blackbird939
New member
- Joined
- Sep 8, 2015
- Location
- Orlando
Hello again. Took some time off but I am back to my B20 from my 350K mile 72 144. Short history:
So, it developed an audible and palpable tap almost immediately. Can't remember how soon after the initial rebuild, but soon.
Here's what I have tried, and probably more I've forgotten:
Today, pulled the motor. Mains and big end bearings were like new. Lifter faces look good to me? Nothing special, don't appear flattened/dished. Cam lobes look good to me, but they seem to have wear off-center, towards the edges. Hmm..
So, I move over to the camshaft timing gear. These all-steel gears were part of the PO's rebuild ~3K miles ago. The cam had 1/~2mm of end play/slop. Should have measured it in place, but you could move it quite a bit by hand, deflecting it from the crank gear significantly. I pulled off the cam gear and noticed that I reused the old brass cam thrust retention plate- yes the spacer was there and in good shape. I had bought a new thrust plate and never installed it, as it was on back order. The old brass one is 3.45mm while the new steel plate is just under 4mm, or ~.5mm thicker. My question after all of this is: Could the major slop in the camshaft be causing the helical cut timing gears to walk out, and slap back, making this tapping on the oilpump/distro gear? That would cause the rough idle too, since I could never get a nice smooth idle, ever. If the cam was moving around, the timing would be out every tap as well? right? One thing I didn't do was replace the small rod bushings as I had a build sheet in the car's documentation. A loose wrist pin responsible for a tap you can feel through the accel pedal would be obvious in hand, correct? No evidence of piston slap on the still-honed cyl walls.
Now that I have this thing out and apart, any suggestions are welcomed and appreciated. IS the cam end play the smoking gun?
- New (Crane?) Cam from J Parker
- Reworked head, new valves, seats, dual springs, etc
- Steel timing geears
- 123 Distributor
- milled block
- new main/rod/cam bearings
- new rings
- overhauled rocker assembly from hiperfauto
- new HSR carbs from J Parker
- new 'better' lifters and pushrods
- OEM oil pump which appeared to be perfect
- new alt, water pump, coil, wires, plugs,
So, it developed an audible and palpable tap almost immediately. Can't remember how soon after the initial rebuild, but soon.
Here's what I have tried, and probably more I've forgotten:
- Pull head: checked leakdown, broken springs, sticking valves, loose seat - nope
- Lifters/pushrods rotate? yes
- Lifters free in bores: yes
- stethoscope all over the engine 20 times; yes
- retorque head bolts to 65lbs, check lash >10 times? yep
- pull plugs one by one to isolate bad cylinder? yep, no change that I could hear
- vaccuum guage? yep, bouncing needle
- measure actual lift with dial indicator at pushrods (and today on-lobes with calipers) 1.34" +/- 0.02" on all lobes
Today, pulled the motor. Mains and big end bearings were like new. Lifter faces look good to me? Nothing special, don't appear flattened/dished. Cam lobes look good to me, but they seem to have wear off-center, towards the edges. Hmm..
So, I move over to the camshaft timing gear. These all-steel gears were part of the PO's rebuild ~3K miles ago. The cam had 1/~2mm of end play/slop. Should have measured it in place, but you could move it quite a bit by hand, deflecting it from the crank gear significantly. I pulled off the cam gear and noticed that I reused the old brass cam thrust retention plate- yes the spacer was there and in good shape. I had bought a new thrust plate and never installed it, as it was on back order. The old brass one is 3.45mm while the new steel plate is just under 4mm, or ~.5mm thicker. My question after all of this is: Could the major slop in the camshaft be causing the helical cut timing gears to walk out, and slap back, making this tapping on the oilpump/distro gear? That would cause the rough idle too, since I could never get a nice smooth idle, ever. If the cam was moving around, the timing would be out every tap as well? right? One thing I didn't do was replace the small rod bushings as I had a build sheet in the car's documentation. A loose wrist pin responsible for a tap you can feel through the accel pedal would be obvious in hand, correct? No evidence of piston slap on the still-honed cyl walls.
Now that I have this thing out and apart, any suggestions are welcomed and appreciated. IS the cam end play the smoking gun?