Long life street roller cam in old SBC 400 block

[Dan Timberlake]

Are there potential issues with OEM manufacturing lifter bore geometry inaccuracy?
I'm thinking I may have heard the bores can be tipped or ?? that would kill a modern afermarket street roller cam conversion.

If so, what kind of checks would help identify if we should stick with a flat tappet before buying a roller set up?

thanks,

Dan T

[CamKing]

Actually, if the lifter bores are not true, you have greater chance of damage with a flat tappet cam.
With a flat tappet cam, if the centerline of the lifter bore does not pass thru the centerline of the cam, it could make the lifter act like it's a smaller diameter on either the opening side or the closing side, and the cam profile that's designed for an .842" diameter lifter could actually over-ride one side of the lifter. If the lifter bore is not perpendicular to the cam centerline, it could act like the lobe has no taper, and the lifter won't spin, or it could act like it has too much taper, and wear the lobe out.
Have the lifter bores true'd and bushed.

[Norris Marshall]

factory lifter bores are not very good for geometry, that, along with the lack of zinc and phos in the oil is driving us to get away completely from flats on sbc type engines. Fords don't seem as bad,

[rebelyell]

?
anyone here have experience with converting flat tappet sbc block (350 or 400) to use OE GM short V6 roller lifters along with OE 5.7L roller blocks' dog-bones and spider? hand-profiling tops of lifter bores to accept dogbones?

[PackardV8]

Have the lifter bores true'd and bushed.

What would be the tradeoffs in just truing the bores and honing for .904" lifters without installing bushings?

jack vines

[Kenova]

Have the lifter bores true'd and bushed.

What would be the tradeoffs in just truing the bores and honing for .904" lifters without installing bushings?

jack vines

What he said.

Ken

[cardo0]

Are there potential issues with OEM manufacturing lifter bore geometry inaccuracy?
I'm thinking I may have heard the bores can be tipped or ?? that would kill a modern afermarket street roller cam conversion.

If so, what kind of checks would help identify if we should stick with a flat tappet before buying a roller set up?

thanks,

Dan T

Lifter bores are a good location to look for core shift. We picked up a 400 block that looked great with almost no cylinder wear but someone noticed the shift you could see in the lifter bores was huge.

[prairiehotrodder]

My machinist has told me that 400 blocks are bad for having the cam tunnel on the loose side. I personally built a 377 many years ago that always had low oil pressure. I did lots of things to try and correct it but eventually i just ignored it and used it. It lasted for about 4 years of serious abuse by a teenager with a lead foot and long drives to street races. Finally i took it apart and found a crack in the cylinder bore. The bearings and bearing spacers were still in very good condition. It was .030 over 2 bolt block. I know this isn't really the info you were looking for but i just thought i'd offer it in case it helps someone.
Brian

[MELWAY]

I built a Clevo years ago and it prematurely ate up 2 solid street roller cams/lifters under 3000mile
I sent block to true lifter bores at .904” diameter. And
4 bore needed to be bushed because they did not clean up
Engine is running happy now

[Dan Timberlake]

I built a Clevo years ago and it prematurely ate up 2 solid street roller cams/lifters under 3000mile
I sent block to true lifter bores at .904” diameter. And
4 bore needed to be bushed because they did not clean up
Engine is running happy now

==============

.904 is a whopping .060" oversize for a nominal .842"Ø SBC.
My first reaction is the stock lifters must have been edge riding like crazy if tipped that much .
I'm thinking careful setup referencing half way down the .842" bore could have cleaned up at .904 easy.

Or, are the OEM nominal centerlines sometimes displaced enough to require such major relocation?

My buddy is committed to this block, so we'll have to rig up some way to measure the lifter bore alignment to see what we've got.
The presumably 100,000 mile stock lifters look to have made it with "normal" wear. A few slightly concave.

I'm thinking there a functional tolerance for angular bore misalignment . I'm curious what folks here have to say.
But will be bugging cam manufacturers eventually.

thanks,

Dan T

[CamKing]

Have the lifter bores true'd and bushed.

What would be the tradeoffs in just truing the bores and honing for .904" lifters without installing bushings?

jack vines

That's fine. I have a few customers that do that, because when they would bore them out for .875" lifters, some of the bores wouldn't clean up, so they would have to go back and bush those bores. With .904" they seem to almost always clean up. With .904", the lifters are more expensive, and with .904" flat tappet lifters, the need a cam with narrow lobes, so the lifters don't hit the adjacent lobes.

[Walter R. Malik]

Have the lifter bores true'd and bushed.

What would be the tradeoffs in just truing the bores and honing for .904" lifters without installing bushings?

jack vines

That's fine. I have a few customers that do that, because when they would bore them out for .875" lifters, some of the bores wouldn't clean up, so they would have to go back and bush those bores. With .904" they seem to almost always clean up. With .904", the lifters are more expensive, and with .904" flat tappet lifters, the need a cam with narrow lobes, so the lifters don't hit the adjacent lobes.

That was a really big issue with the .960" muchroom tappet faces ... cam lobes were narrowed a lot.