[novadude]

How common is this cam gear thrust wear on a BBC? Are we talking 1-in-100 blocks? More? Less? Just curious.

EDIT: Wow... just realized this one is back from the dead! 10+ years. Oh well.. .I'm still curious.

 

[Busted Knuckles]

I've probably torn down 50 - 60 big blocks and have seen this issue on 3. The worst was the last, one of the oddball Mark IV's that are all 4-bolt mains. This thing was chewed up at least .100. Since it had the casting number that I have been told to avoid like the plague, it found another home. I haven't seen it at all on any Gen 6 blocks.

 

[Stokerboats]

I've probably torn down 50 - 60 big blocks and have seen this issue on 3. The worst was the last, one of the oddball Mark IV's that are all 4-bolt mains. This thing was chewed up at least .100. Since it had the casting number that I have been told to avoid like the plague, it found another home. I haven't seen it at all on any Gen 6 blocks.

What is that casting number?

 

[shovelrick]

X2 on casting # I picked up a 2-3 yr old out of "fresh from machine shop" MK IV 4 bolt block that I want to build, maybe?

 

[Busted Knuckles]

What is that casting number?

10069286. I did some research here and a couple of guys didn't care for the block including MJ. This is one of the few casting numbers that all came 4-bolt.

 

[dragginwagon406]

I just picked up a block with some custom machining. Not sure what fits here, any ideas?

 

[Busted Knuckles]

That "custom machining" on the cam boss looks just like the one I described. It dug in deep enough to scrape a bit off of the front cam bearing.
A machinist should be able to touch that up and add a bronze spacer or some sort of Torrington setup.

 

[Wolfplace]

I just picked up a block with some custom machining. Not sure what fits here, any ideas?

That "custom machining" was done by the cam gear it ain't supposed to look like that
Can be fixed in a couple of ways
Machine for a bushing to fill the cavity & run any standard gear set preferably with a thrust bearing of your choice
Machine for a Torrington bearing installed backwards & run a standard gear set without any bearing
This is an aluminum World/Chrysler block I fixed with a bronze bushing a while back.. same issue pictures should be self explanatory

 

[Tom Mobley]

Nobody seems to have a concrete explanation for why some BBs do that and others don't. I've seen some that were real bad.

The rear core plug doesn't limit rearward motion of the cam at all. There's a gap. the rearward motion is stopped by the back of the cam gear hitting the front of the block. On our hot rod engines forward movement of the cam is usually stopped by a button in the cam gear, rides on the inside of the timing cover. Many but not all BB engines are drilled for a thrust plate, which is the best solution for roller cams. This requires a step nose cam. The depth of the step is a couple thou more than the thickness of the plate. Non roller cams require no thrust button or plate at all, ever.

Obviously, any thrust button must not preload the gear against the block.

BTW, real machine shops use mill to machine the front of the block to repair damage.

I don't run HP/HV oil pumps, not needed, not wanted. increases wear on the front of the block. Not a good thing.

That's my story and I'm stickin' to it.

 

[Tom Mobley]

Mike, that last pic it looks like the bronze spacer gizmo is proud of the block. Why is that?

 

[Wolfplace]

Mike, that last pic it looks like the bronze spacer gizmo is proud of the block. Why is that?

Because I haven't faced it yet
It is faced in one of the other pics

 

[dragginwagon406]

I just picked up a block with some custom machining. Not sure what fits here, any ideas?

That "custom machining" was done by the cam gear it ain't supposed to look like that <img src="http://www.chevelles.com/forums/images/smilies/biggrin.gif" border="0" alt="" title="Big Grin" class="inlineimg" />
Can be fixed in a couple of ways
Machine for a bushing to fill the cavity & run any standard gear set preferably with a thrust bearing of your choice
Machine for a Torrington bearing installed backwards & run a standard gear set without any bearing
This is an aluminum World/Chrysler block I fixed with a bronze bushing a while back.. same issue pictures should be self explanatory

Thanks Mike, sorry I didn’t see this reply until now.

How much does time does a typical repair like this take to correct? I don’t anticipate running a roller, but in any case, the bushing idea sounds better to me.

 

[Wolfplace]

Thanks Mike, sorry I didn’t see this reply until now.

How much does time does a typical repair like this take to correct? I don’t anticipate running a roller, but in any case, the bushing idea sounds better to me.

Depends on how it is done. Takes me about an hour
The circle cutout for the insert be it a bushing or bearing is interpolated in the CNC so it is a light press or snaps in

Unless it is worn too bad I do it a little differently on most BBC blocks using a Torrington & leaving a lip on the inner surface like a timing gear with a Torrington has so it locates on the inside.

 

[dragginwagon406]

Thanks Mike, sorry I didn’t see this reply until now.

How much does time does a typical repair like this take to correct? I don’t anticipate running a roller, but in any case, the bushing idea sounds better to me.

Depends on how it is done. Takes me about an hour
The circle cutout for the insert be it a bushing or bearing is interpolated in the CNC so it is a light press or snaps in

Unless it is worn too bad I do it a little differently on most BBC blocks using a Torrington & leaving a lip on the inner surface like a timing gear with a Torrington has so it locates on the inside.

Thanks again.

 

[Schurkey]

My favorite semi-local machinist fixes worn block faces by cutting them and then pressing-in a valve seat insert. Hard as hell, you'll never have that problem again.