valve for that height.

And I'll tell ya, doing them in a big block car with air conditioning, with 620 pounds at full lift is no easy task.


Yeah, mine have been in there for 5yrs now and looking to change them too.
225-240lbs seat pressure and 600-650lbs open pressure

So I feel ya.
 
#11 ·
The last pic in post 4 shows the valve stem micrometer. You measure from the head to the bottom of a valve retainer with locks installed. Few valves will be identical.

It might be easiest to take the measurements to a machine shop and let them measure the springs and you'll have springs with shims for each valve. Don't mix them up!
 
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#12 ·
friend ran the smaller 268H in his 454 way back in the 1991 time frame.
Performer intake and we tried many carbs and timing curves.. it ran the same as my 350 with a 268H in it.. we both had 308 gears .. he had TH400 and I had TH350.
Mine was a 78 nova and his was a 78 camaro.

The 454 would rev to 6000 rpm with the little cam real easy.
I installed the 280H in a 396 with the 911 springs 122 seat pressure and 2.19-1.88 valves.. valve float is 6500-6700 it still needs more spring pressure with that 911 spring.

The 280H will rev to 7000 easy with the right springs.
Max HP on the 268H (the little cam) is at 5700... this is where the HP starts to fall off. The 280H should be more.

The 280H in a 355 will run 12.50's with junk in a 3000 lb ride with some gear.
I would hope 100 more cubes could match that.

This is a good case for you to purchase a book or 2 that explains all you want to know.
How to build and modify sbc cylinder heads.
How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads (Motorbooks Workshop): David Vizard: 9780879385477: Amazon.com: Books

You can use the same information on about any head.
There might even be a BBC head book out there.

Those how to books are very informative.
 
#15 ·
mr 4 speed that 110 seat 330 open would be fine with the SBC
but this is the BBC you will need more.
I have read many people have issues with the 911 spring at 122 seat pressure going into valve float early and even being down on power earlier than valve float.. changing to what Strokerboats suggested (Isky 8005a springs) was done a few times and really fixed the lack of power and low RPM valve float issues.

I would have thought 122 seat would be plenty but I was dead wrong going with 911 springs and the OP has even lighter springs than the 911
 
#16 ·
mr 4 speed that 110 seat 330 open would be fine with the SBC
but this is the BBC you will need more
I have no problems using that spec spring with .520 lift big block Chevy f/t hydraulic cam.Actually,the open pressure might be 340
FWIW,This spec (110/330 or 340) is used on the 454 and 502 HO cams,which are hydraulic roller. IMHO,that is weak for a hydraulic roller but fine for a hydraulic flat tappet street cam.
 
#17 ·
maybe the harmonics come in early then on the comp 911 springs at 122 seat pressure.
Or maybe the 280H comp ramps are more aggressive than some .520" lift cams.
I never thought those magnum line of cams were aggressive though.

When does that HO cam peter out. I know that 280H will pull to 7000 really easy and 7200 with a good tune and enough spring and good head work..I do not mean just pull up there and not make any power..I am talking optimum shift point for best ET and MPH.

Maybe there is an issue with the 911 springs I used on that recent BBC, But i checked and set each one up myself.
I do know that particular cam in the BBC i did does not like the 911 spring.

Or could be the 2.19 -1.88 valves I used were way too heavy along with heavy retainers.
They are not under cut and they are stock stem size.
 
#19 ·
As they're a nice big chunk on the end of the valve stem, yes. But valve stem locks are so small, there's no reason to go Ti. BUT you may need to replace them to match the lighter retainers.
 
#21 · (Edited)
Although I know my cam is done by 6,250, I did have some valve float issues years ago. I think I now have "better" springs and with the lighter Ti retainers, hopefully float will be gone.
 
#24 ·
Chris, I did not see it mentioned, except to bring the piston up in the cylinder. Get a new, or clean (1/4")polypropylene rope, burn both ends, long enough to stuff into the spark plug hole. This will keep the valve up, and easier to work with. You can substitute anything for the above, I just like clean stuff. Disregard if you are going to use air.
 
#25 ·
Good tip Mike, thanks.

So I called Comp and PAC today and their support was drastically different. I specifically inquired about Beehive style springs as there seems to be some very good results with these, though at the risk of dropping a valve in a spring breaks.

Comp said the only one I can use is the 26120-16 which is 155# seat, and 377# open. Most reviews I've seen ran this valve in comparison with the 911 or 924's, so it was good to see.

I then talked with PAC, and they said 155# seat is way too much and that I will likely wipe the cam. He was suggesting a 1931 or 1933 single spring w/damper but those seem to be drastically different rates. 468 in/lb vs 311 in/lb, which is confusing. And then to suggest a beehive spring he asked for valve boss diameter and install height.

So I'm a little lost.
 
#26 ·
Read this spec page on the comp spring and try to under stand it.
It may shed some light on things for you.
155 seat maters not as the cam does not begin wear at the seat it is the over the nose pressure you need to watch.
I ran 135 seat and 345 over the nose on sbc flat tappet solid never any issues and broke it in with those pressures.
I try to stay under 345 over the nose.. I am sure with the correct lifters and cam that would not be an issue.


COMP Cams 26120-16: Beehive Valve Spring Universal | JEGS
 
#28 ·
I do not know if there is a rule of thumb or not..I just now what i like to stay under for my flat tappets.

With correct camshaft surface treating and the correct lifter face you can go way more open pressure.
I have not found a reason to use more than 345 for the cams and lifters I use.
Fact I can get by with a tick under 300 open over the nose. and still rev some cams to 7500 rpm with no issues.

My 268H has 80 seat pressure in my 350 and 1.84-1.50 valves and has went easy 7000+ rpm never miss a beat.
But lightened retainers and those are light valves compared to the BBC

Watch the tach. TH350 and 336 gears and 29.5" tall tires.
sorry crummy video. I made video this to prove a point that 305 heads or small valves do not quit at 4500 rpm.
 
#30 ·
So it finally got warm enough to pull a spring. I used the rope method to hold the valve up, and I must be an idiot or something, because it was not nearly as easy as I expected. Like a stubborn moron, I went with 3/8 rope, and I probably pushed it in 8-10 times and no matter what, it wouldn't push against the valve. So I went and got some 1/4" like suggested, and after a couple attempts, I got it good enough to hold the valve up.

Measured the install height, and found it to be 1.964 off the bottom of the head, and 1.943 with a shim.

With a 924 spring, that's only 97# of seat pressure, and 277# open, when new! It's no wonder I'm getting valvetrain instability.
 
#31 ·
Now that I am finally able to start on the spring change, let me reiterate the need to measure heights on each valve. Whoever cut the seats to allow for modern seals, did a very inconsistent job.

So the first valve I measured @ 1.964
Then 2.001, then 2.037 and then again at 2.037.

I also measured the original retainer vs the tool steel retainer, 2.019 vs 2.037.

All this means I may need to run 0.090" of shims under my 0.060" locator.

Thinking about seeing if the local parts store has -0.050 locks, but not sure that's a good idea to mismatch different valves with standard locks and offset locks.
 
#32 ·
Now that I am finally able to start on the spring change, let me reiterate the need to measure heights on each valve. Whoever cut the seats to allow for modern seals, did a very inconsistent job.

So the first valve I measured @ 1.964
Then 2.001, then 2.037 and then again at 2.037.

I also measured the original retainer vs the tool steel retainer, 2.019 vs 2.037.

All this means I may need to run 0.090" of shims under my 0.060" locator.

Thinking about seeing if the local parts store has -0.050 locks, but not sure that's a good idea to mismatch different valves with standard locks and offset locks.
You can use the .050 locks as a mismatch in sets. (intake only or exhaust only)
 
#33 ·
I guess I'm asking is it a smart idea to mix match with offset locks as in the future, be it me, or someone else wouldn't know and may mix up the locks.

Or should I save the money and just throw up to .090 worth of shims in?
 
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