Valve springs too strong?
Valve springs too strong?
(OP)
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.





RE: Valve springs too strong?
Rod
RE: Valve springs too strong?
How would one measure the resistance of a Valve, I mean what machine would it be?
RE: Valve springs too strong?
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
RE: Valve springs too strong?
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
RE: Valve springs too strong?
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.
RE: Valve springs too strong?
Rod
RE: Valve springs too strong?
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
RE: Valve springs too strong?
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
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RE: Valve springs too strong?
RE: Valve springs too strong?
RE: Valve springs too strong?
RE: Valve springs too strong?
RE: Valve springs too strong?
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!
RE: Valve springs too strong?
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.
RE: Valve springs too strong?
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
RE: Valve springs too strong?
RE: Valve springs too strong?
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
RE: Valve springs too strong?
RE: Valve springs too strong?
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?
RE: Valve springs too strong?
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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for site rules
RE: Valve springs too strong?
RE: Valve springs too strong?
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Valve springs too strong?
RE: Valve springs too strong?
Rod
RE: Valve springs too strong?
For disassembling the valve springs on a cylinder head, the proper way is with a spring compressor but there is an acceptable alternative to this. They make a tool that is magnetized that is specifically for keeping the valve locks from "flying everywhere". This tool is relatively inexpensive and is made by KD tools I think. With this tool, you use a hammer and when the spring is displaced enough, the locks "fly" up into the magnetized hole that holds them in place. This tool also comes with another piece to allow for re-assembly.