Help with valve to piston clearance

[Emo993]

Just bought a 2.2E with S pistone/cylinder and cam, this is a long block so I'm trying to varify what I have and how good was the rebuild 4 years ago (no history). I have been reading Wayne's book, (great) so the question comes up about valve clearance and the correct way to check it... Page 173 and 74 explain it pretty good, but I'm confused, the procedure from TDC Z1 is off of the compression stroke and the diagram 8-2 shows the clearance is closer when the cams are overlapping which is 360 deg (DTC overlap).
Do I need to do the entire lobe, are the valves values closer on the overlap. Thanks for the help. Mark

Just retired, and have had my 914 going to a 914-6 apart for twenty years, need to get things moving....

[Walt Fricke]

Mark

I think you are worrying about things not worth worrying about in your case. If this was a running motor, and you are just going to plug it into your car, you don't need to check piston to valve clearances. If the leakdowns are good, they are pretty clearly enough so that valves aren't hitting pistons.

If it never ran, different story.

However, the time when valves get closest to pistons is in the neighborhood of TDC overlap (i.e., when things change from letting the exhaust out to letting the intake charge air in). When you get around to disassembling this motor, and then making machining changes to things which will affect clearances, then you do mock-ups and check these clearances. This is the only time during the crank's 720 degree travel that valves get anywhere near the pistons.

The procedure is simple whenever you do it, though - pick a minimum clearance, use the adjusters to push valves down that amount, and carefully rotate the motor, being especially gentle at you are coming up on TDC overlap, and leaving it.

I just laid out $200 for a Harbor Freight borescope. Its scope will fit in a 12mm spark plug hole. The $100 one lacks the capture and transfer to computer etc feature, but might work as well for inspection? A guy could use this with its 90 degree mirror) to watch the valve clearance. Once you saw where exactly it got closest to the piston you could then screw the adjuster down more to see just what your motor's minimum is, which might give you some idea of how much you could bump up the CR (assuming you have piston to head clearance to spare) without getting into valve trouble with the cam you have. This might be a better way of avoiding inadvertently bending a valve stem than the "screw down until one hits when turning crank" approach.

[Emo993]

Thanks Walt, yes this engine has never been run. Even though i'm missing the crank pulley, not hard to fine TDC, when i checked the intake valves, i have over two turn (,2mm) great.. Then on the exhaust, still number 1 cylander and i have only .1mm( one turn). Soooo, I took the chain cover off
to check cam timing at a glance. When on TDC, seeing piston though spark hole, the cam seems to be
5 to 10 deg.s counter clock wise, not straight up as Wayne described. Does this sound like poor cam timing...Again, thanks Walt.
I have worked on a lot of cars i.e. Jetta diesel DTI, Jetta 1.8 T five valve, 914-4, Saabs, Jaguar old E,
but this is my first 911. Want to do it wright, if I don't, I will go back and learn more....

[docrodg]

You need something to let you know TDC for certain in order to get cam timing right. Scrounge up a pulley or use a degree wheel with the heads off to locate true TDC (use a dial indicator to measure piston rise and set degree wheel to 0 when rise is at TDC). Then do your valve clearance check. Depending on the engine it may not be TDC. I do the turn-in then a very careful rotation to feel if there is interference, but you MUST be gentle.

[Emo993]

Thanks also docrodg, your right, need pulley and start from square one. Do not want to pull heads if I don't have to. Every thing else looks like it was done well. Anyone reading this have a standard single pulley for a 2.2 I could purchase.
Thanks, mark

[Hcarraro]

Congratualtions on your retirement Mark. I look forward to watching your progress. Fantastic looking engine and a great looking car. Love how you did the scissor lift.

All the best,

Henry

[Walt Fricke]

Well, you need to do this by the numbers.

Pulleys are easy to come by, though that is easy for me to say, living as I do in a metro area with several Porsche dismantlers and lots of Porsche buddies with stuff. Literally any pulley will do for giving you a TDC mark at this point, though eventually you will need your own.

But a degree wheel would also be good. You can locate TDC by making up a piston blocker from a junk spark plug. You gut the plug, and then figure out a way to insert a rod to stick down from it. Allthread would be good here. And to secure it, which may call for more ingenuity, though a welder makes short work of things like this.

You put the #1 piston at BDC or thereabouts, screw in the blocker, and attach your degree wheel. Rotate the crank one way (doesn't matter if CW or CCW) until it hits the blocker. Mark the number on the degree wheel. Then rotate it the other way until it hits. Again mark. This will tell you, say, that your blocker stops the piston at 29 degrees on either side of TDC. Half of that is 14.5, so that's where TDC is. Turn the degree wheel so its 0 mark is 14.5 degrees from where the piston stops (being careful to note which direction is which. Now you have it.

Then check your cam timing - Wayne explains this quite well. Then do the valve dial down bit.

A buddy (goes by Speedo, though I know him by a real name - Lars. What's with this pseudonym business, anyway?) had these clearance issues running 2.2 S pistons in a 2.4. But that involves a longer stroke, whereas yours only needed to meet S specs, all of which ought to be taken care of by using stock dimensions for everything. In your case, if things are tight that might indicate that the case was "decked" to insure all the spigot tops were in a plane and equidistant from the crank CL. And the heads may have also been cut, if just to clean their mating surfaces up. Anything of this sort which raises the CR will also reduce all the clearances - piston to head and piston to valve.

But getting your cam timing checked accurately is the place to start. And you can't really tell an accurate TDC by looking down a spark plug hole. An alternative, which I have never used but have heard good reports on, is a whistler - screw in plug hole and when tdc is reached, the noise stops.

[Emo993]

Walt, the blocker sounds great. I can weld one of those up in a minute. And mounting a degree wheel to it on actual TDC . I'm going to have to spend a little more time reading Waynes cam timing portion, some of it goes over my head (not sure why). And yes, everything you mentioned i.e. "case was decked, heads cut" are all unknowns. I going to Florida tomorrow to help a friend paint his house, so I won't be working on this for a few weeks, but, thanks for all the help, I'll post my finding (results) when I get back. FYI this is the same car I drove to Boulder for the PCA parade in maybe 85/86, was in first place to class until a complaint was posted (not enough tread)......still fun. Mark

[Emo993]

Did have time Walt to make the blocker and a degree wheel. The blocker took a few tries (not good to get weld on the thread) also made it a little longer so thread would not fall into cylinder. mark

[Walt Fricke]

Mark

The cam timing deal will pop into place for you at some time. Basically you are setting the cams using the intake only. With the valve lash set properly (0.004" or 0.1mm), the you adjust the cam so the intake valve opens by the specified amount at the "non-firing" TDC.

Yes, this is in the overlap region, where the exhaust is still open. Yes, there are nice cam diagrams showing that at TDC the exhaust is still open by some amount. But you set the cam with the intake.

Now this number is somewhat arbitrary, so if you use a different cam or have messed with engine dimensions, you then have to check to see that there aren't valve to piston conflicts, or the potential for the same. If there are, you can see if resetting the cam timing ng will resolve them There may be a sweet spot where you have the clearance you need for both valves, and haven't just robbed Peter to pay Paul. I had to do this with a cam once, and it worked - I couldn't use the cam grinder's setting, but found one close enough.

I think factory cams may be literally set at overlap (hence the name), so the intake and exhausts are the same distance off their seats despite both being headed in opposite directions. But I don't know that for sure, and don't know why that would be magic. Someone here knows to that detail. But it is kind of academic.

And if this resetting of the cam timing somehow screws up the cam's performance, they you have to disassemble and cut valve pockets deeper, or add more base gaskets to the cylinders, and so on.

You just have to cross your fingers on piston to head clearance, as I don't think there is a way of doing that on an assembled motor. I just bought a Harbor Freight $200 boresocpe, but doubt that would give you a view of this clearance, which is usually least right around the circumferance of the combustion chamber. If you had a surgeon's arthroscopic tools maybe you could insert the solder strips and then retrieve them to measure?

[Emo993]

Hi Walt, thanks for the information, it did finally come to me....
Soo, back to work, did find TDC with blocker tool, bought the Z-block and cam tools from Pelican. Maped out the cam lobe values on the graph below, does this look like WebCam
S grind as I was told.....does have high lift, are the cams out of time being the valve overlap is taking place around 340 deg, not 360., also the Intake number at TDC Overlap is at 5.68mm( not the 5.0 to 5.4) as published. Mark

[Walt Fricke]

On your fine graph, the lobe centers look to be 210 crank degrees apart. so the cams would be half or 105 degrees. Would that help in identifying the cam? If correct, that seems a bit wide for a performance cam.

My experience is all with known cams, complete with setting specs.

If you advanced the timing even more you could move the overlap to TDC. Would give more exhaust valve clearance, and less intake clearance, if those are issues. If you retarded it to S spec, would alter clearances the other way.

Again, I don't believe that where the intake and exhaust traces cross is that significant, given that it can be moved around depending on how you set the cams. It makes sense that the longer the duration of the cam (I and E), the more lift the intake will show at TDC. So the S cam is 5.2mm or so, while the CIS cams are around 1.0.

But one of the cam gurus will have to chime in, as my store of knowledge has run out on this one.