namasgt

Can someone explain why the lifter is chewed up if only the inner spring failed?

namasgt

Danny

Can you please tell us the symptoms you were having with engine before you took the valve train apart.

DJF1

The symptoms were a rough running engine. That was it.

As for the update, a couple of things. The car is still in the shop, I hope that I'm going to be driving it this coming week. My poor old back is at its breaking point daily driving my track car.

So it turned out that a lot of the springs and mostly the inners were either broken ( about 25%) or had hairline cracks on the way to be broken.
The spring vendor stepped up so i got a new batch of springs FOC to change them all.

I hope that is the end of the issue, the cams were checked and their profile nor their harmonics seem to be the issue. So its one of 2 things, with the second one still "debated". Either the batch of springs had a manufacturing defect, which most everyone is pointing the finger to, or the stock S4 seats were too thick to be used with these springs and cams. As I said this is debated, I'm NOT an expert on this unfortunately to form my own opinion, but one source says its not the other one says it is.

Bottom line is that the seats were also changed to 944S2 kind which are thinner than the stock S4's

So the final verdict is a big fat "I have no clue" what to think, I will be out next week of a substantial amount of dollars in labour and continued uncertainty over the issue. Not ideal, I just hope i dont have to deal with it again.

GregBBRD

I have recorded spring data on virtually every spring that Porsche has made that could possibly fit into these cylinder heads.....Porsche is not "changing the spring specifications". Whoever speculated that is an idiot. Porsche would never do anything like this....they would simply make whatever spring they were "out of" NLA, if they were not going to remake it.....like they do with other parts.

Colins' stage 2 cams might work with stock 928 springs and S3 spring seats. However, the seat pressure would be in the 30-40 pound range.

This combination would not run my lawnmower.

namasgt

So your saying the inner springs on both exhaust and intake were found to be bad or just the exhaust side?
Did you have only one damaged lifter or did all of them look like the one in the picture?

I would closely/visually inspect each spring with a magnifier to make sure they don't have any corrosion pitting or dings on them.

GregBBRD

Sorry, got bored with this thread about springs.....I've been down this road so many times and measured this stuff so many times, figured out what works and what doesn't work....it amazes me that people still sit back and shoot themselves in the foot.

Here's my attitude about springs/engine parts, in general....this comes from 40 years of experience.....so, for some, this will be useless thoughts.

Factory Porsche springs are extremely reliable. They are tested and tortured in many engines, for many hours before we ever "see" them. Porsche needs their engines to be reliable.....they can't "put up" with the "simple" things failing.

"Aftermarket" springs are generally not extensively tested and generally break, after short hours of use.

Use a factory spring, whenever possible....and you will have a whole lot less grief.

Factory Porsche springs can be expensive....up front.....but what do you suppose it is costing to fix this engine?????

Here's my specs/notes on 944S2 springs....I only care about what happens at specific lifts with specific coil clearances (so I know if a certain spring will work with a specific camshaft)...so this is how I measure them. I have also measured dozens of different 928 cylinder heads (with new seats and valves, used seats and valves, and new 968 seats with new 968 valves) and have an "average" available spring distance....so I then know if "fitment" with a specific spring and specific cam is even going to be possible.

General note about 944S2 springs:
Springs tend to "vary" .020"-.040" on coil bind measurements. Each spring must individually be checked for coil bind, when using .060" of coil clearance. Individual spring seat modification (or spring substitution with another 944S2 spring) may be required, when running .060" clearance.

.425" lift, with .060" of coil clearance:
208 pounds open. 83 pounds on seat.
Notes:
With S3 spring seat.....about .020" left over for shimming purposes. Possible to slightly reduce spring pressures by running spring at .080" of coil clearance. Maximum "practical" lift, for this spring. Depending on lobe acceleration, may work with stock lifters and 968 valves.

.500" lift, with .060" of coil clearance:
210 pounds open, 66 pounds on seat.
Notes: With S3 spring seat. Not enough room, for this combination, without modification. Spring will need about another .050" of room (over stock) for this set-up. Spring seat pressure too light for some applications.

.500" lift, with .060" of coil clearance:
212 pounds open, 67 pounds on seat.
Notes: Modified S3 spring seat. Provides enough room for set-up in most cylinder heads however, marginal and shimming may not be possible. Each spring seat will need to be custom ground for fitment. Spring seat pressure possibly inadequate for some applications.

Here's the spring (Factory Porsche) I would be using with Colin's Stage 2 cams:

.500 lift with .060" of coil clearance.
190 lbs. open, 70 pounds on seat.
Notes: S3 spring seat. Cams with less lift can increase spring pressure, if desired. With lightweight lifters, will adequately deal with most all camshaft lobe acceleration rates. Extremely reliable, extremely consistent spring, specifically made for Porsche for racing use.

.500" lift with .060" of coil clearance.
197 lbs. open, 77 pounds on seat.
Notes: Modified S3 spring seat. Notes as above. Perhaps the "perfect" 928 high performance spring for lifts up to .500".

OBehave

Thank You for sharing your years of experience and vast volumes of knowledge Greg! You have just saved sooo many people a ton of time and money. You're the best!

Rob Edwards

Copy, paste, keep.

GregBBRD

Someone just told me that I was too verbose and made it too complex to understand.

Gee, that's uncommon, for me!

Simplified Version:

Aftermarket springs are generally ****. These particular spring have spring pressures that are way too high (my humble opinion).....even if they didn't break.

New cams should always have new lifters. Use the lightweight German made VW lifters.....they are cheaper than the stock lifter.

For cams up to .425" lift, use a 944S2 spring with a 928 S3 spring seat.

For cams with more than .425" lift, use the Porsche racing spring, with the S3 spring seat.

Yes, either spring will cost you more than the cams did......but fixing broken parts and fixing damage will cost more than the springs (and lifters) ever could.

Do it once. Do it right. Drive it.

DJF1

Thank you very much for explaining this in as simple terms as possible. Indeed you are an expert in your field as I am in mine. It would be like posting my analysis of a P+L statement

At any rate, thank you. Its been a nightmare that frankly I have not been looking for. Frankly for people like me its probably not a good idea to own a 928. I'm not a mechanic, nor pretend to understand most mechanical issues. I HAVE to trust people who know what they are doing and these cars besides been needy, they are also in need of people who know how to properly fix them the right way. Therein lies one of the issues. There are very few people who know what they are doing.

Just like you said. Do it Right the first around, which is exactly what I tell my staff in my field!

If I knew what I know now, my decisions in the past at the root of the issue would have been different. Now all I can do is pray that what is done will last for a couple of years till financially I can afford to do it again , right this time, at the time the WP and belts will need to be done.

ptuomov

One idiot here.

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Greg, thanks for the physical fit information for the springs. Those are good data to have.


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One thing that I think isn't receiving enough attention is the acceleration profile of the cam. By my understanding, the spring needs to provide enough load to cancel the negative acceleration of the valvetrain. There has to be enough spring load at each lift.

Looking at the S4 intake profile, for example:



The graph is noisy because it's based on a measurement of a cam, not the spec or the master. The negative accelerations are what one has to worry about in spring selection.

The first thing that jumps out of this is that at low lifts one needs spring only to control the valve bounce and gas flow loads. the graph is just noise there. How much that means in practice I don't know but it probably isn't a lot with hydraulic lifters and and direct acting bucket.

I would guess that the seated load for performance cams could be set based on some simple rule of thumb, like stock S4 seated load * (new reciprocating weight / stock reciprocating weight) * (new max rpm / old max rpm)^2. So if we assume stock seated load of about 45 lbf, increase the redline from 6700 rpm to 8000 rpm, and reduce the reciprocating weight by 10%, then I am guesstimating that 45 lbf * 0.9 * (8000/6700)^2 = 58 lbf is an appropriate seated load for the new cam and valvetrain.

The second thing that jumps out is that based on this measurement, for a linear spring the stiffest spring is needed at 7.5mm lift, the acceleration being -11e-3 mm*degree^-2 or just 11. If we have 10% lighter valvetrain, then that number scales down to about 10. (There's a Spinal Tap reference somewhere buried here.)

The S4 spring rate is about 225 lbf/in or 8.8 lbf/mm, we're looking at 45 lbf + 8.8*lbf/mm *7.5mm = 111 lbf at that 7.5mm point. Alternatively, with the S2 spring and its higher rate at about 300 lbf/in set to 58 lbf seated load, and 10% lighter valvetrain, we'd be looking at 146 lbf at 7.5mm and we could increase the redline from 6700 rpm to 8100 rpm using the formula sqrt(6700*146/1.11/0.9). This assuming the same worst case cam acceleration at the same lift point.

I guess to the extent I have a point here it's that I think (a) the cam profile and in particular the negative acceleration of the profile at various lifts is critical and (b) with that info and some math I think a hobbyist can make some headway in picking the right springs for the cam. What we really need is Colin and Colt to publish the basic acceleration statistics of the cams they offer so we can make educated spring choices.

Just thinking out loud, let me know if I took a wrong turn somewhere.

BC

How does one find the second spring?

You also mentioned the s2 sets going up in price as well.

S3 springs seem to be good for certain uses as well. Much better than s4, at least.

The dyno software seems to like them.

GregBBRD

Not available "over the counter". Only available through racing.

Yes, the S2 springs, which were an exceptional deal, doubled in price to be about the same price as all the other springs in this "size" range (928, 968, etc.) We always wondered why they were so cheap...Porsche finally noticed, too.

There's actually one other spring, from racing, that has higher spring rates, on the nose (for more aggressive lobe acceleration), but not as "crazy" as the Lindsey spring, on the seat.

These are made out of some "uber" material, with lots of hand work, including special polishing and "tail" trimming. And they have an "uber" price.....about $175 each (yeah, multiply that by 32....at least a 6 cylinder engine only needs 24!), depending on what the dollar versus the Euro is doing.

.500 lift, with .060" of coil clearance.
245 pounds open, 80 pounds on the seat.
Note: .040" (approx.) of "shim" space available for pressure reduction or just shims. Modified S3 spring seat.

GregBBRD

Easy to get "lost" in the details that are generally reserved for super high rpm, high horsepower race engines.

I'd submit that it would be very difficult to get high enough lobe acceleration rates to be much of a concern, given the small amount of lift we use, versus the distance that the lifter has to travel to get to that little amount of lift. One would have to draw up a really strange looking lobe to achieve any sort of lobe acceleration to be of any concern.

One could even "flat cut" the ramps on our cams and have the lifter only move at the very top of the lobe (like some current racing cams are designed....significantly reduces lifter/cam friction) and not have excessive acceleration.

ptuomov

Certainly, if the lift is not increased but duration is increased, one can create a valve lift profile that is a lot easier on the lifters and lobes and requires less spring load, for the same rpm. It's the short duration high lift cams that are hard, and I think most people looking for performance 928 camshafts are looking for longer than stock duration.

The negative accelerations not being a concern for out engines leads me to the following question: Why do you need these high spring rate springs then? It's my understanding that the high spring rates are primarily needed to offset the negative accelerations on all cams, not just racing cams.

More specifically and making this concrete, 944 S2 springs are something like 300 lbf/inch rate. Why those 300 lbf/inch springs instead of the gentler 928 S4 springs with 225 lbf/inch spring rate if the negative acceleration is nowhere close to the limit? Is it just that for the 928 the priority is to find a spring that can accommodate the maximum lift without coil bind while simultaneously giving a bounce-free seated load, while the spring load on/near the nose is irrelevant (by being too high for all these springs mentioned here)?

I didn't think it would be possible to run a tangent cam lobe (flat surface connecting the base circle and the nose circle) on a flat follower. The reason why I thought this would not be possible is because the lubrication would not work with the large contact area early in the lift. Perhaps I have misunderstood this issue, or what you meant by flat cutting the ramp or the flank.