Tuesday, May 29, 2007
AV -- PULLING THE PLUG II
Back in the Day, send a VW crankcase to Jack Riddle’s shop (aka Riddle Machine Company or ‘RIMCO’) for an align-bore or other machine work and it would come back with the some of the gallery plugs pulled & threaded for pipe-plugs, which were included with the returned case.
Why? According to Jack, machining caused swarf to get into the oil galleries and it was impossible to clean them out unless you pulled the plugs.
Which sounds perfectly logical, especially to any experienced mechanic or automotive machinist because seeing oil galleries sealed with pipe plugs is a familiar sight to anyone who has worked on aircraft engines or big V8's. And removing those plugs is a normal procedure in order to clean the oil galleries during overhaul. So pulling the plugs becomes a standard part of building a high-performance engine based on VW after-market components. Your engines run sweet, your customers are happy and those mysterious bearing failures become a thing of the past.
Not so with the shade-tree types, for whom pulling the plugs is another of those ‘unimportant’ details. Lotsa folks still don’t pull the plugs, especially on a new crankcase. Their logic goes something like this: New crankcase has never had any oil in the galleries so there’s nothing for the swarf to cling to; that a blast of compressed air is enough to clean everything up. And about here it might be a good idea to go read...
Starting about 1997 professional engine-builders here in southern California began seeing Brazilian crankcases in which the oil gallery for the #4 main bearing was blocked by the factory-installed plug. Which wasn’t a problem because we routinely pulled the plugs... which was how the problem came to light. Nor was it much of a problem to the dune-buggy crowd, folks who routinely did not pull the plugs. After all, the #4 main wasn’t a real main bearing - - it was added when VW found the asymmetric load of the blower caused the pulley to oval-out the nose of the crankcase. In most cases the blockage wasn’t 100% and the #4 usually got enough oil for passenger-car service. But complaints were heard now & then from the dune-buggy set who came up with an Idiot-Fix: running a 7/32" drill down the oil gallery for #4. Sometimes it even worked :-)
But it was a problem for flying Volkswagens, especially those who put the prop on the wrong end of the engine, which back then was virtually everyone. Here’s what Steve Bennett has to say about the problem...
Read both of the above articles and you’ll note significant differences in our methods; Steve drills-out the offending plug whereas I pull it out - - along with three others of that size. Steve threads the bore to accept a 1/8-NPT socket-head pipe-plug whereas I used whatever is available, my preference being 1/16-NPT pipe plugs.
The VW engine uses four 5mm plugs; one for the #4 bearing, two for the oil galleries feeding the lifters and one for the oil gallery going to the reservoir(s) behind #2 cam bearing shells. I’ve never found a long plug anywhere except on the #4 gallery but other engine builders have said they’ve seen them installed at the other three locations, sometimes with catastrophic results. A long plug won’t cause a problem with the lifter galleries but even a partial blockage of oil to the reservoirs behind the #2 cam bearing shells guarantees the engine will have a short, unhappy life, since that single 5mm gallery is how oil gets to all eight of the lifters and through them, to the heads.