My mechanic needs help

[Patrick]

Maybe the question should be how was it different? Power loss/ rough idle/ stumbling on acceleration? And where/ how far had you driven the last trip before you noticed the difference or was it something that just kept getting worse?

I drove a 5 hour drive to Kamloops through the Fraser canyon, a leisurely drive of twists and turns, and returned on the coquihalla highway, a flat out drag race of a road. After I got back I was changing some spark plug wires and I just could not get it to idle right and it stumbled at low revs before getting some power. I timed it according to my service manual and changed the distributor cap and rotor. I then checked and rechecked every wire and plug and found that two cylinders were not firing, or at least pulling the spark plug lead made no difference to the rough idle. Changing wires and plugs made no difference. I fiddled with it for a week, swapping parts back and forth before taking it in to the mechanic recommended by our local classic auto body shop.

 

[70bigblockdodge]

Has to be miss-matched parts where is moper at he will know answer to pushrod lenght

 

[66/440]

Patrick,
I have reread your post a couple of times and am wondering about a couple of things.
First, was the idle miss so pronounced that it was the motivation for the mechanic to pull the heads off?
I have had, as we all have, cars that had intermittent misses and rarely was it something so serious that I felt the need to have the heads removed. There have been a few times that it was that serious and burnt or sticking valves were the issue.

You said that the miss was in cylinders 5 & 6 which is odd that they are exactly opposite each other and their primary shared connection is cam lobes. You also said that you had replaced plug wires, etc. and I want to understand clearly that this was because you were doing routine maintenance or was it because you were trying to solve the miss?

Now that the heads are off did the mechanic identify any valves that were burnt? If he did not would it be possible to check with the machine shop that performed the work to see what their thoughts were? Did you have them install hardened seats so you can run unleaded with no issues?
Are the heads back on the engine? If not it would be helpful to have them cc'd so you have a base line.
Has your mechanic measured the installed valve stem height? This basically is the height from the spring seat to the top of the valve stem. Most of the better machine shops will do this as part of the rebuild but if he sent them to a production type of shop they may not have checked. This will tell you if the theory of the push rod length being too long is correct.

I am also curious about the pressure check that your mechanic says he performed to test compression. You really only need 40 lbs. or less of pressure to check leak-down depending on what type / brand of gauge you are using. The 100 lbs. he says he used is too much and yes it would build more compression due to the extra pressure on the rings causing them to set a little better, but not an indicator of much of anything else.
Explanation of pressure leak-down test: http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/

 

[65sporty]

The machine shop that did the work on the heads should have ck'd the valve installed height. If this is wrong it and the valves are too long they will be held open