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Calling All GM Pro's


the_tow_guy's Avatar
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10-23-04, 04:15 PM   #1  
Calling All GM Pro's

Okay guys, this is a two part question and I'm going to be a little vague about how I ask them and why so as not to influence the responses in any way. These are not trick questions (at least I don't THINK they are).

1. If you were installing a new motor (long-block 350 Chevy, new not remann'ed), what steps/procedures would you follow to ensure the valves were properly adjusted prior to installation because either you assumed they were not set during manufacture or maybe just because you're being extra careful. Please be specific on the steps in your procedure.

2. If you had an engine with valves adjusted very loosely (loose to the point that if they were any looser they would start clattering noticeably but still had no excessive noise), what kind of negative impact on performance or symptoms might you experience.

 
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10-23-04, 09:58 PM   #2  
NO PRO here but here is what I would do.

Set it at #1 TDC compression and get out the manual to see which valves you can set. Loosen each rocker arm untill you have a slight amount of valve lash. then tighten until the lash is 0. Then turn the rocker arm nut the correct # of turns (probably 1 turn). Then rotate the engine 180 degrees and do the other half 8 valves.

This answers assumes you have hydraulic lifters and the cam is not so radical you have to do this in more than 2 steps.

If I don't have a manual handy I do them 1 at a time. Rotate the engine untill I feel the push rod stop falling so I know I am on the base circle of the cam. then adjust as above. Then repeat for the other 15 valves.

If you were adjusted as in your #2 question you effectivly would be at 0 lash. If you have hydraulic lifters they maintain 0 lash if they are working correctly. This would result in no negative performance impact. The only result would be the lifter could not compensate for wear or dimensional changes as the engine heated up or cooled down and you could end up with some valve lash that you might be able to hear.

 
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10-24-04, 03:28 AM   #3  
Well, since you have a new engine and probably no oil pressure in the lifters, I would be very hesitant about cranking down on any lifters. I would just get them as close to zero as possible and adjust them on start up once the lifters build oil pressure. That's going to be a little tricky as you don't want to leave the engine idling too long on initial start up.

 
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10-24-04, 04:55 AM   #4  
Carnut gave an excellent answer,

I would just add feeling "0" lash by spinning the push rod when it just stops.

To answer your question about being extra careful:

I would wait till the cam breaks in to adjust them.

 
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10-24-04, 05:26 AM   #5  
Thanks guys.

Here's the deal. Got the new engine installed (were led to believe the valves come already adjusted and they SEEM to be correct). Problem was we got it all together and cranked it up (after priming the lube system), did the cam break-in procedure that came with it, and it was humming along nicely. Took it down the block to return a borrowed tool and came back; no problems, running fine. About half hour or so later got in it to go to the corner store (****tail hour), got about a hundred yards down the street and the engine started missing accompanied by a slight knocking/tapping sound. Went back to shop. This is on a Saturday afternoon, of course, so all of the technical experts we normally annoy with problems were to the four winds. Scratched our heads and started investigating. My partner (this is his truck, I never break MINE) is leaning toward it being a valve-out-of-adjustment noise, but I'm not convinced that's it. I would be more inclined to think a lifter that won't pump up maybe? It's a regular knock/tapping, increases with engine speed, and seems to be top end vice lower down, but does not seem to be coming definitively from a valve cover area. A little hard to locate the exact location, but appears to be right bank near the back. If you lean over the area of the distributor, it's a little hard to tell if it's centrally located or more near the right bank. Already checked things like loose flywheel, etc. No noticeable effect on engine running (running in the shop - we're not driving it), it hums right along except for the knock/tap. When we pull plug wires one at a time there's a noticeable drop in engine speed. Will be spending the day scratching our heads (or other body parts) trying to figure it out.

 
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10-24-04, 09:14 AM   #6  
I'm going to assume you know not to attempt any repair to the engine.Call the supplier and see which dealer they want it to go to for the repair.At this point it should be a no charge repair performed at a GM dealer.Just be sure everything was done properly by the installer(towguy and freinds lol) before you take it in.If it has a misfire it should be easy to find the cylinder at fault.Maybe a valve spring broke,have you put a vacuum guage on the engine?Does the needle bounce?

 
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10-24-04, 09:17 AM   #7  
Well, no progress today. Valve adjustments all seemed good and our redoing them had no effect. Also pulled the flywheel cover again for a look-see. Beginning to look like something more serious/exotic and will need to talk to the supplier Monday a.m. to see how deep an investigation they will want/allow us to do. We can pull the intake, of course, without approval; but we may have to look at pulling a head for a look around or maybe even the pan (hopefully not, PITA). Coincidentally, this motor appears to have come from the same factory as the one that failed rather badly w/less than 20k miles on it (can see an exhaust valve broken off on, you guessed it, the right bank - #4, and it snapped a rod) that we installed in January. Starting to think it's a factory problem, but figure the supplier will be asking what WE screwed up (NOT!).

Anybody want to take guesses, the winner gets a free tow when we get the answer (in our local area only, of course).

TG

 
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10-24-04, 09:24 AM   #8  
Hi, Davo, was typing while you were posting.

Have not tried a vacuum gauge. The engine does not have a misfire, at least sitting running. Except for the tap-tap-tap, you would never know there was a problem.

The supplier is already reimbursing us for labor on the R&R, so we'll see how they want to treat the post-install problem. Taking to a GM dealer is probably not an option; we have GOT to have this truck back up and running and cannot afford the time a dealership might have it. Except for the problem, we went from the engine being dead 300 miles away to what would have been back up and running in 3 days. Our local GM dealerships are in Punta Gorda of Hurricane Charlie fame, so you can imagine that our doing the work is WAY preferrable.

 
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10-24-04, 09:55 AM   #9  
Sorry I thought you said it had a misfire.A valve spring problem could make noise but not mifire at an idle speed and then misfire under a load.Did you look for cracked or broken valve springs while you were in there?What year truck?

 
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10-24-04, 01:42 PM   #10  
I hope it not something that found its way into the clyinder.

Have bin there and and its not a pretty sight. You say the other engine failed? Did it blow up? I thought you said it broke a valve off.

Did you clean all the debris out of the intake system?

 
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10-24-04, 01:43 PM   #11  
Weren't thinking valve springs so didn't specifically check. He hasn't driven it since the first test drive, so don't know if it will miss under load or not. When the problem cropped up I think he did say it was missing and making the knocking/tapping. We're a little reluctant to take it down the road not knowing how potentially serious whatever the problem is. No doubt we'll be looking at everything under the sun starting tomorrow (or my partner will be; I'LL be running my butt off trying to keep up with the calls). No check engine light BTW.

'99 Isuzu NPR-HD (Gas)

Toyman:
The engine we replaced failed going down the interstate at about 65-70. Truck was coming back from a long haul up to the panhandle. Had somewhat less than 20k miles on it. The engine IT replaced went south @ about 125k when the catalytic converter failed, completely clogging the exhaust. Did something bad to one of the cylinders, but that motor hasn't been opened up yet to see exactly what failed. No way of knowing which let go first on this latest failure, the #4 exhaust valve or the rod. You can look in the exhaust port and see the valve stem missing the valve head and if you wiggle your finger into the cylinder you can feel the piece. Dents in a radial pattern on the oil pan and holes at 3 and 9 o'clock. Coolant in the oil so likely trashed the block, too. Intake was checked for debris and haven't lost any tools or hardware. The noise seems to me to be too regular a beat to be something banging around in the cylinder plus the engine hums right along and never misses a beat, although as mentioned previously we're not driving it to see how it will act on the road. With something bouncing around inside I would think sooner or later it would whack the spark plug and we would get a miss. We've got about 30 minutes running time on it so far all total with no sign that the knock/tap is getting any better or any worse.

Plan of attack tomorrow: Call supplier for guidance, pull intake manifold for a look, possibly pull one or both heads depending on what the supplier says. Pan drop is a possibility, too, I suppose.


Last edited by the_tow_guy; 10-24-04 at 02:00 PM.
 
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10-24-04, 06:49 PM   #12  
If it was debris it will embed in the piston or head. If its loose it will generally pass out the exhaust.

I've seen a big block Ford injest and pass a 3/8" header bolt!

We recently has a 2ZZ Matrix blow up. They looked in the plenum and it appeared clean. Washed out in the parts washer and all kinda junk came out.

Normally you don't see engines gernade in normal service. When they do they send bits and pieces all over the place.

 
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10-25-04, 05:01 PM   #13  
You win the free tow, toyman. Small piece of debris embedded in the #8 on the flat part of the head. About the size of a flattened BB. Don't know where it was hiding, but it obviously came from the piston on the failed motor and had been flung up into the intake manifold and did not come out when we blew out the passages prior to installation. Took 30 minutes of run time to show itself. Only cost us a head gasket set and some time.

 
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10-25-04, 05:56 PM   #14  
LOL.......... do I get to collect up here on Long Island

Or do I have to visit you in Fl !

That is something that people who deal in race engines are very familiar with. The junk gets stuck with oil all over the place.

Glad it didn't cost you guys too much.

 
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