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I-6 Engines For GMCs that came with the Inline 6 Engines

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  #11  
Old July 26th, 2014, 02:57 PM
turbobill turbobill is offline
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Default Re: inline six woes

If a u-joint is causing a driveline virbration, don't ignore or neglect it. In addition to the vibration you feel, those same shock waves are raising havoc on other components such as the tailshaft bushing/bearing, pinion bearings and if equipped, carrier bearing and rubber.

Some will run a while that way, getting noticably worse, others will let go without warning, especially if the needles have fallen out. Sometimes, when they let go, there is much damage to other components attached to or nearby the driveshaft as the unrestrained end of the driveshft whips around

A friend of mine years ago lost a u-joint near the center of his box van (right behind the carrier bearing), the rear driveshaft dropped, dug into the pavement and catapulted the truck onto it's side. This was a larger box van approx 24,000 lbs GVW. His speed was 30 MPH.

My advice, get under the truck, check the u-joints and carrier bearing/rubber (if equipped) for looseness and repair whatever is loose or worn out. U-joints are cheap, relatively speaking.
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  #12  
Old July 27th, 2014, 01:55 AM
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Default Re: inline six woes

Yes! please take TurboBill's advice! a bad u-joint or carrier bearing can cause a lot of other damage.-

As far as an additive for fuel, put a clear plastic fuel filter on it temporarily to see if it loads up with debris and rust when you do that. I would change gas stations before I would buy a water remover additive if you suspect watered down gas. I do try to run ethanol free gas when possible. It ain't the same as the old gasahol from decades ago. the mixed stuff now is crappy quality and expensive for the quality of the product, but there isn't much can be done about it.

DAC
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Last edited by GMCDAC; July 27th, 2014 at 02:01 AM.
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  #13  
Old October 20th, 2014, 01:14 AM
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Default Re: inline six woes

Hi Doug. Have you ever noticed that some guys will post over and over until they resolve their problem and then abruptly stop updating. That hurts.
That being said, I want to post until I'm out of the woods with I-6 woes. As you know, it helps to describe perfectly and consider air, fuel, and ignition when looking into performance probs.
For starters, I believe I was over-attempting to fix my engine bugs by leaning it out. It seems my engine wanted a bit more fuel. Secondly, vacuum leaks have to be addressed or nothing will ever smooth out. MOST all vacuum gaskets, hoses, valves, grommets were checked and replaced as needed. I am also now set up with a paper air cleaner instead of oil bath system (jury still out on this trial).
My latest find is a very faint hiss behind the booster; heard only inside the cab near the push rod. It takes a hose to hear it. It may be a normal sound; but I'm digging as I write. A bad booster usually gets a louder hiss as you depress the pedal; mine does not. However, if I'm not suppose to hear anything at all, then I need to get it right if I'm to move forward intelligently. Am I right? The engine needs to breath exactly as designed. As evidence to this, I disconnected the check valve while the engine was running and the truck stalled out. Hope this helps others.
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  #14  
Old November 28th, 2014, 04:09 PM
jagarra jagarra is offline
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Default Re: inline six woes

I think the best troubleshooting tool in this case is a minivac. I had a defective booster in one my vehicles, no symptoms at all, but a loss of vacuum. When I plugged the line going to booster and pumped up the system it held vacuum, with it connected it would not. Replaced booster and fine running again.
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  #15  
Old May 28th, 2016, 06:57 AM
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Thumbs up Re: inline six woes

Thanks jagarra,
There are so so many variables to vibrations. WOW . Currently looking into a HEI or new flamethrower coil to go with Pertronix pointless set up. I've done mechanical corrections (all needed) like motor mount insulators, slip yoke, bal drive shaft, new u joints, new rear pinion seal, bearing and redi sleeve, etc. I have not ruled out carb at all. I looked down carb (not running of course), gave the linkage a decent push and did not see a straight stream of gas. It came out kinda weak and wand like with a couple extra drips. It's fine once it gets a higher volume of gas. Member Doug makes some good points on these one barrel Rochester B's. Some have suggested crank whip; others vacuum, etc. BTW, I will look into minivac check. Though I don't loose any pressure in pedal.
FYI, throw out bearing is another sore spot. That too can contribute to the effects i'm getting; I think??? They are worn, loose, incorrectly installed, etc. I can hear clutch or bearing friction when clutch is depressed. Also ticking noise if I depress top of clutch pedal (free play area) while driving.
LOL, this is an old thread revived. May get a resolution yet.

For other readers with inline woes, I did find carbon streaking in distributor cap on two towers. Also noted that the rotor was striking the inside of cap too high. It was grazing the plastic in the cap. Got rid of cap and went with a made in America heavier Borg Warner cap and new delco rotar. Plugs are cleaner and engine picked up power, Still have unburned fuel stink. Making progress!
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  #16  
Old May 31st, 2016, 03:05 PM
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Default Re: inline six woes

I was having same problems on my Chevy 230 six, I was making it way to complicated, turns out the pvc valve was loose in the valve cover grommet, I wrapped some tape around it, ran fine.
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  #17  
Old June 4th, 2016, 01:32 PM
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Default Re: inline six woes

I agree with Quest's comments- what does your timing mark say when #1 cylinder is at TDC? If it lines up at "zero", then good. If not, the timing gear chain may have jumped a tooth. Timing is everything...
- you should also be able to spark all of your plugs one at a time, if one is not firing, then this could explain the unburned gas you describe. BUT, running on 5 cylinders would be very noticeable.
- have you taken off the valve cover to see the valves in action at idle? You should see that they all are lifting about the same. A flat cam lobe will make your engine run like doo-doo, as you describe, but it will be "running" on all cylinders.
- have you done a compression check on the cylinders? This could reveal something. Do it "dry" first, then "wet" with a squirt of oil. If your valves and valve train are working properly, then a compression test "wet" will get you a higher number, if not, then the problem may be in the valve/valve train.
- the power brake booster; remove the vacuum hose from your carb manifold vacuum and plug it such that it does not leak, and take it for a spin. Maybe the booster is leaking internally allowing unwanted air into the engine? Not a common problem, but you may find something here.
- the carb; what is the history? If you bought the truck and it has always had the problems you are describing, this is worth investigating. I don't know anything about single-barrel Rochester carbs, but if there is something in your carb that does not belong, like a jet/metering rod that does not belong there. You might want to consider taking the carb off and paying somebody old-school who does this for a living go through it and rebuild it to factory specs. Probably will set you back about a bill-and-a-half. Carburetors can be a bit tricky, even single barrel ones.
I was battling a carb problem with the accelerator pump after it was rebuilt and came to find out that the leather cup (umbrella) was no longer being made, the replacement style was an O-ring on a detent acc pump shaft that was simply rolling itself off and dislodging itself, but this only caused me problems in starting it- once I got it running it ran fine, but getting it fired up was a real chore.

Hope this gives you some help along the way and gets you and your truck happily back on the road.

Cheers,
Jim
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  #18  
Old June 4th, 2016, 07:50 PM
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Default Re: inline six woes

Just so everyone knows...Inline 6's do not have timing chains. They have gears. Some of them had a soft cam gear(I forget what material) that was prone for breaking teeth. Good upgrade would be aluminum gears.
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  #19  
Old June 4th, 2016, 09:30 PM
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Default Re: inline six woes

To add to TJ's comment, he is right on about the timing gears. Here's what can happen to the composite cam gear. I bought a '64 Chevy pickup for parts non-running and this is why it didn't run. This engine is a 250. The 230 in my '55 GMC has the aluminum gear. It makes a bit of a whine, but that's better than having the issue this 250 has!

DAC
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  #20  
Old June 5th, 2016, 03:50 PM
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Default Re: inline six woes

Quote:
Originally Posted by GMCDAC View Post
To add to TJ's comment, he is right on about the timing gears. Here's what can happen to the composite cam gear. I bought a '64 Chevy pickup for parts non-running and this is why it didn't run. This engine is a 250. The 230 in my '55 GMC has the aluminum gear. It makes a bit of a whine, but that's better than having the issue this 250 has!

DAC
That will cause some problems. lol
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