MGB & GT Forum

There was a recent thread which got me to focus on valve springs as a result of a possible diagnosis for a high RPM issue. In that specific case after some further clarification, the OP probably can look elsewhere however because of that I decided to dig up some dirt and do a little testing on a few dozen old/new springs I have in my "spares" bin.

As I stated in that thread, I was pretty shocked to see how much tension was lost on the older springs in comparison to brand new.

I took and measured all of my springs and in addition to finding that the majority of them had lost roughly 20% of their "new" weight(when measured at the installed height of 1.4375" including collet) that about 20% of that group had lost 30%. Also, I found that two brand new springs were significantly out of spec...with two of the eight weighing in at 75lbs.

This all reminded me of an older thread regarding new valve guides and the issues with them being out of spec from the factory. This is the case with springs as well. From now on, I'm going to order 3 or 4 sets, weigh them individually and group/discard as needed. Although each spring doesn't need to be exactly equal, I was told that at that weight they should all be within 5-7lbs so that's what I'll be looking for.

Weak springs can cause valve "float" at higher RPMS's. As I also said in the previous thread, I think for most drivers here even relatively "weak" springs wouldn't ever manifest themselves as an issue as their cars rarely see operation up at the 5k range where such things will start showing themselves. However, IF your driving habits do see that and if it seems that your engine simply falls on it's face regardless of throttle...a 60lb spring weight could indeed be the culprit especially if the majority of the springs are also similarly worn. I also weighed a few just prior to their "coil bind" height and found that the loss rate was linear so that both staic and dynamic weights were lost.

One group of springs I know came off of a car with 45k miles and had lost 20% of their original weight already so apparently it does happen below that in some instances. Also, I know I've received a head which had been previously rebuilt and had fairly low miles but the rebuilder had re-used the old springs. Apparently that's not too uncommon as the owner said that "walk-in's" will often drop off a head and request a "valve job" but looks at the springs as just "hardware" and "if they look good...run 'em".

So...what's the "moral" here? When buying or building a head. Ensure you either specify for new prior or ask the builder afterward if new springs were used.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

5000rpm isn't high rpm for mgb valve springs
Can't go back 5 decades and remember a single mgb engine at any stage of use or wear thst couldn't easily push 5K plus properly tuned.
Yes use new springs when building a head. But engine dropping off as if on a limiter from aged springs?

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Yep...Happens on old SBC's up around 6k.

In a non interference engine you won't do any physical damage but the valve float will not allow complete compression so that the engine will basically act as if it's got a limiter...

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...



Edited 1 time(s). Last edit at 2017-03-24 02:40 PM by HiPowerShooter.

Also, I don't think 5k is very high either however I also didn't think I'd see such a dramatic drop in tension either. I was thinking on the order of 10-15% maybe but as I said, 48 springs showed 20% and another 7 or 8 showed a 30% loss. That's pretty dramatic. My guess is that you'd need to get above 5k...probably more around 5500-6k and be looking for more to see it but I think at those low pressures you'd get some float.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

As I said never once experienced valve float on an mgb at 5K
No matter how tired the engine
Dual springs are hardly taxed at 5k

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LNDRVR4X4.COM
Home of Project "INCARN8'


1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED

RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972

I tested only single springs...

Like I said...I'm not saying it's something to be concerned with however if you've got an issue "up there" and you've ruled out the more common culprits it IS something that CAN happen. Also, more the point was to ensure you're getting *New* springs and those springs are tested on a scale prior to install when the head is off for even a simple "valve job"(seats/seals/surface).

60lb spring pressure is pretty low...no matter the engine.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...



Edited 1 time(s). Last edit at 2017-03-24 03:00 PM by HiPowerShooter.

.

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Life's most persistent and urgent question is, "What are you doing for others?"



Edited 1 time(s). Last edit at 2017-03-24 03:34 PM by riley1489.

Single springs only.

No questions.

Again...I'm not saying that just because your MG is old that you can't go above 5k without floating valves, however IF you have an old engine with 8 60lb springs and it seems that the engine hits a wall at that RPM...it could very well be just that.

I'm not getting into the equations concerning Installed height/coil bind/cam lift/rocker ratio to determine correct springs or anything...just passing on the fact that a significant number of springs which I've removed from heads have seen a significant drop in OEM spring pressure. The loss of that pressure WILL lower the RPM in which valve float will occur. No debating that fact.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

Well understood,

Thanks

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Why are you checking the spring with the retainer? Single springs do not require the retainer and looking at where your scale is, I think you're a bit short. What do you get when you try just the spring at 1.437?

Dale

He doesn't want to go there.

B

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Life's most persistent and urgent question is, "What are you doing for others?"

I am compressing the spring only to 1.4375" not including the collet height. It's not a straight on shot and I also measured it with an external ruler. Makes no difference whether or not I have the collett on or not. I did also compress only the spring at that height and got the same result.

Also, in all reality the height is of little relevance to what I was trying to accomplish which was to establish the percentage of tension loss. The scale has a lock so every spring was compressed to exactly the same height as the others. Since the loss was equal from that or to just prior to coil bind the actual installed height(measured height) could have been randomly chosen and I would have still reached the same conclusion.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...



Edited 1 time(s). Last edit at 2017-03-24 05:33 PM by HiPowerShooter.

Grinding the valve seat and valve face raises the valve stem height, thus increasing the installed height of the valve spring which reduces the spring tension. Some engine builders use “valve spring shims” under the springs to restore the installed height to OEM. Valve spring shims are available in .015”, .030”, and .060”, and may be stacked.

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Be safe out there.
Kenny

Your correct(as per usual) and with this in mind I also measured the tension with one and two .015" shims and the lower valve spring collar in place to see how that affected the tension. I don't have my notes in front of me, however IIRC each shim added 3lbs or so and the collar added less as it's thinner metal.

My friend who owns the shop and has been building engines since 1977 was the one who lets me "play" around. He's always willing to help and more importantly...educate me...in such things. He went into the science of fitting cams/springs/heights etc...and that fine line between enough tension to ensure proper valve return at high RPM and not adding so much that you're robbing HP. He builds everything from single cylinder small engines to (as with today when I helped him setup a build) 800hp strip monster big blocks to Caterpillar diesels . I appreciate his help as well as that which I've learned here as well. I've always been the type to try and learn not only how to do something but why it's done a certain way as well.

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"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

Putting in a cam that calls for 90 lb springs. Do I need heavy duty or double springs??

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