I had adjusted the valves to .006" before the last track event I went to in April. It was about a 4 hour drive to the track and probably 40 or 50 degrees F. When I got there, the darn thing wouldn't idle (dual IDF 40's, 2.1L). No matter what adjustments I made, I couldn't get it to idle when hot (right off the track) but it would idle if it sat for a while. So I came home from the event, parked the car and started on the flare installation.

Now 3 months later with flares on and driving it on a regular basis, it still didn't idle. Again, checked the synchronization on the carbs, idle mixture, etc. Still didn't idle. Thinking logically, if it won't idle hot, a valve must be sticking open. So I let the car sit for a day and pulled the valve covers to find that all 4 exhaust valves had ZERO (more like negative) clearance!

So what happened?

A. The valves all stretched the same length.

B. All the seats got mashed evenly

C. The valves weren't adjusted at TDC

D. It was about 20 deg F in the garage when I adjusted them last


A and/or B? I doubt it.

D seems the most logical but does the valve grow .006" over 60 degrees?

You would think that finding TDC doesn't matter, but I believe it does. Years ago I tried adjusting them with what is now referred to as the "rocking method" using the opposite side valve as a guide with the theory that a valve closed is a valve closed anywhere on the cam. I found when checking the clearance at TDC that the valve did not have the same clearance as measured when using the rocking method. It ended up being too tight at TDC!

On my 914, the flywheel is paint marked at the groove for TDC and 28 deg BTDC. If I used the 28 deg BTDC mark, I was on another part of the cam that resulted in a different clearance than at TDC. The result being a valve held open when the engine is hot and no idle.

After adjusting the valves at TDC and confirming all adjustment through one rotation, it idles perfectly.

Don't use the TDC mark when adjusting valves.

Use the "opposing lobe" method.

Also, make sure that when you tighten down the lock nut, you do not further screw in the valve. That is very common to do, and take practice not to do.

Zach

Also referred to as the "rocking method" which doesn't always work. That was my point.

The "rocking" or "opposing lobe" methods assume that the cam base circle has zero runout.

Small base circle cams have the lobes ground down to the core diameter to give extra clearance for connecting rods used on stroker cranks. Higher lift cams also have smaller base circle diameters than stock lift cams.

So if the base circle is ground down, then the clearance won't be the same as at TDC resulting in too tight of a valve.

20+ years of adjusting valves at TDC. This a first I goofed on and adjusted all 8 at the wrong mark (I think).

Just curious, why is your flywheel marked at 28btdc? Do you time your car with the flywheel? And why please?

Valve seats letting the valves settle in a little too much?

It's a helluva lot easier to see the flywheel mark than the mark on the fan. The PO had cut a little window in the rear sheet metal to see the mark.

got to agre with that the fan marks are hard to see, fly wheel much beter to see.

I alwasy alwasy recheck them gaps after titening the lock nut.

Id regap them and run it a short time adn re-inspect, then run some more, then re-isnepct if they stable no worrys, if they still appear to drift, then they probably are drifting,

goood luck

You are correct that the opposing lobe method is unreliable but not for the reason you gave. The problem stems from the fact that the vavle must be on the seat (closed) at TDC and depending on cam profile, the lifter is commonly still on the ramp rather than the base circle at this point (TDC) which means that setting the valve at the lowest point on the base circle (opposing lode method) can cause it to be held open (slightly) at TDC.

.........................Well you have experienced , and summerized the problem with the "rocking method",of setting valve lash......The "rocking method" only works with VERY mild, or stock camshafts...for all the reasons You , and several others on this post have stated and have discovered for yourself the "rocking method"or "opposing lobe method" simply is not and will not and cannot be as accurate as using T.D.C. as the valve adjustment point....Their are old dogs on this forum that will argue the point with you until hell freezes over. They are simply wrong. I am glad you discovered your problem, before you burned a valve.

Except in this case I wasn't attempting to use the "rocking" method. I somehow consistently used the wrong timing mark that I put on the flywheel. However, the point is just the same. Just because the valve is closed doesn't mean that the clearance is going to be the same at any closed position on the camshaft. This would make a huge assumption that in any closed position, the cam has ZERO runout.

To me, this was more backup to why the other method doesn't work and why the TDC method is the only method I use.

.................And...when building any engine it is imperative to find, and clearly mark T.D.C.....this can be be done accurately with a degree wheel, and a dial indicatur, probe,placed on the top of the piston., averaging, the pistons location at T.D.C as the piston rotates at T.D.C., center the degree wheel on the split degrees.... there are many locations to find the proper technique for finding T.D.C...THEN ..mark the flywheel AND the fan/impeller. You,ll have an accurate T.D.C., not only for checking cam timing, but for Valsh lash adjustments ,and ignition timing...A properly built engine IS labor intensive.

Ok , TDC it is , but is it TDC for every cylinder ?? As that would make sence. TDC for #1 , then rotate engine , watch distributor rotor when it comes upon the next plug wire point for firing ?? This can get confusing with all the tried and true methods.

Jack / Jaxdream

TDC is clearly marked as a notch on the flywheel. I put a dab of red paint on it. I should have used a different color paint for the other mark but didn't have any convenient at the time.



The only tried and true method is the TDC method.

NEVER use the mark on the distributor. That is NOT TDC

The easiest way is by matching the notch in the flywheel with the case mating surfaces as seen through the engine compartment for cylinders 1 and 3 (you may need to push the rear tin aside slightly. Then use the notch in the flywheel with the case mating surfaces as seen through the weep hole in the bottom of the transmission to engine mating surface for cylinders 2 and 4.

Find the notch in the flywheel with your finger thru the hole on the top of the trans. Then make a mark with white paint on the bottom of the flywheel thru the bottom hole. You now can see the notch and mark while under the car without moving from under the car. Simple!

Thanks , Tom , that clears up a lot.

Jack / Jaxdream

...................And...the stock timing marks on the fan/impeller..O/T...are not always accurate.(especially if you have swapped parts around(fans) from other type IV engines.)....And the mark is for TDC for only cylinders #1..and #3., rotating the crankshaft 180 degrees, WITH a degree wheel attached and centered will allow you to Mark TDC for cylinders #2 and #4. Accurately.....now all the TDC marks , will appear(in the view hole , top of engine,) as each cylinder reaches TDC., as you rotate the engine CLOCKWISE, thru it,s normal rotations. I recommend to always rotate the engine in it,s normal rotation for valve adjustments. This is especially true with performance camshafts, which can have asymetrical cam lobes, small base circles, and radical lobe profiles.

Awe hell, i used the lobe method......494 cam, with 0.465 lift, 280 duration, 108 degree lobe center. Think i am ok?

...................In my opinion .....NO.......for all the reasons explained , in this post. Taking short cuts , which is the "lobe" method Will speed up your valve adjusting time. But as they say" you get what you pay for"...less accuracy in the valve lash adjustment...But if your happy what the hell, do it your way.

I doubt it. Check it at TDC and see if it's the same.

.............Here is something else to consider.... The camshaft rotates at 0ne half .../1/2 ...the speed of the Crankshaft....When you are looking at the O/T... TDC timing mark this does NOT mean that the Cam Shafts lobe base circle is absolutely at the mid point of the Base Circle diamenter (the valve adjusting point)...why?...because the camshaft may be mounted onto the cam gear in an "advanced " or "Retarded position". You cannot assume it,s mounted "streight up".(unless you measured it, while doing your cam check procedure). Especially with performance camshafts, that have a SMALLER lobe base circle..(common occurance)..and increased acceleration and deceleration ramps.(lobes)..So you have a stack up of potential problems which can cause valve lash adjustment anomilies, inconsistances...And/Therefore as an example, with every degree of crankshaft rotation, the cam is rotating 1/2 of that rotation and with cam lobes that have a small base circle to allow for the Faster/ Larger cam lobe ramps. One very small circle compaired to the crankshaft.This explanation is by no means complete. It,s intended to help you realize that accuracy in setting VALVE LASH , has many factors affecting it, and is somewhat more sensitive to accuracy IF using a performance camshaft.

I used to have that exact cam in my car, and did valves both ways to see if the opposing lobe method really worked. It worked perfect.

I am now using a cam very similar to the 494 (same lift, but longer duration on exhaust) and guess what. It still works.

All the folks that claim it does not work have probably never tried it to see for themselves. Whatever, its their car. I have tried both ways, and you will be fine using the opposing lobe method to set your valves.

Zach

..................If you are satisfied with getting an" approximation " in setting valve lash thats just fine. Other people may not . It is not as accurate as using the TDC method.... period.

So, after all of this and several other posts on Pelican and Club, seeing that everyone has another opinion, will someone kindly take out all the variables, and possibilities, and just write up a concise step by step for us inept adjusters and put it in the technical section next to Cap'n's valve adjustment write-up?

Thanks

Uh huh. Spending an evening doing this back to back TDC method and rocking method and getting the exact same results is a little more then "approximation."

But as I said. Your car, your time. Do what makes you happy. I have proven to myself that the opposing lobe method works, and it saves considerable time and effort, so I use it.

Zach

I've tried both ways. The opposing lobe method is inconsistent.

It worked for the 2 cams in particular that you have adjusted valves on which is great. You know it works for those, so stick with it.