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911 Valve Adjustment The Backside Method
 
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Pelican Technical Article:

911 Valve Adjustment The Backside Method

Doug Riley

Time:

2 hours2 hrs

Tab:

$13.35

Talent:

***

Tools:

2.5 (.0025-inch) and 3 (.003-inch) thousandths feeler gauges, metric socket set, flathead screwdriver

Applicable Models:

Porsche 911 (1965-89)
Porsche 912 (1965-69)
Porsche 930 Turbo (1976-89)

Parts Required:

0.0025" and 0.003" feeler stock (Pelican Parts part numbers are PEL-LM-0025 and PEL-LM-003 respectively)

Performance Gain:

Properly adjusted valves

Complementary Modification:

Replace your spark plugs

You want accuracy when setting the valves on your 911? This method delivers.

This simple, advanced method of 911 valve adjustment does away with the hard to get at gap between the swivel foot, (elephant foot), and the valve.

This procedure uses the gap found at the other end of the rocker arm.

You don't need that special shim holding tool, just a normal everyday feeler set.

You will use ordinary 2.5 and 3 thousandths feelers as a GO and NO-GO gauges.

Figure one.View of a 911 engine showing insertion of feelers.

Thanks to Tom Hutchinson, aka khamul02.

Referring to figure one.

This method uses the gap between the rocker arm and the cam. As shown by the red arrow and line.

The classic method as described in the previous article uses the gap between the elephant foot and valve stem.

The difficulty with this as experienced by any who have done this procedure is the close quarters around the valve adjusting screw and the need of a special shim holder tool.

Photo one.The tight area at the rocker arm adjusting screw. Notice you need to slip the special shim into the gap between the swivel foot and valve stem. No easy task.

It is simpler to slip a common feeler gauge into the gap between the rocker arm and the cam. Specifically the "backside"(base circle), of the cam.

Photo two. The GO 2.5 thousandths gauge slips into the gap. This is correct.

Notice how easily the gauge is guided into the gap.

Please note the position of the cam lobes in figure one and the photos. The rockers are against the "backside" (the low side or as it is known to cam people "the base circle"). In this position both valves are closed.

As you can see from the figures and photos it is easy to slip an ordinary .0025" feeler gauge into the gap between the rocker and the cam. This is one advantage of this method.

Why do we use a .0025" feeler?

Simple math. The ratio of the rocker as it sits against the base circle of the cam is 1.4 to1.

This means the .004" gap at the rocker swivel foot and valve stem is 1.4 times greater than the gap at the point where the other end of the rocker contacts the base circle of the cam.

So if we divide .004" by 1.4 we get .00286". Actually .00285714286",

So .00286" is a rounded off number. Plenty close for what we are doing.

To answer the question why a .0025" feeler?

Since it is smaller than .00286" it will slip easily into the rocker/cam gap.

We now have a GO gauge, .0025".

As a Go gauge it will slip into the rocker/cam gap unless the gap at the other end of the rocker is less than .0035".

Now the NO-GO gauge .003". This should not slip into a properly set gap. See photo two.

Photo three. The NO-GO 3 thousandths gauge blocked. This is correct.

The NO-GO 3 thou gauge will only slip in if the setscrew end of the rocker/valve gap is greater than .0042". Correct is .004" (0.1mm).

This means if the valve gap is set over .0042", looser than 2 TEN thousandths, the NO-GO 3 thou gauge will catch it.

You have to work very carefully to get this kind of accuracy with a dial indicator.

And of course you can only use a dial indicator with the motor out or partially dropped.

The advantage at this point is it is quicker than a dial indicator and as accurate.

You adjust the rocker arm set screw so it allows the GO 2.5 thou gauge to slip into the gap, but the NO-GO 3 thou gauge will be stopped.

See pictures two and three. Picture two shows the GO 2.5 thou gauge in between the rocker and cam. Picture three shows the NO-GO 3 thou gauge blocked.

This is what you want.

If you have read this far, save yourself some time and check the gaps with the NO-GO 3 thou and the GO 2.5 thou beforeyou adjust any rocker screws.

With this quick check you will find which valves are OK and which valves need adjustment. After all it is unlikely you need to adjust every rocker arm.

Notice you don't need to learn the "feel" to correctly adjust your valves.

The GO gauge slips in and the NO-GO is blocked when the gap is correct .

When you are done, your valves will be set within 3 or 4 Ten thousandths of optimum. No worry about whether you got it right. GO and NO-GO answered that.

No more bent or broken .004" shims. No more dropped and lost screws.

You don't need that special tool any more.

This is a simple quality control check for any other valve adjusting procedure.

Forget about the "magnetic drag or feel". This is GO or NO-GO.

Note: The dimensions in this article are rounded off for simplicity. The actual exact dimensions will vary slightly.

Pelican Parts sells the 0.0025" and 0.003" feeler stock. The part numbers are
PEL-LM-0025 and PEL-LM-003

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Comments and Suggestions:
Kisslust Comments: Wait... Did you look at my picture? I am using the "back end" method... How far should the feeler Guage go in behind the part of the arm that rests on the cam?
August 15, 2016
  Followup from the Pelican Staff: It should do the same. SLip all the way in until it passes the rocker arm and lobe. See attached photo. - Nick at Pelican Parts
Kisslust Comments: How far should the feeler gauge go in? Also guage .025 is not .0025 correct? My guage set only has .025 and .030.
August 15, 2016
  Followup from the Pelican Staff: Your feeler should go in past the adjusting stud. 0.025 is correct. - Nick at Pelican Parts  
whizbang Comments: Hello fellow pelicans! I hope one of you can offer some advice. This is my first time adjusting the valves on my 1969 911E. The car was bought new by father who had it professionally maintained while he owned it. It sat unused for many years in his garage until it came to me.
I've tried both the traditional and the backside method, and have had pretty good success with the latter.
The problem is on #4 there is no gap. Also, loosening the adjustment screw while pointing to #4 does not move the rocker so I can't get a gap to adjust. When the cam moves off #4, the rocker / adjusting screw move just fine. This is similar to problem Norm Peterson described in his march 2012 post. I have the same problem on #5. All the others including #6 are okay. The other issue is since I loosened 4 and 5 to adjust them, I can't put the car back together until I solve the problem.
Any guesses what might be the issue on #4 and #5.
Thanks!
August 31, 2014
  Followup from the Pelican Staff: Could have a bad valve seat, if the valve is sitting too high. Does the stem look higher than the others? - Nick at Pelican Parts  
peterl2 Comments: can you install hydroulig lifters in a 84 carrera and eliminate this valve adjustment all togeather
June 22, 2014
  Followup from the Pelican Staff: I don't believe so. I have heard of people going the other way from hydraulic to solid. I would do some research, there could be a solution out there. - Nick at Pelican Parts  
Tweedle Comments: Would like to check my 95 993, are the clearance the that go & nogo - .025 & .03?
What are the figures for a 993?
thanks
July 26, 2013
  Followup from the Pelican Staff: 993 models utilize a hydraulic adjuster, no adjustment is required. - Nick at Pelican Parts  
gazza new zealand Comments: I also have 91 c2 and wish to do tappets soon you don't appear to have answered jon jan 2010 would also like your advise on thissounds like a very simple method
July 21, 2013
  Followup from the Pelican Staff: The metal sheilds can be removed, they are held on with Allen fasteners, (5mm if I remember correctly). The power steering pump can also be removed. Remove the cover, then loosen the upper pulley bolt, then remove the pulley with the belt. - Nick at Pelican Parts  
hnichols Comments: The great benefit of this method is that it allows you to check the clearances before loosening anything - you can't really do that with the standard method, because it is difficult to insert the feeler gauge when the valve is correct. You might get lucky and not have to do an intake valve or two.

One piece of advice I have is that after adjusting the locknut you should jiggle the rocker before inserting the feeler gauges. I drove myself crazy overshooting the go/no-go sweet spot until I discovered this.

The standard method is still probably better on the exhaust valves where you can eyeball it. then use backside as a backup.
June 26, 2013
  Followup from the Pelican Staff: Thanks for the additional information. We appreciate it. - Nick at Pelican Parts  
Greg Comments: Hello,
so are the numbers different for a '92 964 and can it be done the same way? thanks
January 17, 2013
  Followup from the Pelican Staff: There will be differences. I would grab a repair manual. It will list the special tools, specifications and each step of the procedure. Give our parts specialists a call: 1-888-280-7799 They will help you find what you need. - Nick at Pelican Parts  
white rabbit Comments: Hi Doug,
Thanks for this article. A bit of confusion for me is the identification of the correct "no go" feeler gauge. I am comfortable with the procedure and the .0025 gauge size.
However I have seen the "no go" size listed several ways which may be ok for some but I would like clarification to which is correct to ask for and order for the no go.
1. 3 thousandths
2. .003
3. 0.003
4. .030
5. 0.3mm
Are some of these the same?
Or can I just use my .07mm for the go and a .08mm for a no go gauge.
Thanks for the clarification.
Don

November 12, 2012
  Followup from the Pelican Staff: 3 thousandths of an inch is the same as 0.003". You will have to use this size, 0.07mm is about 0.0027". - Nick at Pelican Parts  
Norm Comments: Hi

I hope you can help me!

I have rebuilt my engine, re-fitted the heads and am trying to adjust the valves. I have followed the usual steps of finding Top Dead Centre and have tried two methods I found on the internet - firstly trying to set No.1 and when this did not go well, trying to set No 4 first of all. The problem I encountered in both methods and both attempts was that there is no gap on No 1 cylinder; the other three cylinders are OK.

The push rods are seated OK. The heads are standard and came with the engine; the cam was bought secondhand and I was told it was the same as an SC

Can you tell me how critical it is to align with Top Dead Centre because when I move the pulley mark to just before 180 degrees, I can set the gap for the intake and then if I move the pulley to just after 180 degrees I can set the gap on the exhaust.

In desperation I have been set to thinking that if I find the rock point on the valve ie fully closed, the timing mark on the pulley is not at 180 degrees or TDC depending upon which valve. Also I have noticed on the net the two different set of instructions give different instructions - one says turn counter-clockwise and the other set of instructions says turn clockwise - which should it be? As a last resort I even re-did it all again going in firing order - valve 1, 4, 3, 2 but still the same problem.

Do you have any clues as to what is wrong or what mistakes I may have made?

Thank you in advance for your help.

regards

Norm Peterson

March 1, 2012
  Followup from the Pelican Staff: Setting the engine at TDC is critical. I would check that the engine is timed correctly. Maybe before doing that, confirm the camshaft are for your engine, you mentioned you were told they were but seeemd unsure. i need to more about your specific vehicle ot be more specific, year, etc. - Nick at Pelican Parts  
crg53 Comments: Great write up and illustrations. I just did my valves and found this method a lot easier than using the Porsche feeler gauge tool. I did double check all the valve with a dial indicator just for peace of mind.
If I can add one thing since we are talking in 1/10000 of an inch, that 0.1 mm which is the spec clearance set by Porsche, is NOT 0.004" but 0.003937 so if you want to do a bang up job, just deduct 0.0005" from the numbers above.
January 12, 2012
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. - Nick at Pelican Parts  
opticalfuel Comments: RE: Clikadjust Tappet Adjuster - in the above comment about mid March 2011....

I am inclined to believe you would have enough room to adjust with that tool. The only question is... DID Wayne try it? I think that is a brilliant solution to an otherwise tedious job, that is fraught with error, stress about burnt valves and the like. Please advise. Thanks!
October 10, 2011
  Followup from the Pelican Staff: I don't any experience with Clikadjust Tappet Adjuster. I have heard of it used before, it would be a tight fit. - Nick at Pelican Parts  
Marsh Comments: Help, I had done the old way many times of both 70T and 73S. Tried to help a friend on his 86 Carerra but could not be sure we were getting the 4mm feeler guage between the valve and the swivel foot. Opened the gap up more but never sure we had it right. Any suggestions as to what we were doing wrong and if we should use the new method?
August 6, 2011
  Followup from the Pelican Staff: Porsche had a slick feller gauge, Part# P213, it worked great for adjusting on your engine.

Starting with Cyl#1 , rotate engine clockwise until you hit Z1 timing mark. Once cyl#1 is done, rotate engine clockwise 120° to next mark, then adjust cyl #6. Once cyl#6 is done, rotate engine clockwise 120° to next mark, then adjust cyl #2. Repeat for cylinders 4, 3, 5.- Nick at Pelican Parts
 
devon77 Comments: Hi, I drive a '79' 3.0 SC, and this weekend tried to the v/v clearances as I thought the engine sounded a little tappety, failed with usual method, the saw this article and gave it a go, very simple. My problem was the 0.003 no go feeler went in easily for every valve ! secondly couldn't get a set of feelers with a 0.0025 guage. So in the end I left everything as it was and put the car back together as I needed it to get to work. Any advice would be greatly appreciated as I'm a frustrated guy. Thanks
April 25, 2011
  Followup from the Pelican Staff: I pulled this text from the article. It answers your questions:

You adjust the rocker arm set screw so it allows the GO 2.5 thou gauge to slip into the gap, but the NO-GO 3 thou gauge will be stopped.

See pictures two and three. Picture two shows the GO 2.5 thou gauge in between the rocker and cam. Picture three shows the NO-GO 3 thou gauge blocked.

This is what you want.

If you have read this far, save yourself some time and check the gaps with the NO-GO 3 thou and the GO 2.5 thou before you adjust any rocker screws.

With this quick check you will find which valves are OK and which valves need adjustment. After all it is unlikely you need to adjust every rocker arm.

Notice you don’t need to learn the "feel" to correctly adjust your valves.

The GO gauge slips in and the NO-GO is blocked when the gap is correct.

When you are done, your valves will be set within 3 or 4 Ten thousandths of optimum. No worry about whether you got it right. GO and NO-GO answered that.

No more bent or broken .004" shims. No more dropped and lost screws.

You don’t need that special tool any more.

This is a simple quality control check for any other valve adjusting procedure.

Forget about the "magnetic drag or feel". This is GO or NO-GO.

Note: The dimensions in this article are rounded off for simplicity. The actual exact dimensions will vary slightly.

Pelican Parts sells the 0.0025" and 0.003" feeler stock. The part numbers are
PEL-LM-0025 and PEL-LM-003 - Nick at Pelican Parts
 
a320 Comments: I have never done a valve adj. on the 911 before. This tech artical was written by 2.7 racer. What are the go, no go numbers for the 3 liter SC engine? Are they the same as the 2.7?

Your tech articals section is great.
Thanks again
Phil
April 6, 2011
  Followup from the Pelican Staff: The valve clearance for all of the engines (1965-89) should be the same: .10mm - Wayne at Pelican Parts  
Ian hammersley Comments: Just adjusted my valves using the backside method. Now the car sounds worse! So I will check them again.... I found that having a head torch was extremely useful. Today I came across this tool http://www.frost.co.uk/item_Detail.asp?productID=8086&frostProductName=Clikadjust%20Tappet%20Adjuster&catID=19&frostCat=Engine%20&%20Mechanical&frostSubCat=Engine%20Tools&subCatID=29 . Do you think this would fit in the available space with the engine still in the car?
March 27, 2011
  Followup from the Pelican Staff: That's a neat looking tool - I used to have something similar a long time ago, and I lent it to someone, and never saw it again. I'll have to order one and see if that is something worth carrying in our catalog! I think it will fit in most 911s engine bays while performing the valve adjustment. - Wayne at Pelican Parts  
mike Comments: hey great article
my garage is 40 degrees is there a minimum temp when doing this adjustment
Also when the engine warms up do the clearances increase or decrease ?
The valve noise gets louder when the engine warms up !
January 31, 2011
  Followup from the Pelican Staff: Nope, no minimum temperature as far as I know. When the engine warms up, the whole engine expands. I'm not sure if that makes the clearances tighter or looser - on some engines it does vary depending upon their design. - Wayne at Pelican Parts  
Cfreed Comments: I like this method a lot. Took me a little while to figure out that you slip the gauges in from the opposite side slip gauge in from the top to measure the lower exaust valves and vice versa. It's still a little tricky but much more reassuring. All of my valves were slightly loose from my attempt at the original way. Number 3 cylinder was the hardest to set for me because it's the furthest forward.
September 26, 2010
  Followup from the Pelican Staff: Thanks for the feedback and additional info. Glad we could help.
- Nick at Pelican Parts
 
Rabbi DJ Comments: Hi. I just bought the "Tune-up" kit of Pelican Parts for my 1984 Carrera and I'm going to try this method. Do you still need to drop the engine oil? Cheers Frank in New Zealand. Great web site.
September 1, 2010
  Followup from the Pelican Staff: You need to remove at least some oil from the bottom of the engine, otherwise it will flow out onto the ground when you remove the valve covers. - Wayne at Pelican Parts  
wkbergman Comments: Hmm, I'm dummer than the average stump. I don't have unusual troubles with the 'old' way of doing this, but am totally unable, in a whole afternoon, to try do it this 'round' way. Do you have to drop the engine and slip in the gauge for the intake from the bottom? If so, I was not able to slip in the gage from the top, to do exhaust.
Also, this is a metric car. Why write this in medieval inches? When I re-convert, I get .07mm for GO and .08 for NOGO, rounded off for the gauges I have.
ps: changed my email to the one that has a 'friendlier' server.
August 4, 2010
  Followup from the Pelican Staff: No need to drop the engine here, you should be able to do everything with the engine in the car. As for the feeler gauges, if you have a set of metric ones handy then great, but those are difficult to find over in the states sometimes. - Wayne at Pelican Parts  
jwakil Comments: Wow, I will try this since trying to find the gap between the elephant foot and valve stem is nearly impossible without dropping the engine or breaking the feeler gauge. Why isn't this the standard method? Why is it the advanced method if it is actually easier?
June 9, 2010
  Followup from the Pelican Staff: Don't know. Not the "German" way? - Wayne at Pelican Parts  
84 Carrera Comments: I am having trouble finding a .0025 - .0003 NO-GO feeler guage . Can you suggest where I might buy one ?
Thanks.
May 2, 2010
  Followup from the Pelican Staff: If it's for the valve adjustment, that's not really what you use. You use the lightly oiled feeler gauges shown here, until they have a light drag. - Wayne at Pelican Parts  
Chris Comments: A fantastic procedure. I was struggling with the special tool, so I tried this method. Very easy and quick. Thank you very much, Doug.
April 4, 2010
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Jon Comments: I have a 91 C2 and the power steering pump seems to be in the way of my access to valves. Is there some way of dropping additional sheet metal to access from under the car? Or - somoe other trick other than removing the pump?? I really appreciate any advice on this knuckle buster. Thx
January 21, 2010
  Followup from the Pelican Staff: The sheet metal unbolts from the engine and can be removed. If I remember correctly, there are a few 4 or 5mm Allen bolts that hold it in. - Nick at Pelican Parts  
mpetry Comments: This is a great method, really fast and easy! I used it and got it right first time. The other trick of course is to do one side of the engine at a time, with 240 degrees of rotation between each ajacent cylinder on each side of the engine.

Great article Doug!

Mark Petry
Bainbridge Island, WA
September 17, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
krobb Comments: What a great method, setting the valve clearances was a breeze.
September 10, 2009
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
mike Comments: i have 1996 porsche tt i would like to put the later model check valve in line with the turbo was wondering what parts would i need and the order it goes in i put rebuilt turbos and want to prevent problem
thx mike
July 14, 2009
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need. - Nick at Pelican Parts  
dav8r Comments: are the feeler gauge dimensions .025 and .030 the correct sizes for a 3.0 SC engine. Also, when setting up the valves, do you do the same proceedure that you normally do to find TDC for each of the cylinders? Thanks
May 31, 2009
  Followup from the Pelican Staff: The correct clearance for the valves is .10mm or .004 inch. I'm not sure what you mean by "setting up the valves?" - Wayne at Pelican Parts  

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