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Assembling 8.1L 502

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Old 07-04-2025 | 10:02 AM
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Default Assembling 8.1L 502

Time to reassemble.

Block is back from machine shop. Bored 30 over, cleaned, crank polished, did not recommend cam bearing change said “they look like new”. Decked 2 thousands.

New Wiseco Forged pistons and New Scat forged rods. Balanced and gapped.



I assembled the pistons and rods. Broke one 2nd groove ring. Waiting till Monday until wish opens to hopefully get the one ring. Anyone have an extra set for one piston?

Cam was cleaned. I’ve slid it into its home.

New GM cast iron heads sent to Machine Shop and moved over the old with new keepers and 4 new intakes and 1 new exhaust valve.



Have a couple questions, the 3 plugs in front above the cam, had holes in them. Anyone have a source for these? Or can I get some iron plugs from the hardware store and drill a 1/16” hole and be good? Below is what it had that machine shop did not return. Most of the plugs were destroyed to remove.



For the plug thread sealant, is Permatex 80632 good for this purpose?


New head bolts came with sealant already. All the head bolts have sealant actually. Can I assume this is the correct sealant to seal from water jackets?

Once the main and rod bearings arrive, I’ll check for oil clearance.

First engine build. Being extra cautious and asking lots of questions along the way. Been turning my own wrenches for 35 years just never a full build.

Anything else I should think of or tips are appreciated.
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Old 07-04-2025 | 12:23 PM
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Yes you can use iron plugs and drill them, but I would use brass, a little easier to drill and easier to go into the holes. I have seen 1 of the plugs drilled but not all three.
I would ask articfriends his opinion on that.
you already know but lube on everything, the good sticky stuff on the bearings, and a light lube on the piston walls and skirts.
when in doubt, just ask. Most of us on here have built engines.
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Old 07-04-2025 | 08:57 PM
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Oil bypass valves. I'm reading the Volvo Penta Shop Manual and it says "install oil bypass valves (pleural). I never removed any out and only saw 1 bypass valve under the oil filter adapter prior to sending to machine shop. It seems there should be another one adjacent to it. Could there be a reason why I didn't have a second oil bypass valve? To clarify, a bit more, VP uses remote oil filter housing and an oil cooler.


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Old 07-05-2025 | 11:58 AM
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There should be some allen style pipe threaded plugs available locally. Easiest would be to drill and tap a piece of metal and screw them in...to drill them in a drill press. Or in a vice pinched with 2 pieces of wood and a hand drill. Small drill bits break easily. You need high speed rpm.

I don't remember the hole size to drill...but should be ok here somewhere. I would do all 3...as per the original block.

Do you have a ring expanded to install the rings? Or are you doing the twist on by hand? They're about $10 to get a ring expanded. Far cheaper than solving a broken ring issue.

Oil bypass:

https://www.offshoreonly.com/forums/general-q/68024-gen-vi-v-bypass-valve-2-a.html

Great to see it coming together.
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Old 07-05-2025 | 05:23 PM
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Originally Posted by Tartilla
There should be some allen style pipe threaded plugs available locally. Easiest would be to drill and tap a piece of metal and screw them in...to drill them in a drill press. Or in a vice pinched with 2 pieces of wood and a hand drill. Small drill bits break easily. You need high speed rpm.

I don't remember the hole size to drill...but should be ok here somewhere. I would do all 3...as per the original block.
Couldn't find brass hex head plugs locally. Did find 1/4" iron male pipe plugs at Home Depot that may stick out too far for the cam gear. Instead, I ordered Brass hex female head (so like the original) head 1/4" plugs from Amazon. Will drill them with a 1/32 drill bit. All three above the cam.

Originally Posted by Tartilla
Do you have a ring expanded to install the rings? Or are you doing the twist on by hand? They're about $10 to get a ring expanded. Far cheaper than solving a broken ring issue.
I twisted on my had. Super quick and easy, no force really needed. Except one seemed stubborn. I think I was the stubborn one. Live and learn.

Originally Posted by Tartilla
Oil bypass:

Gen VI & V bypass valve #2

Great to see it coming together.
That thread was useless. lol. Too many difference answers. But I'll search more on here about that topic before I decide what to do. Seems many like to ether block the pad oil bypass all together.
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Old 07-07-2025 | 09:41 AM
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I don't know for certain on a Volvo, but on a Mercury 496/8.1 they do have 2 oil bypass valves from the factory. The one in the center, and the one off center are utilized on a Merc. Be sure to use GM part number 25161284 as this is the 30psi valve.
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Old 07-08-2025 | 11:02 AM
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Oil Pump:
Opened the oil pump. Held down with five 10mm bolts. The cap had a paper like gasket requiring a light tap with a ball pin hammer to separate. The inside of the cap had some scoring above both gears which my nail could catch on. Also, the the gears had many scoring marks which my nail could catch on along with some pitting or tiny pits. Will order a new oil pump.

For the sake of getting this project done, I contemplated not opening this up thinking it should be ok since I never saw any oil pressure issues. Since I have plenty of time, waiting on parts, and working on other small projects on the boat, I opened it up. Glad I did. Question is, do I stick to the stock oil pump, or upgrade to the higher volume pump. Is there any downside to the high volume pump in an essentially stock engine. Yes its a marine engine that operates at a much higher load consistently vs in an "over the road" application. Is that enough to upgrade? Undecided on this topic and will research other sources. I'm leaning more toward a stock GM pump.

Oil Pump part number: 12555868




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Old 07-08-2025 | 11:14 AM
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Never build a new engine with a used oil pump, they are cheap
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Old 07-08-2025 | 11:15 AM
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High volume Melling is a nice replacement. MEL M77HV
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Old 07-08-2025 | 11:20 AM
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Originally Posted by DrFeelgood
High volume Melling is a nice replacement
Are there any downsides to a high volume. From my short "google university" search, not required for essentially stock engine. The high volume oil pump also takes MORE power to run and there is some potential for the oil pump shaft to shear??

Looking for AC Delco or GM unless there is another Brand (Melling?) thats is more recommended.

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