DOD Delete Theory

[Donal]

well fak.. I may have answered my own question. so in a random post on an archived head porting forum there was one post buried in tread where a guy said there's some built in slop in the locks, so they aren't locked solid like I was thinking. the oil pressure holds them extended on the base circle but there's no check valve in that part like the hydraulic part, so as it ramps up it compresses internally as well soaking up duration. so it's not really about lower compression from not opening the valves enough with the normal lifters, it's opening them to long, where you get more overlap and bleeding off comp at low rpm.

if that's true, at the valve you have a long duration low lift cam on 4 cyl after the swap. almost like a Atkinson-cycle engine but only on 4 of 8 cyl.

which is kinda interesting in theory since my hybrid does have late intake valve closing Atkinson-cycle type cam in it. I've always wondered what it be like with a normal truck cam. but the lack of tuning in the ecm, I'd not try it. sounds like if my disabled and bypassed afm lifters ever fail, I'm buying 8 oem afm lifters to replace them.

Actually the outer sleeve has the roller and maintains contact with and follows the camshaft lobe. The inner or middle sleeve has the visable spring attached to it and the these two components are locked together by the two hollow pins. The pins are spring loaded to maintain the locked condition. When the system supplies oil the the outer sleeve oriffice aligned with the pins, the pins move into the inner sleeve and the two sleeves are un-locked. The unlocked conditions allows the outer sleeve to follow the cam lobe. The inner sleeve no longer follows the cam and is not moving. The inner sleeve, push rod and pushrod seat in the inner sleeve are loaded by the compression of the visable spring and the valve spring to maintain their normal position as if the engine was not running. The visable spring also loads the outer sleeve so that the roller follows the cam lobe.

 

[j91z28d1]

Actually the outer sleeve has the roller and maintains contact with and follows the camshaft lobe. The inner or middle sleeve has the visable spring attached to it and the these two components are locked together by the two hollow pins. The pins are spring loaded to maintain the locked condition. When the system supplies oil the the outer sleeve oriffice aligned with the pins, the pins move into the inner sleeve and the two sleeves are un-locked. The unlocked conditions allows the outer sleeve to follow the cam lobe. The inner sleeve no longer follows the cam and is not moving. The inner sleeve, push rod and pushrod seat in the inner sleeve are loaded by the compression of the visable spring and the valve spring to maintain their normal position as if the engine was not running. The visable spring also loads the outer sleeve so that the roller follows the cam lobe.

yeah, that's how I understand they work watching tear down videos. this was not talking about oil pressure from the top side ports that release the pins, but just main body pressure and some slop between the inner and outer body when locked. I've not personally tested them to experiment with something like that. Just going off what someone said they made sense reading it and the most logical reason I've found.

having good compression at the low rpm of cranking would lead to that post being incorrect. I still hope this works.

I do wonder if the new lifters are pumped up completely as they will be on a running engine. sounds like we will find out.

I do also wonder if there's been different afm factory cam grinds over the years. where some times it works, sometimes it doesn't. depending on grind and engine sizes?

 

[Marky Dissod]

how is the afm lifter adding compression over a non afm on the same lobe?

Although I could be wrong, I don't think V4 mode lifters add compression.

 

[iamdub]

Although I could be wrong, I don't think V4 mode lifters add compression.

It's not the lifter, it's the cam lobe profile. Valve events: Dynamic compression ration versus static compression ratio.

 

[j91z28d1]

Although I could be wrong, I don't think V4 mode lifters add compression.

I was meaning compared to a standard lifter on the same lobe. there's still a missing veritable if a afm lifter doesn't have some give in it removing some duration that causes overlap, but some how other guys, not the op here or seems but the general internet of doing this says you lose 50psi cranking compression from a afm lifter to a standard lifter on the same lobe, my question is how exactly is the afm making more.



dynamic compression. ha I could not think of that term for the life of me last night.

 

[RET423]

Finally got it fired up around 8pm last night, unbelievable how much longer it takes to reassemble in this Envoy chassis compared to the Yukon; this strut style front suspension may be nice to drive but the towers are miserable to deal with for maintenance.

Engine runs great, very quiet and smooth; I did get a random misfire code initially but I assume that was due to working the air out of the fuel system because it cleared up right away. Oil psi is steady 50 at idle warm (as expected with the high volume pump still in place), I have a small coolant leak from one of the plastic heater hose Tee's so I must have cracked that fighting the exhaust manifold (standard GM
Headaches )

No lifter noise as expected and the throttle is very responsive, I would love to check the compression on #4 now that I have let it run for 20 minutes but after the fight it took to get that spark plug in I am not pulling it unless a symptom appears.

I do wonder if GM used multiple grinds on these DOD cams, this is a 2006 gen 4 so it is the first year for the DOD and GM's first attempt at this tech; my information may not be universal to all the DOD models.

I can see several variables that could effect the needed pushrod length after a delete, in my case the factory pushrods kept everything in spec but I do think checking that is an important step to eliminate the worry regarding the valve events.

So my conclusion is, there is nothing to lose by trying this; I don't really want this factory cam but if the factory cam still looks good there is no risk involved in trying to use it. If it doesn't work out the only repeat labor is pulling the valve covers to remove the rockers/pushrods to change the cam; that is a half hour at the most. The rest of the process for a cam change doesn't require any other disassembly of the previous DOD delete work.

I hope this helps those trying to deal with this issue better understand the system, when I read the reports on other sites about what happened when this was tried they didn't include any info about verifying lifter preload or how coked up the DOD cylinders were, just the resulting compression problem and blaming the cam grind for it; I wanted to look at all of the variables so I would be able to confirm or refute the cam as the cause of a compression issue post delete.

I think I did, at least on the 2006 LH6 5.3, the factory DOD cam functions the same with LS7 Lifters as it did with the former DOD Lifters when in V8 mode as long as the lifter preload is in spec after the lifter replacement and the rest of the delete is done properly.

 

[Donal]

Finally got it fired up around 8pm last night, unbelievable how much longer it takes to reassemble in this Envoy chassis compared to the Yukon; this strut style front suspension may be nice to drive but the towers are miserable to deal with for maintenance.

Engine runs great, very quiet and smooth; I did get a random misfire code initially but I assume that was due to working the air out of the fuel system because it cleared up right away. Oil psi is steady 50 at idle warm (as expected with the high volume pump still in place), I have a small coolant leak from one of the plastic heater hose Tee's so I must have cracked that fighting the exhaust manifold (standard GM
Headaches )

No lifter noise as expected and the throttle is very responsive, I would love to check the compression on #4 now that I have let it run for 20 minutes but after the fight it took to get that spark plug in I am not pulling it unless a symptom appears.

I do wonder if GM used multiple grinds on these DOD cams, this is a 2006 gen 4 so it is the first year for the DOD and GM's first attempt at this tech; my information may not be universal to all the DOD models.

I can see several variables that could effect the needed pushrod length after a delete, in my case the factory pushrods kept everything in spec but I do think checking that is an important step to eliminate the worry regarding the valve events.

So my conclusion is, there is nothing to lose by trying this; I don't really want this factory cam but if the factory cam still looks good there is no risk involved in trying to use it. If it doesn't work out the only repeat labor is pulling the valve covers to remove the rockers/pushrods to change the cam; that is a half hour at the most. The rest of the process for a cam change doesn't require any other disassembly of the previous DOD delete work.

I hope this helps those trying to deal with this issue better understand the system, when I read the reports on other sites about what happened when this was tried they didn't include any info about verifying lifter preload or how coked up the DOD cylinders were, just the resulting compression problem and blaming the cam grind for it; I wanted to look at all of the variables so I would be able to confirm or refute the cam as the cause of a compression issue post delete.

I think I did, at least on the 2006 LH6 5.3, the factory DOD cam functions the same with LS7 Lifters as it did with the former DOD Lifters when in V8 mode as long as the lifter preload is in spec after the lifter replacement and the rest of the delete is done properly.

Thanks for all your efforts. And a bigger thanks for sharing real data. There is a lot of misinformation on this subject. You have provided real documented data. In the event or circumstance that you have access to a dod camshaft that has been removed, you can verify that the cam lobs are the same for the dod cylinders and the non dod cylinders.