QUOTE(stugray @ Jan 30 2014, 11:17 PM)
Thanks Jake!
Posted with permission:
Here it is.. Expect many more just like this as these forums grow and I did up and edit my older writings. This has never been posted before, anywhere on the net..
I will be updating this post with pictures as soon as I can get them uploaded!
Enjoy!
Jake
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Valve train Geometry:Explained
Primary objective: For the user to attain the ability to properly set up the valve train of a Type 4 engine equipped with a performance camshaft and upgraded valve train components.
Secondary objective: To obtain understanding of the positive and negative effects of valve train geometry on engine longevity, reliability and overall performance.
Tools needed:
*RAT 25002 Valve train Geometry tool kit
OR
*Adjustable pushrod with span from 26.0-27.8 Cm
*Dial indicator with at least 1” of measuring travel
*Cutting tool adequate for cutting of the pushrods
*Vernier caliper with 11” of travel
*Various hand tools for installation of measurement devices and checking components
*Engine stand capable of rotating the test engine 360 degrees and capable of firmly locking at 90 degree intervals
Components needed:
-Type 4 engine completed to “Longblock” state without pushrod tubes installed, equipped for SOLID LIFTERS (This directive does not pertain to Hydraulic engines)
-One rocker shaft complete with modified 1.7L rocker arms and solid spacer
-Porsche 911 valve adjusters with nuts (NOT IMITATIONS!)
-Set of 8 cut to length pushrods without tips installed
-Heavy duty rocker studs, installed
I’ll begin this article with a bit of writing to help you understand why valve train geometry is so important and why it MUST be checked when any of the following characteristics of your engine have been changed.
- Performance camshaft installed (no matter how mild!)
- OEM camshaft reground (altering its base circle)
- Aftermarket lifters installed (questionable pushrod cup height)
- Cylinder length altered
- Cylinder shims added
- Cylinder heads resurfaced
- Cylinder head gaskets removed (per the VW bulletin)
- Valve seats cut (dropping the installed heights of the valves)
In today’s world it is VERY hard (near impossible) to build an engine that doesn’t introduce at least one of these issues into the build, most builds will introduce three or more of them, thereby altering the valve train geometry even further. Any of these things have an impact on the factory valve train settings, a few thousandths of an inch is all it takes to created inadequate geometry that can have negative effects on the performance and especially the longevity of your engine. These few thousandths of an inch are multiplied by the rocker arm ratio and the net result is drastic.
So, what happens if any of the items listed above exists and you don’t bother with proper valve train geometry?? I’ll tell you- the life of your valve guides and valves and near every other part of the valve train will also be greatly impacted. Having seen many engines that were “rebuilt” with all stock components or worse yet were improperly set up with performance camshafts I can tell you that the wear to these components can occur at as little as 1000 miles or normal use, it doesn’t take a race engine to have premature failures from a lack of proper valve train geometry. The performance aspect of this is the fact that the added side loading of improperly set valve train robs power and the fact that engines equipped with performance cams could lack up to .075 of their advertised valve lift, thus limiting the potential of the cam install, this could make the install of that nice, new performance cam counterproductive to say the least.
Now, with that said lets set the stage for the engine we are going to be manipulating. This engine will be outfit with one of my more popular camshafts, the RAT 9550 which sports .423 valve lift. When doing geometry the duration of the cam doesn’t impact the overall goal so, with this article we’ll only be concerned with actual lift at the valve. No matter the actual valve lift, all the procedures and goals are completed in the same manner, so just substitute your own lift numbers from your cam card in place of mine- if that makes things easier.
Our engine is also using stock 1.7 rocker arms that were modified for genuine Porsche 911 valve adjusters; these are our choice for all engines, even full race applications. If you have aftermarket, ratio rocker arms this article will be of benefit to you, but will not be 100% accurate as your valve adjusters are on the opposite end of the rocker (pushrod end). We will also be using a solid spacer between the rocker arms, replacing the “Spring/shim” arrangement of the stock engine.
There are two overall goals associated with proper valve train geometry:
1- Attaining the advertised net valve lift +/- 5% (indicated on the cam card)
2- Attaining proper valve/valve adjuster alignment at ½ net valve lift
Begin the process by finding a suitable method of attaching your 1” travel dial indicator FIRMLY to the cylinder head; if you use one of our rental kits from the Type 4 store for this you will be able to attach the modified components easily to the cylinder head using one of the rocker arm studs (we have designed this into the kit). The goal is to allow the dial indicator “foot” to rest on the valve retainer, while maintaining the same angle as the valve and ensuring that the rocker arm and valve adjuster do not contact the dial indicator while cycling the valve open and closed, we always start with the number one intake valve, you can work with any valve but number one is the easiest for many reasons. The dial indicator set up is an important part of the measurement process, if this is done in a shoddy manner the measurements you will get will not be accurate, so take great care to make sure the dial indicator is at the proper position and will not be contacted or impacted during valve cycling.
**NOTE- If your cylinder heads have been equipped with dual valve springs, we recommend that the inner springs from your test valves be removed as they will exert unnecessary force onto the adjustable pushrod as well as all valve train components right down to the camshaft. They will also increase the force needed to cycle the engine, requiring more user input.**
Once you have created an adequate means of attaching your dial indicator you can lubricate and install one of your lifters, since we are using the number one intake our lifter is also being installed in that position. Make sure that you lubricate this lifter with the supplied camshaft lube to reduce friction as much as possible since it may take several cycles of the valve to reach your goals. Once the lifter is positioned in its bore, install the adjustable pushrod with the adjustment union toward the cylinder head, this will make slight adjustments easier as you cycle the engine, make adjustments and work through the process. We recommend from experience with our camshafts and MOST Type 4 engine combinations that you start the process with an adjustable pushrod of 27.1Cm. This length of pushrod is the best starting point and will probably be within +/- 5mm of your pushrod length after completing the following procedures.
***Note- understand that not all adjustable pushrods are the same, it is imperative that the adjustable pushrod you choose has the exact same tip radius as the pushrod that you will be using in the engine- if it is not then your work will be wasted! The ultimate is an adjustable pushrod exacting your actual pushrods***
With these things in place add some lightweight assembly oil onto the rocker shaft and rocker arms as well as all other contact points including the valve tips, valve adjusters and all related items, then bolt on your rocker assembly to the cylinder head and realign your measurement device. As always, double check the measurement device and also ensure that your adjustable pushrod is seated in the lifter cup properly, it is easy to improperly position the pushrod into the cup, if this happens all your efforts to this point will be wasted. It is always easiest to rotate the engine stand to the 90 degree position at this point of the procedures and lock it there; things are much easier this way, especially if this is your first experience with these procedures as you will definitely need several engine cycles to achieve your goals.
With your “Cam card” in hand set the dial indicator to true zero ensuring that you have preloaded the indicator with enough travel to reach the desired lift goal, in our case this is .423 for our 9550 camshaft. Generally preloads are set very high to ensure that you will not approach the end of travel at max valve lift, thus affecting the accuracy of the reading. Also ensure that you are “off lobe” on the test valve, if you are partially on the ramp of the cam it will be impossible to start the process from true zero.
With the indicator preloaded and zeroed remove all lash from the assembly by adjusting the 911 swivel valve adjuster to slightly make contact with the stem of the valve. It is important that this adjustment be maintained throughout the processes of valve train geometry, we will refer to this setting as “Zero lash”.
Now that all things are in order attempt to cycle the engine through one full intake event by rotating the engine in the direction of operation (clockwise). While rotating the engine slowly pay close attention to the dial indicator as the valve you are measuring comes “on lobe”, you will see the valve slowly start to open and then accelerate open at a higher rate, pay attention to the dial indicator and count the rotations of the dial, each rotation is good for .100 of valve travel. This first cycle also pay close attention to your measurement set up, making sure that the dial indicator is “happy” on the retainer and that the entire arrangement is still operating on the same plane as the valve it is measuring and that nothing is binding or moving as the valve travels through its events. If your first cycle of the valve was successful, you are ready to move on to actually measuring the net valve lift, the first of our two goals.
Once again ensure that the dial indicator is zeroed then cycle the valve fully open paying attention to the distance the valve has traveled, especially as it gets close to the values stated on the cam card. Generally your first attempt will only get you within .040 of your goal, if you are lucky- don’t get frustrated if your numbers are pretty far off base from the specs on the cam card, it will just show you how ineffective “default” settings are in this area and what you might end up with if you hadn’t completed these processes.
Now is where things get interesting:
The following parts of the processes require perseverance; trial and error and patience, if you lack any of these stop the processes and come back to it later. If you happen to be the type of person that chooses to create math formulas and models to simulate these processes, give up right now and come back to the real world, then understand that most of the biggest mistakes that are made in this area are made by Engineers, software geeks and those that choose to put their emphasis in trying to out smart the engine on paper! Let the dial indicator do the work, you just pay attention and leave your software and slide rule in the office. I have had literally dozens of individuals try to come up with jigs, tools, software and formulas to get through these processes- they wasted more time than anything else, but most of them also wasted components because they spent their time paying attention to something other than the engine, that’s a HUGE “No-no”
Each of you that are working through these processes have different engines with variables that are also different, this spans from camshaft to the other seven impacting factors discussed previously in this article. Due to this you will have to enter the remaining portions of the article knowing that “results may vary”.
On my first cycle my net valve lift with the RAT 9550 and a default pushrod of 27.1Cm came out to .400, not bad for a first cycle as my net valve lift goal is only .423. Based on experience with this cam I decided to shorten my pushrod length very slightly (1/8 turn) and then compensating for the reduction in pushrod length by an adjustment of the 911 valve adjuster. Take great care to ensure that you only move the adjuster enough to get back to the “Zero lash” that you familiarized yourself with earlier in the processes, when you are at true “zero lash” you will be able to rotate the pushrod easily, but not feel any lash in the rocker arm assembly.
With the pushrod slightly shortened and the adjuster compensated, cycle the valve open again and note the difference in the new total valve lift value. According to your combination you may see a gain OR a reduction in total lift, there are no rules here because of the vast amount of variables being present. This is common sense, if you lost net valve lift from the first cycle, then you went the wrong way with the slightly shorter pushrod and your combo may want a tad longer pushrod with the adjuster compensated for the alteration- remember that this is a “trial and error” procedure, so no big deal!!!
Keep cycling the valve with slightly altered pushrod lengths, always compensating for the pushrod length change with an adjuster movement, always keeping the “Zero lash” in the sweet spot. With my engines after 4 cycles and 3 slight pushrod reductions I ended up with .420 net valve lift, well within the +/- 5% rule that we created earlier in the article.
***NOTE It is sometimes possible to net MORE valve lift on the intake valves than the cam card calls for, if this happens take advantage of it within the 5% range, if you end up with more than this for net lift start questioning the cam card for accuracy, don’t allow the intake side of things to go over 5% more lift than the card specifies. If this happens you may actually imbalance the port flow of the heads as it is very odd to ever get the full net lift from the exhaust side of the engine due to the rocker arm ratio and rocker/head design***
After reaching your goal with the total net lift it is time to tackle the second portion of the goal on the intake valve, attaining proper valve/valve adjuster alignment at ½ net valve lift. After reaching this you’ll go on to the exhaust side of things if your camshaft is a dual pattern cam with altered specs on the intake and exhaust valves.
With the pushrod and measurement devices still in place and unaltered on the intake valve the next steps are to ensure that your “sweet spot” for net valve lift is also not creating side loading on the valve at ½ the net valve lift, this is THE most important part of these processes and what you have been working to manipulate from the beginning of this article. It is important for you to understand that a few thousandths of net valve lift should ALWAYS be compromised in favor of better adjuster/valve alignment. This alignment is what wears components and promotes engine failures; it’s your biggest enemy.
This is the point where you’re full valve lift values need to be used to determine the true “1/2 lift” position of the valve, we will use my engine as an example. I was able to attain .420 net valve lift from my arrangement, by dividing this value by two I came up with .210, so my “1/2 lift” point will be at .210 of valve travel. It is important to understand that your “1/2 lift” value is NOT what the cam card specifies divided by two, it’s the actual net lift that you attain by doing these procedures that is to be used, my cam card specified .423, but I came up with .420.
Now that true “1/2” lift has been calculated, cycle the engine clockwise to this position, mine was .210 and then pay very close attention to the valve/ adjuster relationship. This is the point where the valve and valve adjuster must follow the same plane; they must appear as one unit, imagine them as being one solid piece, that’s how straight they should be. If your valve/adjuster are not totally straight you will need to either alter pushrod length or install correction shims under the rocker arms, the specs of your engine will dictate which route to go.
I always make an attempt to alter pushrod length slightly to correct misalignments of valves/adjusters when I am working with these processes, 90% of the time with our cams the best results will be found with this method, vice adding correction shims under the rocker arm assemblies. If you plan on working in this manner do yourself a favor and remove the measurement device, rocker arms and be careful NOT to alter the length of the pushrod, at least not yet. This is due to the fact that you spent a lot of time finding the optimum pushrod length and smart people will measure that pushrod PRIOR to altering its length to correct alignment issues. If you do this you can always default back to your optimum pushrod length to swap approaches to curing the alignment issues, if you have to- it’s a good insurance policy.
Now that you have measured and recorded the pushrod length reinstall the rocker assemblies, pushrod and measurement devices and ensure that you are back at “zero lash”, you should be as long as the pushrod length and adjuster have not been altered. With everything back together SHORTEN the pushrod by 1/8 turn and then compensate for the change at the valve adjuster to attain zero lash once again. At this point cycle the engine to the previous “1/2 lift” value (mine was .210) and see the results that your change made on the geometry. You may find that the results are satisfactory, or that they have been made worse, if this is the case you may have needed to LENGTHEN the pushrod instead of shortening it. If that’s the case, no sweat just go the opposite direction and remember to compensate for the adjustment with the valve adjuster. Continue to recycle the engine making changes, noting the results of your efforts on the positions of the geometry until you reach that perfect alignment that we are looking for when the valve, and adjuster appear to be one piece. This may take HOURS to do and if it does you’ll understand why our work is not cheap as most of our engines have EVERY cylinder set up individually, usually taking a full day of labor.
When all is said and done and you have achieved a satisfactory result you can then cycle the engine back to full lift and see what the new total lift actually is, as long as it’s within 5% of the cam card you will be fine as you must remember that ultimate geometry is well worth a few thousandths of net valve lift. If you lose more than 5% of your lift you may have to consider starting over and using a correction shim under the rocker pads to try and overcome the alignment issues without losing lift.
It is important that I state the fact that it’s sometimes impossible to achieve ultimate geometry without the use of a correction shim under the rocker arms. If you were able to complete the above processes with satisfaction, skip this portion of the article, if not pay close attention to these procedures.
I start by going back to the default pushrod length of 27.1Cm and then installing a .015 rocker pad shim under the rocker assembly, I do NOT alter the pushrod length, I simply use the valve adjuster to get back to “Zero lash” and then begin all the processes over again and note the differences that I have gained with the correction shim in place versus without it. If the alignment is better than previously, but still not perfect I go up to a .025 or .030 correction shim and then repeat the processes and cycles. Typically at this point you will see great benefits or you will see great issues with the alignment, at this point you must decide which of the previous set ups gave you the best alignment with the default pushrod (the only engines that should need more than .030 correction shims are equipped with longer than stock valves, 99.5% of reader should NEVER need more than .030 pad shims). When this is decided put that set up back under the rockers and then complete the procedures by slightly changing pushrod and adjuster positions, keeping always in mind that you MUST be at “zero lash” to do any measurements accurately. Continue cycling and noting the differences until you reach the best valve/adjuster alignment possible.
Now that you have attained adequate valve lift as well as proper valve/adjuster alignment it is time to remove the adjustable pushrod and measure its total length. As you have noted we refer to these measurements in Cm and mm and we advise that you do as well as the measurements are easier to make and precise cuts are also easier. Using the Vernier caliper and taking great care not to alter pushrod length AT ALL, measure the overall length of your pushrod and note it as “Intake pushrod length”, most lengths will be 26.9-27.4Cm measured tip to tip.
If you have a dual pattern camshaft your cam has different profiles on the intake and exhaust and while these specs may not have altered the lift specified on the cam card they will affect the valve train geometry as the duration has slightly changed, so ALL THE PROCESSES THAT WERE COMPLETED FOR THE INTAKE MUST BE REPEATED ON THE EXHAUST VALVE!!! One thing to remember is that you can’t have different thicknesses of correction shims under the rocker pads, so the arrangement you came up with must be retained and only the pushrod length can be altered to correct geometry on the exhaust side. Generally our cams like 1mm less length on the exhaust than on the intake, so that’s a good default pushrod length to start with. After properly attaining the exhaust pushrod length carefully remove it and measure it tip to tip with the vernier caliper, note its length as “Exhaust pushrod length”….
With the geometry behind you it is now time to finalize the procedures and get the valve train buttoned up. The remainders of the procedures are important and attention to detail is a must or all the work you have done thus far will be wasted. In these procedures you will be measuring pushrods, cutting pushrods, cleaning them internally to remove debris and then installing the pushrod tips. If at this point you have had a long day, or don’t feel your best, STOP and come back tomorrow- this is important and can’t be rushed!
Fetch your set of 8 pushrods and closely compare them with the adjustable pushrod, pay close attention to the tips. Then grab your set of 8 uninstalled pushrod tips and measure them from their seating surface (where they seat against the pushrod) up to the upper most portion of the tip. Our pushrods measure exactly 1 Cm which aids with the next portion of these procedures.
Keep in mind that your pushrods will need to be cut to length that will be accurate when the tips are installed, accuracy is VERY IMPORTANT! I’ll use my engine as an example here and use my intake pushrod as the guinea pig, I ended up with a total tip to tip pushrod length of 27.0 Cm, the tip of my pushrod measures exactly 1 Cm from seating surface to the tip so my pushrod without the tip installed should read exactly 26.0 Cm.
Now that you are ready to cut the pushrod here are some pointers:
Using the vernier caliper, lock it to the exact length that you will be cutting your pushrod, in my instance that was 26.0 Cm, so that’s where I have locked my calipers. I will use these locked calipers to ensure that all the pushrods that will be this length will be exactly the same. This will make all your valve adjusters protrude the same and will also help with assembly/reassembly later down the road. I have differing lengths of intake and exhaust pushrods, so I’ll have 4 of each length and we’ll be using an etcher to mark these “IN” for Intake and “EX” for exhaust…
There are several ways to cut pushrods, the most accurate method is using an archery cutter (my preferred method) closely followed by using a lathe to cut the material, local machine shops can do this, but ensure they do not bend your pushrods as well as cutting them! The other method is the old fashioned way with a hacksaw or other manual cutting device. I’ll include the instructions for this method within this article as it is the most popular for the DIY Type 4 Builder.
If cutting the pushrods manually its is a must for you to cut the pushrod about 1mm too long purposely as there is a margin for error with any manual means of pushrod cutting. Doing things this way will allow you to use a file, grinder or belt sander to perfectly fit the pushrods into the vernier caliper- now you see why we locked the caliper earlier, its not only a measurement tool, but it also allows us to create a standard for all the pushrods to be fit to…. When doing this remove very small amounts of material at a time constantly checking the fit of the pushrods into the caliper and also ensure that you do not remove more material from one portion of the pushrod than the other, this will affect the seating of the pushrod tip and it’s just not cool….
Once all the pushrods are cut to the proper lengths and fit snugly into the vernier caliper debur the top of the pushrod and make sure there are no sharp edges or partially attached material, sandpaper polishes this surface quite well. With all this out of the way it’s time to complete the pushrods by installing the tips. The cutting process creates a lot of debris that ends up inside the pushrod; this debris is begging to end up clogging up a passage in a rocker arm or worse yet, seizing a rocker shaft. To remove this debris, I choose carburetor or brake cleaner to blast the inside of the pushrod clean and then follow with high pressure compressed air and a cleaning patch similar to what would be used for rifle cleaning. When a patch can passed through the pushrod and not have any foreign object debris on it, the pushrods are clean enough to be completed.
To complete the pushrods it is best if you have two old lifters to use as installation tools. These old lifters will have the needed radius to support the tips correctly to allow the pushrods to be completed DO NOT USE NEW LIFTERS FOR THIS! Install and slightly tap a pushrod tip into the pushrod, once it is started straight into the pushrod go ahead and use the second lifter to drive the tip into place with a hammer, ensure that the tip is seated all the way against the pushrod and repeat this process until you are finished with all 8 pushrods.
Once al 8 are completed its time for the moment of truth, grab the vernier caliper and set it to the setting that your finished pushrods were supposed to be, since my intakes were 27.0Cm I will use that measurement and check my work. If your finished pushrod is more than .010 (ten thousandths of an inch) shorter or longer than the specified length you calculated you will have to scrap those pushrods and start over, as I have stated accuracy is of utmost importance!!!
So there you have it, once all of this is completed you can clean the pushrods once more and then install them followed with the rest of the valve train components and have the peace of mind knowing that you have properly set your valve train geometry.
All content including pictures and text is Copyright 2006 Raby Enterprises Inc. Unauthorized publication of this article in part or whole via any method is strictly prohibited.
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Jake Raby
Cool
Invaluable info.
but really, thanks for sharing your knowledge.