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B20 tapping update - cam endplay?

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:
  • 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,
Installed everything, ran the car in per the break in recommended all over the web, 20 minutes at 2000-3000 rpm, etc. Zinc additives, etc etc.

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? :-(
 
Camshaft end float is 0.020-0.060 mm or 0.0008-0.0024".

A dial indicator is the easiest way to accurately measure clearances this small.

However, if you feel that is has obviously more end float with your old thrust plate, try the new one and see if it obviously tighter.

Did you check the end float on the distributor/oil pump drive gear?
 
Camshaft end float is 0.020-0.060 mm or 0.0008-0.0024".

A dial indicator is the easiest way to accurately measure clearances this small.

However, if you feel that is has obviously more end float with your old thrust plate, try the new one and see if it obviously tighter.

Did you check the end float on the distributor/oil pump drive gear?

Haven't tried that yet. In another post, I was asking about how it all fits together. I think I figured it out, but with the new plate, there is zero clearance. So, going to try to shim either the ring or the plate this weekend.
 
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