stiff spot again in 93 se engine - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-11-2008, 10:00 PM   #1
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Default stiff spot again in 93 se engine

You guys remember the stiff spot I had in my engine when turning it over by hand? A similar thing is back again. I have the engine back in the car, completely assembled. I can't run it because I don't have all the fluids in yet - but I have the ability to crank it with the key, with all spark plugs in. Cranks, but not smooth.. It'* got a "hard" spot in it, like the starter slows down briefly, steadily rhythmic. Right after the slow down, when it picks up speed again, I can hear a "fump" sound, like a lot of air was just released. Not a knock, or something hitting, but like one piston has a LOT more compression than all the rest. Could one lifter bleed down a lot more than all the others? Or could one not bleed down near as much as the others? Am I just worried about nothing, all will smooth out once it starts up and everything gets oiled up and all the lifters get pumped up and all the cyls burn off any and all oil that I squirted in the spark plug holes? I had one rocker off, just to look at it, about a year ago.. when I did that, does that allow the lifter to "expand" so that now I have one valve being opened more than all the rest, and this will settle down once the engine is running? (that doesn't make sense to me, but just a shot in the dark) If I crank the engine over by hand with a wrench on the balancer bolt, I can feel this stiff spot, it is every other rev of the crank, but it does not feel like a bind, rather it feels like more compression. (Before, it was every rev of the crank, and went away with oil squirted in the spark plug holes) A lot of typing here, any thoughts? Mike
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Old 04-12-2008, 01:41 AM   #2
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You could test your idea about the lifters, if you pull the plugs and try to crank it by hand. If it goes easily without the tight spot, that would indicate compression.

I had a similar problem with an engine on my stand at the moment. (Toyota V6) The first time I installed the crank and main bearings, I had a tight spot. I removed the bearing caps and carefully cleaned the mating surfaces on the caps and the block, then re-assembled it. No tight spot.

I was greatly relieved that it smoothed out. If I had not been able to turn it easily by hand, I would have paid to have the block and bearing saddles align bored - $130.
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Old 04-12-2008, 09:27 AM   #3
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Default more detail

When I pulled the motor over a year ago, it sat for a while, all holes plugged to keep dirt, critters out. After I finished rebuilding the tranny, I put the engine on the stand, started pulling and bagging parts. Just superficial stuff at this time. I removed the rocker covers, and it looked like rust under the bolts that held the rockers. Uh oh, I thought. I pulled one and then realized it was some type of threadlocker / sealer, I was very relieved. I then reinstalled it, torqued it down. I then turned the engine over by hand, no plugs, and it was noticeably harder to turn when that rocker was moving to open the valve. I thought this was strange, I don't remember having that with ANY other engine I had ever had apart. It eased up significantly with a few revs. So, I thought maybe a lifter expanded, which I thought was odd too.. but.. the last engine I had apart was an early 80'* chevy small block, maybe a lot of rules had changed.. Anyway, this stiff spot was every other rev of the crank.
Not too long ago, I had the stiff spot when just turning the crank. (timing chain off) that cleared with a squirt down each spark plug hole.
Assembled the engine enough to spin it up to check the oil pressure. No spark plugs installed, starter had no rise/fall sounds, it sounded nice and smooth. Now, with the plugs installed, I have this. Sure sounds like I'm moving more air (and thus compressing more air) with one piston, I suppose it could be just that. I can't imagine I've got any problems internally, the engine ran great when pulled. Years back, I wouldn't give any of this much thought, I'd reassemble and fire it up, engines would smoke and run rough for a bit until things got cleared out and cleared up and pumped up and whatnot.. Trying to be ultra careful here, probably way overthinking the whole thing. Mike
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Old 04-12-2008, 09:57 AM   #4
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Similar issue happened to me when I put the motor in the SSEi back in '06. None of us could rotate the engine a full 360*...would go about 345* but that was all. Turned out carbon had loosened up in the head, and was enough to block the piston (used engine).
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Old 04-12-2008, 04:55 PM   #5
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When you installed your crank with assembly lube, and then installed the Main caps torqued to spec.... Did you at that point give the crank several rotations to make sure that there were no tight spots and that the crank was able to turn freely?

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Old 04-12-2008, 05:17 PM   #6
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Default Not torn down that far

Engine was only torn down far enough to replace gaskets, except for the head gaskets. Didn't mess with anything like the crank, pistons, cam, valve train, except for that one rocker. Which is why I'm surprised at the stiff spot - because nothing was touched that deep.
Question: Are these interference motors? I was turning the crank by hand with the timing chain off.
Mike
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Old 04-12-2008, 07:15 PM   #7
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All I can tell you is that its not a 0 deck motor... The piston crown sits a hair above the top of the block...

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Old 04-13-2008, 09:29 AM   #8
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Default Re: Not torn down that far

Quote:
Originally Posted by TROYPORT
Question: Are these interference motors?
Our 3800s are not interference motors.
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Old 04-13-2008, 09:45 AM   #9
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Default Re: more detail

Quote:
Originally Posted by TROYPORT
Anyway, this stiff spot was every other rev of the crank.
I am sorry I missed this important point the first time I read your post. A tight main or rod bearing would reveal itself every revolution. You have properly assessed the problem as cam / valve related. I wonder if it is possible, as you guessed, that all the lifters leaked down over time except for that one, and that caused a greater resistance when you got to that valve? Or, that one lifter may be stuck in the full up position. The only way I know that a lifter can expand is with oil pressure filling the body. If the tight spot is not so bad that the engine could be turned with a heavy 1/2" drill, I would recommend pre-lubing the engine by filling the crankcase, pulling the plugs and turning it over with the drill for a few minutes before attempting to start.
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Old 04-13-2008, 11:04 AM   #10
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Default I'll just move forward

Thanks for the input. Before I installed the engine, I cranked it over without plugs via the starter to pump up the oil, I had a thread going, because I was surprised that I had 70 psi at cranking, but it was 38 degrees, 10w30, and the pump was packed with vaseline. The engine was very smooth, no funny spots. Turning it over by hand (socket wrench on balancer bolt) it was smooth. The "funny" spot was noticed when the plugs were installed. the "fump" noise is an air noise, not a clunk or a knock. I'm relatively sure I'm just getting concerned over nothing.
I was sure these engines were not interference engines, but the imagination starts to wander sometimes, I got to thinking that if it was, maybe I tagged a valve when I had the timing chain off and I was spinning the crank, although it would surprise me that I could do damage by hand if I was tagging a valve, and now I had something bent and/or hung up.
I'm slowly getting closer to starting it, just a few things to hook up, but I am waiting on mineral oil for the AC system, I am returning it to R12 and need to flush the compressor well to remove all traces of the pag oil, I'll have the AC system closed up but not evacuated, biggest unknown at this point is my rebuilt tranny.. When I start if for the first time, aside from scrambling looking for fluid leaks, I'll be holding my breath on the tranny, it was my first time on a transaxle rebuild, could be an interesting first 5 minutes. Off to Germany for work early in the week, so no progress will be made this week, I hate traveling like that, it'* a helpless feeling when the plane leaves the ground headed for Europe, best case scenario is I'm 24 hours from getting back home should something happen to my girls. Not that it will, but I just like coming HOME every night.

Mike
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