427 rebuild

[Roger G.]

I am needing a rebuild for a 69 427/400 with 4 speed and 3.70 posi. This was prompted by a leakdown test that looked like this
1 3 5 7
35% 18% 16% 23%


2 4 6 8
18% 43% 33% 30%

The engine is out of the car, and the builder has done an inspection. It was rebuilt in the distant past. It had newer valves and apparently just a hone- no overbore. The deck was flat
and will not need to be redecked. He said the heads would need a light shave. No obvious cracks in the heads or block.

He said the oil came out clean, but there was a lot of metal dust in the oil pan. The cylinders were scored, and would catch a finger nail. The bearing journals were pretty ate up, he said they were radially scored. He thought the wear on the pistons and bearings was from metal shavings getting fused into the moving parts.

He recommended hot tanking it, a torque plate rebore .03 over, replace the pistons, bearings, and valves, grind the crank, and balance it out. The rods looked good he said they were worth keeping.

He said the camshaft showed a little wear, and could be kept, but he wanted me to think about a roller cam. He said it would keep the idle lope, but give better performance.

I also asked about boring to .02 over, to try and preserve as much of the block as possible, but he said the pistons may be hard to find for the 427

Any thoughts on the camshaft choice, or other questions I should ask? Thanks

[Joe L.]

Re: 427 rebuild

I am needing a rebuild for a 69 427/400 with 4 speed and 3.70 posi. This was prompted by a leakdown test that looked like this
1 3 5 7
35% 18% 16% 23%


2 4 6 8
18% 43% 33% 30%

The engine is out of the car, and the builder has done an inspection. It was rebuilt in the distant past. It had newer valves and apparently just a hone- no overbore. The deck was flat
and will not need to be redecked. He said the heads would need a light shave. No obvious cracks in the heads or block.

He said the oil came out clean, but there was a lot of metal dust in the oil pan. The cylinders were scored, and would catch a finger nail. The bearing journals were pretty ate up, he said they were radially scored. He thought the wear on the pistons and bearings was from metal shavings getting fused into the moving parts.

He recommended hot tanking it, a torque plate rebore .03 over, replace the pistons, bearings, and valves, grind the crank, and balance it out. The rods looked good he said they were worth keeping.

He said the camshaft showed a little wear, and could be kept, but he wanted me to think about a roller cam. He said it would keep the idle lope, but give better performance.

I also asked about boring to .02 over, to try and preserve as much of the block as possible, but he said the pistons may be hard to find for the 427

Any thoughts on the camshaft choice, or other questions I should ask? Thanks

Roger-----

I'd say your engine builder knows what he's talking about. I, too, always prefer going 20-over rather than 30-over. However, he's right; it will be difficult or impossible to find 427 pistons in 20-over size. You may be able to find them in conventional cast (which is what was originally used) or forged. I don't recommend either of these types, though, for your application. Go with hypereutectic cast and, therefore, with the 30-over bore size.

I also agree with the engine builder's recommendation of an hydraulic roller cam and lifters. Personally, I think an hydraulic roller is the only way to go. You don't want some wild grind, though. You want one that will be close to the original flat tappet grind in terms of performance characteristics.

[Roger G.]

Re: 427 rebuild

Joe,

Thanks for your input. The builder is very experienced and conservative. He was sensitive to the stamp pad issues, and told me if the block needed to be decked, he knew of a way to get it done without affecting the pad, fortunately it wont need decking. He also didn't seem to like baking the block to clean it, and knew someone who could hot tank it. He also mentioned the roller cam would be better when the engine was started after sitting for a while.


The motor ran pretty cool before being taken out, usually about 180, maybe because of the wear on the rings and cylinders. Is it going to be hotter after the rebuild?

[Duke W.]

Re: 427 rebuild

Is "idle lope" your primary "performance" criterion? IIRC the OE 390 HP engine has little lope at 600 idling in neutral, but has massive low end torque that "idle lope" kills.

You have an opportunity to restore is back to its original performance characteristics with a lot more top end power and revs if you massage the heads.

Your choice...

Duke

[John B.]

Re: 427 rebuild

Roger, I am in the process of rebuilding my 68 390HP 427. Like yours mine was done in the past. It had a speed-pro hydraulic flat tappet cam in it that was a little bigger than the stock GM cam. It ran good and sounded right, but one of the lobes was gone and others showed signs of wear. So, I am going with a hydraulic roller setup. I chose a cam with the same duration as the speed-pro cam that was in the engine on a similar centerline. With the hydraulic roller that gets you a good bit more lift, but I am assured that it should idle similar to what was in the car, but have more power and torque. We'll see. One issue with the roller cams is the the tendency of the cam to walk and therefore the need to control end play Most folks use a cam button that interfaces with the timing chain cover to setup and control cam end play. I did not like that system for several reasons, so I went a different route. The front of my 68 block was drilled and tapped from the factory for some type of cam system that I am told was used on marine engines. Just so happens that the spacing of those holes is such that a cam retainer plate from a Gen VI big block factory roller cam will work. Cloyes makes a timing set that works with the retainer plate. So, if your block has the drilled and tapped holes (I am told that most if not all did have them), buy your cam with a stepped nose as would be used in a factory roller motor, get the retaining plate and timing set, you can basically replicate the system used by GM for their roller cam motors and have what I believe is a much better engineered system.

John

[Paul D.]

Re: 427 rebuild

John, can you post the part numbers of the retainer and cloyes chain set up. I am doing a 496 and this may work better than a button. Also did you change the iron dist gear for a bronze one?.....P..

[Roger G.]

Re: 427 rebuild

Roger, I am in the process of rebuilding my 68 390HP 427. Like yours mine was done in the past. It had a speed-pro hydraulic flat tappet cam in it that was a little bigger than the stock GM cam. It ran good and sounded right, but one of the lobes was gone and others showed signs of wear. So, I am going with a hydraulic roller setup. I chose a cam with the same duration as the speed-pro cam that was in the engine on a similar centerline. With the hydraulic roller that gets you a good bit more lift, but I am assured that it should idle similar to what was in the car, but have more power and torque. We'll see. One issue with the roller cams is the the tendency of the cam to walk and therefore the need to control end play Most folks use a cam button that interfaces with the timing chain cover to setup and control cam end play. I did not like that system for several reasons, so I went a different route. The front of my 68 block was drilled and tapped from the factory for some type of cam system that I am told was used on marine engines. Just so happens that the spacing of those holes is such that a cam retainer plate from a Gen VI big block factory roller cam will work. Cloyes makes a timing set that works with the retainer plate. So, if your block has the drilled and tapped holes (I am told that most if not all did have them), buy your cam with a stepped nose as would be used in a factory roller motor, get the retaining plate and timing set, you can basically replicate the system used by GM for their roller cam motors and have what I believe is a much better engineered system.

John

John, thanks for the information. Where on the block are the tapped holes located? Would you happen to have a picture you can post?

[Dick W.]

Re: 427 rebuild

John, thanks for the information. Where on the block are the tapped holes located? Would you happen to have a picture you can post?

Those holes are on the thrust surface where the cam gear meets the block.

[John D.]

Re: 427 rebuild

Trust but verify....I'd go look at the bore and crank to be sure....

[Larry B.]

Re: 427 rebuild

Those bolt holes are each side of the cam wear pad. They were used whenthe timing was gear to gear ,no chain, therfore nothing to hold the cam.The cam at that point ran backwards. The Cloyes button works just fine but use the Hex A Just timing set. it has a thrust bearing behind the gear and makes degreeing the cam a snap. Your hydrulic roller is the way to go if original doesn't matter. But get a custom grind not a the guy at CAM HELP or the computer nerd at SUMMIT who has never seen a engine apart pick a 3\4 race cam which means 3\4 down the page.

[Joe L.]

Re: 427 rebuild

John, can you post the part numbers of the retainer and cloyes chain set up. I am doing a 496 and this may work better than a button. Also did you change the iron dist gear for a bronze one?.....P..

Paul------

thrust/retainer plate (if center-to-center between holes is 3.29")----GM #10168501

thrust/retainer plate (if center-to-center between holes is 3.62")----GM #10088128

retainer plate screws (these are button head screws designed for this application)-----GM #14093637

Cloyes True Roller timing set-----9-3149A (this is a HD single row roller timing set)

IMPORTANT: All of the above-referenced parts can only be used if a factory-type hydraulic roller camshaft (i.e. Gen VI big block-type) with reduced diameter of front of #1 camshaft journal and small bolt circle camshaft sprocket mounting pattern is used. Many aftermarket camshafts for Mark IV big blocks use the standard bolt circle big block camshaft sprocket mounting pattern. These cannot be used with a thrust/retainer plate and must use a thrust button to control camshaft movement.