S10 2.8 engine vibration

[rfoll]

I have an 85 S 10 that was given to me in trade for a tune-up on Chevy truck. The S 10 was purchased new by the previous owner, a neighbor, and has 130,000 miles on it. It is a very basic truck, The only options are the V6 and power steering. It is the last year of the carbureted engine, and as near as I can see, the only electronics are the HEI ignition system. The 3.08 rear gear and the T4 BW 4 speed allow 21 mpg like clockwork. It runs like a top, but in high gear at around 45 mph, the engine vibrates enough to be irritating. My calculations say this is between 1700 to 1900 rpm. I have confirmed it to be engine, because if I shove in the clutch, the vibrations go away. It doesn't vibrate at speeds above 55 mph, and it seems to be worse when the engine is hotter. Is this a characteristic of the early 2.8 engines? I am wondering if the EGR or Smog pump could be causing this. I'm not inclined to start pulling hoses an removing belts in fear of disrupting fuel calibrations. Are any of the later engines smoother, or was the issue solved when the engine morphed into the 3.1? I would like to keep this low mile truck for it's economy and utility, but I spend a lot of time driving between 40 and 50 mph. Any thoughts or information about his problem will be much appreciated. Thanks, Rick.

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[Truckedup]

I had a high mileage 82 S10 2.8 4 speed that had a vibration around 45 mph in high gear ...It got less but did not disappear when the clutch was pushed in...it was a driveshaft phasing. Once fixed it was better but the truck always had a vibration....I had a 91 with a 2.8 5 speed that was much smoother running

That's a clean machine just begging for a LS swap....

[barnym17]

check your motor mounts condition, exhaust hangers, etc with age the rubber deteriorates and can cause this.

[JoePorting]

I'd start with rebalancing the tires, or if they are old, replacing the tires. They might be 10 or 15 years old if it's been sitting around.

[rfoll]

The vibration is there if you rev the engine in neutral at a dead stop. I did have a driveline vibration from an eccentric pinion yoke, but it got changed. When the 2 were in sync, it was really bad. I can't help but wonder if the egr is affecting it. I've seen stuck egr valves make an engine run rough, but this engine is so quiet its hard to tell if it's a misfire or just vibration. I'm baffled by the bundle of vacuum hoses, many go to the carb. This is a fuel economy rig, I have enough gas guzzling hot rods. Since it is such a low mile vehicle, I plan on keeping it a while. I am curious if it would be feasible to put a 3.4 from a Camaro in, and if they were any less likely to vibrate. The 60 degree V6 architecture is unfamiliar to me, it's not a small block Chevy.

[Brian P]

That engine is a 60-degree V6 with 60-degree offset crankpins. It should not have vibration inherent in the design.

Is the vibration when held in that RPM range in neutral the same as in gear and with the clutch pushed in, and is it the same when accelerating in gear through that RPM range or coasting in gear down through that RPM range? If it's always the same, that suggests a mechanical source as opposed to an ignition or carburetion source - especially if it's the same when coasting down in gear.

While not specific to that engine, broken clutch pressure plates and the like will cause mechanical vibration ...

[Walter R. Malik]

A question as has already been questioned ... if it is only an engine vibration what does only "in high gear" have to do with it...?
If it is merely just the engine, It should vibrate in any gear at that RPM level.

There are a few different versions of flywheel counter-weighting on 2.8L engines, 3.1L engines and 3.4L engines

[JoePorting]

I'd keep it original. Maybe it's just a vacuum leak. Replacing all the vacuum hoses would be a cheap solution. I've had a number of vehicles that ran better after doing that. If every vacuum connection is loose and leaks a little, that will add up to one large leak.

[rfoll]

A question as has already been questioned ... if it is only an engine vibration what does only "in high gear" have to do with it...?
If it is merely just the engine, It should vibrate in any gear at that RPM level.

There are a few different versions of flywheel counter-weighting on 2.8L engines, 3.1L engines and 3.4L engines

The high gear discussion is there because I can calculate RPM with the 3.08 diff and 27" tall BFG tires. I have no idea what the 3rd gear ratio is. It vibrates in other gears as well, but the load is less and it doesn't stay at the required RPM, only revs through it. In town driving gives me plenty of time to be driving 40-50 mph where the vibration occurs. If it were a clutch or flywheel problem is should be worse at higher speed. My research so far shows the longitudinal 60 degree V6 engines all using the same flywheel. Intake and exhaust manifold interchangeability is questionable. The local PicknPull sells engines for $180 if I wanted to find a 3.4.

[ja411]

It's not EGR. At idle if you open the valve it stalls engine. At speed hot it can be 0-100% open and not stall or vibrate. Is everything stock or original? Simple misfire, carb. tuning, ignition? The automatic flex plate and manual flywheel have different balances. Long bed? Drive shaft and or center bearing. Is anything broken in manual transmission, chipped tooth, bearings?
Joe

[Xnke]

GM sold the Camaro 3.4L as a crate engine replacement for the 2.8L S10 for several years. It was delivered with a Crane 260H cam fitted.

The all-iron 3.4L from the Camaro will accept all the trim and dressings from a 1988+ 2.8L S10 engine. It will make about 40Hp more than the 2.8L, with the better cam and bigger displacement, because the heads are identical to the 2.8L engine. If you've got a TBI 2.8L, upping the fuel pressure a few PSI from 13ish stock to 15ish on the stock TBI will allow the TBI computer to "dial in" the fueling a bit, and it will run decently. It can run excellent with a computer tune and a 4.3L V6 throttle body, which will require boring the intake manifold for the larger throttle bores.

2.8L S10's sold prior 1988 (may be 86, can't quite remember) could have small main journals, and are externally balanced. The oil pan and front timing cover is differently shaped, so it is a distinct difference to the 1988+ engines. Only the earliest engines had the small mains, but they were all external balance til around 1988, and all external balance engines have an oil pan that bolts to the bottom of the timing cover with an angled flange, instead of having the oil pan wrap under the timing cover with a semi-circular cutout for the front main bearing. These earlier engines are more prone to vibration, and will literally shake themselves to death if you were to put the wrong flywheel on them-the 3.4L and late 2.8L engines were neutral balanced and the flywheels do not interchange with the older engines. The dampers on the front do interchange, as all the dampers were neutral balance.

All *longitudinal* mounted GM 60*v6 engines produced after 1988 are internal balanced, 2.8L, 3.1L (introduced in 1990) and 3.4L versions (introduced 1993) all use a neutral balance flywheel. 3.1L and 3.4L engines share the same crankshaft.

Since your engine is a 1985 carbed engine, it will be externally balanced-and will have a weight cast into back of the flywheel for the counterbalance. It will also have the three-bolt front timing cover flange for the oil pan. The engine RPO is LR2, and was supposed to make 115HP and 150ft-lb.

I would check and make sure you do not have a broken finger on the pressure plate, or a broken plate strap. The clutch on these trucks is a 1300lb pressure plate-pretty light-and I have changed a number of them with broken or bent diaphram springs and broken pressure plate straps. Unfortunately, without redrilling the flywheel to the Nissan pressure plate pattern, I have not found a clutch that reliably improves on the stock offering for the S-10 externally balanced flywheel.

[rfoll]

GM sold the Camaro 3.4L as a crate engine replacement for the 2.8L S10 for several years. It was delivered with a Crane 260H cam fitted.

The all-iron 3.4L from the Camaro will accept all the trim and dressings from a 1988+ 2.8L S10 engine. It will make about 40Hp more than the 2.8L, with the better cam and bigger displacement, because the heads are identical to the 2.8L engine. If you've got a TBI 2.8L, upping the fuel pressure a few PSI from 13ish stock to 15ish on the stock TBI will allow the TBI computer to "dial in" the fueling a bit, and it will run decently. It can run excellent with a computer tune and a 4.3L V6 throttle body, which will require boring the intake manifold for the larger throttle bores.

2.8L S10's sold prior 1988 (may be 86, can't quite remember) could have small main journals, and are externally balanced. The oil pan and front timing cover is differently shaped, so it is a distinct difference to the 1988+ engines. Only the earliest engines had the small mains, but they were all external balance til around 1988, and all external balance engines have an oil pan that bolts to the bottom of the timing cover with an angled flange, instead of having the oil pan wrap under the timing cover with a semi-circular cutout for the front main bearing. These earlier engines are more prone to vibration, and will literally shake themselves to death if you were to put the wrong flywheel on them-the 3.4L and late 2.8L engines were neutral balanced and the flywheels do not interchange with the older engines. The dampers on the front do interchange, as all the dampers were neutral balance.

All *longitudinal* mounted GM 60*v6 engines produced after 1988 are internal balanced, 2.8L, 3.1L (introduced in 1990) and 3.4L versions (introduced 1993) all use a neutral balance flywheel. 3.1L and 3.4L engines share the same crankshaft.

Since your engine is a 1985 carbed engine, it will be externally balanced-and will have a weight cast into back of the flywheel for the counterbalance. It will also have the three-bolt front timing cover flange for the oil pan. The engine RPO is LR2, and was supposed to make 115HP and 150ft-lb.

I would check and make sure you do not have a broken finger on the pressure plate, or a broken plate strap. The clutch on these trucks is a 1300lb pressure plate-pretty light-and I have changed a number of them with broken or bent diaphram springs and broken pressure plate straps. Unfortunately, without redrilling the flywheel to the Nissan pressure plate pattern, I have not found a clutch that reliably improves on the stock offering for the S-10 externally balanced flywheel.

From this it would seem that I would want to look for a later internal balance engine.