[Nathaniel1234]

Pic

[Nathaniel1234]

Pic 2

[Bill Hanlon]

The 4 bolt water pump and associated timing cover are not notorious for improper spacing between the impeller of the pump and the cover like later pumps that used a divider plate. However, I'd use some modeling clay to measure the clearance between the impeller and the big opening in the back of the cavity that it spins in. I don't know what the measurement should be, but on later style pumps 0.030" or so is desirable. Don't forget to use a gasket when you make the measurement.

Just curious, where did the temp sensor plug into the engine at?

Someone will probably chime in soon with the "reverse rotation direction" pump old wife's tale.

[Nathaniel1234]

Thanks Bill, yes I have clearanced the plates closer to the impeller on 65 and up water pump assemblies by modifying the plate insert. Can I modify that piece in the back of the cavity?

There is a female thread in that custom piping which housed the factory 1955 water temp gauge sensor, I just threaded in a autometer sensor in exact same place.

The 421 SD (it is a 61 actually, not a 62 like I said below) is not a reverse flow cooling engine like what came originally in 55. I did wonder if maybe the 55 radiator might operate differently as part of a reverse flow system, but didn't really think so.

[Bill Hanlon]

Assuming the radiator has the capacity to cool the 421, the reverse flow through the heads on the 55 engine vs. the 421's "normal" flow shouldn't make any difference at the radiator. Besides that, you said the radiator was cold while the engine was hot.

More thoughts on "clearancing" the 4 bolt pump: Bolt the pump into the housing WITHOUT the gasket. Turn the pump by hand. If blades hit the casting, pull the pump and install it again WITH the gasket. If it no longer hits, then the clearance in less than the thickness of the gasket. If it didn't hit WITHOUT the gasket, then the clearance is more than the thickness of the gasket.

Clearance testing is a lot easier with the later pumps that use a divider plate. You can check them with the pump removed from the engine.

[Jack Gifford]

Originally Posted by Nathaniel1234

... it is a 61 actually, not a 62 like I said below...

That confuses me, since the '61 SD (or "heavy duty" as Pontiac called them back then) stuff was actually based on 1960 parts. For instance, my '61 SD aluminum Tri-Power manifold is an exact fit on '55-60 heads. Is there possibly some question about hot coolant finding its way out through that weird water manifold?

[Nathaniel1234]

Thanks Jack, well it has a 1961 date code... Looks like a "G" I think, which would make it July...

I will look closely at the manifold... I hope not!

[Nathaniel1234]

Not leaking into valley pan area...