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How to balance your valve train


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VALVE TRAIN BALANCING

 

Many of you who know me have heard me say that the valve train in my engine is balanced to within + or – ¼ gram. Well I am going to tell you how I did it,

First you need to have access to a very accurate balance (or scale), and you need to make a fixture to allow you to check the “levered†weight of your rockers. The other things that are very handy are a computer with excel and a tray (or several trays) with at least 84 total compartments (this is for an L series motor). Each compartment should be numbered from 1-84 using some sort of permanent marker.

The next thing you need is to purchase a brand new set of rockers including all accessories i.e. retainers, valve springs, lash pads etc., it is important to buy high quality parts, preferably Nissan parts although mine came from Motorsport. It is also a good idea but not necessary to purchase a new cam at the same time.

 

P2150004.jpg

Assembled rocker assembly with lightened, polished, and balanced rockers and components.

 

You can see in the above picture what the results of all your hard work will look like, so lets get started with what you need to do now. Since you have all your new parts it is time to put your tray(s) to use. You can use any order you want (but I started with my rockers, then retainers and so on), and put one piece in each of the numbered compartments (each half of the retainer locks gets its own compartment). Also you should separate the valve springs and give each spring inner and outer its own compartment. Make sure each piece is completely clean and free of all foreign materials including any oil or rust inhibitors. Now on a piece of paper write the numbers 1-84 (if you have sticky labels you can use them and stick one inside of each compartment), weigh each piece you have at least three times and average the weight then write the weight on the paper or the label. For your rockers this is the unadjusted weight and it will change. After you are satisfied with the weights you attained put some oil or WD-40 on the parts so they do not rust.

Inspect each rocker for any defects and make sure the braze that holds the wear pad on the rocker has no gaps in it. Put a piece of masking tape over the pad on the rocker to protect it. Take the rockers one at a time and using a grinder wheel with a medium grit wheel very carefully radius the tip as you see in the pictures below.

 

rockermod5.jpg

rockermod2.jpg

rockermod1.jpg

 

After the tip has been ground down weigh each of the rockers (pull tape off before weighing) again as part of the goal is to get the weight of each rocker as close as possible to the next. Re-tape the rockers and using a Drimmel tool with a small diameter drum sander remove any and all casting lines and sharp edges (except the sides of the pads) from each of the rockers, while doing this you should make sure that you work front to back and NOT side to side. All the sanding marks should run front to back when you are finished. Again remove the tape and weigh each rocker, as you have been grinding on the rockers you should be biasing the material removal on the pivot side of the pad in order to bring the weights closer to each other. Once everything looks more like the above picture 1.2 and your weights are within ½ gram of each other it is time to start polishing the rocker. You will polish at this time only the pivot side of the rocker. Start by using a very fine sanding drum on your Drimmel then go to grit impregnated rubber polishing wheels and lastly to a felt wheel with polishing rouge. Remember to always work front to back and NEVER side to side, when you are done the pivot side of the rocker should look almost like a mirror and you should not be able to see any sanding marks in the metal.

 

pivotmod.jpg

Customized pivot for measuring the “levered†weight of a rocker

 

Now it is time to weigh the rockers using the “levered†weight fixture (picture above), make sure the rocker and the fixture are completely clean with no traces of any foreign material. Place the fixture next to the scale and adjust its height so the rocker sits level between the fixture and the surface of the scale, make sure the rocker only contacts the scale with the tip. Carefully and lightly tap the rocker on the pad with a pencil to make sure its full levered weight is resting on the scale, write down the reading on the scale then remove the rocker and do the same thing again with the same rocker, do this at least five times for each rocker then average the five readings. After you have an average levered weight for each rocker you now need to radius and polish the valve end of the rockers to bring the weights down to within ¼ gram of the lightest one. When you are finished with this last step record the levered weights of the rockers, apply oil or WD-40 to them and place them in their respective compartments.

After you have each item numbered and weighed you need to fire up your computer, open excel and create a series of 84 cells numbered 1-84 and containing the weight in grams of the piece assigned that number. Using a calculator add the weights of a group of items together then divide that number by the total number of items to get an average weight, as an example I have 12 retainers and their weights are (in grams) 26.966 + 27.139 + 27.240 + 27.312 + 27.413 + 27.590 + 27.645 + 27.737 + 27.814 + 27.878 + 27.998 + 28.106 = 330.868 divide by 12 = 27.572. After doing this with each item i.e. inner spring, outer spring, rocker levered, lash pad, retainer, keeper left, and keeper right (do NOT use the rocker actual weight) add the average weight of each item together to get an overall average weight for example 155.293 grams. This weight will become your target weight for each rocker assembly. Now comes the real fun…

Using the excel spreadsheet you created with all your weights in their own individual numbered cell you now need to mix and match parts together in order to achieve your target weight of -in our example- 155.293 grams plus or minus .25 gram or in this case 155.043 to 155.543. You may find that no matter what combination of parts you use (you have 7056 possible combinations) you can not get all of them within the .25 gram tolerance, if you run into this case look for any individual part that is notably below or above the weight of all the other parts and use the difference in weight from the other like parts divided by two to bias your average and use that as a new target weight for your rocker assembly.

This whole process took me approximately three months to complete and left me with a rocker assembly that weighed in at 153.644 grams with the greatest plus weight adding .211 grams and greatest minus weight being .212 grams which falls well within my tolerance of plus or minus .250 grams.

This exercise will not provide you any extra power from your engine, but it will increase the reliability and longevity of your engine plus the reduced weight will lower your overall engine mass allowing the engine to rev quicker and smoother. Do not attempt to do this if you do not have the time, tools, patience, room and or ability as it is not an easy job and it will not go quickly, but you’ve got to love the bragging rights.

 

Miles Gray

(Dragonfly)

 

 

valvecomponents.jpg

Springs, standard pivot, keeper, and lash pad. All but the standard pivot should be weighed as they are all part of the balancing process.

 

 

 

rockercomponents.jpg

Unmodified rockers from the front and from the side, mouse trap spring retainer, and mouse trap spring. Only the rockers are weighed.

 

 

keeperassy.jpg

Left and right retainer locks and a valve stem seal. Locks should be weighed individually, the seal does not need to be weighed. *Locks are also referred to as keepers*

 

 

scaleside.jpg

Mettler single pan balance that I used for weighing all my parts. This balance has an accuracy .1 milligram.

 

Dragonfly

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After reading (and posting most of the same pictures) this post http://forums.hybridz.org/showthread.php?t=126226 I decided to post the above "article" that I had written a long time ago but never got around to posting.

 

Dragonfly

 

Wow - much more info than I thought I would get - thanks again. Interestingly, I was thinking along these same lines, but had not yet formulated a plan - this is very helpful.

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rockermod1.jpg

 

Re-tape the rockers and using a Drimmel tool with a small diameter drum sander remove any and all casting lines and sharp edges (except the sides of the pads) from each of the rockers, while doing this you should make sure that you work front to back and NOT side to side.

 

 

Dragonfly

 

One question.. You say "front to back," do you mean from the left to the right in this picture? Pivot end towards valve end and vice versa, as opposed to "top" and "bottom" in an assembled sense?

 

Secondly this guy...

scaleside.jpg

 

Must've set you back a penny or six... Any chance that a balance with an accuracy down to .01 gram will cut it for this job? obviously the greater the precision of the scale, the greater the precision of the results...

 

Nice write-up! Somehow I doubt it will be among the more frequently UTILIZED write-ups here, but thats just because too many people are too lackadaisical with their engine assembly. Thanks!

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Any chance that a balance with an accuracy down to .01 gram will cut it for this job? obviously the greater the precision of the scale, the greater the precision of the results...

 

Nice write-up! Somehow I doubt it will be among the more frequently UTILIZED write-ups here, but thats just because too many people are too lackadaisical with their engine assembly. Thanks!

 

The .01 gram is not going to help you much (it is equal to 10mg) but it is still much better than stock. You may be able to find a fairly cheap jewelers scale and use that for the smaller measurements than use your .01 gram scale for your larger measurements. A jewelers scale will usualy allow you to select grams, mg, or carats, if not you will have to convert. You are correct that the greater the precision the better the results.

 

One question.. You say "front to back," do you mean from the left to the right in this picture? Pivot end towards valve end and vice versa, as opposed to "top" and "bottom" in an assembled sense?

 

Yes that would be pivot end to valve end, the reason for that is that all of the microscopic (and larger) lines that you create from grinding and polishing are moving along the load bearing axis and therefore will not weaken the part. That is even more true if you do the same thing on connecting rods, always work from end to end.

 

Dragonfly

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I just took the time to read through this article in detail, and it is a really interesting procedure - I hadn't really considered trying to mix and match the components - very thorough.

 

I did notice one thing, though (and I kinda hate to even mention it, considering how much time you put into it)...

When coming up with the balance figures, I believe that you should only consider half the weight of each spring, as one end of each spring is always stationary - this is the same rule that you use to figure the spring's contribution to the unsprung weight in your suspension. Also, same reason that you use the "levered" weight of the rocker.

 

Sorry to bring this up, but I figure if you're gonna be anal, you might as well be really anal... :mrgreen:

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I just took the time to read through this article in detail, and it is a really interesting procedure - I hadn't really considered trying to mix and match the components - very thorough.

 

I did notice one thing, though (and I kinda hate to even mention it, considering how much time you put into it)...

When coming up with the balance figures, I believe that you should only consider half the weight of each spring, as one end of each spring is always stationary - this is the same rule that you use to figure the spring's contribution to the unsprung weight in your suspension. Also, same reason that you use the "levered" weight of the rocker.

 

Sorry to bring this up, but I figure if you're gonna be anal, you might as well be really anal... :mrgreen:

 

Youv'e got a good point... but I could not figure out how to accurately weigh only one half of each spring. In doing it the way that I have outlined you still end up with an overall tolerance of + or - .25 gram from your nominal value (weight) you just have to deal with the fact that the mass that is moving is actualy less than your nominal :mrgreen:.

 

Great Article Miles!

 

Stiky! Stiky! Stiky!

 

I take this as one of the highest compliments I can get, thanks Tony and thanks admins for making this a sticky.

 

Dragonfly

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Youv'e got a good point... but I could not figure out how to accurately weigh only one half of each spring. In doing it the way that I have outlined you still end up with an overall tolerance of + or - .25 gram from your nominal value (weight) you just have to deal with the fact that the mass that is moving is actually less than your nominal :mrgreen:.

 

I'm pretty sure that all you have to do is just weigh the whole spring just as you did, and divide that value by two for use in your calculations. The springs are concentric with the motion of the valve and they are constant spring rates, so I don't think it needs to be anything trickier than that.

 

The reason you want to measure the rocker the way you did is to try to accommodate the fact that the weight distribution of the rocker is not constant. In this case it makes sense to get the overall weights the same, as well as the "levered" weights. This ensures that the rotational inertia for each of the rockers ends up essentially the same (they do travel in a small arc about the pivot point, so rotational inertia is appropriate).

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Yes that would be pivot end to valve end, the reason for that is that all of the microscopic (and larger) lines that you create from grinding and polishing are moving along the load bearing axis and therefore will not weaken the part. That is even more true if you do the same thing on connecting rods, always work from end to end.

 

Dragonfly

 

Thanks for the machining lesson! I discovered the answer to my question in TimZs thread as soon as I posted it and moved on.. but the explanation is MUCH appreciated.

 

On the subject of weighing "one half" of the spring... couldnt you tie a string in the center (or the center of gravity, or the point beyond which the spring sees no motion, unsure which) and then fasten the other end of the string to a fixed arm, and weigh the moving end? If it's a matter of finding the center of gravity, I am sure you could get at LEAST a guesstimate based on the length of coil on moving end versus length of coil on stationary end..

 

Obviously I am in a *bit* over my head here, but thats where my ideas seem to function best.. If I am not pushing the envelope I am not really learning, the "familiar" stuff needs hands on experience to make into real knowledge.

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On the subject of weighing "one half" of the spring... couldnt you tie a string in the center (or the center of gravity, or the point beyond which the spring sees no motion, unsure which) and then fasten the other end of the string to a fixed arm, and weigh the moving end? If it's a matter of finding the center of gravity, I am sure you could get at LEAST a guesstimate based on the length of coil on moving end versus length of coil on stationary end..

 

I would think that it could be done the way you described but you would almost require labratory type conditions in order to have any real accuracy and repeatability. A lot of people would consider going as far as I described initally as going beyond the point of deminishing returns, I feel that the additional complexity of creating a biased weight for the springs (inner and outer) has truly gone beyond the point of deminishing returns. One of the things to keep in mind about this entire procedure is that it is not creating any power it is only assisting longevity of the parts. As stated in the other thread the time could be used better in other places (as far as creating additional power).

 

In a nut shell by doing this balancing work you are creating a more fluid interaction of parts which in general will cause the parts to last longer and handle greater extremes but will not create any power that is not already there.

 

Dragonfly

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I would think that it could be done the way you described but you would almost require labratory type conditions in order to have any real accuracy and repeatability. A lot of people would consider going as far as I described initally as going beyond the point of deminishing returns, I feel that the additional complexity of creating a biased weight for the springs (inner and outer) has truly gone beyond the point of deminishing returns. One of the things to keep in mind about this entire procedure is that it is not creating any power it is only assisting longevity of the parts. As stated in the other thread the time could be used better in other places (as far as creating additional power).

 

In a nut shell by doing this balancing work you are creating a more fluid interaction of parts which in general will cause the parts to last longer and handle greater extremes but will not create any power that is not already there.

 

Dragonfly

I fully understood the second part of your post after reading through initially. Regarding the first paragraph, I can only say that *I* wasn't the one who started the "anal retentive," I just joined it because it looked like fun :-P Seriously, though, I also have a tendency to inspect and attend to each detail, on each leaf, of my tree so to speak.. My comments regarding the "technique" were made just to further clarify my own understanding, and educational experience. I didn't expect to hear that it was worth DOING, just pondering how it might be done.

 

Call it a "What if I was an engineer on a Formula One team?" pipedream if you want.

 

Thanks again for the explanations, if this thread isn't stickied yet then I am DEFINITELY bookmarking it.

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Regarding the first paragraph, I can only say that *I* wasn't the one who started the "anal retentive," I just joined it because it looked like fun :-P

 

I know you're just joking, but all I was advocating was adding the simple step of dividing the number you got for each spring from the scale by two. There is a solid engineering reason to do this, and it will give more accurate results for the exact same amount of work. That's all.

 

As 1fastZ pointed out, this will only be completely accurate for linear rate springs, but that's what mine are, and that's what dragonfly showed in his pics.

 

And yes, the whole argument is probably academic anyway, but if you're going to go to the trouble...

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  • 2 weeks later...

I'm with Miles on the Longevity issue. This is not so much for power, it just makes things last so much longer. Until you weigh stuff accurately, you really can't tell how much difference you have. On large industrial engines I was aghast that the pistons were weight-matched within 10 POUNDS! (10" bore, 10.5" stroke with 900rpm operating speed...) I talked with one of their oldtimer technicians, and for some Naval Craft, they hand file the pistons on the balance pads to within 1# of each other, and it really helps with how the engine runs onboard ships...but for grouted stationary installations they figured WTF. Well, I did the first engine using a Bathroom Scale and did the pistons to within 1/2 a pound "more or less" just because I was curious. Took me a good 32 hours of work by hand. I really didn't tell anybody I did it, just did. When that engine started up the amount of vibration reduction was amazing! Where the handrails on the engine used to vibrate visibly, you could not even FEEL them moving afterwards. Now 32 man hours of work on something that takes a crew of 8 men a week to accomplish working around the clock is not a big investment in time IMO...and given the improvement in vibration reduction was well worth it. It was not required, but the time to do it was minimal. Since my time in VW's, half a gram was always the standard for just about any part. And even on stock engines I'd take the time to at least weight match everything that got torn down. Deburring Chevy pressed rocker arms, etc. It's all back to what I've said in the past...there is no real secret for speed or power, there are three basic elements:

1)Preparation

2)Preparation

3)Preparation

The difference between the engine that makes 208HP and the one that makes 147 using the exact same components is found in one of the three steps mentioned above, plain and simple. The reason one engine will last 2X as long as another assembled with the exact same components will be found in one of the three steps mentioned above as well.

 

As for compliments to Miles, it's partially my own sloth...welll in a big part my own sloth. It's going to be WAY easier for me to explain what I do to the top end when assembling something by linking this post if it's a sticky than if I have to bookmark it and find it again later! LOL

 

But even for the raw information contained, it's stickyworthy IMO.

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  • 1 month later...

definitely did not go to these extremes of measurements but just followed along in the how to modify your Datsun book. Took a postal scale and just filed off in the areas shown in this thread until I had a good weight reduction and then matched all the rocker arms in weight. Wasnt neccesarily looking for specific weight just consistency between all the rockers in weight.

 

Noticed a big difference in how the engine revved definitely revved quicker. I have been autocrossing my car and track daying this car for a number of years now with no related failure in my valvetrain. Definitely not afraid to rev the engine or baby it.

 

Got a free evening and want some more performance for free, definitely give this mod a try.

 

Pee yella 240 # 186 Track day Z Car Convention!

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