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How Not to Build a Motor
Phil Singher

Some years ago, our 122S needed a new motor. In those days, there was no World Wide Web -- in fact, I didn't know anything about personal computers except that I didn't need one. I didn't know anyone else who cared about old Volvos. In short, my knowledge and resources were limited.

What I did have was some experience, enough money, a lot of enthusiasm and an ipd catalog.

Having been taken by professional garages in the past (in fact, that's how we'd come to have this "completely rebuilt" worn-out motor in the first place), I decided to do this rebuild myself, farming out only the machine work I couldn't do at home.

As soon as I had the head off, I knew that this was no simple "hone and re-ring" job. Number one cylinder was worn oval and number three looked like it had seized at some time. The big ridges at the tops of the cylinders meant lots of wear below. I'd clearly need an overbore and new pistons.

Way back in my muscle-car days, I'd excelled at making Chevy motors run worse. I'd found that bolting a big Holley double-pumper carb on a stock motor didn't make it go any faster, it just made the gas mileage go from poor to dismal. Tossing in a big cam -- just the cam; I couldn't afford the lifters, pushrods or valve springs -- was useful mostly for bending the stock pushrods and/or snapping rocker arms in half. Several times, I ended up spending untold dollars not affording to do the job right and then paying someone else to take my botched mods back out.

I learned from these mistakes (some, anyway) and spent the next decade driving a '64 VW bus, which I steadfastly refrained from "improving" beyond putting a large sun/moon decal in the middle of the rear window (which got me stopped and searched by uniformed officers whenever they got bored, or something).

Anyway, I'd learned that performance and economy come from attention to detail and doing the job completely the first time, so, sitting down with my ipd catalog and a calculator, I carefully selected absolutely everything the motor would need. I quickly picked out modern seals to replace the old felt units, a high-flow oil pump, all the "block sundries," gasket sealer, assembly lube, red spray paint and myriad other small items. The critical decisions, of course, were which rebuild kit and cam kit to buy.

The 2-liter big bore kit was, at the time, actually less expensive than the 1.8-liter kit with pistons in conventional oversizes (and the catalog assured me that such a large overbore held up well in a rugged Volvo block), so that choice seemed obvious -- I couldn't see any downside to increasing displacement. I pondered the cam kits for a long time. Finally, remembering those snapped Chevy rockers, I opted for the relatively mild "Street Torque" kit. I felt this combination would produce lots of punch without incurring any penalties in reliability or gas mileage. I was sure our old B18 would perform at least as well as a stock B20; probably better.

In some ways, everything turned out great. The rebuild went quite smoothly and I was proud of the resulting motor for years. It's still running reliably 80,000 miles later. But, knowing what I know now, I would never build a similar motor again.

What's wrong with it? Same as with the Chevy motors: I picked the wrong combination of parts and I didn't do the complete job. That's my fault, not ipd's. In fact, in those days, were it not for ipd, I would never have been able to rebuild the motor myself at all -- I could have been suckered by another shyster garage, I could have grown disgusted with the whole Volvo thing and you wouldn't be reading this. I'm not saying their stuff doesn't work if it's put together right.

The first problem surfaced at the machine shop, where I'd put in a lot of effort convincing them that it's perfectly fine to do a huge overbore on an old B18 block. This is not cheap -- they have to bore the block .060" three separate times and then take another pass to get it all the way out to .187" over, and they're going to charge for that. The old block, however, didn't believe my repeated assurances and went to scrap on the final pass when the boring machine cut into a flaw in the casting, opening a hole from the cylinder wall into the water jacket. I then had no choice but to find and buy another block for a second try.

I've since learned that such voids are not uncommon in the earlier B18 blocks. Volvo improved its casting process over the years and the later B18s (identifiable by tapped holes for alternator mountings and A/C brackets) are much safer to overbore. My second block was still the early style, but we were lucky with it.

The second problem appeared as soon as I started this shiny red, brand new, balanced to a gnat's eyeball, supposedly high performance motor -- it was enormously picky to tune. I rejetted its downdraft Weber carb, messed with the valve lash and played with the ignition timing a lot, eventually experimenting with several different models of distributor. After weeks of work in these areas and a trip to the muffler shop for a bigger exhaust system, it felt pretty punchy and made a fine, snarly sound. I declared it ready to go and a job well done.

I guessed I could live with some minor flaws. It always detonated a little until fully warmed up. No matter what distributor was in it or how I tinkered the advance curve, it pinged under load at low rpm. There was an annoying vibration between 3000 and 3500 rpm. It got 23 miles per gallon (running on the top fuel grade available, of course). And, most embarrassingly, it ran on (Dieseled) alarmingly half the time it was shut down, hot or cold, rain or shine.

All of these bad manners are the price one pays for high performance, I supposed, and the car obviously ran much better than it had with a worn-out B18. There was a powerful psychological factor at work as well -- I had built this motor with all the care I knew how to give it, I had bought parts from an outfit that knows its stuff, I had spent lots of money and many hours of work. It must be good!

Well, no. I gradually began finding the performance less and less satisfying; so gradually, in fact, that I was never sure if I was just getting jaded, or if the performance was actually deteriorating. At one point, I decided it was the latter -- just after I mounted a tach in the car and discovered the thing wouldn't rev much over 4000 rpm. Surely, I'd been able to hit 6000 a few weeks earlier! Or?

As learned more about what makes makes motors run right and what doesn't, I changed my mind. This motor runs pretty much like it always has; it's my expectations that have changed, particularly now that I've put our 1800S into sound driving condition. That one's motor is a completely stock B18B, Volvo's factory high performance motor of the day. Guess which motor makes more power: the unmodified 1.8-liter at 6000+ rpm, or my home-grown 2-liter at 4200 rpm? Guess which one idles smoothly, doesn't vibrate, and doesn't detonate, ping or run on? Correct the first time.

What part of the job had I inadvertently left undone? A big overbore should be accompanied by custom head work and all I'd had done was a regular valve job. Why should it? Because the B18 head and B18 combustion chambers were carefully engineered to match the B18 bore. The shape of combustion chambers is critical in controlling burn characteristics, resisting detonation and pinging while translating the chemical energy in the fuel into kinetic energy in the pistons (we're talking "squish" and "quench" here). What had changed?

A major factor in determining compression ratio is the area of cylinder wall swept by the pistons on each stroke. The swept area rises steeply with an increase in piston diameter -- long story short, the big bore pistons jam an increased volume of gas into the old combustion chambers. The B18 big bore kits therefore come with thick head gaskets (.080" vs. .050") to keep the compression within reasonable limits, effectively increasing the volume of the chambers by making them taller. This results in chambers not only too narrow for the bore, but also too far away from the pistons. The effect is, predictably, detonation, pinging and (at least, it's my explanation for) a tendency to run on -- the liabilities of high compression with none of the performance benefits that might come from actually having it.

A note here: Various parts suppliers and engine builders favor using thick head gaskets, even in stock rebuilds. The thinking is that it's necessary to lower compression to accommodate today's lower-octane fuel. It's the wrong way to do it, if it is indeed necessary at all. Resist.

Another mistake was in my choice of cam. The B18 head has ports and intake valves that are suited to flow the volume of air B18-sized pistons will pump. The dynamics of this are way beyond the scope of this story, so let's just leave it for now by saying such a head on a 2-liter block is restrictive at higher rpm. What's necessary to compensate (somewhat) is to hold the valves open longer -- increased duration. Opening them wider -- increased lift -- does little to boost the airflow (picture running water through a garden hose -- there comes a point where opening the tap wider has no effect). I picked a cam that has a lot more lift than stock, but no more duration than Volvo's lowest-performance cam; useful in some applications, but practically useless in mine.

Because of the steep slope of the ramps on the cam, the valves open and close at higher-than-stock velocities for any given rpm. There's also a higher-than-stock parasitic load on the motor just in compressing the double-wound valve springs that come with the kit, which are theoretically necessary to snap the valves shut again at that high speed. I use the word "theoretically" because, as the motor only spins up to 4200 rpm anyway, the valves never actually reach a velocity that requires the special springs.

There are also lesser problems with rocker arm geometry, as the whole head (and therefore the rocker assembly) sits .030" higher than usual on the thick head gasket -- the rockers can't deliver the full lift designed into the cam (whether it would do this particular motor any good or not) and more parasitic power loss (and increased wear) from side loading in the valve guides.

Something that did make me happy was how strong the motor pulls around 3000 rpm. Velocity of the gas entering the intake valves is a major factor in performance, and, over a certain rpm range, the suction of the big pistons and small ports does produce fast airflow (with increasing rpm, this is negated by other factors). But I've got another modification going that works against this benefit: the downdraft Weber. Because the airflow has to make a right-angle turn entering the manifold, turbulence is created that limits the velocity achievable. This is why side-draft carbs -- even plain old SUs -- offer inherently higher performance for in-line motors; the gases get a straight shot at the intake valves with a minimum or roiling around.

None of this is ipd's fault. The B18 big bore kit is the same as the perfectly legitimate B20 rebuild kit except for the thick head gasket that makes it possible to install it into a B18 -- whether that's a good idea or not is up to you and me. The B20 big bore kit (to 2130cc) is inherently less problematic, requiring a smaller overbore and a head gasket that's only .010" thicker.

So, with the best of intentions and the knowledge I had at the time, I made some dumb choices. What would have been smarter to do on a similar budget?

1) Go with .030"-over pistons (or the minimum necessary to clean up the cylinders), thereby minimizing the combustion chamber mismatch. If you want a 2-liter motor, rebuild a B20.

2) Take the money you didn't spend on extra overboring and put it into some basic head work. Have the combustion chambers matched, have the obvious turbulence-inducing obstructions in the ports ground out (enlarging the ports further requires an experienced Volvo engine builder, but any decent machine shop should be able to do the basic work safely). Install bronze valve guides. There's more performance to be had from this than from increasing displacement 200cc.

3) Now, with deck height and combustion chamber volume known, select a head gasket of whatever thickness you need to get the compression ratio you want. This is the only sure way of knowing what the compression ratio will be. Custom gaskets are available and not particularly expensive.

4) Select a cam that matches the displacement, head and intended use of the car. With a Volvo "C" cam and 10:1 compression, the later B18Bs were rated at 115 hp (SAE) -- considerably more performance than our old 122's B18D at 90 hp -- yet perfectly tractable and undemanding in daily use. The "D" cam is burlier yet. Neither requires special valve springs. In a B20 motor, the ipd "Street Performance" cam (Isky VV71) has made many people happy.

(If you have a little money left over, you're not limited to these archaic cam grinds. Unlike here, Europeans have continued to develop cams for OHV Volvo motors -- they cost more, but it's worth pointing out that many other options do exist.)

5) Freshen up the old SUs, fit them with needles to match the mods you made (or didn't make) and pocket the $150 or so you saved by reworking those instead of buying a Weber kit.

I'm soon going to replace the old motor I built, but -- for all its flaws -- it's not junk, either. The bottom end is now functionally a stock B20, it's balanced and it shouldn't have much wear on it. I've got a B20 head to work up that will match it properly. With a different cam and SU carbs (or maybe D-Jet?), it will again see service for many more miles.

And that's how we learn, isn't it?

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