Valve springs too strong? 1

[HoofHarted]

I have a 16V cylinder head that I'm trying to fit Merc valves to. The Merc Valve Springs are slightly longer, smaller in diameter and are much stiffer, than the orginal springs. I would like to know if it possible to use these springs with the hydraulic bucket lifters and not break the camshafts from excess force.

 

[evelrod]

It's hard to see a valve spring that is so stiff as to "break the camshaft"...Truly, however, springs that are too strong for any application WILL cost horsepower and possibly work a severe hardship on the valve train! Too soft can cause float problems with aggressive cam profiles. It is always a compromise between performance and longevity.

Rod

 

[HoofHarted]

I also thought as much. Someone told me this story and he reckons that is one of the main purposes of a billet shaft. So this got me thinking and then worrying.
How would one measure the resistance of a Valve, I mean what machine would it be?

 

[evelrod]

There are a few engines, throughout racing history, that have developed a reputation for breaking camshafts. I race one of them, a Lotus Twincam. Even though the reputation exists, I have never broken a cast iron camshaft since I started building the things in 1966...Possibly because I like soft springs? Dunno. However, leaving no stone unturned approach...With our newest engine built last year, I am using an Omnitech prepped cylinder head that has a pair of billet camshafts (with soft springs, 85#seat-250#open) that are tested to 9500 rpm.

The only "test" that I typically do to an engine that I have assembled while it's still on the stand, is to turn it over with a torque wrench and record what it takes to 'break it loose' and what it takes to keep it rotating. The numbers have always been a good gauge as to what the engine will be like in service...rule of thumb.

Rod

 

[marcusaurailius]

Hoofharted, too stiff a spring will as mentionrd ,rob hp

but more of a problem i have found,is the wear of the cam/followers is very high,.

o,e. ones seem to be better than after market ones at standing up, are you going to use the o.e. cam,and followers??

regards Marcus

 

[HoofHarted]

I would like to use the orginal cams and new Bucket lifters. One of the main reasons why i like the Mercedes valves over my standard ones is that it has a 3cotter groove.
Ok hows this for a simple comparison; When i was stripping the 16v head i used a socket and a hammer to remove the upper valve retainer (Come on we all do it). Easy, one hit and the cotters fall out. When i was stripping the Merc Head, i tested the same method with no results.
Now Surely Wouldn't this simple test swing one's vote. And if it's concern bout wear how does Merc Overcome This? They Use Rocker arms with hydraulic lifters.

 

[evelrod]

In high rpm race engines we use single groove split locks...stronger, less failure prone!

Rod

 

[evelrod]

Oh, one more thing...especially for the 'shade tree branch' of automotive builders...

I have, on occasion, used a brass tube and a mallet to loosen the split locks, but never bashed away and bounced the retainer/springs/split locks all over the shop floor. That is what the valve spring compressor is for!!! DUH! I saw some of my 'friends' doing this back in the 1950's and even then, I thought it a stupid practice.

Rod

 

[patprimmer]

I have to say I never considered bouncing valve stem split locks out, I guess for several reasons, being they get lost and you need to lay the head over at an awkward angle.

I do lightly compress the valve spring with the compressor then tap the compressor over the valve spring to break the retainer free, then fully compress the spring.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Lou Scannon]

Pat's technique has always worked for me.

 

[HoofHarted]

Rod Im not arguing with you but how would a single cotter groove be stronger than a 3 cotter groove? Enlighten Me.

 

[NickE]

HoofHarted, fewer stress concentrators due to the grooves.

 

[Lou Scannon]

From an admittedly limited engine sample size, my observations are that the triple grooves are used for a passive valve rotation system in which the keepers butt together leaving the valve free to rotate within them. The triple grooves/ridges tend to be deeper/more prominent than the single grooves/ridges, making them more incrementally more difficult to remove, by whatever means.

 

[SincoTC]

I haven't been in the "infernal combustion engine" business for a long while now, but I can remember a couple of occasions when an engine builders substitution of longer, stronger, non-standard valve springs resulted in broken camshafts.

However, these weren't caused by the strength of the spring, but by the coil-bound or shut length of the spring being exceeded by the cam lift. Both engines were OHC, iron cams with shimmed lifters, so nothing much to "give". On one engine the breakage occurred when torquing down the cam's bearing caps and the assembler didn't stop and investigate why a cap went "tight" with a gap under it, he didn't notice that the adjacent lobe was on-peak and couldn't see that the spring under the lifter bucket was closed solid, so he just tapped the cap and pulled harder, until there was an expensive bang! On the other engine, the guy managed to get the cams in, but then, when he couldn't turn it over to set the clearances, he decided to go ahead and refit the engine and use the starter to turn it over, what a dork!! This one was a DOHC, and the result was one bang plus a stripped sprocket and a broken chain that saved the other cam, but did nothing to prevent some pistons arguing with those valves that were still left open before he could release the key.

I agree with evelrod and patprimmer about the dubious practice of bouncing out the retainers with a mallet and socket or similar. I would say that by the time you've found all the bits that didn't go in your eye or through a window, the proper compressor was often quicker, especially with valves at an angle!

 

[HoofHarted]

I always appreciate most of yours guys input and thanks to many your unfortunate accidents, others, including myself, can learn from and even prevent.

It sometimes seems odd how a person can view something and interpret it differently. But I suppose such is life with its continual mistakes ad remedies.

I will go forth and use my NEW OEM Springs and cotters not the ones where I so "dubiously and carelessly bashed with my eyes closed" thus sprayed engine parts across my garage. Because even though I had hoped to use the Mercedes Parts I was not intending to use the original old parts. Why would I waste my time compressing a spring that I have no intent on re-using? It just seems that the outdated "dubiously stupid practice" is a bit quicker.

 

[tbuelna]

HoofHarted,

If the new spring is longer (free length) and smaller in diameter, then it is likely going to be overstressed in your application. A smaller mean coil diameter and greater working deflection both tend to increase spring stresses.

The only exception would be if the wire cross section is smaller, or the number of coils is greater. However, both of these characteristics would produce a lower spring rate. If the spring rate of the new longer spring is similar to the old spring, then it is also likely to coil bind at max valve lift. You should check for this condition before running your engine.

As for the slightly higher spring forces acting on the rest of the valvetrain components, as long as they are properly lubricated and cooled, it should not be a problem.

Regards,
Terry

 

[Rob45]

Overly stiff valve springs are also hard on the valves themselves.

 

[MAFTec]

Terry,

Can I go back to your comments? As I would like your advice and comments on the following - I have a similar issue, I am upgrading an old engine PRV V6 (in this case the early turbo version), and in the pursuit of increased output the rev range is going to need to increase. I have studied the various generations of the engine, and the later engines (n/a with increased rev range) used shorter springs (fitted with spacers). These springs are smaller in diameter, and also have smaller wire diameter for the coils. They achieve the same full lift poundage, and accommodate the required valve lift. They are also lighter then the original springs.

I need to machine the old casting head to accept the later arrangement, given your comments from previous, am I correct in understanding the later springs should be more resistant to coil bounce – lighter and smaller diameter? Is this generally true with smaller diameter springs if the rest of the poundage rates remain the same? I assume the stresses in the spring are higher though, so fatigue life may be shorter? I presume my understanding that overall the later arrangement is actually an improvement, thought I had better check this whilst asking all these questions – apologies.

I would appreciate your input with this mater.

Thank you,
Martin

 

[BrianPetersen]

SincoTC, a so-called engine "builder" who assembles an engine with non-standard valvetrain components without checking for coil bind is not worthy of the name!

 

[BigVlad]

I agree with SincoTC - coil bind is the real danger.
Also the "traditional" type of spring compressor seems best suited to pushrod-type heads. OHC heads seem to usually have high "skirts" around the edge that make it very difficult or impossible to apply the compressor to the spring. If you haven't got the proper compressor, what are you going to do? Be held up possibly for days looking for the right tool or use the hammer and socket method?