[T2] engine oil pump / second oil cooler , engine improvement

[John Anderson]

I've been lingering on this one, but really figure I'd finally chime in.  Several comments.
 
First, the stock T4, unworn moves plenty of oil.  Like plenty of oil to support the 2.4 liter race engines I used to build for my buddies 914 autocrosser, pumping to a BIG front mounted oil cooler, even when the cases were getting on the loose end, even to some degree under cornering and intermittent starvation (that even with the stock 914 baffle plate) until we went dry sumped.  But it moves plenty of oil, if you can get it to the pickup, which in a bus usually isn't an issue.
 
Now the "unworn" is the key.  But most T4 (heck even a lot of T1) oil pumps, are pretty unworn, even the used T4 pumps still poking around in service in 2013.  The thing about the T4 pump that makes it annoying is that it can only be "rebuilt" or "blueprinted" so far.  I have no idea about the guy providing the "rebuild" service for $100, and all in all I'd say that if he puts 1 hour labor into your pump, it is money well spent.  But I would say, there isn't much to do in this pump.  The only thing you really can do is press out the stationary stud, and hone the intermediate plate or whatever you want to call the inner part of the thing just like you'd hone the cover on a T1 pump.  Do that at home if you like.  Use some red Loctite or peen the stud on re-assembly if it is a deep one, if short one, just the loctite.  I guess he might hone or lap the face bored into the pump body (the outside part) itself but if he does, god bless him, that is
 pretty tricky...  But a little end wear there doesn't really matter if you cleaned up the other side nice and flat.  The wear, where it matters, the gears and cylindrical surfaces, they are what they are, no one can do anything to improve that, you can follow Wilson's advice on looking at the gears.  I presume if it is too worn, the guy just rejects it for "rebuild" but then again, unless real abused, they don't wear that much.  I always clean up the intermediate carrier and blueprint the inlet and outlet on a stock pump.  As long as the gears have just a light burnish on them, and nothing ANYWHERE near what you could nearly catch with a fingernail, it will make plenty of pressure and volume.
 
The Melling iron pump.  Long rumored to be so bad because the iron body.  I've never seen one leak, and I've seen more of em than most casual bus owners.  YMMV, conventional wisdom say they do all the time.  If they do, I'd lay odds it is more often the long known issues that pump bodies are often machined too small (and less so in the T4 that the case has worn too large) than it is the differential expansion rates.  I don't like putting iron adjacent aluminum though, and there are other solutions just as cheap, so I don't know it adds anything, other than the fact, that most of the time with most cam gears, it probably fits and works.  I guess also on a positive note I think the Melling (at least back in the day) was made with better tolerance on the OD than many aluminum pumps.
 
Which leads us to what most people, Raby included have done for years.  Use a good quality OEM aluminum T1 pump.  The trick here where it gets tricky is the current world of aftermarket cam gears.  Back in the day, aircooled.net sold a nice OEM pump, I think a 26mm gear, where it was clearanced to work with a stocker, and perhaps a WebCam gear.  They also supplied a cover clearanced not to hit anything.  I don't think they sell it anymore.   Hell even a stock T4 pump doesn't always clear an aftermarket gear (sometimes the cam bolts rub the studs holding the pump together.)  So when you build it, you got to try it, then ideally you got to silly putty it, then you got to try it some more.  You have to assure that there is good clearance when you rotate all parts held towards each other.  You may have to clearance the cover depending on the style and the thickness of the pump (height of gears) you select.  You just have to assure that it works,
 before you bolt it together.  It is also why one really can't swap out an oil pump with unknown cam gear selection in situ, without pulling apart an engine.  But then again the chances of needing to do that (of oil pump wear being a reason for low oil pressure in itself) are again pretty damn low in an engine that would otherwise still be a runner.
 
Anyway makes me glad I bought 5-6 stockers NOS about 10 years ago at $50 each, cause most of the time they work still, but there is nothing hard about making sure a T1 pump fits, just takes 20-30 minutes on engine assembly.
 
John