'78 Bus Runs Rough, Possible Vacuum Leak

[Amskeptic]

O.k. I've ordered the adapter to use my new oil pressure gauge with the 1/8-27 fitting in the M10-1.00 sender hole. I'll have to wait patiently for the mail carrier.

In addition, I bought a dial indicator and the magnetic holder gizzie so I can measure my end play. I seem to recall reading that you can measure end play with the engine in the bus by simply pushing (with all your might) on the fan hub, set your dial indicator and then push the clutch in. Did I dream this? I even seem to think it was Colin that wrote that, but I can't swear to it and hope he won't sue me for slander. Author aside, does this sound like a reasonable way to get a ballpark end play measurement?

Your leakdown test suggests a tired engine. The endplay measurement via the fan pulley is a decent diagnostic aid. I think you get a better sense of the endplay with the alternator belt off. It does not take a massive shove to move the crank back and forth, but there is a little twist action that helps the crank move forward. Then get a screwdriver and pry the pulley back using the fan housing as a fulcrum. Do it several thousand times and you will get the subtle click of a decent .004" or a slight thunk of a .006" or you will get a hundtaclank of a .008" or even a slide-whangfundabonk of a .018".

Lousy leakdown results that show up in the intake tract with wheezing can quickly wreak havoc with the AFM, particularly when it is only one cylinder. Then you get to watch the wiper go into caniptions of rattling back and forth during cranking.
Colin

[dtrumbo]

So no end play test yet, but I did do an oil pressure test. According to Mr. Wilson, low oil pressure can be an indication of wear. Well I've got oil pressure to spare.

800 RPM = 19 PSI
1000 RPM = 24 PSI
1500 RPM = 38 PSI
2000 RPM = 51 PSI
2500 RPM = 54 PSI
3000 RPM = 54 PSI

So it seems the bypass is working as the pressure stops increasing with RPM at 54 PSI.

So the plan... this winter I'll drop the engine, clean it up, pull the heads and see what's what. At that time I'll see if there's any indication that my case has or has not been bored larger. Then we'll see what the availability of bearings look like. If available, I'll probably bite the bullet and do the whole rebuild, otherwise I'll just get the heads rebuilt and see if I can keep going until bearings come available at which time I'll do the bottom end.