lookn for pics of pointer setups using 18" degree wheel

[JoeMag]

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

[Catorce]

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

[Neil Harvey]

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.

[mikedsilva]

Originally Posted by Catorce

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

um... why not?

[JoeMag]

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

[Trackrash]

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.

[Neil Harvey]

Originally Posted by JoeMag

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

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.

[Trackrash]

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.

[JoeMag]

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.

[Neil Harvey]

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.

[JoeMag]

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...

[stownsen914]

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.

[KTL]

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






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

[Neil Harvey]

Originally Posted by stownsen914

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.

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

[Neil Harvey]

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.

[JoeMag]

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

[Trackrash]

Originally Posted by Neil Harvey

A little long here but stick with me.

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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.

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

[Henry Schmidt]

[Neil Harvey]

Originally Posted by Trackrash

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.

[Trackrash]

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.