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


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Old 02-22-2008, 09:49 AM   #1
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Default stiff spot in engine..

Hey guys, my engine is down to almost the bare block, heads are on, wasn't going to mess with those. I turned the engine over by hand, and I have a "tight" spot once on every rev of the crank. At first, I thought I didn't take out one of the plugs. That is NOT good. I haven't touched the lower end at all, there should be no reason whatsoever for there to be bearing issues, I'm thinking maybe one of the cyl walls has some crud on it, near the top or bottom, since it is once per rev. I would think that if there was something in the middle of the stroke, I would feel it twice..
Engine has never been left open, that is, there is no crud that fell down in there, I suppose it is possilbe that there is a dead mouse on top of one of the pistons, by highly unlikely.
I thought I would squirt some tranny fluid in each spark plug hole, spin it a few times, let it sit and see what happens. I don't really want to take the heads off.
I'm 99.9% sure it isn't in the valve train, since it is once per crank rev, but to be sure I could remove the timing chain - is this an interference motor? Don't want to tag a valve.
Thoughts? Opinions? Mike
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Old 02-22-2008, 10:35 AM   #2
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Try squirting some fluid in the cylinder stops and see if softens the feel, this will only cause some minor smoking on start up.

I cant see this as a valve train issue, do you have the rockers and push rods removed?
You can get or borrow a bore scope to save the head gaskets, but if you find something then they'll have to come off anyways.

Try the timming chain idea, would only take a minute to rule it out.
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Old 02-22-2008, 10:47 AM   #3
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Default okay

I highly doubt it'* in the valve train, since it is every rev of the crank, if it was the valve train then it would be every other rev of the crank. For sure, I'll remove the chain just to see. I'm guessing that it is something in one of the cyls, possibly I didn't get enough oil in every cyl and there is a little rust in there, right at the top. Hope I don't have any pitting, damn, I'd be pi$$ed. I turned it over a few times by hand just trying to diagnose, and it got easier already, so I don't think it is an earth-shattering thing.. I'll do the squirt over the weekend.. if it clears up completely or near completely, think it'* safe to not investigate any further?
I've been inside a lot of engines in my lifetime, this is the first time this has happened.. Either just bad luck, or I've lost my touch, or are these engines more sensitive than the trusty small block chevy? It hasn't run in almost 2 years.. Mike
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Old 02-22-2008, 10:56 AM   #4
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No the engine block is tough as nails, yeah a slight rust build up would feel rough.
Softening with a few hand turns is a good sign.

Was recently into a series 1 block with chipped piston and softly scoored cylinder wall with no rough feel. Could make the scooring out with your finger nail only.
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Old 02-22-2008, 11:56 AM   #5
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While we were prepping my new motor for install two weeks ago, we were running revolutions with a 1/2" ratchet on the engine stand. While I'd pre-lubed the main and rod bearings, as well as the cam bearings and balance shaft bearings, and in spite of no valve train installed, the motor was somewhat stiff until I squirted a little oil in each spark plug hole with the engine rotated on the stand so the piston was perfectly vertical.

Motor freed right up and spun great. There was no rust or carbon buildup, either. It had been completely cleaned.
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Old 02-22-2008, 12:04 PM   #6
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Default probably no cause for concern..

..but since I had fully expected relatively little resistance and certainly no stiff spots in this engine, since it had not been messed with, my gut reaction was "Uh oh, what happened here.."
I will squirt it up and see what happens.
BTW, years back, could spin up the oil pump before the distributor was installed, make sure there was oil "at the ready" before a rebuilt engine fired the first time..
I plan on packing the oil pump with vaseline, that'* what we did on the old chevys, install the front cover and put in oil before anything else is assembled, (like intake, rocker covers) and cranking the engine with the starter without the plugs in it, to get some oil up and into the galleries, - is this still the thing to do, or is there another way, or what.. again, an old school guy making sure a stupid mistake does not cost me, since this engine is newer and a little different.
Willwren, I guess the simple question is how are you prepping the lube system for first start up? After two years, I'm sure my engine is awefully dry. Mike
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Old 02-22-2008, 12:15 PM   #7
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We added oil as we built it up, poured on the valve train and a few quarts in the intake valley.
We left the connector off the Coil pack and Bill cranked it untill he was up to preasure then pluged the coil pack in and fired it up. Smooth as can be.
Bill also pre-filled the oil filter before installing it.
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Old 02-22-2008, 12:54 PM   #8
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Default mice?

You know, the perfect way to describe this is: Remember the trick of stuffing clean rope in the spark plug hole of a lawnmower engine so you can stop the engine from spinning when removing the flywheel nut? And when you didn't have enough rope in there and with resistance you could get that rope compressed enough that it would continue to spin but with resistance at TDC? That'* what I'm talking about, like there'* a cushion at the top of one of the cyls... Not like a bolt or a socket, and not like rust on the cyl, there'* no noise and no roughness.. Man, could a mouse have gotten in there? When I pulled the motor, I had all the holes taped up, I don't know what I could have missed, but in thinking about it, I spun the motor once about 6 months ago and I think it had the stiff spot then - before anything was done to it! I wonder if I can see enough through the spark plug hole to see something in there. Damn.
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Old 02-22-2008, 01:10 PM   #9
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The rope trick is how I swaped out my rockers so I know the feeling.

Bore scope would help, maybe a small mirror and led flashlight?
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Old 02-22-2008, 08:23 PM   #10
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Default solved

Removed the timing chain, still there, not valve train. A few squirts of penetrating oil followed by a few squirts of motor oil, turned it over a few times, now smooth as glass. I guess I got nervous over nothing. Must have been a little rust or something like that, just one little spot. Good to go, I do believe... Thanks.. Mike
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