Should there be a Cam Thrust Plate on a 66 427???

[Christopher A.]

I just finished degreeing my new cam and while doing so I noticed that there are two tapped holes around the cam where it would appear a cam plate would or should be installed. Should there be a cam thrust plate installed for my 427 motor??

Thanks

[Christopher A.]

Re: Should there be a Cam Thrust Plate on a 66 427???

I just read on another forum where it states that early big block Chevys did not use a cam retaining plate. Why did they put tapped holes in the block then??

If i could just get a confirmation, i would feel a lot better.

[Anthony P.]

Re: Should there be a Cam Thrust Plate on a 66 427???

No retainer plates on those motoers to my knowledge

[Joe L.]

Re: Should there be a Cam Thrust Plate on a 66 427???

I just read on another forum where it states that early big block Chevys did not use a cam retaining plate. Why did they put tapped holes in the block then??

If i could just get a confirmation, i would feel a lot better.

Christopher-----



No Mark IV big blocks that I know of used a camshaft thrust plate. The first use of a camshaft thrust plate that I know of was for Gen VI big blocks introduced in 1996. These engines used a roller cam and thus required a thrust plate. So, why did Chevrolet provide drilled and tapped bosses for thrust plates on most Mark IV and Gen V blocks? It's one of the "great mysteries" are far as I'm concerned.

It is possible that a thrust plate was used for some HD truck applications of the Mark IV and Gen V blocks. I don't see why they would have been necessary but they might have been used. However, why they would drill and tap most blocks when only a few required it is beyond me.

[Clem Z.]

Re: Should there be a Cam Thrust Plate on a 66 427???

the bolt in thrust plate was used with the 2 gear gear drive reverse rotation cam sold by chevy back in the day. cam 3879652 ,thrust bearing 3864862, cam gear 3856351, crank gear 3860086, distributor 1111095. the chain drive cam was called "A" package and the gear drive cam was called the "B" package. i still have a cam and gears around here someplace

[Joe R.]

Re: Should there be a Cam Thrust Plate on a 66 427???

the bolt in thrust plate was used with the 2 gear gear drive reverse rotation cam sold by chevy back in the day. cam 3879652 ,thrust bearing 3864862, cam gear 3856351, crank gear 3860086, distributor 1111095. the chain drive cam was called "A" package and the gear drive cam was called the "B" package. i still have a cam and gears around here someplace

I just love it when one of the "Great Mysteries" is solved and put to bed!!!!!

JR

[Clem Z.]

Re: Should there be a Cam Thrust Plate on a 66 427???

I just love it when one of the "Great Mysteries" is solved and put to bed!!!!!

JR

one advantage of living to be old if you can remember.

[Joe L.]

Re: Should there be a Cam Thrust Plate on a 66 427???

I just love it when one of the "Great Mysteries" is solved and put to bed!!!!!

JR

JR------


Well, I'm afraid it's still somewhat of a mystery. The thrust plate would be necessary for gear drive camshaft applications as well as roller lifter applications. However, as far as I know, GM never used either in any Mark IV or Gen V PRODUCTION application unless they used gear drive for some HD trucks. Even for post-factory engine builds of the Mark IV period, conversion to either gear drive or roller lifter was extremely uncommon. So, why not just provide the bosses as part of the casting and let the engine builder add the tappings if required? For small blocks, which could also be converted to gear drive or roller cams, they never even provided the bosses for the thrust plate screws until 1986 when the PRODUCTION use of roller cams began. Can you imagine how many tools that Tonawanda wore out drilling and tapping those thrust plate bolt holes that would never be used in 99.99%+ of the cases.

And, yes, I realize that GM drilled and tapped the front motor mount holes for small blocks even to this day and drilled and tapped oil cooler fittings for some big blocks, most of which were never required. However, there were PRODUCTION applications for those features and any block could be used in SERVICE for an original PRODUCTION application requiring those features.

I just cannot think of any other case in which GM provided features requiring machining on blocks or cylinder heads to support SERVICE-ONLY installations.

[Bill M.]

Re: Should there be a Cam Thrust Plate on a 66 427???

unless they used gear drive for some HD trucks.

I have an SAE paper (presented 10/18/65) detailing Mark IV design features which shows a gear drive for trucks...mystery solved.

[Joe R.]

Re: Should there be a Cam Thrust Plate on a 66 427???

JR------


Well, I'm afraid it's still somewhat of a mystery. The thrust plate would be necessary for gear drive camshaft applications as well as roller lifter applications. However, as far as I know, GM never used either in any Mark IV or Gen V PRODUCTION application unless they used gear drive for some HD trucks. Even for post-factory engine builds of the Mark IV period, conversion to either gear drive or roller lifter was extremely uncommon. So, why not just provide the bosses as part of the casting and let the engine builder add the tappings if required? For small blocks, which could also be converted to gear drive or roller cams, they never even provided the bosses for the thrust plate screws until 1986 when the PRODUCTION use of roller cams began. Can you imagine how many tools that Tonawanda wore out drilling and tapping those thrust plate bolt holes that would never be used in 99.99%+ of the cases.

And, yes, I realize that GM drilled and tapped the front motor mount holes for small blocks even to this day and drilled and tapped oil cooler fittings for some big blocks, most of which were never required. However, there were PRODUCTION applications for those features and any block could be used in SERVICE for an original PRODUCTION application requiring those features.

I just cannot think of any other case in which GM provided features requiring machining on blocks or cylinder heads to support SERVICE-ONLY installations.

Joe, I don't think Tonawanda or Flint ever thought about how many holes they drilled that were never used. Just think of the big block head! If they wanted to save drill bits and taps they would have designated the heads right and left. Then they would only have to have drilled one end of each head.
I'm sure machining was a "shotgun" approach worked out by Engineers smarter than the average bear on this board!
Remember they were using CNC machines (punch card readers) back then! You could not have a union worker changing the program for each block and could not coordinate dealer orders and productions orders.
Most blocks either big block or small were generic and didn't have any personality until the guy at the end of the line matched up orders and stamped them.

In the end all we know is that the holes were drilled and tapped and only someone like Ol Clem knew what to do with them!!!! Lucky Ol Clem!!!

JR

[Christopher A.]

Re: Should there be a Cam Thrust Plate on a 66 427???

Thanks for the replies. The whole reason i questioned it was due to the holes being threaded. Surely this question comes up somewhat frequently when people are rebuilding engines, or maybe not, considering i could only find one other post on the internet about the whether or not the early 427s should have a cam plate.

Another question: How far should i be able to pull the cam sprocket away from the block without the distributor or rockers adjusted? It seems like there is a significant amount of movement when i pull forward on the upper gear. Does the pressure from the valvetrain keep the cam from walking forward?

[Clem Z.]

Re: Should there be a Cam Thrust Plate on a 66 427???

Thanks for the replies. The whole reason i questioned it was due to the holes being threaded. Surely this question comes up somewhat frequently when people are rebuilding engines, or maybe not, considering i could only find one other post on the internet about the whether or not the early 427s should have a cam plate.

Another question: How far should i be able to pull the cam sprocket away from the block without the distributor or rockers adjusted? It seems like there is a significant amount of movement when i pull forward on the upper gear. Does the pressure from the valvetrain keep the cam from walking forward?

a properly ground cam has the lobes ground on a slight taper and with the radius on the bottom of the lifter this causes the cam to be pushed to the rear of the block. the gear drive cam needs the the plate because of the angle on the gear teeth if the engine got spun backwards the force of the angle on the gears would pull the cam forward as the teeth angle when the engine is turning the correct direction cause the force to be rearward

[Joe L.]

Re: Should there be a Cam Thrust Plate on a 66 427???

I have an SAE paper (presented 10/18/65) detailing Mark IV design features which shows a gear drive for trucks...mystery solved.

Bill------


Yes, that solves it. I suspected that the situation might have some sort of truck involvement. That would result in a PRODUCTION requirement for the thrust plate. I don't have very much in the way of information on HD trucks and engine components thereof so I could not previously determine if a gear drive was used for such trucks.

The thrust plate provisions are actually a boon for anyone that wants to install a retrofit roller cam in a Mark IV big block. They don't have to use a thrust button; they can use a stock-type thrust plate which is superior to a thrust button.

[Christopher A.]

Re: Should there be a Cam Thrust Plate on a 66 427???

Fortunately the new cam from crane has the correct width lobes is ground correctly according to my measurements and from what i have read, but i can't say the same for the previous cam.
Thanks for educating me.

[Clem Z.]

Re: Should there be a Cam Thrust Plate on a 66 427???

Bill------


Yes, that solves it. I suspected that the situation might have some sort of truck involvement. That would result in a PRODUCTION requirement for the thrust plate. I don't have very much in the way of information on HD trucks and engine components thereof so I could not previously determine if a gear drive was used for such trucks.

The thrust plate provisions are actually a boon for anyone that wants to install a retrofit roller cam in a Mark IV big block. They don't have to use a thrust button; they can use a stock-type thrust plate which is superior to a thrust button.

chevy 6 cylinder engines used gear drive cam with a thrust plate. check the part number and see if the 6 cylinder used the same thrust plate