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Old October 25th, 2025, 06:22 PM
Prowbar Prowbar is offline
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Join Date: Dec 2020
Location: Friesland, the Netherlands
Truck: 1965 GMC 1500, 478 V6, SM420
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Default Re: '65 GMC 1500 project. From the Netherlands

Still working on preparing everything for re-assembly.



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Found the culprit of the dirty oil issue... used the wrong oil filter gasket.
Fel-Pro doesn't supply the right gasket for a spin-on oil filter adapter in their gasket kit and I never bothered to check. This allows some oil to bypass the gasket from dirty to clean side. Live and learn.
Decided to not run the bypass blocker, I'll stick to the OEM bypass from the get go. I found the specs for the differential pressures in the filter I'm using on Bob Is The Oil Guy forum (I've did a lot of reading and research on oil and filtration)

Instead of the typical Wix 51049 I'm going to run a Baldwin filter instead.
I cannot find any reliable filtration data on the 51049. Only found a "micron rating" of 21 (I'm assuming that's nominal, meaning absolute should be higher) I'm sure its a good filter but I don't like "not to know things".
I'm going to run a Baldwin B1428. It has the same 13/16-16 thread and diameter and gasket location. This filter has an anti drain back valve as well.

Specs from BITOG:


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B1428

BX=2: 12 microns (nominal rating, 50% efficiency)
BX=75: 25 microns (maximum reliable filtration ratio, 98.67% efficiency)
Established Micron Rating: 12
Average Efficiency: 89.44 %
Burst PSI: 300

Flow
3PSI: 2GPM
5PSI: 5GPM
10PSI: 9GPM
15PSI: 11.5GPM

The V6 has a 14 GPM oil pump according to the GMC advertisements. This is probably the rated max flow at 3800 rpm. Now this isn't the actual flow to the filter and bearings. A large part of the flow goes back to the pan without passing the filter via the oil pump pressure regulator. Oil pumps are oversized to account for worst case scenarios.

Filtration with the B1428 is excellent. Even the max. particle size at 25 microns is smaller than half of the bearing clearance. This isn't gospel but should put it in perspective.

With a 11 psi bypass valve I'll need a flow of at least 9 GPM for the bypass to open. Pretty sure the oiling system isn't capable of flowing 9 GPM. Only time the bypass opens it at a very cold start when the oil is thick and you decide to rev the engine to the moon or when the filter is clogged. Oil, even most multigrade oil, is thicker when cold so there's more resistance to flow through the filter. 11 psi is quite the differential pressure. I don't expect it to open anytime soon.

I don't know what viscosity of oil and the temperature they tested this with though. I'm assuming 10W-40 at operating temperature. But judging by the provided data and comparing flow numbers above I'm pretty sure the bypass will rarely open.

Except the intake and head gaskets I'm making all my own gaskets. Head gaskets are the 305 V6 gaskets that I'm converting using my little setup that I showed before. The old head gaskets that I did that way look mint so that gives me confidence.



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Making gaskets is fun I think. I like doing it.

Here's ones of the old head gaskets. Looks mint, as you can see I used some additional sealer. Got it as a recommendation, basically don't use that stuff because all it does is plug up the coolant holes in the cylinder head. Fel-Pro doesn't recommend any sealer either so no need.



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The timing cover protruded .016" above the oil pan gasket rail on the 478 block (this is the 305 timing cover) With the cork gasket this didn't pose a problem, but now that I'm using the oil pan spacer I went ahead and milled the surface to even them out. See the result below.



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Gapped all the new piston rings. Made sure I gapped them to spec at the bottom of the bore, just below where the top ring stops at BDC. Only needed to gap the chrome plated top rings, the cast iron 2nd and 3rd rings needed no gapping, they were right in the middle of spec already.
Have a little trick up my sleeve so I can freshen up the old oil control rings. I'll share that when I get to it.



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Right now I'm working on the cylinder heads. Will be covered in a later post. Have some interesting things to share there as well.
Attached Images
File Type: jpg Gasket mismatch.jpg (198.0 KB, Multiple views, 8 clicks)
File Type: jpg New gasket.jpg (112.4 KB, Multiple views, 8 clicks)
File Type: jpg Timing cover gasket.jpg (285.3 KB, Multiple views, 8 clicks)
File Type: jpg Oil pan gasket.jpg (289.5 KB, Multiple views, 8 clicks)
File Type: jpg Timing cover alignment.jpg (165.9 KB, Multiple views, 8 clicks)
File Type: jpg Milled timing cover.jpg (187.1 KB, Multiple views, 8 clicks)
File Type: jpg Gapping piston rings.jpg (143.3 KB, Multiple views, 8 clicks)
File Type: jpg Old head gasket.jpg (227.2 KB, Multiple views, 8 clicks)

Last edited by Prowbar; October 25th, 2025 at 06:35 PM.
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