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A Performance killer in these small power output engines.

What is it? Its over springing the Valves. All you are doing is wearing out parts and adding to the power losses. Remember every 2 revolutions the engine must push against the valve springs.

What parts get accelerated wear? Rocker arm faces, Cam lobes, valve guides, Valve seats, Valve margins, Springs Retainers and the Springs themselves.

Spring settings need to be calculated. Seat pressures are more about valve margin widths. Porsche typically show this in the spec’s as an installed height. What they are really given is a determined seat pressure for those that have no way of measuring the pressures. It is a lot easier to measure the height. Everyone doing this has access to a Vernier or similar.

Nose pressure or open pressures is about the spring and its design. In a lot of what I read and hear, the tendency is to over spring the valve “in case” I over rev the engine. Springs and their setup are a calculated equation, not guessed at “in case”. Valve train weights, engine speeds and the camshaft design all play a factor here. Unfortunately, a lot of cams sold today have horrible harmonics built into them, requiring the valves to be over sprung to dampen out the harmonics. Add to these nasties, the trash coming up the chains from the crank induced harmonics.

A well design camshaft should have good behavior beyond the engines RPM limit with some safety built in for an over rev.

So, what’s the correct seat and nose pressures. These should be supplied by the camshaft supplier once the valve train weights and engine use are known. For example, we have just finished testing a new camshaft for an air-cooled engine project we are involved in and those seat pressures are 59 and 82 lbs for an engine that will redline at 8000 RPM with a safe over rev to 8300 RPM. This engine uses Titanium valve train parts which allows these numbers to be safely run.

Another example is a 2.9L engine with stock valve train with seat pressures of 61 and 80 lbs. This engine revs to 8000 RPM. Another, the cams we designed for Jeff’s (homebuilt) 2.8L engine in Australia has seat pressures of 58 and 64 lbs and revs to 8000 RPM. Cam design and choice the of spring both play a part here.

When I read of seat pressures of 90+ and in some cases well above 110Lbs, I cringe. I cannot imagine the wire stresses involved here. I have inspected some of these aftermarket springs and the wire material they are made from is not very good. The wire used in the some of the German springs is extremely good and allows for very high wire stress numbers to be run. Some of these aftermarket springs could not get away with these higher numbers due to the material they are made from.

Great for selling parts, but horrible for the engine performance. But there are circumstances where higher numbers are required. Weights and engine speeds require this, but again, this needs to be calculated. And in some cases of these high numbers, titanium retainers are sold to go along with the springs. For street engines, use care when deciding on titanium and where it’s used. Spring retainers is a great place, but these need constant inspection and life’ing. Tool steel is far better choice for street engines.

So, when you hear about adding spring pressures and an engines RPM limit, they are not directly connected. You choose which way you want to lean here.

As an engine person, I calculate and give an engineered solution. As an owner you may want to disregard this and go with what you have heard and what many others do. Over spring the valve train and compromise the engines performance.

Just remember the person who should be advising you on springs and their settings is the cam supplier, not a parts house, selling parts.

I receive many calls each week asking for advice. I give my opinions here, not necessarily thinking I know it all nor do I think my way is the only way. There are many out there doing great work.

I have decided to write additional papers on how we go about rebuilding these air cooled engines. I won't give away our secrets, but give our opinions and way we do each part. Most of the assembly work is well documented and written about enough to bore most. I wont go there. But I will go into areas where many do not have access to or know about.

Eg., cleaning, what is clean, pre machining checks, what and how this is achieved, what needs to be machining, what and when to do certain procedures. What parts to consider when building an engine, their design and their use. How to go about spec'ing out an engine for a particular use,

The above is out of sequence, so the next installment will be more as you build, starting with what to do and look for in the engine case, then the crank etc, each part that's next in line.

Old 12-08-2019, 07:02 PM
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Correction.

It should have read, Seat pressures are more about valve SEAT margin widths.
Old 12-08-2019, 08:39 PM
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Old 12-09-2019, 03:26 AM
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What is your feeling on boosted engines and seat pressure? There seems to be two camps; one says more boost, more spring (and the factory seems to fall in this camp. Look at the installed height difference on 930's). The other camp says that even if the boost could push or hold the valve open, it doesn't even happen at a critical time, so keep the seat pressure the same.
Old 12-09-2019, 06:22 AM
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Quote:
Originally Posted by dannobee View Post
What is your feeling on boosted engines and seat pressure? There seems to be two camps; one says more boost, more spring (and the factory seems to fall in this camp. Look at the installed height difference on 930's). The other camp says that even if the boost could push or hold the valve open, it doesn't even happen at a critical time, so keep the seat pressure the same.
I guess each engine needs its own specification. My initial thoughts would be, its more about transferring the added temperatures to the seat from the valves more than the higher pressures.

In any turbo engine, we tend to use a slightly wider seat margin than in a NA engine. Especially on the exhaust side. Turbo engines require a different valve material and a different seat material.
Old 12-09-2019, 08:58 AM
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Thank you Neil for posting this. I've seen your advice in earlier posts about not overdoing it on valve spring pressure. The nose pressures you mention here are way less than what I've heard about with some of the commonly available aftermarket performance springs for 911 motors. I'm glad to benefit from your experience, and will look forward to your future contributions.
Old 12-09-2019, 09:41 AM
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There’s certainly room for improvement on the legacy crop of cams used in 911’s. With modern cam profiles comes reduced need for excess spring pressure. In an ideal world the valve spring would bind before mechanical interference like the newer cup engines. I really like how they loft the valve off the nose for increased lift/duration at high RPM’s but limit lift with spring coil bind. Not sure how backwards compatible that technology is but man that would be great! Probably not realist on a street car anyway.
Old 12-13-2019, 10:24 AM
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Not sure it is ever a good idea to limit the valve motion by spring coil bind. Nor is ever a good idea for the valve to “leave” contact with the camshaft.
Old 12-13-2019, 10:45 AM
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I was wondering when I read K24's post if that is really what Porsche is doing for valve control on cup cars ...
Old 12-13-2019, 01:26 PM
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Old 12-13-2019, 01:50 PM
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Originally Posted by K24madness View Post
There’s certainly room for improvement on the legacy crop of cams used in 911’s. With modern cam profiles comes reduced need for excess spring pressure. In an ideal world the valve spring would bind before mechanical interference like the newer cup engines. I really like how they loft the valve off the nose for increased lift/duration at high RPM’s but limit lift with spring coil bind. Not sure how backwards compatible that technology is but man that would be great! Probably not realist on a street car anyway.
If you are referencing the radius follower used in these engines, they control the valve motion but the lift is still based on the cam lobe. You never want the valve to lose its contact with the cam.
Old 12-14-2019, 09:51 AM
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The following is a step by step guide what to look for, ask for and expect when rebuilding your 911 engine. This is my opinion on what should be done. It’s not the absolute nor is it the only way.

There are many companies that do excellent work. If I have left out anything or there is a better way, please add to this. I welcome other opinions and additions that I may have forgotten about and missed. As I said in the earlier post, I will continue to write these papers about rebuilding these engines. As I get into the other internal engine parts, I’ll get into details of how we go about this work. A lot of what has been written in books never gives options of what can be accepted other than the absolute specifics. Building engines is about right and wrong, but it is not necessarily absolute.

You can change the spec’s some, have different tolerances if you know what you can do. I will cover a lot of this and hope an engine builder’s perspective more is enlightening rather than what is considered the absolute and only way. I’ll cover a lot of the assembly tricks as well as how we do some if the machine work.

911 Crankcase.

Before you start to undo the very first nut or bolt, have a good understanding of what and why you are doing this. Did something break, is it worn out and to what level are you going to rebuild it. What is my budget. Who am I going to do any sub outside labor, who am I going to buy the rebuild parts from? Make sure they know what they are doing. If they offer machine repair work, do they do it themselves or do they sub it out to a 3rd party. My advice is always to deal directly with whoever does the work for you.

Another important thing to figured out is, do I have a good clean area to do the disassembly, it will be messy and many of the parts removed will be oily and dirty. Do I have somewhere to store them while the disassembly process is underway. Do I have all the necessary tools?

Take plenty of photos before you even undo the first nut or bolt. Take care noting where each service line goes, under or over, through or around. Have containers to put parts in and keep them separate. Go to your local restaurant supply wholesaler and pick up some large plastic bussing tubs, the trays used for flatware, etc. They are not expensive.
Take notes as you go. Measure and note where each bolt is installed. Where parts are tied off with ty-raps or clamps.

Plan what you wish to achieve each time you work on the engine. Go slow and be deliberate. This way you will keep your area as clean as possible. Keep a clear bench space and only have the tools you need to do whatever you may be doing out. Clean them and put tools away as you go. I am big on this at my company. I have a huge issue when I see tools on the floor or left on the engine. I supply benches for tools to be placed on and its makes me laugh when a bench that is 8 feet long and 3 feet deep is covered with tools that have not been used for hours, and the tech is working in a 6 inch square space. How you take care in how you work tells a lot about how you will build the engine.

As you remove each part, take a good look at it. Note any damage or repair required and note this in your written notes. Take photos as well. If the part is a part that is involved in the lubrication system, look for how the oil has flowed on the part. This often can tell how the engine failed or was about too.

Now the engine is all the way apart, the engine case is in two parts. You have the 4-5-6 side of the case, right hand side still attached to the stand probably. The first inspection will be the main bearing shells. These tell if there was any issue with dirt, clearances, misalignment and will confirm if any detonation was occurring. Take time to look at the #1 thrust bearing for wear. This can tell if the clutch as operating correctly. Anything you see on the bearing faces should also tell the same on its mating crankshaft journal. The 1st motion shaft or as its known by most as the intermediate shaft bearings will show wear as well. These often show misalignment of the oil pump when last assembled to the case, wear on the trust faces as well. All typical.

It’s a good idea to number the shells as you remove them. Inspect the backside of the bearing shells, this shows if the bearing shells were moving. The case particularly the magnesium cases move around from the crankshaft flexing and twisting. The crank will move the most at the #7 and # 8 bearing. The reason the #8 bearing is a fully round 1 piece is to hold the crank from moving as much as possible. Unfortunately, the case flexes as can be seen often where the #7 bearing housings cracks where its relieved for gear clearance. This becomes the first major check. Is the #7 main housing cracked?

Inspect where the main housings bores mate along the case parting line. These are often called the saddles. In most engines these would be called the main caps. Typically, they will show a lot of moment happening. Take a note where the most fretting has occurred and photograph it. Now is the time to inspect all the studs and other fasteners that hold the case together. We remove all the studs from the case half’s so the case parting line can be checked for straightness, lapped if required or machined in the case repair. This is a good time to remove any of the hardened glue or Loctite that got stuck around the stud. It also will tell you if you have any threaded bores that will need repairing. Look at the mounting bores for the gearbox and at the front where the rear cross member bolts too.

Clean most of the heavy oil carefully from each case half watching out for unusual markings, broken parts etc. Make sure you have a good container close by to put all the oily paper towels into. Note, Auto parts stores, Home Depot, Lowes sell heavy duty blue paper towels.

Once done and most of the oil is removed, you are can take better look at each case half. Look at the cylinder deck surfaces for marks etc. If you have a straight edge, check to see if the decks are flat and even height. Once the case halves are fully cleaned a better inspection can be done.
If you removed the case studs, now is the time to lap the parting surfaces. Use 400 grit paper and a lapping block. You can quickly see if the parting surfaces are flat. If they are not, this needs to be remedied before you attempt to measure the housing bores for size.

Now its time to really clean the case half’s. In your initial planning, you would have decided if you are going to do this or send it out. Some advice here. If you send it out, make sure you know what “their” cleaning process is, and ask to see something that is cleaned.

Here is how we go about cleaning parts. We remove the two front galley plugs and the one in the rear. I’m calling the front of the case at the crank pulley end and the rear at the flywheel. There’s a reason for our madness here too. Parts are cleaned by hand to remove any oil, heavy dirt and grime. Anything that can be removed by scraping, rubbing and wiping is done. Then the parts go through solvent cleaning with scrubbing with nylon brushes, galley brushes and scotch bite. The main oil galleys are flushed with nylon brushes and the oil galleys to each bearing bore checked. Then the parts are washed with cold water to remove any last solvent. Then the parts are washed in our hot water recirculating tank. They are then clean enough to handle and do any machine work to. We do add another ultrasonic cleaning process after the hot tank if no further work is required. The parts are then blown dry with clean air and placed in a large parts oven to dry. Remember to blow out every threaded bore as the water will lay inside and “corrode” the threads somewhat and make threading the fasteners back into, difficult.

Why do we do this, this way. To keep all the cleaning solutions as clean as possible for as long as possible. Therefore, I suggest you find out whoever cleans your parts, how and what they do. A dirty hot tank will leave a dirty film on the parts. Clean is subjective, clean to one person is dirty to another, so make your mind up as to what level of clean is acceptable to you. A dirty part can hide demons below the dirt.

To be cont'd.
Old 12-18-2019, 07:33 PM
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Cont'd from above.

Now the case halves are clean, you can then inspect all the mounting parts for cracks and defects. The case should be crack checked by non-destructive means, Zyglow penetrant fluid is applied, the excess carefully wiped off, the parts oven dried then inspected with an ultraviolet light. If you do not have access to this, select a shop that does, or you can buy a 3 pack of crack checking fluids.

You can test the piston oiling valves for cleanliness, direction and operation. If any are blocked, they can be cleaned and checked or replaced and included in the repair work.

Now the case is cleaned, crack checked and found in good useable condition, it needs to be measured. The main housing bore needs checking along with the cylinder decks for their height, crank centerline to deck, flatness and surface finish. The washer platforms where the through bolt washers sit also need inspecting. Often, they get gouged and need a touch off with a counter facing tool. If you have a bore gage and a micrometer you can set the bore gage up to measure the case main housing bore. The specs on this give a 0.019mm, (0.0007”) variance from low to high in tolerance. Remember, you are measuring the housing bores for size and ovality, not alignment. Usually though, if the bores are out of spec, so is the alignment. The only way to properly measure the alignment is with a boring bar centered on the front and rear bores and with an indictor measuring at each housing bore. Honing is often done to the main bores but remember, honing follows the bores already in the case. The hone will center on the front and rear bore and touch off on the middle bores only where it touches. It can be used to straighten, realign and make the bores round, but care must be taken doing this. It can mess up bores if not performed with care requiring oversize boring to be done. Boring removes more material, usually 0.010” overall each time.

This is beyond most at home, so this must be considered initially who is going to do this. Looking at the main bearing shells can tell if the alignment is off. You will see uneven wear marks of the face of the shells. It’s a good idea before you send the case out for work to know what needs to be done. It also is a must to know after the work is done that it is done correctly. You are the assembler and it’s your responsibility to make sure you are assembling correctly sized parts. The shop doing the repair work is responsible for making sure its correct, but if you assemble the engine with incorrect parts, you will be responsible for the time and any other parts used.
Once you receive the case back from the machine shop or having done the work yourself, the case parts must be thoroughly re cleaned, re checked for correct size and specification. The case should always be bagged in a large plastic bag so that no contamination can happen while it’s not been assembled. Now you can plan the assembly process. Re fit any fasteners, and the rest of the parts that fit inside the case. Use the time at the beginning of this work to decide upon what consumables you will need and use. What type of sealing glue, Loctite and any other assembly lubes you may need?

This is my opinion on what should be done. Its not the absolute nor is it the only way. There are many companies that do excellent work. If I have left out anything or there is a better way, please add to this.
Old 12-18-2019, 07:34 PM
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Thank you Neil for sharing your knowledge and time. My 3.2 heads you re-built look wonderful. I have the top and bottom Wrightwood gaskets sets/head studs and will be venturing down the path you describe above soon.

Happy Holidays.
Old 12-20-2019, 01:05 AM
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Add check cam timing before disassembly. When I was at the dealership, no big deal, people rarely changed cams or timing while it was under warranty. Now that these engines are getting up there in years, there's no telling what kind of cams you'll find in there. And if they've been reground on original cores, it's easiest to go back to your notes to see what timing it had before you pulled it apart.

And if you're new to this, keep a parts diagram next to the engine when you begin teardown. It could have had machine work in a previous rebuild that necessitated shims under the cam housings, or thicker (or no) shims under the cylinders.
Old 12-20-2019, 08:01 AM
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One thing that came to mind for me was a tip for how to split the case. As in, you have all the perimeter nuts and through bolts removed (don't forget the two acorn nuts inside the oil cooler housing and the unique M10x1.0 nut inside the chain opening near the intermediate shaft) and dangit, the case just won't come apart! I have a nice brake pad spreader/caliper piston press that works great inside the breather cover atop the case. I gently spread the case open there to start and then use a similar means of spreading the case at the pulley end using the studs which mount the engine support console.

I'm not implying people should use the same method I do. Just throwing it out there to invite other people's techniques that use less "specialized" tools than my brake pad spreader.
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Old 12-20-2019, 08:17 AM
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Stromski makes a very cool tool for this job.Fred
Old 12-20-2019, 09:13 AM
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This has been a very interesting read. Topical, as I built a 2.7 long block like 10 years ago, and am just finishing up the rest of it now. It sat sealed up in the basement for like 10 years. It was line bored, case pretty much rebuilt; heads rebuilt to stock specs with stock springs. I agree with your assessment of over-springing the valvetrain. Wasn't that always marketed as an anti-float mechanism?
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Old 12-20-2019, 08:13 PM
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I'm keeping my contribution to those areas where many may not know or understand. There is already a huge amount written about how to disassemble or assemble these engines. Maybe I can add a few tricks etc later. The main purpose is to educate those interested in areas they may not have any idea about.

My main thought here is to show that there are no absolutes involved in rebuilding engines. In some areas you can rebuild these engines without fear often written into some of the books used as guides.

If you know what to look for, what to ask for and what to expect, then hopefully there will no part of this to fear at all. I have written before how many write, "I'm about to start the dreaded cam timing"! This is the easiest part of rebuilding these engines. Knowledge is a wonderful thing and can remove fear in an instance.

Please contribute and add anything that is relevant.
Old 12-21-2019, 11:26 AM
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Neil, many thanks for taking the time to share your wealth of knowledge. They are always an interesting read and I am richer for them.

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Old 12-27-2019, 06:59 AM
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