[Dragncar]

Was that a hyd roller cam ? Specs ?

[PAUL K]

Originally Posted by slowbird

Yes

I said lifter bore .... Not bores 😜

[Sirrotica]

My first job out of Vo Tech I worked in the local Pontiac dealer service department. They had a RA IV block that had broken a lifter bore with the stock RA hydraulic flat tappet camshaft that got warranted thru the factory.

Like Mike, I've never used a brace with any cams used in a stock Pontiac block. I've used, solid roller, flat tappet, or hyd flat tappet, but since I have always raced on a dirt oval, and the cams aren't as aggressive as drag race cams tend to be.

Since seeing the RA IV block that broke on a street car with the OEM cam and lifters, I've tried to look for the thickest castings if I had a choice of blocks to choose from. Many of my engines were built on 2 bolt blocks, so I could pick and choose. When it comes to 4 bolt 428 blocks I used what I had, but it evidently still had enough meat to hold up to 3 years of dirt track racing with hydraulic, and solid flat tappet cams. In 1971 I paid $50 for that complete 428 4 bolt main from a 69 Grand Prix. It had a spun rod bearing and had been disassembled at the aforementioned Pontiac dealer I worked at when I was 17 YO. Everything was on a pallet. It needed the crank turned and I rebuilt it for my 69 GP racecar in 1977.

The block was decked and squared, and engine was balanced also and used 1971 D port heads with 12 to 1 TRW slugs. After ruining 7 pistons with too much compression and no high octane fuel available, Nunzi recommended the larger volume, 71 400 big valve heads to lower the compression to suit the fuel that was available at that time, it worked out just fine.

I still have it in storage just as it was pulled from the race car in 1980, I need to get it over to my garage and disassemble it to see how it held up. WOW it's been 45 years since I retired it from racing, time flies...........

[mgarblik]

That picture of the broken lifter bore looks to be a nice, thick cross section. I have raced blocks that were thinner than that. So what happened? Just no way to know for sure unfortunately. I don't think it's a common as the internet tends to indicate. But obviously, there it is, a broken block. Lots of hard work and effort wasted unfortunately. Would some sort of brace kept this from happening? No real way to know IMO. I doubt a brace would hurt anything. But save the block? Not qualified to answer that.

[Dragncar]

This guy broke 2 ! blocks with the same hyd roller cam.
sb's blocks looks like hyd rollers too.
I do not trust them.

[GOAT8U2]

Maybe the cam or lifter brand/type is a more universal issue, possible preload or even oil weight etc. With 55+ year old blocks making more power than factory it's also a possible metal fatigue issue etc.

Glad there's 2 aftermarket blocks that are fairly priced.

[Steve C.]

Roller pressure angle. Unlike a flat-tappet, a roller lifter experiences side thrust, which at higher-pressure angles, can distort the body.

Many years ago, a rule of thumb touted was that a lifter bore brace is typically not necessary until the duration at 0.200" valve lift approaches or is over 200 degrees duration.

And related to this, back then Jim Butler included a list of solid roller cams offered in his catalog (they were Comp Hi-Tech .420 rollers), and with that listing of cams he mentioned specific lobes that he stated "should not be aggressive enough to break lifter bores". Those lobes were from 252 at .050 (169 at .200) thru the top lobe with 282 at .050 (195 at .200).


.

[performerrpm]

i dont think i really need the brace for this ud solid roller im putting in....its only a 271/[email protected] which i think plenty have ran a cam in this range with no problems...but since i bought the brace for this block and figure this cam and one other i have is the biggest im gonna put in a stock block, the 2nd cam is slightly smaller but ill use it with the mega brace. all the rest of my stock blocks will use tamer cams.

however i may have got ahead of myself...im putting in .045 restrictors,all the galley holes are just under 1/4" perfect for the 1/4x20 tap i used. ive only done one side but then i started thinking maybe i should not have tapped the whole depth of the galley so that i can tighten it up against the bottom thread?

i started looking and seen where steve 25 recommended just that. you guys think red loctite will keep them in place? i was going to use it any way just for safe measure but now it seems like im gonna be relying heavy on it holding.

[242177P]

Originally Posted by performerrpm

... maybe i should not have tapped the whole depth of the galley ...

Could mangle/deform the bottom threads on purpose.

[Dragncar]

Originally Posted by performerrpm

i dont think i really need the brace for this ud solid roller im putting in....its only a 271/[email protected] which i think plenty have ran a cam in this range with no problems...but since i bought the brace for this block and figure this cam and one other i have is the biggest im gonna put in a stock block, the 2nd cam is slightly smaller but ill use it with the mega brace. all the rest of my stock blocks will use tamer cams.

however i may have got ahead of myself...im putting in .045 restrictors,all the galley holes are just under 1/4" perfect for the 1/4x20 tap i used. ive only done one side but then i started thinking maybe i should not have tapped the whole depth of the galley so that i can tighten it up against the bottom thread?

i started looking and seen where steve 25 recommended just that. you guys think red loctite will keep them in place? i was going to use it any way just for safe measure but now it seems like im gonna be relying heavy on it holding.

The @ .050 numbers by themselves do not mean a thing as far as being aggressive enough to break a lifter bore. What is the advertised @ .020 numbers from that cam ? Subtract one from the other and if you get 32 or larger its a more safe cam.
My cam was .265-.275 @ .050, does not sound aggressive right ? It was very aggressive, had a number of 29 and ended up with 34. Had it reground to .265-.274 which sounds about the same, but its not.
I just finished the season. I beat on the motor and it held up just fine . I am as quick as the Chevy Ford guys I race with but they all have race gas engines. Pontiac pump gas power baby !

[performerrpm]

Originally Posted by Dragncar

The @ .050 numbers by themselves do not mean a thing as far as being aggressive enough to break a lifter bore. What is the advertised @ .020 numbers from that cam ? Subtract one from the other and if you get 32 or larger its a more safe cam.
My cam was .265-.275 @ .050, does not sound aggressive right ? It was very aggressive, had a number of 29 and ended up with 34. Had it reground to .265-.274 which sounds about the same, but its not.
I just finished the season. I beat on the motor and it held up just fine . I am as quick as the Chevy Ford guys I race with but they all have race gas engines. Pontiac pump gas power baby !

i dont have the cam card for this cam, i only know that it ran best degreed in at 101.5° and the @ .050 specs. i also know it did ok in another stock block with no brace so hopefully the brace is just extra, that and if a cam change is done later it will hopefully be good to go

[RUDOLFSSON]

Here's an engine I'm doing for a friend, 1969 428 block.
I do this to all roller cam builds.

My own billet aluminum retainer sets:

8 mounting spots.

Huge surface area for epoxy (dykem area becomes epoxy area).

I finish grind them so they seat well at the most vulnrelable spots, that way I can preload these areas before the epoxy cures.

I have programs for both casting numbers 97X and 48X today.



Thanks,
Kris.

[Skip Fix]

Glad you chimed in Kris.

[Geoff]

The lobe lift is what breaks lifter bores. Because more LL means a smaller base circle, with more of the lifter body hanging out of the bottom of lifter bore. That gives the lifter more leverage against the bore & they can break. An analogy is a wheelbarrow full of dirt. You cannot lift it, so you make the handles longer for more leverage.
Roller cam lobes have changed. A few years ago, 260 @ 050 duration with 0.400" lobe lift was big. Now, Comp has lobes that are 235 @ 050 & over 400 lobe lift, not lifter borer friendly...

[J.C.you]

Originally Posted by Dragncar

What cam was in it ? Cam card still around ?

Sorry don’t get in here much, been long time ago but the comp 280-284 comes to mind that was in it.

[BarryStreek]

Originally Posted by Dragncar

Wrong answer. Those aluminum blocks are fit down close to the bottom of the lifter bores. And brace's that use only what, four 5/16 bolts that some are drilled and tapped right into your cam bearing boss's. you know, the area where blocks can split up the middle are in no way as held down as good as the SD brace. Have you ever took a good look at one ? Where those steel plates that spread the load among the bottom of 4 lifter bores are far stronger than even your brace. Which does have some good aspects to it but you would be better off if you incorporated steel plates that go under the lifter bores to hold it all down.
I am happy that people are making parts for our old engines we need. But that brace has been the standard for a long time now and I do not see that changing anytime soon.
Can your brace distort a lifter bore enough to make a lifter hang up if you over tighten it ?
Have you taken a good look at a SD brace and fit one ?

Thank you for the detailed reply I really appreciate the insight. You're clearly very familiar with the SD brace. I haven’t had the chance to fit one personally yet, but now I’m definitely curious. Could you share more about how it distributes the load across the lifter bores? Also, have you ever seen a case where over-tightening actually caused distortion? Just trying to learn from real-world experience

[Dragncar]

Originally Posted by BarryStreek

Thank you for the detailed reply I really appreciate the insight. You're clearly very familiar with the SD brace. I haven’t had the chance to fit one personally yet, but now I’m definitely curious. Could you share more about how it distributes the load across the lifter bores? Also, have you ever seen a case where over-tightening actually caused distortion? Just trying to learn from real-world experience

The full SD brace is in 4 sections, 3 of them grab 4 lifter bores and the 4th gets 3 and kinda gets one in the corner that does not really need anything.
Those steel plates are pretty thick, thick enough to hold the threads for the 3/8" fine thread grade 8 bolts. They go under the lifter bores and sandwich them with the cast aluminum parts on top.
They fit pretty tight to the bottom of the bores. Have machined angles cut outs for the bottom of the lifters to slide by. What you do is take a file or grinding stone and remove the casting flash on the bottom of the bores so they fit flush.
You do the same thing on the cast pieces. set tem on top of your lifter bores and take a Sharpie and mark the high spots and stick them in a vise and gently grind away where they touch until they fit nice and flush. Be careful not to grind away too much as you can take to much away ruining your "clamp". They are too expensive to ruin now.
Those steel plates are the key IMO. Far better than 5/16" bolts simply pulling down from holes you drill right on top of your cam tunnel bosses.
I have distorted lifter bores myself in the first brace I installed. You can do it. You need to have a ft lifter with you when you are doing the final install with Red Locktight on the bolts. As you go don in torque , do it in steps you need to work fairly quickly and slide that lifter in the bores making sure they do not drag.
My last one is is at 35 lbs, less that the recommended 40 lbs I believe. I felt good about it. In the back of my mind was, if I heard a little "crack" torquing them them to the final step, all that money and work I had into my block was lit on fire.
Note, the first brace I installed I did not do much grinding to the aluminum. Just filed the casting flash on the bottom. I believe I had enough distortion to drag a lifter was because the contact points were more concentrated on spots so they pushed down more in a smaller area and I got the distortion. The last one I did had so much fitting and grinding the load was spread out and I did not get any distortion.

[RUDOLFSSON]

Part 2 from my latest install on a nice 97X block.

Sandblast the retainers for better bonding, preload the weak areas with bolted connection and 1" high 360° epoxy bead cures @ various surfaces (not only the weak ones).

Thanks, Kris

[Half-Inch Stud]

Originally Posted by Geoff

The lobe lift is what breaks lifter bores. Because more LL means a smaller base circle, with more of the lifter body hanging out of the bottom of lifter bore.... A few years ago, 260 @ 050 duration with 0.400" lobe lift was big. Now, Comp has lobes that are 235 @ 050 & over 400 lobe lift, not lifter borer friendly...

Small base circles bust bores.

Photo above showed CYL #5 Bore busted: Bore hoop not in tension, so just why-how did thaat happen?
My guess (Small base circle + roller wheel failure + top lifter edge catching Bore edge + hanging-up = Lobe smack on next cycle), or just because of a roller wheel failure.

I'd expect an unsupported Pass-Side bore to bust before ANY DS bore.

[Dragncar]

Originally Posted by Half-Inch Stud

Small base circles bust bores.

Photo above showed CYL #5 Bore busted: Bore hoop not in tension, so just why-how did thaat happen?
My guess (Small base circle + roller wheel failure + top lifter edge catching Bore edge + hanging-up = Lobe smack on next cycle), or just because of a roller wheel failure.

I'd expect an unsupported Pass-Side bore to bust before ANY DS bore.

I always understood that is was not lift that breaks the bores. It was how quickly the lifter accelerates on the corner of the lobe. By the time the lifter is getting near peak lift the dangerous part of the lobe has already gone by and its just lifting straight up, more or less.
That Scott Brown cam Jake's son had in his 4" stroke stock block had a lot of lift. It was over .760 lift and lived.
Its too important of a issue when trying to get a near max performance cam in a stock block to not fully trust a real deal cam expert like Scott Brown or Tim Goolsby. Let those guys make the call, or someone like them who is very familiar with OEM Pontiac blocks and what they can take.
When I sent my Comp SR can to Tim at Bullet he just fuzzed the base circle and took .014 off thetip, max lift area. But the intake opening ramp was made less aggressive. It was so close of a re grind I did not have to get new pushrods or re degree the cam. Same pushrods and straight up after the first install.
He told me I would loose 10-15 HP and I was fine with it. After all if you have a issue your block is scrap metal. Easy choice, engine runs great.