4 Cam Valve Timing - The Chopstick Hack

Discussion of 4-Cam Type 547 engines (and all the Fuhrmann racing variants) and cars that powered them.
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Bill Sargent
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4 Cam Valve Timing - The Chopstick Hack

#1 Post by Bill Sargent »

Per the factory shop manual, setting valve timing on a 4 cam motor involves numerous disassembly and assembly steps of the cam shafts to allow drag levers to be removed in order to change the valve lash cap to a thicker or thinner one to adjust the valve timing. You check the valve timing, remove the cam shaft and drag lever, change the lash cap, reassemble, check timing again. Repeat until happy.

At least this is what you do if the timing is within about 5 degrees. If it’s out more than that you probably need to remove a head or the short valve drive shaft to shift one spline in the direction needed.

If the timing is within 4 to 5 degrees there is a much simpler method to remove the drag lever to change a lash cap. Get a bamboo chopstick. Cheap pine or plastic will not do - they are not tough enough. Rotate the motor to open the valve that needs a lash cap change. The exhaust or intake manifold, depending on the valve in question, will need to be removed for access. Stick the chopstick in the open valve and rotate the motor to close the valve, holding the valve open. The drag lever may now be removed and the lash cap changed. After the lash cap is changed and the drag lever reinstalled, rotate the motor to open the valve and remove the chopstick. The timing can now be rechecked.

The bamboo chopstick is tough enough not to be chopped off by the valve but soft enough not to damage the valve or seat. See photo below and note valve bite marks on the shorter chopstick. The factory probably did not suggest this method as there were not many Chinese restaurants in Germany in the 50s and 60s. 🤣
IMG_3235.jpeg
I cannot claim credit for this method -Jacques LeFriant and Mike Young taught it to me.
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Harlan Halsey
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Re: 4 Cam Valve Timing - The Chopstick Hack

#2 Post by Harlan Halsey »

There's another method taught to me by Bill Doyle: you depress the valve with a tool which screws on to one of the studs, pivots and depresses a rod which passes the cam lobe and bears on the retainer.
Depress the valve and you can change the lash cap. Of course you need to get it close with the gearing first, that's what the marks are for. I think the tool is a Bill Doyle special, or part of it is.

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Martin Benade
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Re: 4 Cam Valve Timing - The Chopstick Hack

#3 Post by Martin Benade »

I read this but was baffled how you’d alter the timing without throwing off the valve clearance so I studied the online service manual. I thought I’d post my findings for others with a casual interest like me.

The valve lash caps are not the regular clearance adjustment method, I think it’s sort of a coarse pre-adjustment spot, and due to the action of the finger followers it alters the timing too. Once the timing is corrected with lash caps, then the final running lash is set by raising or lowering the pivot point of the finger follower.

Someone with actual four-cam knowledge should correct this if I’ve gotten it wrong.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#4 Post by C J Murray »

I have never worked on a 4-cam so I should comment too. :D

On every car or motorcycle engine I have ever worked on there is an opening point and closing point that is specified as correct. There is either a clearance setting for the measurement or a lift dimension specified. I always ignore those numbers except that I use those specs to determine the correct "lobe center" and/or "lobe separation". This eliminates the confusion of all the various methods spelled out by different manufacturers.

It is easy to calculate the lobe center desired by calculating it from the opening and closing specs regardless of what the clearance or lift is in the spec. When checking to see where your cam is timed you simply determine the opening and closing points at either zero valve clearance(if you have an adjuster) or whatever clearance is there when no adjuster is available(I use .050" lift off the seat for both if I can set the clearance to zero) and use those numbers to determine the lobe center by making a calculation.

There is no need to use an exact valve clearance to time a cam.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#5 Post by Martin Benade »

Yes they go through that. It’s just that I’m used to OHC valve shims that only alter lash so this sounded counterintuitive, but it makes perfect sense after a bit of reading.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#6 Post by C J Murray »

Martin wrote: Sun Mar 03, 2024 11:32 am Yes they go through that. It’s just that I’m used to OHC valve shims that only alter lash so this sounded counterintuitive, but it makes perfect sense after a bit of reading.
Valve lash does not change the cam timing other than increasing or decreasing duration. Same goes for rocker ratio. More rocker ratio or less valve clearance increase duration but the lobe center is more important. Rocker ratio obviously also increases lift but some cam lobes do not work well with high rocker ratios and some engines like the 616 are difficult to fit with higher ratio rockers. Major performance changes require changing the cam shape.

The OHC shims only alter lash. Any system of valve actuation has some way to adjust lash and that has no affect on the phasing of the camshaft.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#7 Post by Jeff Adams »

The "valve lash caps" on a four cam are not lash caps in the traditional sense. The valve clearance is adjusted with the ball head screw in all cases, and has nothing to do with whatever thickness the cap is. On four cam engines, I call them valve stem caps so they don't get confused with anything related to lash or clearance.

The geometry between the cam lobe, drag lever and valve tip is pretty complicated. There is a page and illustration in the Carrera manual that explains it for those interested. Unlike most overhead cam engines, the centerline of the camshaft rotation is not directly above the centerline of the valve stem. The reason for this is not explained, but my theory is that Fuhrmann understood the need to have a mechanism for adjusting the cam timing on each individual valve. The cam lobes and drag levers were machined very precisely and pretty much the same, but the cylinder heads and clocked position of the keyways on the camshafts were not. The offset of the camshaft and valve stem centerlines, in conjunction with the option of using variable thickness stem caps allowed more accurate cam timing on assembly.

As CJ pointed out the valve clearance will not affect cam timing, only duration and ever so slightly. However as the engine wears a little and the valve stem raises up a small amount the cam timing will change. But not any amount that will make a significant difference.

The valve stem caps are very similar to what Porsche used later on 906 six cylinder engines to adjust lash, as these engines used special rocker arms with no adjustment screw and elephant's foot. I have seen 906 caps used in four cam engines. They work but aren't correct, the 9mm pocket in the 906 caps is too big for the tips of the four cam valve.

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Re: 4 Cam Valve Timing - The Chopstick Hack

#8 Post by Harlan Halsey »

Well, as someone who has built and raced Carrera engines, my comment may be out of place here, but anyway: First cam timing is well explained in the Carrera Guide. You can get any lobe to within 4 deg, with the gear train. But the other lobe on that shaft may not be within 4 deg due to differing position on the shaft. This could be corrected with an offset key, but this is not suggested. However, you can rotate the follower around the shaft axis by thinning the lash cap and recovering the lash with the adjustment screw. Thickening the lash cap has the opposite effect. By this process I have adjusted all 8 valves to +_ 1 deg.
I've also measured the opening and closing angles every few thousandths all the way to the top. With a new cam this will reproduce the symmetrical lift curve shown in the manual.
Does this bench work matter? No. There is so much flex in the cam drive shaft train that as long as you are within the Porsche spec of +_ 4 deg. the valves won't hit the pistons and there's no measurable effect on power of further correcting the cam timing.
It is unfortunate that Carrera lash caps are unique and rare. Both the inner valve stem diameter and the overall diameter are important. Alfa, MGA Twin Cam, etc. aren't right. One can machine them on a lathe and then harden them. There is a hard, machinable material, one hardness up from Stress Proof which I tried, but haven't done the post race analysis.

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Re: 4 Cam Valve Timing - The Chopstick Hack

#9 Post by C J Murray »

Mostly it sounds like the machining precision is not up to the standards demanded by the design/geometry of the engine.

All engines are susceptible to incorrect valve actuation geometry due to machining errors except maybe bucket over valve OHC designs. Today many engines use OHC designs with rocker arms that pivot at one end, rest on the valve at the other end, and have cam lobes pushing in the center. Most have rollers now to allow high spring pressure without cam wear. Datsun SOHC engines used them without a roller as did the Ford 2000 four cylinder.

If the 3 points of contact are where they are supposed to be and the cam is ground accurately then adjusting the height of the pivot point should be all that is needed. Why couldn't Porsche get the valve stem heights correct and the rockers made precisely which should have saved them huge amounts of labor as well as providing consistent performance? I don't expect that I will ever work on one but I hope to see the parts in person someday to understand them better.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#10 Post by Jacques Lefriant »

Hi CJ
This discussion illustrates the lack of understanding of the people who are crazy enought to work on these engines. In a perfect world the pivot height would be preset and lash caps would solve the cam timing if the heads were machined correctly then if you are happy with +-4* you could achieve that. If you had a lot of time and the precision to make measurements and wanted to optimize the settings you have the flexibility to do such. Then the assembly becomes a problem in time management/benefit analysist. Building an engine with all new parts is by the book and is possible now. rebuilding a Frankenstein engine without having done a few is brutal. The next time you in SoCal i will make you demonstrate how you would do the cam timing.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#11 Post by C J Murray »

Jacques Lefriant wrote: Mon Mar 04, 2024 4:43 pm The next time you in SoCal i will make you demonstrate how you would do the cam timing.
I wouldn't go to SoCal without visiting you for sure. I always learn from you. I tend to be pragmatic and the pushrod engines are simple, light, reliable, and make more power. And did I mention cheaper? The 4-cam is artwork like my Ducati 750SS or Manx or Veto KTT Mk8 which also have bevel driven cams. Very classic. Beautiful. I am not likely to own one unless you give me a smoking deal on a Carrera 2.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#12 Post by Bill Sargent »

Interesting how fast this thread devolved from a quicker method to set 4 cam valve timing to an esoteric valve train geometry discussion. I was trying to share something I was taught that saved me significant time.

Harlan, my friend Gregory Campbell made a special tool similar to the one you described Bill Doyle having made. The special tool’s advantage over a chopstick is not having to have access thru the intake or exhaust to insert the chopstick - so less disassembly. Also removes the need to rotate the engine to insert/remove the chopstick. I may copy Gregory’s design.

I will leave everyone with a video of a motor on Jacques Dyno the Thursday before the Lit Meet.
outputVideo.mp4
(9.25 MiB) Downloaded 66 times
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Re: 4 Cam Valve Timing - The Chopstick Hack

#13 Post by Martin Benade »

Was my brief explanation gleaned from the service manual correct enough for those of us that will never touch a four-cam? I was curious and found it interesting.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#14 Post by Jacques Lefriant »

Hi Martin
The shop manual was created for dealerships to allow them to service customer engines. When they were built at the factory the cam timing was done on a fixture and the gears marked for the assembler. The race engines and subsequent cam timing done by the engine builder/tuners like Al Cadrobbi and Heinz Bade to name a few had their own theories. I would venture that most builders of these engine spend much more time for little gain in the performance in trying to hard to get "perfect" timing. Conversly if you do not check each lobe at the prefered Checking height(200*duration) checking the lift and starting out with the valve stem at factory height you can get a bag of worms.
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Re: 4 Cam Valve Timing - The Chopstick Hack

#15 Post by Bill Sargent »

Martin - adjusting the valve timing undoubtedly alters the valve clearance but I have never bothered to check. The main purpose of changing lash cap (or as Jeff calls them valve stem caps) is to adjust the point at which the valve is fully open relative to the movement of the piston.

Each 0.5 mm of lash cap change equates to ~3 degrees of valve timing change. The lash caps came from the factory in 0.25mm increments from 1 to 3.5mm.

After the desired timing has been obtained on all valves you then set the valve clearances using the spring loaded ball adjuster.

Jacques developed a spreadsheet in which you record at what degree before or after TDC the valve opens and closes for a certain lift. I usually measure 2 points on the way open, max lift and 2 points on the way closed. The spreadsheet then calculates the valve timing. A copy of the spreadsheet for the 587/1 motor built to early 904 specs in my 59A is attached.
2022 09 26_P97290 Valve timing and CAM specs.pdf
Valve timing spreadsheet
(52.19 KiB) Downloaded 64 times
Also attached is a short video of my set up for cam/valve timing. The rev counter off the flywheel is to keep track of how far I am from the match point where a head can be removed. The rev counter is another Jacques invention.
outputVideo.mp4
4 cam Valve timing set up
(9.78 MiB) Downloaded 69 times
Regards,

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