Thought I was almost done... #6 piston hitting intake valve during valve adjustment.

[LeeH]

I'm too tired and frustrated to list all the details. Here's the Reader's Digest version:

'82 3.0L with WebCam 20/21 cams... otherwise stock. Ran great before 6 bent exhaust valves due to over-rev.

Heads done by machine shop suggested by Porsche shop. Pistons and cylinders left undisturbed.

Cam timing has been checked more times than I can count. Specs below. They're set right at 2.05 mm at Z1. Ready for final valve adjustment. Set #1, Set # 6, turn crank... and it stops dead about 350 (NOT 110 as originally posted) degrees later. Back off #6 intake valve adjuster and it turns fine. What am I missing?

[Jeff Alton]

How much material did the machine shop take off the heads when the mating surface was refinished?
Did you measure your deckheight? If so, what was it?
Are you sure you have the cams in the correct side? This is an easy mistake to make.

On another note, did you remove the pistons and cylinders and replace the copper base gasket or did you leave them on the shortblock. Not sure I understand your meaning of "undisturbed".

Cheers

[LeeH]

No matererial was removed from the heads. Deck height at 1mm. I've checked that the cams are in their correct side.

When I say undisturbed I mean I didn't remove the cylinders from the block. The dimensions of the engine shouldn't have changed since the engine ran a month ago.

[axl911]

Dumb question here, but don't you mean set cylinder 1 and 4?

[LeeH]

Originally posted by axl911
Dumb question here, but don't you mean set cylinder 1 and 4?

I was talking about the valve adjustment.

[tech 1]

Lee, I'm not a betting man,but...................if I were.......... Cam timing is off! So, let's start from the beginning.I don't ever set the cam timing with all of the rockers in. You need just #1 intake rocker and #4 intake rocker.Set the engine @ Z1,#1 cyl. Turn both camshafts so that the punch mark points straight up. Adj.#1 intake valve to .004",You should now be at #1 firing...&...#4 overlap. Now insert the your timing dowels.Rotate the engine 360 crankshaft degrees. Note!!!! there are 360 degrees in a crankshaft circle,but......720 degrees in a cam circle! Now adj. your camshaft timing on the left (driver's) side of the engine only cyls. 123. Set timing to 2.0. You are now at Z1(tdc) firing for cyl #4 and overlap for cyl#1. Repeat the same process on the other side.Somehow you missed something here.Let me know how it goes and I'll walk you through the next step.You can call me at the shop (760) 873-8923,or E Mail me direct sgabishop @ verizon.net.I'm sure we can figure this out simply. The next step is very important too. Valve to piston clearance.I can walk you through that too. Tim.

[john walker's workshop]

maybe one cam is 180 out. it's happened before.

[LeeH]

Originally posted by john walker's workshop
maybe one cam is 180 out. it's happened before.

I'm open to any and all possibilities.

I verified #1 piston is at the top of its travel at Z1 and this corresponds to the heel cam on the #1 follower. #1 intake valve starts to open 350 or so degrees later with 2.05 mm of lift at Z1. Moved gauge to #4 intake. Spin crank. #4 intake starts to open around 350 degrees later showing 2.05 at Z1.

My original post was incorrect. The #6 intake valve hits the piston around 350 degrees AFTER I adjusted the valves for #6.

[LeeH]

Another question.... The set range for this cam is 1.9 - 2.2 mm at .10mm lash. At 2.08 on the right side I'm just a bit over the mid point of that range. Would setting the cam timing at the lower end of 1.9 possibly change the geometry enough to have adequate clearance?

[gtihop]

When I set my cam timing I did it towards the higher end of the range. (.067"). I found that the no 1 and 4 intake valve didn't have the proposed 1.5mm clearance during the valve-piston check. It was too close by (.25mm). I had to reset timing to .057" and all clearances are good. You wouldn't think that the slight difference would matter but it did. Now we'll just see if it runs!!!!!

[J Richard]

Lee,

Unless you do these all the time these are a pain in the butt.

I had a motor all together and running before I found out I did something wrong, so at least you caught it! When you get to this level of frustration it's easy to get fixated and miss the obvious. Bottom line is if piston is hitting valve, no matter how many times you've checked, its wrong. It really takes getting things way out of sync to lock up the motor, so I think you've either got the cams reversed, one is out 180 degrees, or your timing on the back side of the lobe instead of the front. If you are anywhere near the lift range the motor will still turn over so I'm suspect of a larger issue.

1. Since you didn't pull the jugs, the issue of pistons upsidedown and base gasket clearances shouldn't be an issue. Overall clearances should be within range since the thing ran before, so I would put that out of your mind.

2. You mention it but are you sure you have the right cams on the right sides? If so put that aside.

3. Put the guage back on #1 and watch the cam lobe, and make sure you are getting the specified lift on the start of the lobe, as the valve is opening, not closing, you can get the specified lift on either side of the lobe, so you have to watch the cam. not just spin the motor and read the guage.

4. Do the same for #4, again watching the cam to make sure it is on the opening not closing of the valve.

5. If this checks out the only other option is you have one of the cams 180 out.

anyway take a deep breath, have a beer and give it a whirl... let me know how it goes.

jim

[LeeH]

Thanks for the info Jim. I not swearing to anything at this point. I caught enough of my own errors during this process to make me very concerned about any that I might have missed.

That being said, I'm trying to understand how the cam could be 180 degrees out and still be opening the intake valves for #1 and #4 at the proper place on the crank rotation.

I'm probably going to pull the rockers and just start the whole cam timing process over from scratch... I'll probably yank the pins and try to time it toward the low end of the range first. There's no way I'm going to make the DE Saturday so the pressure is off.

[tech 1]

Lee, I'll be at the shop on Saturday,call me if you need help.Tim.

[Eagledriver]

Even if the cam is 180 degrees off the piston shouldn't hit the valve. I've never built an engine with that cam profile but maybe you don't have enough clearance for that setup. Maybe that is why you bent all the valves before. Did you check the clearance on the first build? Yes adjusting the timing can get you more clearance but probably not enough if you have contact at that setting. When I built my last 2.7 with 911S cams I had to relieve the pistons by about 1mm even with stock RS pistons.

-Andy

-Andy

[LeeH]

Tim - I greatly appreciate the phone consultation yesterday. Let me know if you end up at PIR in February.

Originally posted by Eagledriver
Even if the cam is 180 degrees off the piston shouldn't hit the valve. I've never built an engine with that cam profile but maybe you don't have enough clearance for that setup.

I'm under the impression that the WebCam 20/21 grind is supposed to work with the stock CIS pistons.

[john walker's workshop]

never had a problem with 20/21s.

[LeeH]

I tried to troubleshoot this, but haven't figured out what the problem is. I put the dial gauge on each cylinder, adjusted the intake valve and spun the engine. One thing I noticed is that the intake valve for 5 & 6 start to open about 30 degrees sooner than they should. Those are the only cylinders where they hit the valves.

What I don't understand is how this could happen if #4 opens when expected. I've looked at the right side cam and it seems to be doing exactly as I would expect. For lack of anything else to try I'm going to start from scratch on the right side. What bugs me is that if it works I'll have no idea why.

[2.7RACER]

Lee,
A simple test. Rotate your engine clockwise until you are at Z1 compression for number 1. The numbers at the ends of the cams should both be straight up. Exactly straight up.
If you stop at Z1 compression for number 4, the numbers should be straight down. Exactly straight down.
If either cam is significantly off it will be apparent.
Good luck.

[LeeH]

Update: I set the cam timing on the right bank just under the mid point of the range, installed the intake rocker for #6 and it now clears the intake valve. I think it's just clearing with little room to spare at the closest point. I'm going to chart the clearance for the intake and exhaust on #6, then set the cam timing toward the bottom of the range and see how much that helps.

[john walker's workshop]

a metric dial indicator is best. too many folks miscalculate when it's a US one.