Engine and Transmission Tech

Today we started up and the new 4.0 in my buddies car. About 2 to 3 minutes after initial start up, the carb backfired and the engine shut off suddenly. After a couple of cranks, it was obvious there was no spark. Checked all the wires, coil, etc. All looked good. Removed the dist cap and cranked the starter, no rotation of the rotor. Pulled the dizzy and the drive gear stayed inside the cover. Close inspection revealed that the roll pin had sheared. Luckily I was able to pull the gear out with a pair of long reach needle nose pliers. I grabbed a spare gear and roll pin to compare and saw that the sheared roll pin was much smaller than the ones I have always used in the Rovers before. The distributor was a Mallory Unilite. The new 4.0 got a Buick 215 timing cover with the larger gear kit. I can only assume that the force required to turn the bigger gears, cold 20/50 oil and all of the petroleum jelly in the pump for initial priming was too much for the little roll pin. The pump gear spun freely with a screw driver, so no binding there. Once the broken pin pieces were drifted out, I was able to drill the holes larger to accept a larger pin. Reinserted the dizzy and fired it back up. Ran it for 20 minutes at 2 grand with no more drama and shut er down. If you buy one of those aftermarket distributors, I suggest you check the roll pins. Today could have been a real bad day.

I had a related issue with a Mallory Unilite that I bought used years ago. My engine has ancient Range Rover cover with 215 type pump gears, also with bigger gears. I fitted the distributor and the engine fired right away. The thing is, there was no oil pressure at all. I checked the distributor shaft and previous owner had cut the shaft. There was no blade to drive the pump... I did not notice it at all, the dizzy looked pristine and had the correct drive gear :-) So I removed the gear, tig welded some material in the shaft, dressed it with a file and it has been running since with no problem.

The lesson I learned: do not assume, check ! (not related to your case)

For the benefit of you guys who are running the long oil pump gears, a little history may be in order. Those gears, if I remember correctly, are the ones used in the stock big block oil pump. They are 1/4" longer so they should produce about 25% more volume if all else was equal, which it is not. These longer gears are fitted by adding a pre-manufactured spacer plate to the pump body to extend the pump cavity and pinning it in place. However the gear bores must be precisely machined and the location accurately fixed to maintain the existing clearances, which is essential to obtain that flow increase without metal-to-metal contact. This is often a problem due to larger clearances in the spacer plate. Any mis-fit here can and does reduce flow considerably. The second issue is that the longer gears increase the loading on the distributor gears and the distributor gear roll pin by the same 25% and this is enough to cause pin shearing and drive gear wear. In all cases where long gears are fitted it has been found that the use of bronze drive gears is almost a necessity to reduce this wear problem, which can and has stranded quite a few drivers.

This oiling mod has a long history, as it was the first thing tried in an effort to improve bearing reliability. However more recent developments have demonstrated that far better methods are available. The Buick small block has a 50 year history of oiling system improvements and these encompass almost every single improvement imaginable. From those wide ranging efforts over the years the best options have been distilled out to the point where today we understand the SBB oiling system like it has never been understood before, and a list of well established and proven methods now have an established track record. Extended oil pump gears are no longer on that list and they have not been there for at least a decade and perhaps two or three, depending on who you talk to. The reason is that better and more effective methods exist.

The list starts with the most basic modification, replacing the oil pickup with the 5/8" tube pickup from the later V6 engine, and continues through oil galley modification and proper bearing setup. This is where the properly set up SBB truly begins and since all Rovers are at heart SBB derivatives it applies equally well. I cannot emphasize this point too strongly, Buick engines run tight oil clearances. If you don't believe it spend a little time studying factory bearing specs. Main bearings, rod bearings, cam bearings, rocker shafts, and lifter bore clearances. Buicks run tight clearances! If you overlook this one detail you have already lost the game and no band-aid on the pump is going to fix it for long.

Obviously to run tight clearances your geometry must be correct but this should not be a problem with today's methods. Bear in mind that as little as .0005" extra clearance will exponentially increase the oil flow through a bearing. Also, wear is diminished with closer fits. Experience has taught us that with proper fits and clearances the stock oil pump gears are quite adequate for even extreme applications. For performance oriented builds or for increased reliability in street engines further modifications are encouraged. First among these is the use of a so called "booster plate". Externally these look similar to the spacer plate used with extended gears but the differences are very significant. The plate is of steel rather than aluminum and it is not machined for gear cavities. Instead it provides a new end wear surface for the gears, aids in setting up gear end clearance (a very critical dimension and one which should be set as tight as possible without producing excess drag), and by several accounts most importantly, stabilizes the pump cavity to reduce bypass flow around the gears. Pump gear end clearance on the order of .0005" or less is not uncommon and as the body is aluminum whereas the gears are steel this clearance will increase slightly as the parts warm up.

Next is enlarging the pump pickup galley through the block. This is enlarged using a long step drill from the nominal 1/2" size up to 5/8" and can be done without tearing the engine down and even with it in the car. Any competent machinist can make this drill from a standard 5/8" drill bit in fairly short order, or it can be purchased or in some cases borrowed. Finally, the passages are ported at all points of flow changes, particularly bends, junctions, and passages within the pump and timing cover. One further modification is to fit a special double groove bearing as the front cam bearing. This allows full oil flow around the bearing to the far side lifters and rocker shaft, as well as in some of the iron block engines feeding one of the main bearings.

These are the primary state-of-the-art recommended oiling system modifications, incorporating 50 years of improvements. A few variations exist such as redrilling cam oiling passages to put oiling at or near 3 o'clock but those are getting into the realm of diminishing returns and are not really something that the average builder will consider necessary or worth doing. But the foregoing mods are those which can be done on any engine, and should be done on any but the most basic low output commuter if the engine is to see any hard usage at all. The most important point I can make is that the correct oil clearances used throughout the engine do reduce the oil flow requirement to the point that the stock pump can easily supply the needed volume and pressure. Enlarging the pickup passages insures that the pump is not "sucking air" or cavitating. Even if all the above mods are not included the pump and pickup mods should still be done and the porting is easily done and highly recommended.

For those with the extended pump, it is difficult to go back without a complete teardown and bearing re-fit as often these engines were set up loose to begin with, but the extra capacity and heavier weight oil usually suffices for a time. A bronze gear on the distributor would be useful insurance though.

JB



Edited 1 time(s). Last edit at 03/28/2011 10:37AM by BlownMGB-V8.