NB 1.8 Valve Springs

Guys,

 

My head builder asked me to request a rule change. I know this is not the place that approves rule changes but........ , I do not belong to SCCA and NASA will follow SCCA. SCCA will listen to those here if you guys agree that the requested rule change is valid. So posting here.

 

He states that our spring pressures are inadequate. Brand new springs are measuring aprox. 25 to 30 lbs on the seat, and 70 to 75 open. He states that with the valve, decking, and head work we are being allowed, the pressure is reduced from the stock spring pressure. Even if it was still at stock pressures, the spring is fine for street use, but with sustained RPMS over 5K, stock pressure is causing unneeded wear and tear on the pistons and valves. We are bouncing them on the seats and floating them over the nose. Shimming will just get us back to stock pressures if nothing else.

 

I personally have gone through 3 sets of exhaust valves this year, and have damaged 4 pistons. He is recommending that we are allowed to shim, or use different springs. We know that there are springs out there that will provide 100 lbs over the nose that look identical to stock springs. We don't know yet if they come from a Mazda or whether they are aftermarket. If what I am experiencing is common, then those here have seen exactly what I am seeing. So I thought Id post and get your thoughts.

Any information on how high the RPM’s were after a missed shift or improper downshift?

Something is very wrong if you are having valve failure at that rate.  What type of failure?  Bent, burned, tulipped? 

This horse has been dead for many years, though I admit to kicking it occasionally anyway.

Despite the 1.6 factory service manual explicitly calling for additional shims to correct for lost seat pressure, the SMAC & CRB chose to ignore it (and very basic machine shop best practices), and passed a rule outlawing the practice.

As I recall (those with better information or memory please correct me) a teardown at an early runoffs discovered such shims. The car ultimately passed but the precise details were obfuscated and before long the new rule was introduced.

At the time one builder in particular was doing quite well and part of his approach to matching combustion chamber sizes and possibly to get other advantages was to selectively sink some valves deeper than others. Of course whether for routine overhaul or something trickier, cutting the seat also results in less seat pressure, hence the need for shims.

Back then quite a few 1.6s were also having catastrophic valve failures at the tips. I tested a bunch of valve springs, original and brand new, and found the new ones less consistent in both free length and rate than the originals. Given that, I used additional shims when assembling all of our heads and screamed bloody murder when the rule was blindly and (IMO) stupidly added.

Of course it didn’t stop the guy they were targeting, it just forced him to go to more expense (passed on to customers) by replacing seats to stand other valves up and ultimately get more benefit than before. So, not only did the rule fail to accomplish anything useful it backfired, increased costs and further hurt the little guys just trying to compete honestly within the rules. (If the FSM says I can, then damn it, I CAN! Until someone decides they don’t like it.)

So, rant out of the way, James is not way off base here. From what I’ve seen in engines from multiple builders, the valves & seats are taking too much of a beating for the pathetic cams and spring rates that we run. I’m not saying that the cause is definitely one thing or another but his machine shop guy is right to raise the question and should be highly critical of the answer.

Steve, you're accurate on all that I'm sure but the valve problems (just among NB's) of even a few years ago seem to have quieted down a lot. One engine builder I've used bitched about not getting good spring pressure but worked through it in the build process with correct valves, springs, guides and shims.  Gotta believe that the folks building most of the engines now have figured out how to select parts, machine and assemble heads so that they are reliable when not over-revved.   

 

In this case for James there has to be something fundamentally wrong with how his head is being prepped or there is consistent over-revving or some other engine condition that isn't right. 

 

I've never had a valve problem with any of my cars that wasn't self inflicted.  Many can probably say the same.

I had very few valves issues over the years. I have seen more this year than ever before, probably more than the last 4-5 years combined.  My issues have been tulipping new valves.. We have even moved the margin in more conservatively and still see it occasionally. Mostly on VVT as the 6D valve is shit.. Super thin on the edges.  I think these failures are directly related to new casting numbers on the heads of the valves. Pretty certain Mazda is sourcing the valves from a new supplier and I don't believe they are as good as they used to be. 

Tom “correct valves, springs, guides and shims” won’t solve the problem that I described. “Correct” is OEM, or more accurately and to Jim’s point, whatever Mazda is selling these days. We can’t use different springs or valves, guides aren’t the problem, and we MUST use one and only one stock thickness shim. Arguably you are not allowed to replace the seat, (or the guide I suspect) but a new seat is often the only way to salvage a head and still pass tech. As for tuliped valves, they certainly go back more than a year and include ‘99-‘00s. Perhaps it is poor quality material, that’s why I made a point of not being definite about the causes, but James and his engine guy are not wrong in questioning the idiotic rules. And it gave me another club to swing at the equine corpse.

BTW James, the first quick visual check of valve springs in tech is probably the color of paint marks that come on them. Some people may remove that intentionally so it doesn’t flake off and end up in the engine but I don’t think that’s much of a risk. Anyway, I do not know if tech keeps specific wire size and coil counts for each model/variant along with current replacement parts. The original 1.6 springs haven’t been available for many years and their own crate engines were shipped with springs that fail every FSM measurement. For years Sunbelts shipped with something better that they sourced and likewise one of the other “pro” engines I tore down. I’d be surprised if there isn’t still some fudging going on out there, to solve problems that cost power and reliability. (Anything stiffer than required to control the valves just increases parasitic losses, which is why it’s idiotic to make such a big deal about them in the first place)

For what it's worth, in 2016 when I built by 99 engine, I did a bunch of measuring of rates. 

• I bought new mazda springs, and had two engine sets of used springs on hand
• There was a surprising amount of variation in spring force as measured at nominal compressed height. 
• I also found most of the used springs to have a higher force than the new mazda springs. 

 

I would be in favor of allowing shimming per the rules.  Just need to ensure there is a specified dimension in the rules so that spring compressed length is not shorter than stock, AND there should still be the "L" dimension to prevent people from sinking the valves too far (though not sure why you would do that).  Somebody submit a letter....

I am not an engine builder. When I see a piston, it is a bad day. That being said, most of the valve issues I have seen have been following an over rev. Especially on the VVT. Remember the NB motors are sold lifters, so no cushion if the valve contacts the head. NA's have hydralic lifter (HLA) that do give some cushion on an over rev.

 

As Jim says above, most of the failures are tulipped valves. Would increase spring pressure increase the rate of tulipping?????

 

D

For what it's worth, in 2016 when I built by 99 engine, I did a bunch of measuring of rates.

• I bought new mazda springs, and had two engine sets of used springs on hand
• There was a surprising amount of variation in spring force as measured at nominal compressed height.
• I also found most of the used springs to have a higher force than the new mazda springs.

I would be in favor of allowing shimming per the rules. Just need to ensure there is a specified dimension in the rules so that spring compressed length is not shorter than stock, AND there should still be the "L" dimension to prevent people from sinking the valves too far (though not sure why you would do that). Somebody submit a letter....

It sounds like we have traveled the same path. I have measured many hundreds of springs over the years. More than a decade ago I bought bags of them from Rock Auto and they were absolutely indistinguishable from those I bought from Mazda, paint marks and all. Clearly Mazda was already using the same aftermarket source to meet a level of demand generated by racing. That’s not meant as a jab at them, no manufacturer is expected to maintain a supply of true OEM (and more importantly, original quality) parts indefinitely. It does bother me when even with our discount the prices from Mazda are considerably higher than other sources of identical parts but that’s a different topic. From what Jim has said above and in the past it sounds like NB valves have probably gone the same way, I know it has already been an issue in tech. In any case we should not be forced into extreme measures if simply allowing shims can at least partially mitigate the problems.

As for sinking valves, certainly that is generally considered counterproductive. However, if you look at enough of these heads you see large variances in the chambers, in how high up the seats sit, etc. Taking the taller ones down a bit can allow better matching of camber size and therefore compression so that decking of block and/or head raises compression on all without causing one oddball to go over. And depending on the particular combustion chamber, piston dome, cam profile etc. it isn’t necessarily a bad thing to, for example, sink all exhaust valves a bit deeper than the intakes. I don’t have any specific test data for that on these engines but I know there was some work done along those lines on the 1.6. As I mentioned above, after shimming was outlawed they simply shifted to the more costly approach of raising intakes rather than sinking exhausts, and gained a bit more. Or so I’m told.

I am not an engine builder. When I see a piston, it is a bad day. That being said, most of the valve issues I have seen have been following an over rev. Especially on the VVT. Remember the NB motors are sold lifters, so no cushion if the valve contacts the head. NA's have hydralic lifter (HLA) that do give some cushion on an over rev.

As Jim says above, most of the failures are tulipped valves. Would increase spring pressure increase the rate of tulipping?????

D

Dave, tuliped valves are commonly caused by very high lift cams with steep lobes and in turn require very stiff springs to control them. The result is the valve being slammed against the seat at high velocity and with great force. Our whimpy engines are at pretty much the opposite extreme so your question is perfectly logical. However, when seat pressure is too low the valve is not controlled and will bounce. When full-open rate is too low it can “float” (hang open or even over-shoot) rather than follow the cam. Both are bad and both can occur even with a “good” spring if the installed height is too high as occurs with even routine resurfacing of the seats. Add to that even a minute change in spring specs or consistency issues and you have real problems.

Ok, Again I am not a head builder. But I discussed your comments with my builder and didn't leave until I thought I understood him.

 

First my damage: I have bent and cupped valves. They are not tulipped nor have any of mine ever been tulipped. The bending is being caused by piston interference which is absolutely happening from an over rev, The over revs have never exceeded 8K though. All damage has been on the exhaust side and primarily on #2-4 cylinders.

 

Per head guy, tulipped valves are not caused by them impacting the seat. That is indeed the force that creates the tulip, but is is excessive heating of the valves that conditions the valve metal to be tuiliped when it impacts the seat at normal impact force. He agrees with Jim that it is likely the metal has been changed if this is a recent problem. That said, he states that the valve bouncing on the seat is causing excessive heat. When the valve seats and stays seated by correct seat pressure, then the valve cools. That said, if we increase the seat pressure, do we then exacerbate a tulip issue?

 

The bending of my valves is happening in the over rev and banging into the valve relief of the piston. Yes it is an over rev, but not a high over rev. If it is floating at 8K rpm enough to interfere with the piston, then the valve is still floating over the nose of the cam at 6.5 to 7K as well. Just not enough to interfere. So the question becomes how much spring pressure and rate do you need to control the valve at our RPMS? He states that 35 seat and 75 over the nose is not enough and that we could add 20 to 30 lbs without having to worry about parasitic power loss. Besides shimming he stated we could lighten the retainers and get a little improvement with our current springs. Probably not enough to keep from bouncing and floating though.  The cupping I am seeing is also caused by too low of seat pressure. So in his opinion, every failure type I have seen plus the tulip you guys have seen would be improved if we had heavy springs.

 

Maybe the answer is to just not over rev the engine. But that only solves the valves being bent. It does not fix the cupping and potentially the tulip. If what he is saying about heat is true, then over rev or not, our engines are running hotter than need be and we can get more life and reliability out of the motors by allowing us to shim or to run different springs.

 

IMO, taking a run at the other spec body will not work unless SMAC approves for SCCA. The reason, and I would agree with the reason, is that it is one thing to ask competitors to run 2 different sets of tires, it is something else to ask them to have two different head configs. Two different head configs would be cheaper for me to deal with if I ran both orgs than having to deal with two different tires. But for the average guy, this would be more expensive than two different tires.

 

So in spirit of spec class racing we do  not want to create additional costs for competitors. But I think we can all agree that you are not competing if you don't have a built head. So if you are building a head, what is the additional cost of allowing us to run shims? $10 maybe? What does a new valve cost? What does it cost to have a valve job done for cupped valves? What does it cost for unnecessary over rev damage?

 

Anyway, I have met my obligation to my head guy to pose the issue to you guys to consider.

Steve, there is definitely still fudging going on if 75lbs is what the nose pressure is on all model years. I know it is going on because I have seen 100 lbs nose pressure on a SM head that had used springs. But I couldn't tell the springs apart from a visual inspection. But I am not as good as others that look at many many different springs.

Have you had any tuliped valves that were not also bent?  I would expect a bent valve to lose the ability to properly contact the valve seat, which on the exhaust side would cause poor contact area for heat transfer all the time, resulting in valve overheating, and thus wear. 

 

I am not knowledgeable enough to say if valve bounce could cause overheating...but the one time I was able to see valve bounce measured in a live running engine, the bounce didn't account for that high a of percentage of the time normally spent contacting the seat.  Thus, I would assume the difference in valve cooling to be similarly small. 

Never had any tuliping of my valves

High combustion chamber temps can cause valve issues even if they aren’t bouncing, and the way we tend to tune lean with quite a bit of advance I expect things are marginal to begin with. If things lean out a little more at the track due to fuel used, environment, a weak injector, or whatever then sure things can stretch or burn. I haven’t checked EGTs, perhaps someone has, but I saw indication of too much heat on the same cylinder or two I’d probably get my injectors rechecked. If they all seem to be getting too hot I’d question my timing and AFR. Any sign of detonation? What plugs do you run?

Tom “correct valves, springs, guides and shims” won’t solve the problem that I described. “Correct” is OEM, or more accurately and to Jim’s point, whatever Mazda is selling these days. We can’t use different springs or valves, guides aren’t the problem, and we MUST use one and only one stock thickness shim. Arguably you are not allowed to replace the seat, (or the guide I suspect) but a new seat is often the only way to salvage a head and still pass tech. As for tuliped valves, they certainly go back more than a year and include ‘99-‘00s. Perhaps it is poor quality material, that’s why I made a point of not being definite about the causes, but James and his engine guy are not wrong in questioning the idiotic rules. And it gave me another club to swing at the equine corpse.

By correct I meant best available among OEM parts.  Some years ago I had an engine built and sent builder 2 heads with all the old valve train parts plus all new valves, springs, shims, retainers, etc...  We had a fair amount of discussion about the variations he found among the parts and yes old valves and new valves showed some differences.  He machined and assembled the engine using what he thought was the best combination.  Again though never had a valve problem over the years except once caused by 3rd to 2nd shift on a straightaway by a "guest" driver. 

 

Will leave it to those who are more knowledgeable but if a 2nd shim or thicker single shim makes heads more reliable without getting into some other prep/tech rat hole it should be considered. 

Maybe separate issue but maybe not...with regard too plugs...there is a stock recommended plug by Mazda which I assume is heat related. Is this ok? one step cooler? 2 steps cooler? What say you smart guys?

 

Assuming airflow is a constant...is fuel(injector amount)the only cause of leanness? Does the heat of a plug affect the explosion heat? In other words...is it a combination of factors or one thing that can cause exhaust valves to overheat/glow? Which leads to problems James has described...