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Discussion Starter #1
I am in the home stretch of a complete 'resto-mod' on a 1971 142E. I was finishing up the complete rebuild of the engine and was checking the gross lift on the valves. The gross lift (measured at the valve spring retainer) varied between 0.397" and 0.403". I expect (hope) that a lot of the variation was due to problems with getting the dial gauge lined up perfectly with the axis of the valve. There is not a lot of flat surface area for mounting the magnetic base which holds the dial gauge. I did have one valve (#2 Ex) where the gross lift measured out at 0.413" (I repeated the measurement a couple of times getting results with +/- 0.002").

Before I get to my questions, some related details on the rebuild.
- New Volvo D camshaft
- New IPD lifters and push rods
- Rocker faces were ground to remove the wear groove from valve actuation
- Valve clearances were set to factory (cold) settings

The Volvo green shop manual does not provide any lift specifications for the D camshaft or specs for the rocker ratio. An item that I found on the 1800philes forum indicated that the D cam would have a gross valve lift of 0.42" with a rocker ratio of 1.5. I didn't check the cam circles before I installed the camshaft so I don't know what the actual 'lift' on the cam is. I attempted to make a crude measure of lift at the top of the push rod and I estimate that my rocker ratio is more like 1.45 (except for that odd man out with the gross lift of 0.413"). I have found references to rocker ratios of both 1.45 and 1.5 for the B20 engine.

Now my questions:
  1. Does anybody know what the lift ratio is supposed to be on the B20 rocker arms, or conversely, what the gross valve lift should be with the D camshaft and stock rockers?
  2. Any guidelines on what is a reasonable variation in the lift ratio for B20 rocker arms (or what is a reasonable variation between the gross lifts measured at the valves)?
  3. While checking around, I only found KG Trimning offering up an alternative to the stock B20 rockers (VPD is not an option). Does anybody have experience with their rockers? Are there any other alternatives to the B20 rockers?
  4. If the variation in the gross lift is excessive, is anybody aware of a machine shop with a proven track record in re-profiling the B20 rockers to provide a consistent rocker ratio (whatever it should be)?

Thanks
 

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Rocker ratio is nominally 1.5:1, but it does vary a bit from rocker to rocker. I measured an Isky-ground clone of a dealer D cam a while back, and cam lift is .290. Multiply by 1.5 and you get .435, subtract the valve lash of .016 and that gives you valve lift of .419. Be sure you are setting lash to that spec, not the .020-.022 Volvo calls out for the B20B engine.

I did have a set of rockers matched to 1.51:1 years ago, and it's not worth the trouble or expense. Even very well ported heads don't respond to lift very much, and can't really use anything over .400 on the intakes, and much less than that on the exhausts. Just adjust the lash accurately so you have the same duration on each valve, and you'll be fine.
 

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Discussion Starter #3
Thanks for the response. Cold clearance was set to 0.016" when I did the measurement. Adding the lash into the lift calculation would bring me much closer to the gross lift listed on the 1800philes web page. I had assumed that when they referred to it as valve lift it was the actual lift at the valve, not the max offset on the cam profile multiplied by the rocker ratio.

I am curious about your comment of adjusting the lash to get consistent valve opening duration. Do you use a degree wheel to confirm the opening position and duration for each of the 8 lobes? That is something that I have never bothered to check.
 

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Discussion Starter #4
While we are at it, another item that Volvo does not specify is the deck clearance. My clearance(s) measure out at 0.02" +/- .001. Any comments on what the deck clearance should be on a B20E? With my 0.030 over size pistons and a total clearance volume of 53cc, the calculated compression ratio on the engine works out at a hair over 10.5:1. I have read comments by some forum members about the benefits of reducing the clearance volume. However, that would push my CR up and I am not sure that this engine can support a much higher CR (maximum octane rating fuel that is available is 91 or 92).

Do people reduce the clearance volume below 0.02 and if so, how do they deal with the higher CR, or do they open up the combustion chamber slightly to increase the clearance volume?
 

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A small variation in lash causes more variation in valve duration than one might think, while rocker ratio has a minimal effect. If you get the lash the same on all the valves, duration will be consistent. That's a lot more important than variations in the lift.

I usually deck the block so final piston-to-head clearance is .032" at TDC. So, if you have a head gasket that crushes to .034" (which is what the current gaskets advertised at .030" thickness actually end up doing), you want the pistons .002" above the deck. Note that the piston / rod stacks will not be exactly the same length, and that the stroke may vary a bit as well (I had one crank that had .013" less stroke on one journal than the others right from the factory -- that one is scrap metal now). The only way to really get that even is to do a test assembly on the block, measure for the lowest piston, deck the block for that one and then take however many thousands are needed off the other piston crowns. This is the sort of thing blueprinting is all about.
 

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In 1967 I did my first Volvo overhaul after working on Ford Flatheads,Buicks, etc. The only pistons I could find that I could afford ($4.70) were 1/16" too tall where the head surface was flat, so I milled 'em off 0.075" in that area only. Put it back together and it ran pretty well for 40,000 miles. Then it blew up at 75 mph, filling the car with smoke, even with the windows down. My driving was mostly freeway driving and not much different from race driving (B16 engine) . Since then I have been reluctant to recommend milling tops of pistons. All 4 pistons had two cracks in them and two of them had round holes in the tops near the cracks. I sold the carcass for $175 and shortly thereafter bought my first 444 for $200. I'm afraid those days are gone for good!
 

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Discussion Starter #9
My engine is assembled; but, not back in the car. However, the only local engine shop that I would trust to do decking is fully committed supporting the local race community so I am going to pass on this (since I would like to get the car operational in this lifetime). That said, if the engine ever had to come out in the future, it is something that I might consider.

Reducing the clearance volume as you suggest would push the compression ratio on my stock combustion chambers above 11:1. Do you open up the chamber to reduce the compression ratio or have you done other chamber modifications that allow you to support a CR that high!
 

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I'm not reducing the volume beyond advertised factory specs. A B20E has 10.5:1 static CR with the pistons at zero deck and with a .030" head gasket. The way Volvo actually built them, the pistons are anywhere from .015" to .025" below the deck, and the Elring head gaskets listed for the E and F are .050"+ thick (I don't use those). I do open up the chambers, but it's to unshroud the valves rather than to reduce compression.
 
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