Hello,

in my stock 71 350, i have #7 Heads with Rotators on the Intake Valves and solid retainers on the exhaust valves.

i know that the rotators benefit is to increase lifetime of the valves, but i have also heard that theyre a lot heavier that solid reatiners, maybe leading to issues at higher Rpm.

since the rotators are only used on the intake valves, these spring pockets are deeper than the exhaust spring pockets (i guess, 1972 7a heads have both pockets deeper because of using rotators on intake and exhaust vlaves).

has anyone here ever used spring cups on #7 heads to compensate the depth of the rotator pockets to use the same solid retainers on the intake valves like on the exhaust valves?

i replaced the stock old valve springs some time ago with Melling VS720 (stock specs) springs, but still have the trouble that the engine can barely do 5k rpm without falling on its face, backfiring and valve train noises, until i let the the pedal loose, then everything is operating normal again. Till around 5k, the engine pulls good without any issues. My guess was, for a stock engine, stockish valve springs should do the Job, but obviously not. Maybe it would help to replace the heavier rotators with retainers. With these problems, bringin the car to detent/kickdown always makes me nervous, specially when the trans goes from 3rd to 1st.

Somehow, i guess im missing something here, engine is completely stock with a brand new timing chain. i guess, even if stock, it should be possible to wind it up to around 5k rpm without the issues i have.

Or, the issue is on the trans and i maybe should try to bring the WOT shifts down to about 4800rpm (governor)?

every thoughts are apprechiated.

greetings from Austria

 

A spring cup isn’t as thick as the rotator but you can add shims underneath it to make up the difference. Use one that fits via the guide size, not the O.D.
And I’ve checked into those Melling springs before, I think they’re pretty light to begin with.

 

Ok, thanks for the information. Is it a common practise to eliminate the rotators that way?

I mean, if it would be not necessary, i would try to avoid eliminating the intake rotators. I mean, i doubt that these engines had the symptoms i have at 5k rpm when they were new. I just read somewhere that rotators CAN cause similar problems at higher RPMs due to theyre weight and no damper spring.

Yeah, you told me that theyre pretty light, but theyre listed everywhere as a cross reference for the stock spring which is GM #411225 i think. I dont know the stock spring specs.

Even, i purchased these Mellings because i thought for a Stock replacement, it wouldnt need any fancy stiffer spring. But maybe i was wrong. Maybe get a set of NOS GM Valve Springs?

is it really necessary to purchase stronger Springs from comp, lunati, edelbrock and so on for a simple Stock replacement? I even have the stock cam in there (for what i know).

I read in a different thread on here that someone has/had exactly the same issue, but there was no solution in this thread.

 

These are the specs the 71 CSM lists for the 350:

 

You can build up the spring seat as mentioned above in Post #2. Oldsmobile offered a kit at one time to remove the rotators and install the non-rotator valve retainer and a thick shim to install in the spring pocket. Did you have the Melling valve springs checked and installed shimmed to the spec pressure? Do they still check satisfactorily at the specified pressures?

 

Yeah, i thought that too that the rotators can get eliminated that way. Curious if there maybe is a spring cup thats already has the correct thickness so no additional shims under it would be required.

I once saw a thick cup kit listed as a rotator-elimination kit for chevy big block exhaust valves.

BUT, i assume that with proper (stiffer?) valve springs, there should be no need to change over to solid retainers?

To be honest - no, i havent checked the Melling springs for pressure. I assumed that this is not needed when doing a simple stock replacement process, unlike when installing a aftermarket cam.

I only measured from the bottom of the spring pockets to to the retainers/rotators to make sure that the installed height is 1.670, which it is.

Right after i installed the springs, the problem was fixed for some time, but in fact that it came back, its maybe a sign that the Melling springs arent the best quality. Who knows.

What i find a bit odd that it seems like no one here is replacing valve springs to stock specs. I mean, a lot people drive these cars around with stock engines, and due to 50 year old valve springs, i thought its common practise to replace them somewhen.

Its even hard to find a bit stiffer single valve springs with the same dimensions and installed height like the stock ones are.

 

And that is exactly the same specs as the Melling VS720

I'll be honest with you, I am not an Oldsmobile "guy" as far as performance goes but I would be very surprised if that engine even when brand new would easily turn to 5000 rpm. I bet it would be done with at about 4500

Maybe some of the real Olds guys will tell me I am wrong

As far as getting rid of the rotators, most GM rotators make the installed hgt about .120" shorter compared to the stock flat retainers. They make valve locks that move the retainer down on the valve .060" That combined with a .060" shim and it should be pretty close. I don't like piling up a bunch of shims if it can be avoided.

http://www.pbm-erson.com/catalog/ers...ocks/pbm205-60

 

Thanks for your answer!

The fact that the Melling VS720 have the same specs than the stock springs is what makes me wondering that i have floating valves at 5000 rpm.

Sure, i know that my 8.5:1 comp engine with its stock cam will not make anymore than sound at these RPM, but, due to my TH350, i GET those RPM when i stomp on it and the trans detents from 3rd to 1 at some lower speeds. Maybe the Problem here is really my Trans. It seems like in detent, with WOT, the upshifts are delayed. No worn out clutches, i have the Transgo shift kit installed, and when it shifts, the shifts are tire chirping firm.

The problem first came up when i swapped from 2.56 to 3.23 gears and it was the same with my stock governor and with the chevy style governor i have in the trans now. WOT shift points should be around 4800 RPM, so i tried with the calibration springs of the the transgo kit, but with the next lower setting it had its WOT shift points way too early at around 4200-4300 RPM.

I understand that i could purchase a real governor calibration kit with weights AND springs to calibrate the WOT shift points more accurate, but i dont understand why theyre not at 4800 RPM with the stock governor and why i have floating valves at 5000 rpm. I would guess that GM built in some "safe range" before valves start floating, even on non performance engines .

So i have to figure out if the trans is the problem or the valve springs. Or both.

 

One more thing to think about . . . . is your tach correct ?

 

I assume it. Its a Sun Super Tach II, maybe i can compare it to my timing light which shows rpms too.

But since its an automatic transmission, installing the most accurate tach in this world woudnt solve my issue.

 

Interesting. I had one of those tachs in my first race car and it ended up being almost 600 rpm off. It was reading high.

Having an accurate tach would at least let you know if you really have an engine issue. What if you are actually spinning it to 6000 instead of the 5000 you think you are ?

 

Yeah, your right, that makes sense.

definitely a point to check! I have an Autometer tach lying around, ill try to hook it up in the Cutlass and compare them so each other and to the Timing light.

thanks for your help!

 

Edit:

I got myself a installed height micrometer to check the shimming of my valve springs again.

Used the nylon rope through spark plug hole method to pull the valve springs and measure the valve spring installed height on each valve. I found out that when i installed the new Melling VS720 Springs i did the shimming incorrect due to the lack of the right measuring tools back then. Nearly every intake valve spring was installed at around 1.690 instead of 1.670, which is the factory correct installed height for stock springs. I shimmed them all as close as possible to 1.670 with comp 1.480 OD shims and took the car for a test drive. Valve float is gone. Pretty happy about that now. I assume that since others here told me too, these stock replacement springs are on the weak side (around 80lbs closed) , and because of that proper shimming is very important.

in detent, car winds up to 5000rpm without any valve floating now, but i will try to recalibrate my governor for WOT shift points at 4800rpm. For my feeling, WOT shifts are a tad too late for a stock engine.

 

Rotators are almost the same weight as the non rotator ..within a gram or two.

you won’t notice any difference in rpm