• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Motor Shaking/vibrating

R

Rodd

Recruit
Messages
1,735
Reaction score
1,054
Location
Antelope, CA
Last night I turned my truck off for about 4 hours and when I started it the truck shook violently. So bad that my cheeks were shaking. I drove it a mile home and it shook and the motor labored all the way home. No SES light. After I got it home I tried to diagnose it and the battery light came on. I replaced the alternator and still has the same symptoms. Any thoughts?
 
Low RPM can keep an alternator from "turning on". Misfire on one or more cylinders can lower RPM at idle. Advice is to be careful just tossing parts at it as the alternator could be still good or burned up from low RPM combined with age/miles. We are not there so we can't say for sure if the alt was bad or just a symptom. For example alternator as a symptom story here: http://www.thetruckstop.us/forum/threads/1991-r-v-burb-350-runs-better-with-alt-disconnected.45472/

Start with the basics.
1) Air in fuel system - do you have PSI at the water drain? Clear return line off IP looking for bubbles. Failed lift pump, fuel gelling...
2) Smell your fuel: does it smell like gasoline? (I always recommend you get and keep fuel receipts so if you ever get a load of water logged or gasoline contaminated diesel fuel you have proof to assist the station in paying for your injection system replacement.)
3) Electrically separate and test both batteries. Esp with alt trouble.
4) Clean Grounds.
5) PMD: *groan* where is it and what kind, if any, extension cable on it?

When the truck is cranking does it sound normal or is it skipping a low/no compression cylinder? You have 8 even starter loading sounds per 2 rotations. Missing one of these regular times loading sounds indicates the starter zipping past a dead hole. You would know it if you hear it.
 
Thanks war wagon. Lately it has been running a little rough. I added some sea foam and it helped a little but then got worse once I filled the tank up again. I don't hear any skipping when cranking. I was also thinking grounds. I will go down the list and hopefully one of them fixes it.
 
Sea Foam contains iso-propyl alcohol, aka dry gas, and could have removed water from the fuel tank bottom and run it past the water separator fuel filter and through the injection system. Water and injection systems don't mix.
 
Vibration issues. When they go it can take out the crankshaft- then everything else.

Look at it for anything obvious, then grabbit and give it a yank in all directions. If you can cause any movement, its toast.

I was thinking more along the lines of War Wagon, but anytime I hear "vibration" I always rule out HB first because it is an engine killer, and no $ diagnosis.
 
Because dirt can obscure the fact: There are two rubber thingys to go bad on the crankshaft. The Harmonic Balancer is one and the other is a vibration damper for the belt drive. The belt drive has a bearing in it's center and should just knock if it fails.

On this thought of Will's check every item on the belt drive. I have blown compressor idler pulley bearings, after the clutch has burned off, so badly that they shook the vehicle. Bearing race cage came apart and all the balls went to one side letting the pulley bob ~1/4". Don't know why it didn't just lock up. Vaccum pump, idler pulleys... Feel, spin, and watch them all.

Yes, is the engine firing on all 8 would be the question to ask before going through the suggestions of mine above.
 
Well the diagnosis is a sheered off keyway. That isn't the worst of it, The keyway in the crank shaft was elongated so now the key is too loose. Any tricks to fix that?
 
Oh my heck You might have lost the engine. Dont start it again until fixed!

Iirc someone here did that a couple years ago...

I have oversized keways so it is wider both sides of the crank, then a step sized keyway.
Also welded them up, but that is way more involved.

If you are not rock steady with a cutting tool, tow it to a machinist. You are comparing pricing vs a new crankshaft and all the mess that goes with it like main and rod bearings. Crank can be swapped without pulling heads, but is a pain.

After the crank is fixed and you know your not pushing the truck into the lake, buy a new balncer. Make sure compressor is free when off & powered up, and all other pulleys are spinning right. A hung up compressor can send a shock load.

While you're there items:
You will be pulling the timing cover to get access to fix keyway. Possible timing chain or gear drive. How old is waterpump. I hate those jobs so like to do them when it's open that far.

Pics of how bad for other ideas of fix?
 
Will L. said:
Oh my heck You might have lost the engine. Dont start it again until fixed!

Iirc someone here did that a couple years ago...

I have oversized keways so it is wider both sides of the crank, then a step sized keyway.
Also welded them up, but that is way more involved.

If you are not rock steady with a cutting tool, tow it to a machinist. You are comparing pricing vs a new crankshaft and all the mess that goes with it like main and rod bearings. Crank can be swapped without pulling heads, but is a pain.

After the crank is fixed and you know your not pushing the truck into the lake, buy a new balncer. Make sure compressor is free when off & powered up, and all other pulleys are spinning right. A hung up compressor can send a shock load.

While you're there items:
You will be pulling the timing cover to get access to fix keyway. Possible timing chain or gear drive. How old is waterpump. I hate those jobs so like to do them when it's open that far.

Pics of how bad for other ideas of fix?
Click to expand...
I will get pics tomorrow. It's at a friends shop. I was wondering if there were oversized keyways. So you think a machine shop could fabricate one? The other suggestions that were given to me was to use some JB weld to stick the keyway in and once it cures file/sand it down. I don't know if this will work or not. The other one was to drop the front dif and then the oil pan to replace the crank from the bottom.
 
Hell no on the jb weld. Pull the timing cover off. Weld it with a welder. Cold wrap the crank with wet rag. Hire a welder/ machinist if you dont know how.

Or pull the timing cover off. If you are DAMN STEADY HANDED (if not then a machinist, or mechanic that is also an amazing tatoo artist). Measure the size of the step key needed. Buy it dont make it. Then cut the keyway to the new size with with a dremel sized cutter. Againwrap the crankshaft with a wet rag to keep it's temp down..

I have removed a 6.5 crank leaving the heads on and pistons in the cylinders, but engine was on a stand. Easy access, and it took patience. Idk if it can be done in frame.

Put everything back together, change oil, and go.

Other option is new crank. Leroy sells scat crank for $400. New main and rod bearings. New gaskets.

Either way I would not trust the balancer. Make sure to use installer tool.
 
Last edited:
Will L. said:
Hell no on the jb weld. Pull the timing cover off. Weld it with a welder. Cold wrap the crank with wet rag. Hire a welder/ machinist if you dont know how.

Or pull the timing cover off. If you are DAMN STEADY HANDED (if not then a machinist, or mechanic that is also an amazing tatoo artist). Measure the size of the step key needed. Buy it dont make it. Then cut the keyway to the new size with with a dremel sized cutter. Againwrap the crankshaft with a wet rag to keep it's temp down..

I have removed a 6.5 crank leaving the heads on and pistons in the cylinders, but engine was on a stand. Easy access, and it took patience. Idk if it can be done in frame.

Put everything back together, change oil, and go.

Other option is new crank. Leroy sells scat crank for $400. New main and rod bearings. New gaskets.

Either way I would not trust the balancer. Make sure to use installer tool.
Click to expand...
I'm not a welder or a machinist. I've replaced 3 IP's but never any internals of an engine. If I am understanding you correctly when the timing cover removed the part of the crank with the keyway is exposed? What is welded the keyway into the crank?

From what I'm understanding her are my options:
1. The first and easiest option is to buy an oversized keyway and have a machine shop cut it down to size.
2. Have a machine shop/welder weld the keyway into the crank.
3. Take the motor out and replace the crank and the mains, etc.
4. Replace with a new optimizer. Preferable
 
Call engine machinists in Sacramento there is a bunch there, some have to know how to fix the keyway in the crank that is damaged. If they know how to fix it, they will let you know. This is not an easy, learn as you go task. Take pics and have ready to send to them.

I know an excellent welder that is in the bay area, worked with him a few years. I will try to get ahold of him tomorrow. If he is tied up, he might know a good recommendation.

Post pics asap.

1. The crankshaft gets cut to the size of the oversized keway is one option.

2. Welding up the crankshaft where the metal is damaged, then finished back to original keyway size is another.

3. Yes

4. Yes
 
Took the words right out of my mouth, @Will L. ! The easiest/cheapest/safest would probably have the damaged keyway in the crank cut to the next size up and use a step key (exactly what it sounds like, used for a shaft and pulley where the keyways are two different sizes, ie: 5/16" shaft keyway mated to a 1/4" pulley keyway). Step keys are available through Grainger and Precision Industries and any competent machine shop should have various sizes in stock.

I personally would NOT try having the crank snout welded up and the keyway recut for several reasons. Thermal shock to the cast iron crank, throwing off the trigger for the CPS a few degrees when the balancer is indexed to the new keyway and accessibility, to name a few. Carefully widening the keyway on one/either side of the center line (depending on how it's chewed up) and then using the appropriate step key (offset or centered) to the next possible oversize sounds like a more viable option to me.
 
Remember the keyway is the cut out part of the shaft, the key is what fits into the keyway to index whatever is slid onto the shaft, just so we keep the terminology correct and avoid confusion.
 
Thanks guy's that is great info. I'm headed to the shop to get the pictures. I have one other question. Can the machinist cut the keyway to the next size up while the crank is still in the truck or does it have to be removed?
 
It can be done in place -with patience, and it is not a fun task.

Guys, listen: I am kinda torn here on telling him cut it himself with a dremel or not. I am so used to just choping into stuff that none of it scares me and I dont know where to draw the line for someone new to this stuff. Can someone who understands what cutting a bigger keyway is chime in wether or not he should try it? Husker6.5 is very accurate with the dangers of the transfered heat on the crank, it could quickly go wrong. But I think nothing of welding on fuel tankers like I used to do also, so it is perspective and mine is out there sometimes.
I really dont want to lead him into trouble, and dont want him dropping a bunch of cash he could save too.
Input please.
 
Having worked industrial maintenance for several years, I would have no problems attempting something like that free-hand, or perhaps fabricating a jig to help with alignment and depth (the keyway must be 1/2 the depth as it is wide, ie: a 1/4" key has a 1/8" deep keyway in the shaft and pulley. Out of expediency I had to make a step key once (working graveyard shift, there is nobody open at 2am!) at work, but I was able to use the drill press and the adjustable table and used a 1/4" square-shouldered carbide burr to take a piece of 1/4" key stock and make it into a 3/16"x1/4" step key. Took 0.0626 off one side and then set depth and took 3/32" +.001 off the top. You need that .001 so that you can get the key in.

Bottom line, unless he's damn confident he can do it and has the skill/tools, take it to a machine shop where they can do it on the truck.
 
You must log in or register to reply here.
Back
Top