Pulling a Compression Test on my Stock Rebuilt 400 Small Block Chevy Engine

okay folks we're back working on the truck you know what that means another week has passed how are you doing donny oh pretty good how about you pretty good they're still laughing about your uh distributor video yeah you know got to do what you got to do to get ready all right so we have been trying to sew this quick review this is a 86 gmc sierra pickup we've been working on because i can haul arcade games on it and i'm trying to fix this thing up really nice i drove it for a long time uh back in the day somebody swapped a 400 engine into it it originally would have like a 305 in it the engine got down to its last legs we took it to have it rebuilt so we we had it rebuilt they reinstalled it could not get it to run we it was it was rebuilt by a reputable rebuilding place but the guy that installed it wasn't that good at tuning them so he never did get it to run we took it to another place uh that guy got it to run but it don't run very good so he couldn't figure it out either so now we got it here where donnie's messing with it so we've been doing everything to it so what have we done so far we took the uh the aluminum intake they had on it off and put a cast iron intake on it we put a new distributor new timing i mean uh set the timing new spark plugs new spark plug wires we've ordered spark plug wire retainers to keep them off the manifolds haven't got those in yet uh that carburetor is new we adjusted the carburetor so basically we've got it running but it's not running great the the problem we have is with it it's got a ton of vibration at low rpms as soon as rpms come up the vibration comes up so a couple people in our comments were we're a couple weeks ahead on the videos yeah so y'all are a couple weeks behind but in our comments were people are telling us to look at the flywheel and the harmonic balancer we have done that both of those are definitely 400 but we still got a vibration in it let me let me explain too the first guy pulled the engine and took it to a rebuilding place and the rebuilding place would you vouch for them danny yeah they're pretty good they're pretty good and we know the guy that actually did the machine work actually fairly well and we know that guy's really good the guy that does the machine work for this particular engine rebuilding place well they made the short block sent it back to the first guy the first guy though and he was very upfront about this at the beginning he's one of the only guys i could get to work on it and he told me from the beginning look i don't rebuild engines i can swap an engine but i you know he he's not good with the rest of it well they gave him back a short block which meant he had to put the intake back on it the oil pump the fuel pump all that stuff and the guy just he's he's never really done that so he it wasn't his thing so anyway long story short whenever he could get it to turn over but he had the same problem where it was vibrating but he couldn't get it to idle but anyway the vibration thing from the very beginning we knew about the difference so this is a 400. we knew about the difference between a 350 and a 400 being the crank and that the 400 is externally balanced the 350 is internally balanced so while i was standing there the guy called the engine rebuilder who's a pro i mean these guys do a bunch of them and asked them on the phone hey man are you this thing's got a vibration are you sure you put a 400 crank in it donny wouldn't a 350 crank go right in it i mean the bearings might be a difference the bearings might be a different size but length and everything yes they'll go in there and it will actually de-stroke it you know de-stroke it down and make a racing engine out of it basically so anyway we called the we he called the builder right there in front of me the guy that had done all the machine work and everything and asked him hey did you put a 400 crank in this or is it got a 350 crank in it we're going to order another harmonic balancer and the guy said the guy just you know matter-of-factly like he was pissed off the guy said well buddy you dropped me off a 400 engine so i put a 400 crank in it you know so i'm pretty confident that the guy put the right crank in because he thought it was insulting that we even asked him which you know i can agree with him but we're trying to track it down so anyway we're pretty sure it's got a 400 crank but who the hell knows so we've just um tell them what you checked i just checked the flywheel and the harmonic balancer both of them are weighted the balancers got cut out in it and the flywheel's got weights welded to it so i'm pretty sure both of these are 400. see yes and uh to clear up what a couple people have been saying uh whenever they were whenever we were messing with the starter the starter does have uh it's it is only supposed to go halfway over the flywheel the flywheel's in the right place there's no washers on the harmonic balancer i mean not the harmonic mounts or the torque converter all of that looks right so we think we're good with the starter part we think we've got the right flywheel we think we've got the right um balancer and when you get on the thing a little bit the vibration goes away yeah if you could keep it say a thousand 14 1500 rpm it's fine it runs smooth it's nice and smooth but with it this thing's sitting there idling it's sitting there doing this constantly like it's got a race cam in it and it shouldn't be doing that that now and whenever we rebuild it uh we rebuilt it just as mild as possible this engine before had been bored over 40 so it is bored over 40 but we didn't put a we didn't put a crazy cam in it or nothing that's supposed to be as stock as we can get it um so it's idling and it's running and we drove it in the last video as you saw um it drives we need to work on the brakes a little bit but uh another thing i've noticed when i was driving it i went out front there and really stood in it and uh it launches pretty good but out there once the tires get to spinning out there about 15 feet the tire stops spinning and it loses all power now you didn't you weren't racing right in front of town hall where you went a little bit we were just now you know the people from town hall probably watched this donny i wasn't racing but i was getting we were just testing the engine we now we know we're not supposed to do that we're just checking it out we did it out there because it was a safe place to do it where we hit the brakes and everything anyway but it it's losing power out there about 10 or 15 feet 20 feet out after the tires are already spinning and no it didn't shift gears so it should have just pulled the tires off and it didn't so that's another what's going on so so we are down to in our opinion valve problems or cam problems now donnie they already saw the video too of you adjusting the valves so we did adjust the valves by ear but it could be that we got one sticking open sticking shut well i'm hoping somebody's going to tell me on this video what i'm supposed to be doing but i think i'm going to pull a compression check on it and see if i can see anything with that i hate to tear the front of this thing off pull that cam out to look at it with you know no kind of nothing i'm trying to find a smoking gun and i ain't found one yet so we're trying to sherlock holmes at people on my arcade games when i work on them i figure out all the things that it's not doing right and i start at the beginning so we've tried to do that so we did fuel we did air carburetor and fuel uh we did spark and so now we're down to mechanical stuff inside the engine you know so we've got a compression tester kit i bought a while back look at this danny boom look at that one notice how it has that um amateur never been used look i did use it one time on my volume we might end up getting that down here eventually um so yeah we didn't even mention that the other week when we was talking about oh yeah got a plymouth too okay so uh we uh we're gonna pull out a plug donnie has uh unplugged the wiring on the distributor so that the engine cannot start because there's no spark and then we're going to plug in the compression test we're going to remove a spark plug on the first cylinder turn it over a little bit see what kind of compression readings we get and then move on to the next one the next one the next one we're gonna check all eight of them and see if we can find one hopefully completely dead now people might say well why the hell well because we're looking for the problem the worst thing that could happen is we get eight good compression tests [Music] test that's what i think what do you think yeah if we get one that's you know uh nothing then we can uh pull the valve cover and adjust on that valve and uh look at that or you know check to make sure the push rod is going up and down worst case pull the head and look at look at the valve seats and everything and we got something to look at you know it's i don't think it's anything major because this if it was a hole in the piston or you know a bad ring or something it would just be puking the smoke out of it and it's not doing that um i mean i don't know what it is all right so we're gonna i'm gonna get a piece of paper i'm gonna write down these compression tests and we're videoing it so we're gonna have a permanent record of the compression test donnie what do you think about that yep that's good all right so we'll uh let me get something right on and then we'll we'll start uh setting it up all right donnie what'd you do i took out the number one and the number three just to make it a little faster all right the two plugs out they took the plugs out he said they're a little rich a little rich a little black now remember we just put these in there's there is two miles on these damn things if that if that okay so that's that uh we have hooked up the compression gauge to the very first plug i'm going to hold the pedal all the way down so that it opens up the carburetor and then i'm going to turn it over a few times and donnie's going to see what that gauge goes up to holy hell number one now that could be a little false because it could be a wet reading i mean we're holding the gas open wide open and turning it so it could be a little high because of wet cylinder okay well i'm gonna write that down we're looking at 150 exactly that's one uh 150 okay i think 160. yeah we're gonna go with 150 that's close enough to 150. all right cylinder three donnie said it was a little bit higher and it dropped a little bit yeah the gauge is losing pressure just ever so slightly let me see 120 there are two hatches 30 40 okay so that's actually 145 and it's dropping slightly okay number five and he's right it was a little bit higher and started dropping well it's still pretty high okay so yeah they're all pretty good you know what that makes me think hope the gauge works all right got 140 on this one donny thinks i didn't hold it long enough though but we uh that's you know still well within uh i mean that's only seven percent off the highest one and our chilton manual is telling us we can be 25 all right okay donny wants to retry it out go for it danny well i'll be damn he's right okay you're right it hit 150. how did you know it's gonna do that he could just tell people he could feel it in the air tonight all right cylinder two we are uh now i know it's getting all pretty much the same reading every time i have used this on another engine though and got varying readings but it was a worn engine this is a brand new build so you would expect them to be pretty damn close wouldn't you you would done all right so that would maybe might have been a little bit lower though donny all right it went up to 150 it would go more he swears 150 so we're gonna put 150 on our chart here let me show you our chart i've been keeping meticulous records okay so here's here's our records so so far cylinder one was what was cylinder one again donnie oh okay just to confirm what was cylinder three was uh uh three was 150. okay yeah that's what i got okay i'm gonna jump around see if you remember uh cylinder seven you remember what that one was i know i skipped one there but uh i believe it was 150. yeah all right so this one's a little bit higher but i did i let it turn over ten times though usually i've been doing eight so you know what i think it was 150. number six did it get up to 150 done yep donnie claims 150. don't don't ignore that it says 140 right now he says it was at 150. all right number eight same deal pretty much on 150. okay let's write it off there all right folks here are my meticulous notes i took uh i took very precise readings and we came up with 150 pounds of compression is it measured in pounds 90 pounds per square inch i believe 150 psi on each cylinder now you may be saying i don't know ronnie i think some of them were 142 or that one kind of looked like 152. but i don't think the exact number has to be exact it was about 150 on all eight of them so we don't have any uh cylinders that are way off which would lead you to believe that there's something wrong with the uh piston rings or what we were thinking were the valves now donnie yeah did we not just prove that it is not the cam i don't know what we proved [Laughter] all right so if anybody knows what the hell they're doing and because we don't let us know down below we're trying to give everybody more information so they can help us figure it out so we've got a vibration the thing just doesn't idle quite right new rebuilt carburetor adjusted it with a vacuum gauge seems good a new distributor seems good new plugs new wires harmonic balancer uh flywheel flywheel appears to be for a 400. we've got 150 pounds of compression which i guess is pretty decent engine's board 40 over we believe we've got a mild cam in it i would think donnie if the cam was a problem where a load was missing that would mean that you wouldn't get a valve or an exhaust opening at the right time yeah you wouldn't get it open all the way which is which is the reason that it could be a cam problem you know whatever people say it could be the cam they're talking about the lobe being ground off which means that it wouldn't open a valve all the way well i don't know if it would open the valve all the way or open it where you know it's already fired so yes it did open but it's open late but that was closing late the compression would be the compression would be all off though wouldn't it i don't know if it would or not um basically i called the machine shop my buddy over at the machine shop and he told me that he thought it might be the cam's bad in it that one of the lopes on the cams already wore off it's making that happen which may have happened if it was ran for any significant amount of time without oil pressure um so i don't know you know i figured this compression check we'd find one that was way off and we'd go yep there it is but nope there it ain't it could be the gauge though i mean i i tried the plymouth it was a slant six and i i got six different uh measurements but they were off like 10 or 15 pounds from each other so i mean it ain't it seems like a gauge and the gauge looks like it's working right the way it the way that it pops up yeah i think we're cool with that all right so that's that folks so uh it's running but it's not running great so if you got any if you got any ideas things we should check or if you if you agree that it's the cam didn't he replace the lifters though yeah we replaced the lifters twice in it now donnie looked at the lifters and thought that they looked fine yeah the bottom of the lifters i looked at him after he pulled them and swapped them there wasn't no wear on the bottom of the lifters but the lifters might be harder than the cam and you might not get anywhere on the lifters i don't know to be honest with you but what we'll do we'll uh i've heard i've heard before if you if you uh swap a cam or if you if you swap a cam or you know if you pull a head you're supposed to put the lifters back in the same shaft they were in so that the wear still matches up so they could wear so anyway what are you going to say when we get these plugs back in here we'll start it up with a glass on the front of it here so you guys can see the vibration in it yeah okay cool all right folks so this is what we're working with donnie has put this coke bottle on the hood which will serve as our uh vibration gauge okay now just so you know what what we're dealing with here right i'm not even in the truck starts right up let me give it a little gas huh well that was a lot oh hell you better come catch it all right so leave your comments below let us know what you think tell them what to do donny subscribe to the channel give us a thumbs up for filming it and we'll catch you on the next one