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1999 Tahoe No compression on rebuilt engine
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Spiercev
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Jun 14, 2016, 7:52 PM
Post #1 of 20
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1999 Tahoe No compression on rebuilt engine
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Hello there guys,
So a friend and I rebuilt a vortec 350 5.7 engine and put it all together and it cranks over like it has zero compression. Sounds like the same all the way around like the valves are stuck open. When we were setting the valve lash we had the cylinder at tdc on compression and tightened it till the pushrod stopped turning then did another 3/4 turn and did that for all the valves. But we noticed half way through doing them that one we had already done was a little loose so we lined tdc up again and it was loose
We did the same procedure and tightened it more till it was 3/4 past snug. I noticed after that that the valve springs looked like they were pressed down more than normally but thought we did it right so i didn't really look into it but that was the only thing that I think can make it do what its doing now.
Any thought on why we had to retighten them and what we nee to check to get compression? I'm about to go re do all the valves but wanted to see if some has any other input/ideas. Sorry thats long. Thanks!
Extra info: we have done another one of these engines before and taken apart a couple of them, this one has new pistons oil pump, rebuild kit with all gaskets, was bored cleaned and what not... Also all new bearings of course.. Crank ground too..
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Tom Greenleaf
Ultimate Carjunky
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Jun 14, 2016, 11:43 PM
Post #2 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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My site is down for exact procedures but from crude memory of most Chev. small blocks since forever you tighten the rocker arm nut down to bottom at TDC or maybe totally off TDC (either way an exact procedure) then back off counting turns NOT tighten more!
Your valves can't shut so you don't have any compression as the valves are all open. Just blow in spark plug hole at TDC now it will blow air right out thru intake now.
The crude base settings and torque specs all thru this general block which is about 60 years old now in basics can run but by the "R" code ignition is now not a distributor turning thing anymore.
General with even good old "Detroit Iron" engines there's a time to give up which IMO is about the time a crankshaft isn't in spec the thing is a mooring as in boat anchor. Can't think of a more cooperative block design than this one yet it still has it's own DNA if you will with crank and bearing caps. The original bore to do that was ONCE and all you get. Anything after that is just Band-Aid work to buy some time.
When I say DNA for a block I mean when cast new it was line bored under the torque it would have as a spec. So intolerant a new bit when 100% new could only do a few it that each unique to itself. You can never swap bearing caps or it's game over and other things throughout.
Said it's the most forgiving design I know of yet still subject to age old failures. If you just did the top end the bottom would quickly fail and so on.
Suggest you find a whole good running engine to work with when one needs total help or croaked for plain wear and use or another reason.
It's only new once as said. That's all you ever get. If you want it to last at all "rebuilt" isn't the way - new is not part by part but the whole thing,
T
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Hammer Time
Ultimate Carjunky
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Jun 15, 2016, 2:10 AM
Post #3 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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It sounds like you are trying to do this with lifters that are not pumped up yet. I would back them off until they are a little loose.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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kev2
Veteran
Jun 15, 2016, 6:41 AM
Post #4 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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X2
"sounds like you are trying to do this with lifters that are not pumped up yet"
disable ignition remove plugs, disable injectors, CHECK oil for excess fuel*.... then crank to obtain oil pressure then start your adjusting.
* overly cautious BUT an easy check.
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Spiercev
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Jun 15, 2016, 7:24 AM
Post #5 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Okay..awesome thanks guys. So do the cam roller lifters actually change length when there is oil pressure inside of them? Or what exactly do yall mean when you say they get "pumped up"? On the last engine we built we did it before we primed the oil and it turned out perfect. But they maybe have oil in them idk lol. So disconnect the plugs and loosen them all and can I just turn it over with it not starting to adjust the valves? Or do I need it to start first?
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Hammer Time
Ultimate Carjunky
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Jun 15, 2016, 7:37 AM
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Re: 1999 Tahoe No compression on rebuilt engine
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Hydraulic lifters fill with oil for resistance and self centering
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Spiercev
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Jun 15, 2016, 7:39 AM
Post #8 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Okay thanks, so do I need to loosen the valves first, then turn it over and make sure oil is coming outta the push rods top and then adjust them?
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Hammer Time
Ultimate Carjunky
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Jun 15, 2016, 7:56 AM
Post #9 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Correct
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Hammer Time
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Jun 15, 2016, 11:42 AM
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Re: 1999 Tahoe No compression on rebuilt engine
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I've always done it with the engine running although it can be messy.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Hammer Time
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Jun 15, 2016, 12:32 PM
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Re: 1999 Tahoe No compression on rebuilt engine
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Back it off til it clatters, slowly bring it down until the clatter stop and the SLOWLY go the specified turns.
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Spiercev
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Jun 15, 2016, 1:08 PM
Post #14 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Okay, is it okay if some of them are still tight untill I get to them or should I start them all looser? I turned them all prolly a turn or so out and most of them I can turn the push rod now. Havent started it up yet to adjust them all
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Hammer Time
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Jun 15, 2016, 1:17 PM
Post #15 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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You're better off starting loose. The engine will run smoother and you won't do any damage..
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Spiercev
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Jun 15, 2016, 1:18 PM
Post #16 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Okay thanks👍 I'll see how it goes.
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Spiercev
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Jun 18, 2016, 2:48 AM
Post #17 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Okay. Got all the valves done and it runs really good now. I have the same compression on all cylinders. The weird thing is I was testing the compression on each cylinder as I was adjusting the valves and i couldnt even do 3/4 the way after the pushrod stiffened up before I lost compression. Usually I would have done 3/4 a turn. I know some people do 1/2 and some do one full so I usually compromise at 3/4. But this was more like 1/8 on all the valves. I went past that it would pop the valve open to much. Kinda weird? I'm not too worried about it now but would like to know if anybody has had that happen before? Thanks for all the help!
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Hammer Time
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Jun 18, 2016, 3:36 AM
Post #18 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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There is no debate or opinion on how much to turn it. The spec is 1 turn, end of conversation. I told you to turn it slowly. The lifter will reposition slowly. The spec is to put the lifter piston in the center of it's travel.
The question is, did you have it backed off all the way before adjusting. That has to be done slowly too. It may start to clatter and then stop meaning the lifter has pumped up and it's not backed off sufficiently yet.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Jun 18, 2016, 3:38 AM)
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Spiercev
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Jun 18, 2016, 4:12 AM
Post #19 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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Ah okay. I had them loosened up to where the rocker would move slightly. And then tightened from there. I turned the engine over several times where I had it set at 3/4 a turn and there was no compression at all. I've done these once before and have not had this problem. So if the rocker pushes the valve down with one turn then how is it getting compression? That whats confusing me about this lol. Is the lash or specified pressure on all the valves dependent on if the lifters have oil in them? Or some other piece? Inhad the compression tester olin each cylinder as Inwas setting them to make sure they had pressure and if I went 1 turn they would have not had any.
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Hammer Time
Ultimate Carjunky
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Jun 18, 2016, 4:17 AM
Post #20 of 20
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Re: 1999 Tahoe No compression on rebuilt engine
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You need to forget about that compression tester. It has nothing to do with this process. You were going to do this running and apparently changed your mind. You're just running in circles here. The lifter needs to be backed off totally and the engine run to get the lifters fully pumped up. Make the adjustment with the engine running.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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