You must also consider the upper and lower timing gear relationship and distributor gear and camshaft gear relationship when adding these thrust washers or thrust bearings. Many novice Oldsmobile engine builders take shortcuts and add only the bearing or bronze thrust washer behind the camshaft to move it forward. When the camshaft is moved forward by this method, the two gears do not mesh properly and can wear prematurely. If you maintain the OEM thrust surface location with proper machining, you should have no issues.
Thrust Washers
Competition Cams manufactures a .041-inch-thick bronze thrust washer (PN 225) that protects the engine’s camshaft thrust surface when it is not feasible to machine your block for a roller thrust bearing. You do, however, need to machine that thrust washer thickness off the thrust face of the camshaft to provide the proper alignment between the timing chain set and the distributor gear to maintain the proper lifter-to-lobe relationship. I do not recommend installing bronze thrust washers without machining the block or camshaft. This is especially critical with flat-tappet camshafts. Proper lifter rotation does not occur if the .060 lifter-to-lobe offset is not maintained.
This .041-inch-thick bronze spacer is available through many Oldsmobile vendor sources and from Comp Cams. It is always a good idea to use a thrust bearing or thrust washer to protect the front of the block from wearing.
Head Bolts
I convert from the factory 7/16-inch-diameter head bolts to 1/2-inch-diameter head bolts (or studs) whenever the customer allows. There is plenty of material in the block to do so, and this adds valuable clamping force to the 10-head bolt design, which makes this modification a no-brainer. Drilling by hand is not generally acceptable unless you’ve made a tool to keep the drill perfectly square to the deck. To do it yourself, you could make a tool that bolts to the deck of the block and allows you to drill and tap the hole absolutely straight. As long as the hole is on location and is perpendicular to the deck, it doesn’t matter if you use a hammer and a chisel to do the job. I prefer to do the job on the precision CNC milling machine, though.
Big-block Oldsmobile engine blocks are generally pretty reliable for engines making between 600 and 650 hp. After that, you should consider a bottom-end girdle. I have seen many block failures, and with a little Internet research you can find many Olds engine-block failure photos that can help you draw some of your own conclusions. Olds experts agree that the most common failures occur at the number-4 main-web areas. The use of solid motor mounts, which are fastened to the block in this area, is the leading cause for failure. All of the engine’s torque and vehicle weight is transmitted in this motor-mount area via two 7/16-inch-diameter bolts.
The use of front-mounted motor plates and rubber mounts with engine torque limiters should help. The main reason for the failure is the design of the block. There is simply not enough material in critical areas to hold the crankshaft in place and resist block flexing. A number of girdles from different manufacturers can stiffen the block. Some of these girdle manufacturers made them at one time and do not make them anymore, some have them in stock, and some are made only to order.
These girdles all have a slightly different design. These main girdles have been available through such companies as Mondello Performance, Product Engineering, J&S Machine, Rocket Racing, Product Engineering, Dick Miller Racing, Jeff Smith Racing, and Noel Engineering. The goal of these girdles is to reduce block flex and keep the oil-pan rails from spreading due to the thin main webs.
The first type of girdle, the “halo” girdle, is available through both Dick Miller Racing and J&S Machine and bolts onto the block with very little (if any) modifications to block or oil pan, unlike the so-called pan rail-type girdles. It bolts on top of the numbers-1 to -4 main caps and ties them together. Most 403-ci-engine enthusiasts use this style of girdle for ease of installation and cost. I have seen many 403 engines destroyed due to block breakage, but fewer if the halo girdle had been installed on them. I consider this modification cheap insurance for these engines.
To determine if an engine block has siamesed cylinders, look through the freeze plug holes to see if the cylinders are connected. A standard non-siamesed block has a space between the cylinders to allow coolant to pass through.
The Program Engineering girdle (shown) uses steel inner caps, but my preference is the stock caps with a billet girdle surrounding the three main caps and tying everything together.
The Noel Engineering girdle is the strongest girdle made for an Oldsmobile engine. Notice the keyed main caps. Once this whole thing is bolted together, the block and the caps cannot move in any direction. The quality of these girdles is impeccable. Quite a bit of time is involved in making them and they are not cheap, but if you want the best, this is it.
The Noel Engineering girdle has cross-bolted mains, and the 3/4-inch-thick girdle pan rails are torqued to the engine-block pan rails with a nut and stud in every bolt hole. These are the strongest of all the girdles, but unfortunately, there were only a few made, due to the expense in small-run manufacturing.
Jeff Smith made only a few girdles, but the design worked well and is a proven piece.
This is the beginning stage of the BTR one-piece billet engine-block girdle. It starts out as a 150-pound piece of steel; when finished it weighs a mere 18 pounds.
The second category of block girdle is a one-piece unit, either manufactured from a single piece of billet or a series of welded-together parts to make it a one-piece unit. This girdle bolts to the oil pan rails of the block and the girdle material ties the two rails together by crossing over the main caps and tying everything together. Many 800- to 900-hp Olds engines have successfully used this style of girdle. These have been made through Jeff Smith Racing, BTR Performance, Rocket Racing, and Mondello Performance.
The third category of girdle is a bolt-together design that is available through Product Engineering and sometimes available through Noel Engineering. The Product Engineering girdle kit comes supplied with steel main caps for numbers-1 to -4, pan rails, and fasteners. The pan rails bolt in place and bolt into the -1 to -4 main caps through the side. The girdle sold by Noel Engineering is a little more sophisticated. It is installed in the same manner, but the supplied main caps are tightly keyed and bolted to the pan rail sections. I think this is the