Project 350/351 engine: Part 5 - 350 Chev

By: Guy Allen, Photography by: Andrew Britten

Date: 14.10.2013

Chevrolet 350 small-block engine

Part 5: Our giveway 350 Chev engine is looking like a bought one now it's been through the final act of assembly - here we track how it all came together

Chevrolet 350 small-block engine

Project 350/351 engine: Part 5 - 350 Chev

FINAL ACT

After what seems like a phenomenal amount of work, we’re finally ready to bolt together our 350ci Chev engine. While the base design is older than a lot of the people driving them, this example is essentially brand new, with some important updates to areas such as crankshaft, camshaft, pistons (Hypatec) and heads (now alloy Precision items). There are also some familiar names, such as Edelbrock and Holley, thrown into the build mix.

Various components have been measured, balanced and machined (see UC issues 350 and 352), so now it’s time to sling it all together. Actually, ‘sling’ isn’t exactly the right term. Wander over to the bench being used by Sean Griffioen at Top Torque and you’ll see it could double as an operating table.

So, where do we start? "We put the bearings in the block and the caps," explains Sean. "We check all the clearances to the crankshaft and make sure they’re all correct and don’t need adjusting. We fit the rear main seal, put our assembly lube in there and drop our crank in. We put our main caps on and tension them. We don’t shim crankshafts anymore; if there’s an issue we either line-hone or grind the crankshaft to suit.

"Next up are the piston ring gaps. We put them in the bores, check our gaps, and put the rings on the pistons." Why so much emphasis on the ring gaps? "The ring expands in the cylinder as the engine heats up. If the ring gap is not correct the ring can butt-up and seize in the bore. On the other side if the gap is too high, that’s when you get blow-by into the crankcase, oil leaks and all sorts of horrible issues."

Part of getting that right is accurate boring equipment, which Top Toque has in-house. Are consistent bores important? "Absolutely, it’s critical for any motor. We always make sure our tolerances are the same regardless of whether it’s an early engine or a later, technically-advanced performance engine.

"Correct tolerances make the engine a better package and you’re giving it the best shot at life that you can. If it’s got excessive clearances, it’s already half worn-out."

Fitting up the piston and rod package is the next step and here, a lot of prep work has been done. "We balance everything – pistons, conrods, the crankshaft, our flex plate and our harmonic balancer. This doesn’t give any more power, but it makes the engine run smoother and makes it wear evenly, so you’re not getting one bearing copping a harder time than another.

"We put our camshaft in, set up the timing and then dial it in so we get as much out of it as we can. Essentially we’re checking to make sure it’s right and adjust with the gearset to the specs provided by the maker," says Sean.

"Your engine will still run if it’s not quite right, but by the same token you’re not getting the absolute best out of it." The model we’ve gone for is a middle-ofthe-road grind, aimed at a lively end result nearing the 350-400bhp mark.

"It’s still a fairly streetable engine," Sean says. "Nothing that’s too wild or going to shake the engine out of the car."

Across the bench, the new alloy cylinder heads are ready to go. It seems like a shame to fit them, as they’re beautifully finished. "We fit the gaskets, lube the bolts and bolt them down to the correct torque," explains Sean. "Once the heads are down we set up the rockers and check the rocker ratio and rocker swipe to make sure it’s not hammering out a valve." Essentially Sean and his crew are ensuring the rocker is hitting the valve ‘square’ to avoid early wear such as worn guides.

"We mark the top of the rocker and turn the engine over, making sure the rocker is sitting centrally on the valve, so it’s not pulling it out of or into the engine. That stops the guides from wearing out and make sure it’s actuating properly."

By this stage we’re on the home stretch and the plot has taken a recognisable shape. Now we’re gathering up the tinware, which Sean happily describes as "all the nice shiny parts such as the rocker covers, timing cover and sump. We dress the engine, make it look smart".

Capping off the powerplant is the carburettor. All too often we hear of people fitting giant carbs to their engines, wrongly assuming that bigger always means more punch. It ain’t necessarily so. "We’ve gone for a Holley 650," says Sean, "which is a good-sized carb for the power the engine will produce. It still leaves a little flexibility if someone wants to go a little further with
the performance."

It seems simple enough when you watch an expert at work, but how about an engine assembly ‘top tip’ for us mere ASSEMBLY IS one thing, what about the all-important test and run-in period?

The good folk at Top Torque are running in and testing new and rebuilt powerplants all the time, so how do they go about it? "We put a zinc additive in it and fill it with coolant and oil, warm it up and run the engine for 20 minutes at 2500rpm to run the camshaft in. During that time you’re checking the oil and water pressures and everything else to make sure you’re on the money.

"From there they [the owners] run the car to 500km and then give it an oil and filter change. Over this period, don’t drive it like you stole it and don’t drive it like your Grandma. That’s my
advice to everyone.

"The engine is built to work but it’s not ready to race. At 500km we go over everything, pressure test the cooling system, check the mounts are all in place, pull the plugs out and make sure they’re looking good. If it’s okay, we send it out for the rest of its life."

RUNNING IN

Assembly is one thing, what about the all-important test and run-in period?

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