[Alizar]

My front & rear bearing seals are starting to leak oil pretty good so I think I'll be rebuilding my engine soon. I'd like suggestions on things I should do while I have it apart? The car is a 1966 Bonneville with the TH400 transmission. It's a convertible that will spend most of it's life cruising so I'm not after max hp. If there are good bang for your buck reliability/performance upgrades I'd like to do them while I'm in there. My dad rebuild the engine sometime in the early 80s but as far as I know it's still pretty stock. It's the lower-end 421 with 092 heads and came with a 4-bbl carb, but I converted to a Holley Sniper EFI a couple years ago. I also picked up a pair of tubular headers (Doug's) I'm hoping to install during the rebuild.

I'm not too concerned about keeping it original and I'm considering aluminum heads, just not sure if they are worth the cost over rebuilding the originals? What about a hydraulic roller cam - are they worth it? I'm leaning towards forged aluminum pistons & new rods, but open to suggestions here too.

The practical side of me says to just keep it relatively stock / low-cost, but what's the fun in that? This car has been in my family for 55 years and will someday be passed on to my sons so I don't mind spending a little extra money now to avoid regrets or rework later.

[25stevem]

You need to come to a decision about the heads first due to there impact on running aftermarket pistons and or a cam with more lift then .450”.

One thing that I consider mandatory is to get those original 421 connecting rods out of the motor so you or your son’s do not blow up that nice 4 bolt main block.
I would go for a set of Edelbrock D port heads with 72 CCs and then run a dished piston to leave you with a true 9.8 compression.
The stock AFB Intake is a heavy pile of crap, but you should be able to make a solid 320 Hp with it.

The 421 rods are forged, but weaker in the I beam area then the cast rods are.

A 60 psi oil pump and a HD drive rod should be on your parts list also.

The Dizzy should be knocked apart cleaned up and the inside advance shaft lubed up with fresh synthetic wheel bearing grease .

[Goatracer1]

Those connecting rods are NOT forged. They are the same part number as every other Pontiac V8 that year. You have to make up your mind whether to go high performance or build a cruiser. Forged pistons and aluminum heads are a complete waste in a cruiser. Also the use of a roller cam probably wouldn't be worth the expense.

[tom s]

When I built my 421HO a couple years ago I used a set of 96 heads and a 068 cam with a 66 tripower.Runs great would not change much.Used a first version Pertronix in the dizzy.Used a set of Autotec pistons and a set of late cast rods with ARP bolts.It’s in a 62 GP and now has a Bathtub with a pair of AFBs.Tom

[25stevem]

Hey Goatracer1 this should interest you.

Here’s two pictures of one of the 8 original connecting rods out of a 66 421 that I had in a Bonnieville of the same year.
Please note that it’s forged even though it looks maybe 90% like the common cast rod used since 63.

[Goatracer1]

Pontiac Chassis Catalog 5-1-69 , 66-70 F/8, T/8, P/8, GP/8 exc Ram Air or 303 Connecting rod PN: 541000. I have no way of telling what did or didn't come in your car.

[25stevem]

Goatracer1 here's some info out of my Pontiac parts catalog.

[geeteeohguy]

Originally Posted by 25stevem

You need to come to a decision about the heads first due to there impact on running aftermarket pistons and or a cam with more lift then .450”.

One thing that I consider mandatory is to get those original 421 connecting rods out of the motor so you or your son’s do not blow up that nice 4 bolt main block.
I would go for a set of Edelbrock D port heads with 72 CCs and then run a dished piston to leave you with a true 9.8 compression.
The stock AFB Intake is a heavy pile of crap, but you should be able to make a solid 320 Hp with it.

The 421 rods are forged, but weaker in the I beam area then the cast rods are.

A 60 psi oil pump and a HD drive rod should be on your parts list also.

The Dizzy should be knocked apart cleaned up and the inside advance shaft lubed up with fresh synthetic wheel bearing grease .

This is solid info. Looking at the car and the driving style, etc. I would recommend NOT running a roller cam (have seen many destroyed engines due to roller bearings failing and taking out the block) but would source a decent 068-spec or similar hydraulic flat tappet cam and buy some NOS USA made lifters off the internet or here. Be sure to measure the cam lobes for taper prior to installation if it has been manufactured in the past 15 years. And check the lifters for crown on a flat piece of glass and leakdown by filling them with oil and depressing the plunger.

[1968GTO421]

Originally Posted by geeteeohguy

This is solid info. Looking at the car and the driving style, etc. I would recommend NOT running a roller cam (have seen many destroyed engines due to roller bearings failing and taking out the block) but would source a decent 068-spec or similar hydraulic flat tappet cam and buy some NOS USA made lifters off the internet or here. Be sure to measure the cam lobes for taper prior to installation if it has been manufactured in the past 15 years. And check the lifters for crown on a flat piece of glass and leakdown by filling them with oil and depressing the plunger.

Many thanks to Geeteeohguy for the above.

Found this article on measuring lobe taper. Is this the best way or is there another way using simple tools/measuring devices we already have?
Thanks.

https://www.motortrend.com/how-to/ch...-lifter-bores/

[sdbob]

I rebuilt and put a 65 421 in my 63 GP after original gave up about 1970. Used 66 GTO heads,stock rods ,stock pistons,068 cam. Broke 3 t10s,then put m40 in it. Ran very well. When I learned about rods. I had taken engine apart. It had 7 of those wide parting line rods supposedly forged and 1 of the cast rods. The came out of low mileage wreck 2+2. I rpmd many times to 5400- 5800,but with street tires no slicks. Block went to machine shop and was 'lost,misplaced,basically stolen as guy went out of business.. I still have rods pistons and std std crank.

[Alizar]

Thanks for the feedback guys and sorry for the slow response. You're right I need to decide if I'm building a cruiser or a hot rod. I guess I'm trying to find the right balance of cost/performance and get a better sense of my options to help me decide. Since I have the "regular duty" 421, it seems like getting it to the equivalent of the 421 Super Duty / HO is a reasonable goal. Seems like at minimum I'll be doing a cam.

I agree that the main thing I need to decide is what to do about the heads. At minimum I'm leaning towards the "large valve" D-port cast iron heads from 1967 & later. It seems like these options will cost me ~$1,000-1,500, but how much power would I gain? What about installing hardened valve seats on these iron heads- is that necessary?

The other option I have been looking at are the top end packages Edelbrock/Butler sells that come with the aluminum heads, intake manifold, cam, etc. Butler tells me I can expect 100-130 hp/tq gains with one of these, but are the gains really that high? Cost is ~$4,300 for a flat tappet cam setup which I think I could justify if the gains are in that ballpark and that's all the extra cost, but I want to make sure I'm not missing anything?

I plan to pull the engine next week, so I'll have a better idea of what shape everything is currently in.

[Alizar]

Originally Posted by 25stevem

A 60 psi oil pump and a HD drive rod should be on your parts list also.

The Dizzy should be knocked apart cleaned up and the inside advance shaft lubed up with fresh synthetic wheel bearing grease .

What is an HD drive rod?

[25stevem]

They drive the oil pump off the bottom of the Dizzy gear.

Butler and KRE has them .

[77 TRASHCAN]

Originally Posted by 25stevem

Hey Goatracer1 this should interest you.

Here’s two pictures of one of the 8 original connecting rods out of a 66 421 that I had in a Bonnieville of the same year.
Please note that it’s forged even though it looks maybe 90% like the common cast rod used since 63.

Are theses, considered to be rubber rods???

There was conversation here about Kauffman "D" port heads that were being shipped, filling orders. Just a thought. Their stock "D" port heads would work week for a 421. BUT will the valve reliefs in t he 66 421 pistons be correct?
I've read (here) the the valve placement in the Kauffman "D" heads is the same as the stock iron Pontiac heads. AND that the round port Edelbrock valve placement is not the same as the stock iron heads......

Are the "D" port Edelbrock head valve placements the same as stock?

[b-man]

I would build an engine that’s powerful and has an emphasis on low end and mid range torque. You’re wanting to move a heavy car with some kind of highway rear end gear.

I would use one of the popular offshore made forged connecting rod sets. The 421 rods are inferior to the later cast factory rods that most folks don’t bother rebuilding anymore due to the cost coming close to that of new forged rods.

I would use some 6X-8 400 heads on it along with a factory 1972 cast iron intake and a ‘76-‘79 Quadrajet that’s been reworked by a pro. I wouldn’t bother porting the heads, I would upgrade the exhaust valve size from 1.66” to 1.77 and install hardened seats. New Ferrea stainless valves intake and exhaust.

Crower 60916 cam with whatever quality hydraulic lifter set that you can find after careful research. I think the exclusive Crower grind cams likely have better quality control than most of the equivalent ‘white box’ generic cams like the 2800, 2801 and 2802 that Summit sells.

https://www.summitracing.com/parts/c...D_BwE#overview

You can drop a 455 crank (4.21” stroke) right in there or you can keep the 4.00” 421 crank. Your heavy convertible would probably appreciate the longer stroke 455 crank.

If you do the 455 crank choose the 6X-8 101-105cc heads, if you stay with the 421 crank go with the 6X-4 92-95cc heads. Shooting for 9 to 9.5:1 with a moderate amount of cutting the head surface with no need for dished pistons, have the block cut for zero deck or within .005” of that.

Reworking your 092 heads and upgrading to hardened seats as well as the machine work required to convert to screw in rocker studs (6X heads already have that feature) would end up costing the same or more than just doing up a set of 6X heads to begin with. Also the 092 heads don’t have pushrod guide plates only slots milled into the head casting that sometimes are worn out. With 6X heads that’s a non issue, they all came equipped with guide plates from the factory along with the much more reliable screw in rocker studs.


The stock ports on the 092 heads are inferior to the 6X, and if later on (or now) you decide to do porting work the 6X are one of the best head castings for that.

You will end up with a solid 375-400 hp with stock reliability and it will look stock under the hood. All the accessories and throttle cable will bolt on just like stock. You could even get by with keeping your factory log style exhaust manifolds as long as you upgrade to a nice mandrel bent 2-1/2” exhaust and whatever free flowing mufflers you choose. I like the Dynomax 17749, they’re powerful and fairly quiet which you’ll likely appreciate when cruising with the top down.

[John Milner]

There were at least some 421's with cast rods. I own 2 of them. One is a '65 YH and the other is a '66 YH. I ended up using factory 455 SD rods in the '65 and used the factory 421 cast rods in the '66. Here is a picture of my '66 YH short block from when I re-built it with the factory cast rods/new arp bolts. I pulled this engine out of a '66 Catalina station wagon and it still had the factory timing set and GM bearings in it when I disassembled it. In any event, aftermarket forged rods will be stronger.

[77 TRASHCAN]

Bart,
Thanks for that input.
I've always thought putting a 4" crank (aftermarket) in a 400 block was a great idea, using 6X-4 heads. Not a lot of fancy machine work needed, good breathing heads, for the displacement. Custom pistons would be needed, but that's not difficult, thankfully, these days.
Engine could utilize a mild build and still have amazing power!!!

[74Grandville]

I would over build bottom end. I understand it may be a waste used at stock, but it's not being limited if you'd like to upgrade in the future.

[Scarebird]

I would examine it first and see what it needs if anything.

Do a leak down test before disassembling.

[SD421]

When I rebuilt m 1966 421 motor I bought RPM rods that are 4340.
Nice to know I won’t grenade the motor.
Auto Tec pistons dished 23 cc and 670 heads give me about 9.3 to 1 compression