Fresh B20 engine tapping mystery

Dial caliper - as in vernier caliper with a dial? Requires a super steady hand! A dial gauge on a magnetic base will give more consistent measurements of valve lift. Measuring movement off the top of the retainer incorporates the effect of rocker ratio and cam lift. Measuring direct pushrod movement eliminates rocker ratio; but, is exceedingly hard to do as the pushrod has to remain centered during the measurement.

Adjusting your valves so that the clearance variation is within 0.01" is too much. You will not get an accurate measurement of the variance in valve lift. Stock total valve clearance is around 0.02" (depends on which engine / cam) and you should be doing a go / no go measurement setting the clearance to within 0 to + 0.002" of whatever the clearance recommendation is for your cam. To help get a more accurate lift measurement, you can zero out the lash on each cylinder (at TDC firing) just for measurement purposes - takes the variance in valve clearance out of the lift measurement.

Volvo B18 / B20 rockers purportedly have a reputation for variance in the effective rocker ratio. I measured valve lift on a fresh B20E rebuild (D cam with stock springs) with the original rocker faces resurfaced to remove the wear grooves. The valve lift variance from the average lift was -1.7% to +2.1%. This is a combination of rocker ratio variance, cam lobe variance and measuring error. My take was that the variation in rocker ratio is perhaps a bit overplayed, or I lucked out and got a good production run (I think not). They do have a deserved reputation for having a rocker ratio that is uniformly less than the claimed ratio of 1.5 (mine are closer to around 1.4).

Your valve lift variance is around +/- 8% from average. The internet wisdom says that the Volvo B series rocker ratios can have a very large variance. However, based upon my experience you would have had incredibly bad luck in order to get a batch of rockers with rocker ratios that far out. I think the rocker lift variance is oversold which kind of leaves the cam as the culprit. However, I would do a more accurate valve lift measurements before jumping to the conclusion that the cam is toast. Also, even if the cam is wearing, if you have reset the valve clearances the noise should go away until the cam wears and the clearances open up again.

Finally, your average valve lift is around 0.40". Is that what the cam spec sheet says the lift should be with the stock rockers? If the spec sheet says the lift should be more, then the cam probably is definitely toast. If 0.40" is the correct lift, then why would you bother putting in double valve springs? The stock D cam has a 'rated' valve lift of 0.42" with a 1.5 rocker ratio and works satisfactorily with the stock single springs (as long as you retain the OEM red line). Higher effective spring rates just increase wear and parasitic losses. If you do compare the actual lift with the spec sheet lift, take consideration of the fact that your rocker ratio is probably less than the commonly assumed value of 1.5.

sksmith said:

Cam / lifter break-in on flat tappet cams can be hard on the cam with heavy-duty or double springs. Hope that's not your case.

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This. Those lifters are solid. They need a liberal coat of moly assembly lube and break-in oil with moly.
New cams can flatten a lobe in <100 miles.
Put a dial gauge on the rockers and see if the lift at the valve is consistent.

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smncutler said:

Bump. Did OP reach a diagnosis?

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Yes. After all of the diagnosis coming up empty, I pulled the whole motor. Really had no choice. It was just too noisy and I’d never feel ok driving anything with a persistent knock like that. Saw almost no measurable wear anywhere in the motor during the second rebuild - except - excessive play in the cam/timing pinion retention plate. I had the original brass(?) plate, and I used he PO’s old metal timing gear set. The brass plate was badly gouged! There was ~4mm (if I remember correctly) of lash or slop in the cam assembly when fully torqued. You could manually pull and push the cam and hear a nice crisp *TAP*. You could not only hear and feel the lash, you could pull the cam forward and clearly see it move slightly out of plane with the timing gear.

My advice: if you have exhausted all other options, you could attempt to pull the timing cover off and try to nudge the cam forward and back. Maybe even try it through the fuel pump port.

My friend was still puzzled though. Even if there is excessive play, there should be no longitudinal forces pushing + pulling on the cam per-revolution. The play should not cause a persistent tap every single revolution? Right? BUT.. the PO, or his rebuilder, must have 'manually milled' the pinion gear's shoulder to 'flat'. Like with a file or belt sander. Yeah. So, it's shoulder wasn't perfectly flat. It would act like a cam itself, or a little ramp, and move the whole cam in and out -and on every turn of course. I took it to a machinist and had it properly flattened. Then dialed in the lash with some shim stock behind the ring spacer on the cam to within spec.

Why did I reuse that old plate and not buy a nice, new hardened plate from IPD? And just not be a cheap SOB and spring for new timing gears? I don’t know. I did put in a new hardened plate, however.

That was it though, nice quiet b20 now.

Congrats!

JohnMc said:

-Another thing that can make nasty tapping noises that are vaguely valvetrain related is too much gap at the cam thrust plate. There's a spacer between the cam snout and the cam gear, when the gear is tightened down it's supposed to leave a few thou's worth of clearance on the cam thrust bearing. If the thrust plate is too thin, or the spacer is too thick, or the cam gear isn't snugged down onto it, then the cam can slop back and forth in the block, making a somewhat deeper clacking noise. This generally quiets down at higher RPM's when the cam gear gets into a most steady pull torque (oil pump drag?) and isn't pushed forward by the lifters passing TDC on the lobes. You can most easily check this by taking the fuel pump cover plate (or fuel pump) off and seeing if the cam has any side to side movement when you briefly run the motor.

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Nailed it! Post #14.

The cam does not always have consistent torque. It gets pushed forward by he valve springs as the lobes pass TDC, especially at lower RPM's. This back and forth torque working against the angled gear teeth makes the cam push forward and backward, and really makes any slack on that thrust plate noticeable.

JohnMc said:

Congrats!



Nailed it! Post #14.

The cam does not always have consistent torque. It gets pushed forward by he valve springs as the lobes pass TDC, especially at lower RPM's. This back and forth torque working against the angled gear teeth makes the cam push forward and backward, and really makes any slack on that thrust plate noticeable.

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Yep.. exactly correct, he nailed it. I did try this maneuver at first - through the fuel pump port, but not with it running. And, of course, I didn't take into account that the cam was under tension by the valve train, so it didn't move easily. Had I just tinkered a bit more and loosened the rockers... Also, I stubbornly couldn't allow myself to believe that it could be this- since I could 'feel' it up top in the head. Must have set the valves 10 times. In either case, it had to come out to fix it.

As you can see, the answer was here all along.

JohnMc said:

Some spitball idears:

-Another thing that can make nasty tapping noises that are vaguely valvetrain related is too much gap at the cam thrust plate. There's a spacer between the cam snout and the cam gear, when the gear is tightened down it's supposed to leave a few thou's worth of clearance on the cam thrust bearing. If the thrust plate is too thin, or the spacer is too thick, or the cam gear isn't snugged down onto it, then the cam can slop back and forth in the block, making a somewhat deeper clacking noise. This generally quiets down at higher RPM's when the cam gear gets into a most steady pull torque (oil pump drag?) and isn't pushed forward by the lifters passing TDC on the lobes. You can most easily check this by taking the fuel pump cover plate (or fuel pump) off and seeing if the cam has any side to side movement when you briefly run the motor.

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John.. this was it. Hat's off to you.

Your headache will save some one from one.