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I've had a problem with my 406 breaking up badly above 4 grand and finally concluded it must be the lifters. Trust me, that wasn't my first choice but as I've written here before, I've eliminated the carb as a source and replaced everything in the ignition system with the exception of the distributor which had been recently inspected for runout and end play. When I built this motor, I was suspicious of the lifters but don't remember exactly why now but think it was because they were an unknown brand.
After replacing the spark plug wires a few months ago, I took it out and attempted several runs over 4 grand with no change in how badly it broke up. If I stayed on it, it would make it to 5500 but with no power and missing badly. During my last run, I heard clattering and immediately pulled off the road and opened the hood. It was also missing at idle now and I could tell it was the valve train making the noise but as I stood there listening, it slowly quit making noise and began idling smooth again. I decided the hydraulic roller lifters were not holding up under the higher RPM and that was my problem.
I located some AC/Delco lifters and ordered a set and have had them for several months waiting for the right time to dig into replacing them. I was still driving the car around town in the meantime. It had plenty of performance below 4 grand so I was still enjoying it. Now with 90+ degree days, it seemed like a good time to work on it considering my shop is air conditioned.
When I lifted the intake manifold, I was shocked to see a dog-bone on top of the spider finger that was supposed to be holding it down! I knew there was no way I assembled it like that but could also tell the spider was undamaged. And miraculously I could see the two lifters were still properly oriented in their bores! How or why they never rotated and wiped out the cam is beyond me. Perhaps a natural tendency to stay in alignment while rolling on the cam lobes is all I can think of. When I removed the spider, the dog-bone fell back into place on the lifters confirming that they were still in proper alignment.
Next I started the process of removing the rocker arms and pushrods to be able to replace the lifters. As I backed off the nut on one of the rockers, the stud snapped off flush with the bottom of the nut. Apparently the 3-4 threads of engagement were enough to hold it in place! Unreal! I was able to place my finger against the broken surface of the stud in the nut and rotate it out so there was no binding. These are first gen Trick Flow heads and this is the second broken stud so they're all being replaced with ARP studs.
After pulling the push rods, I discovered how that one dog-bone ended up out of place - one side is broken out! I couldn't see that initially as it was on the side toward the block. How or why it broke is a complete mystery but I now believe that was the clattering I heard as it being knocked around and finally ending up on top of the finger of the spider where it got quiet again. I am going to check the lift on those two cam lobes but as I rotated the engine to remove the other dog-bones, those two lifters seemed to move the normal amount. I imagine the broken piece is sitting on the bottom of the oil pan. And speaking of oil pan, I had the car on a lift recently and found oil all over the lower part of the engine. So I pressure washed the engine and decided to do an oil change and search for the oil leak while I was at it. Well, all the oil pan bolts were only finger tight! That would account for the oil!
The other surprise was the nut on the vibration damper was backed partially out. That fits with all the other loose parts! I'll take it out completely and put some Loctite on it but that's really not an option with the oil pan bolts considering how oily they are now. Next is ordering the studs and a replacement dog-bone, then put it back together and see whether or not those lifters were my problem. Wish me luck!
I have some 1st Gen Trick Flow heads that I was going to use (they have a couple to 5 thou miles on them with a flat tappet cam.) I was going to switch to a roller and have already changed the springs. After your stud problem I think I will swap out to ARP while I’m at it.
I have some 1st Gen Trick Flow heads that I was going to use (they have a couple to 5 thou miles on them with a flat tappet cam.) I was going to switch to a roller and have already changed the springs. After your stud problem I think I will swap out to ARP while I’m at it.
Yes, I would definitely change the studs. I've just ordered the ARP #134-1701set.
The only rockers I found to work with those heads were Crane Gold aluminum. I tried the OEM stamped steel, forged steel with roller tips and some other type I can't remember and could not achieve a acceptable contact patch with the valve stems. I believe their original advertising said the OEM rockers would work but early users found that not to be true and many recommended the Cranes.
I had made an adjustable pushrod to get the correct contact patch and then was fortunate to find a big block pushrod that was nearly identical in length so I saved the cost of custom pushrods.
Last edited by 65air_coupe; 06-26-2022 at 06:01 PM.
Wow, you are lucky, if the roller lifter went sideways you would see tracks on the cam lobe and the lifter wheel would show impact marks. You are using the OEM lifter tray from a 350 block in the 406. If I remember correctly the OEM lifter tray set up only allows a certain amount of lift? I am thinking it is around .480 but that number would need to be researched. Parts don’t just break like your one dog bone did. They break like that because they are being pressured to do a job they are not designed for. I am guessing, kind of like assuming that you have clearance up to 4,000 RPM and run into interference above 4,000 RPM. Maybe coil bind in the valve springs, Look for witness marks on the coils where they may be touching at high RPM. There may be 100 other possibilities but coil bind is possible to give you all these troubles. Broken stud on the rocker arm, breaking up at 4,000 RPM. What ratio are your rocker arms? 1.5 or 1.6? Not to many things work perfectly from 0 to 4,000 and then cause problems.
I did test a set that looked much like that but I don't think they were Comp Cams versions. I could not center the contact patch on the valve stem and learned there is an amazing variation in the geometry between various rockers.
Last edited by 65air_coupe; 06-26-2022 at 03:54 PM.
Wow, you are lucky, if the roller lifter went sideways you would see tracks on the cam lobe and the lifter wheel would show impact marks. You are using the OEM lifter tray from a 350 block in the 406. If I remember correctly the OEM lifter tray set up only allows a certain amount of lift? I am thinking it is around .480 but that number would need to be researched. Parts don’t just break like your one dog bone did. They break like that because they are being pressured to do a job they are not designed for. I am guessing, kind of like assuming that you have clearance up to 4,000 RPM and run into interference above 4,000 RPM. Maybe coil bind in the valve springs, Look for witness marks on the coils where they may be touching at high RPM. There may be 100 other possibilities but coil bind is possible to give you all these troubles. Broken stud on the rocker arm, breaking up at 4,000 RPM. What ratio are your rocker arms? 1.5 or 1.6? Not to many things work perfectly from 0 to 4,000 and then cause problems.
Thanks for chiming in Mark. I never saw any information about OEM lifter tray limitations and will have to research that further. My lift is 0.520 so it's definitely over the limit you're mentioning but I don't see how the lifter tray plays any role in that. It doesn't move under normal circumstances unless there's an issue where the OEM lifters and the dog bones have a lift limitation. And all sorts of bad things are doing to happen if that's the case as either the lifter is falling below the dog bone then catching an edge of it on the way back up and causing it to impact the side wall of the lifter valley or the lifter stays inside the dog bone but lifts it up as it rises beyond the combined limitation of the two. I'm not sure how the latter scenario would lead to breakage but it's certainly something that shouldn't be happening.
I wanted to stay away from after-market roller conversion hardware because they never get the same reliability testing that goes into OEM parts. And besides being costly, early versions had lots of breakage and just looking at many of them makes me think they're going to be trouble. I will check for evidence of lifter bind but I'm fairly confident I checked for that possibility when first building this motor. I'll also see if I can dig up specs for those springs and heads. I'll report back with what I find.
Stock lifter/dog bone/spider configuration is good for lifts less than 0.550" and speeds less than 6,000 rpm
Gen 1 Twisted Wedge heads with dual springs are good for lifts up to 0.600" w/460#/in spring rate
XE282HR lift w/1.5 rocker is 0.510/0.520 which equates to a max spring pressure of 340-350#
Dog bones are 0.270" thick w/0,030" recess, lifter flats are 0.575", lifters sit about 0.050 below top of dog bone
Max lifter travel within dog bone is 0.575 - 0.240 + 0.050 = 0.385"
Cam lobe lift equals 0.520 / 1.5 = 0.347"
Looking at those last calculations, it's possible that the steps on the sides lifter were striking the underside of one of more of the dog bones. I have no idea what effect would be, especially considering they're near the end of travel so their speed is at their lowest when and if it even occurs. When I assembled the motor, I spun it with the starter while watching for any contact between lifters and dog bones and saw none but that's a visual inspection only. A dial indicator might show something different.
So it's clear there's no coil bind and the OEM parts are fine for a street car. I can only assume the broken studs are why Trick Flow changed to ARP studs with the second generation heads. It's going to remain a mystery why that one dog bone broke and now I wish I had identified that lifter to inspect for any marks. I may still go through them all just to satisfy my curiosity. I'm not happy with the prospect of putting it back together without knowing the root cause of the failure.
EDIT: If I can't identify the corresponding lifter, I may just pull the pan and retrieve that broken piece just so I can inspect for contact with the lifter or valley side wall.
Last edited by 65air_coupe; 06-27-2022 at 01:10 PM.
Is the block a factory roller setup or has it been modified for the dog bones. They’re close stock no telling where you are if it’s a modified block. Make sure the flat on the lifter doesn’t hit the dog bone at max lift.
Look for witness marks of contact on the bottom of the dog bones. Even if they clear while rotating your block by hand you need extra clearance for when the RPM rises and the lifter actually raises a little more than the cam lift due to rotational energy, I suspect you would need somewhere between .020 and .040 extra clearance to clear at 5,000 RPM. Guys who raced High RPM engines with big cams installed rev kits that were springs mounted between the lifter and the heads to keep the lifters from floating up at high rpm. There must be a known number to be calculated in. Something messed with your nice engine. I don’t feel good putting a project back together till the smoking Gun is found. I do not think swapping lifters would change anything unless one brand allows more lift inside the dog bone than the other brand.
Well this is disappointing. The suspect lifter was obvious and I found one other with less damage. While I know the worst one is on an exhaust valve which makes sense since there's 0.010" more lift, I don't know where the other one came from. I'll probably inspect the retainers next.
So now I know the root cause but I'm unsure what I'll chose for a solution. A lower lift cam is an obvious choice but that's big bucks and a lot more tear down. For those reasons, I'm considering having the retainers relieved on one side to allow the lifters to rise higher without making contact.
I'm open to suggestions for a milder, roller cam at this point. I know many don't regard Comp Cams very highly but I've had no issues with this one but tell me what you'd pick. I could always go to 1.6 rockers if I really wanted to keep all the horsepower but I can't use what I have now so probably won't take that step.
For reference:
406 ci, 11.1 compression ratio, Twisted Wedge 63/180cc al. heads, 5 speed w/3.70 diffy. Street use only.
Last edited by 65air_coupe; 06-27-2022 at 11:47 AM.
Is the block a factory roller setup or has it been modified for the dog bones. They’re close stock no telling where you are if it’s a modified block. Make sure the flat on the lifter doesn’t hit the dog bone at max lift.
It's a modified block. Based on my calculations, there's 0.040" nominal clearance but most of the retainers rest on an 'as cast' surface that's been squared to the lifter bore so there's going to be variation. However I decide to proceed, the travel of each lifter above the top surface of the lifter bore will be measured to determine actual clearance to the underside of its retainer. I'll do that now for each location which will give me a guideline of how much clearance to allow. Three lifters show signs of contact and I'll be able to determine what hole the other two came from.
06-25-2022, 05:50 PM
Luckiest SOB
