lookn for pics of pointer setups using 18" degree wheel
 

Any have some pics to share of how you setup a pointer for a large degree wheel?

For what? Please don't say cam timing.....

For a DIY, Drycleaners sell them. You get one with every shirt.

You may have to do some bending, but for a 1 time use, they will work fine. Just make sure you dont bump it when using.

um... why not?

How do u time cams using degree wheel? ... do set them looking at something known like max lift point?

The cam timing on these motors is set / measured at TDC overlap.

Any Porsche repair / rebuild book will give the procedure. The stock crank pulley is usually sufficient.

It has also been covered here, if you do a search.

Correctly.

You are setting the valve timing on the lobe center lines, regardless of the flank grind quality. Its the proper way to set the valve timing.

The cams in these engines have both lobes on the same shaft, so as you move one centerline the other will move the same amount. This is the separation angle.

Setting the cams by lift at TDC, relies upon the separation angle on each shaft being the same. Many cams we have measured are not very accurate and the final valve timing is off between left and right sides, and even on the same shafts.

Full lift at a desired crank angle is what you will set the cams at. But, if the lobe sep angles are cut poorly, regardless of what method you choose, the valve timing will be wrong.

Its a good way to check the cam accuracy by measuring the lifts at different crank angles. You want the same lifts at every valve the same. No point in expecting the airflow into each cylinder to be the same if the valves open at different times and amounts.

The whole exercise here is to obtain or get as close as possible, the same cylinder BMEP in each cylinder. Then fuel and timing values will produce the same torque and the overall engine performance will be increased.

Manifolding inefficiencies, heat rejection, friction etc all play a huge part in dropping the output from each cylinder. Why add the valve timing to this, when you can control this when the building the engine.

Neil, very insightful. However I have never seen a cam timing spec for the angle of the lobe center. Are you suggesting that the lobe center should always be set at Zero degs at TDC of the piston? Or is this spec available, but generally not published? Or are you just making a point of checking the accuracy of a cams specs?

BTW to answer the OPs first question I used the case parting line as a pointer.
http://forums.pelicanparts.com/uploa...1550437771.jpg

Neil -- so I have 3.8 rsr (factory) cams in my motor (touched up by daugherty). I don't quite understand the rsr cam specs (pic off daugherty cam site). At what angle should max intake lift be set at?

Gordon -- thx for info. yea i'm familiar with standard method of timing cams. I got an 18" wheel and ended up making pointer from 1/8" wire and attached around bottom of outer case bolt then pounded end of pointer flatter. I'd say I can easily get to 0.5 degree resolution.

http://forums.pelicanparts.com/uploa...1550439095.jpg

If you are installing RSR cams, I would assume you are building an engine for racing. You should be timing the cams using a degree wheel.

The above spec sheet shows 4.6mm lift which shows the Intake valve advanced. The spec shows the lobe separation angle of 109°. This never changes with these 2V engines on the cams. They can be different separation degrees on different cams, but 109° will always be 109° on these cams whatever the timing of the cams.

We always use a degree wheel to set the cams. The lift at TDC is an easy way to set the valve timing using only a dial indictor showing lift. The problem here can be the mark on the pulley being correct and never knowing exact TDC, and any dwell over TDC the piston has, etc.

In most cases, close is probably good enough, but when building engines professionally, this should never be the standard. This is the same as setting the valve springs at a certain installed height and not pressures. It never takes into consideration the differences in the springs, nor the valve margin widths etc.

We will fit a degree wheel before the heads are fitted and find true TDC by splitting the differences each side of the TDC mark on the wheel. This way you can measure the valve drop for valve clearances too.

You could set the centerline or full lift on either the exhaust or Intake lobe. The Intake is easier. 4.60mm will correspond to a intake lobe centerline of some crank degree after TDC. This number can be changed or (advanced or retarded) to move the full lift position . If you fit a degree wheel, and set the intake lift at TDC at 4.6mm, you can always rotate the crank clockwise past TDC and go until the valve is at full lift. This will then tell you the Intake lobe centerline number. From here it is math exercise to find the Exhaust centerline. But, this should be checked on the engine to see if the cams have been cut correctly and or the rocker geometries are correct. Street engines and DIY assemblers probably will never do this. Most repair shops will never do this either.

I cannot think any cam company would ever develop a cam design unless they used the lobe centerline method. When choosing a cam, it should be done with an understanding of the intake flow numbers. Most cases it seems people go with what is known and well tested.

It needs to be known there are other alternatives to the standard cam designs historically sold.

Looking at the RSR spec's above, I would never use a cam with 0.490" lift on the exhaust if the Intake was 0.490" as well. We found many years ago, a performance gain when lowering the exhaust lift. This is not always the case, but our work in the Porsche 2V engines has always netted power gains when we lowered the exhaust lifts.

Professionally we have to do everything correctly and leave nothing to chance.

Thanks. Yes race motor. I built few years ago but did not time with degree wheel. I will be interested to see hoe close I was as I marked everything so I could assemble as I took apart. I’ll check lifts and exh centerline.

I’ve heard there r better cams than rsr, but that will need to wait for now...

To support Neil's point, when I built my 2.7L race motor years ago I checked cam timing with a degree wheel on the race cams I put in. Mostly because I was young and ambitious/curious. I was surprised to find that the right and left cams were ground slightly differently. One side was off such that if I just set them using the intake lift at TDC method of setting them, the exhaust timing was off by several degrees. I think I wound up setting them to split the difference so the intakes were different by a couple degrees right to left and similar for the exhaust.

Here's couple of good pics pilfered from nippy's engine build thread with Mike Bruns

http://forums.pelicanparts.com/uploa...1547323510.JPG

http://forums.pelicanparts.com/uploa...1547323510.JPG


YTNUKLR (Scott) once shared a good summary of using the degree wheel instead of the typical TDC overlap lift spec for a DC 20 cam:

• Get a degree wheel. Any one will do.
• Obtain a true TDC indicator. Stomski Racing makes a good one.
• Rotate the engine to BDC, install the TDC indicator and the degree wheel. Wheel orientation doesn't matter.
• Make a pointer from some stiff wire and bolt it to the engine somewhere to point at the degree marks.
• TDC indicator WILL interfere with the piston so CAREFULLY rotate the engine until you feel the piston bump against the TDC indicator. Write down the number of degrees read at your pointer.
• Reverse the rotation carefully until the piston bumps the TDC indicator again. Note the number of degrees again.
• The measurement will give you TDC--it's exactly 1/2 way between your two degree measurements.
• Now (VERY IMPORTANT) with the dial indicator mounted, adjust the valve clearance so clearance=0.
• Next, rotate the cam to begin lifting the intake valve 0.050".
• The DC20 cam is supposed to lift the valve 0.050" when the engine is 8deg BTDC on Cyl#1.
• Remember where you marked TDC? Go clockwise from there 8deg with the crank, holding the cam in position.
• Then, holding everything steady, snug down the bolt!

This is a more accurate method than the lift specification (2.2-2.4mm) because it takes valve clearance out of the equation and the degree wheel is MUCH more fine grained than the crank pulley.

The general formula for determining at what degree setting you should set cams for a 0.050" lift setting (typical cam mfg specs.) is:

Degree of BTDC=((Intake Duration measured at 0.050")/2)-(Lobe Separation Angle)

In this case, (242/2)-113=8

Unfortunately, this very common. Does it make a difference, absolutely it does.

A little long here but stick with me.

My advice here, is not to use a dead stop to find TDC. Use the dial indictor you will use to find full lift on the valve. Dead stops tip the piston some and on many of these 2V engines the dead stop will be cantered and the domes are uneven.

This should be done before the cylinder head is installed. Bring the head up to TDC and zero out the dial indictor. Zero out the pointer on the degree wheel too. Then carefully turn the engine backwards, around half way between BTD and TDC. Then turn it clockwise until the dial indictor shows say, 0.020" before TDC, (0.50mm) and record the degrees before TDC on the degree wheel. Then turn the engine through TDC until 0.020" ATDC, (0.50mm) and record this number. Add together and divide by 2. This is true TDC removing any piston dwell. You may have to reposition the pointer to the new zero TDC mark on the degree wheel.

Not sure what the metric dial indictor may read, but I hope you get the idea. It doesn't matter where you stop before zero on the indictor as long as you do the same on the other side of zero. You are splitting the difference here.

This should be done exactly the same way when degree'ing in the cams. If the cam card suggests 114° ATDC for the intake lobe centerline, carefully turn the cam to full lift and the crank to 114°. Be carful here as you may have some piston interference until you go over TDC with the piston.

Put you dial indictor pointer on the spring retainer and zero it out at full valve lift. Lock the cam bolt snug and do the same as you did when TDC'ing the pointer. Turn the engine backwards carefully and back clockwise and stop the indictor at 0.020" before zero on the dial and record the degree # on the crank. Turn past TDC to 0.02" and record this number. Add both together and divide by 2. This will then be the actual intake lobe centerline.

The same can be done if its easier, when the Intake cam lobe is fully open, (valve closed) engine would be 114° past TDC on the compression stroke. You would place a flat disc pad type pointer on the nose of the Intake lobe and instead of measuring the lobe at full open lift, you will be measuring the intake lobe at full valve closed, or 180° cam degrees opposite to the above way. As long as you time the 4-5-6 side the same, you are timing the cams 360° "away" 180° cam degrees "away". Exact same cam positions just often easier to find a good position for the dial indictor to show zero.

I used 0.020" as an example here. Not sure what a metric dial face will show. Just pick a number each side of zero on the dial face. This will degree in your cams a lot more accurately than doing the lift at TDC method. You can test each lobe for the same centerlines, the lobe separation angles and each lobe lift. You may be very surprised at the in accuracies of your cams.

Thanks Neil... So much for the piston stop I just made over the weekend.

I have not seen this spec advertised. You learn something every day around here.

It appears in the Porsche world, lift at TDC is the cam timing spec typically given. I'm sure it's to make the cam timing easier. But its not very accurate.

2V cams will always be created with the lobe sep angle and the intake centerline numbers being the main factors, for any engine they are made for. The design will give the lift numbers at TDC and these are what are given out for a setting number.

Close enough is good enough is what is considered here, typically. But there are too many areas for error. Cam grinding errors, rocker arm regrinding errors, cam housing machining tolerances etc.

When you set the timing positions at the crank, you can check the lifts at any angle side to side. For those that what to make sure their engine will produce the most power possible, its these little things that make a big difference.

A couple of things come to mind here. How accurately can one really determine the lobe center? Are we to assume the lobe center is at the highest point of lift? What about an asymmetrical lobe design, does that matter?

Also the alignment pin used to time the cam may only get you close to your desired exact degree location, from my limited experience.

Neil, thanks for your expert experience here, and I am just thinking out loud.

The problem when listening to Neil Harvey......is that YOU are not Neil Harvey. Yes he is 100% right. Yes there could be errors. But Porsche provides a spec which gives you decent timing in the end, decent enough to have a motor that runs for 100K miles or more on that timing spec without issue.

Throw in a dial gauge to determine #1 TDC instead of relying on the case parting line and you're even better.

Neil's experiences are bleeding edge race cars where they were trying to squeeze out every bit.

The average shade tree mechanic at home probably ought to just follow the manual.....

Nothing wrong with learning the finer points of cam timing instead of just blindly following the manual and hitting the timing spec. It's not that hard to employ a degree wheel and get your timing set up a different way. Plus the degree wheel process gives you assurance that your pulley marks are where they should be (or are not where they should be)

Let me tell you, Its a pain in the ass being Neil Harvey!!!

Point taken, but engines do run better when all cylinders have the same valve timing. Yes, Porsche gives a spec, but that works only if the cams are ground correctly and the rocker arms are refaced correctly. The way I suggested allows you to check.

Also, I do read these forums and often I read about unfortunate circumstances where a DIY made a mistake and the engine fails after rebuilding, or similar. The forum readers all give their sympathy and give the owner a thumbs up it will all be Ok.

Then you read about a shop having the same misfortune and the wrath of this forums lets loose on the shop. Double standard, maybe whichever position you are standing I guess. To eliminate this from happening we have chosen to build at a level where we make sure we cover all areas.

But we are human too and we do make mistakes. Its a matter of catching them before the engine leaves here. My past work history taught me one way only and one right only. Curse, maybe but it is humbling when the opportunities I had most will never have.

Totally agree. However, I am still looking for the correct spec for the lobe centerline to time my cams.

As a side note, Porsche used two or three different timing specs for their SC/ Carrera cam, right?

I have heard that the factory used different cam timing specs for the SC era engines. I think it was just the spec for setting of the cam timing that they changed, but I’m not sure of that. I think I read it in Bruce Anderson’s book.

As for the centerline spec for your cams, if I’m not mistaken you can calculate this if you have the intake and exhaust opening and closing event specs, which I’m sure is published for factory and aftermarket cams. Or find someone who has a cam doctor machine and have the cams measured.

Scott

I don't have the 911 SC spec book handy (because I have yet to cut one apart and scan it) so I only have the '84-'87 Carrera spec book that I scanned.

http://forums.pelicanparts.com/uploa...1550686720.jpg

I do have the '72 to '81 Workshop Manual handy and it has all the cam information for the engines. Here's the SC pages.

http://forums.pelicanparts.com/uploa...1550687063.jpg
http://forums.pelicanparts.com/uploa...1550687070.jpg

You can see the cam part numbers are different between SC & Carrera. But it's been said for a lot of years Carrera and SC cams are the same profile and the only physical difference is how the ends of the cams are fastened. That's sort of true since the specs of both cams are VERY close- note how the opening and closing degree descriptions are nearly the same for each.

But the point of my sharing this is to confirm the TDC overlap lift specs are indeed different for SC vs. Carrera according to the factory documentation. But they're quite close to being the same exact profile. Dougherty just lists one grind for his SC/Carrera cam

Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

But getting back to the factory info, I guess it shouldn't be surprising that the TDC overlap lift specs are different since we're talking about different engines with different displacement, different piston dome volumes and different compression ratios?

Lastly, Web Cam has an interesting page with a lot of info to digest (or ignore) for whoever's curious

Web Cam Racing Cams Inc. / Degreeing

From what KTL found, it looks like the durations of the SC and Carrera cams are the same at 234 deg intake and 226 exhaust. For some reason the SC specs say those measurements are taken at 1mm lift (one common value for listing cam duratioms) and the Carrera says .1mm. Who knows, it could be a misprint.

The opening and closing events are different due to the SC specs having the cams advanced by 3 degrees (hence the different TDC specs). Could be the same physical cam profile though.

Lobe center will be full cam lift/valve lift.

As for accuracy, that will depend upon your equipment and how clever you are at measuring true TDC and max lift.

A or symmetrical cams will both have the max lift at the designed lobe center. Cams with lobes that are more rounded, will appear to have a moving lobe center, but this is where you need to take two readings before and after full lift and average them out.

Alignment pins etc, will always have some slack in them. This is why it is important to always turn the engine in its normal rotation when taking measurements, so all parts are on their loaded side. Often the play in the alignment pins is enough to find the desired lobe center number. I cannot remember, but you could see 1° crank in the slop. I may be wrong here on the amount, but I do know its quite common to get the desired number just by taking the slop out of the pins.

How accurate do you need to be? We try to obtain a max of 0.25° ether side of the desired number. A lot comes down to the accuracy of the degree wheel too. Most of the mass produced wheels are Ok, but the larger diameter and the more expensive wheels are more accurate.

Many will think its not necessary to go to this extent. "The engine runs just fine". If that floats your boat, then that's Ok by me. We all have to choose our own level of expertise.

How well does the Stomski electronic degree wheel work is it as good
as a mechanical wheel ?

Any electronic rotary encoder will be vastly more accurate than a degree wheel.

This one sticks to the pulley with 4 neodymium magnets purchased from McMaster. You can turn it to adjust, but it takes a few pounds to pull it off. Stable.

I did a little analysis and I'm convinced you can stick an Iphone to the degree wheel, not even centered on the wheel and the Iphone will read the rotation accurately. I put a couple magnets in the Iphone plastic case.

http://forums.pelicanparts.com/uploa...1550757600.JPG

http://forums.pelicanparts.com/uploa...1550757922.JPG