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6.5L Vibrations, any ideas what it can be?

S

Scott_2255

Active Member
Messages
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Hello, I am experiencing some pretty intense vibrations on the 6.5. Between 1800 and 2100 it vibrates terribly, rattles the dash and the truck. Above 2100 and below 1800 it seems normal. I've had the truck several years and understand the 6.5 has vibrations but the old tired one seemed smooth compared to this. It vibrates when driving or in nutral or park. Here is the info on this thing...

Newly rebuilt engine, less than 40 miles on it due to faulty injection pump (Thanks SS Diesel for the faulty pump and not returning my warranty claim). The injection timing offset is currently -1.14, desired and actual are always matching and with advance timing off its around -3.05. Timing and offset confirmed and set with Tech II clone. I have tried turning off injectors one at a time and it doesn't change anything only rpm and rough sounding engine.

When I shut the engine off there are no clunks or anything, it sounds solid and tight.

List of parts on the engine besides, new pistons, bearings, rings, all internals
Refurbished Injection pump was repaired and tested by an authorized Stanadyne repair shop 2 weeks ago. Pump wasn't advancing (See other post on that)
New Bosch matched injectors
New Scat crank
New Fluid Damper
New Leroy Diesel accessory crank pulley
New timing chain
New Polyurethane motor mounts (Energy Suspension Black)
New water pump, new fan clutch
New heads
Vac pump removed.

I have tried running engine with the serpentine belt off to eliminate water pump, alternator, power steering and fan clutch issues. Its slightly smoother but issue is still there. If I can get the vibration issues resolved I might make an idler pulley to reduce belt vibrations. It's a gates belt and is the correct one for a 97 without vacuum pump, tension idler pulley is withing the marks for a belt that is good.

The only other thing I can't recall is if Scat Cranks come shipped with the locator pin in them and possibly I don't have the flex plate in the correct clocked position. Its been nearly a year since I started re-assembling it and l can't remember. I couldn't see the crank bolts very easily with flex plat installed but I'll look again tomorrow when its lighter and warmer.

I posted some videos of the torque converter unbolted from the flex plate and the belt vibrations on you tube. With the torque converter bolted up it was slightly smoother at idle. The flex plate does look like it has a slight wobble but not sure if that's it. The flex plate is mounted with the counterweight side of the flex plate towards the block and counter weight is installed.

Here's the links for the videos if that helps.

Thanks for the input and help.




 
I am wondering about the motor mounts. you list urethane mounts which are a more rigid material. I had replaced my mounts with some aftermarket rubber and seems to vibrate the floor board and dash somewhat at idle more than before with my old mounts. even worse in cold weather too.

I couldn't tell how bad the vibration is in your videos wether it's an imbalance in the crank, balancer or flex plate, or just a resonating vibration from the engine into the frame from rigid mounts.
 
I know others are gonna ask. did you have the rotating assembly balanced before assembly using a OEM style balancer and not the fluidamper at the machine shop? only other thing I can think of is maybe one or more injectors are imbalanced pushing more or less fuel than the others. having those balance and pressure tested is recommended for a new build.
 
That flex plate looks VERY SUSPICIOUS.
unplug fuel solenoid.
Set up something to test RUN OUT on flex plate-
Get underneath with a remote starter button.
Watch it crank. Maybe record in slow mo with the phone. Don’t be afraid to put up few minute long video with 30 seconds of cranking.

Then wait 30 seconds for starter to cool.
Then record another 30 seconds of cranking recording at normal speed.

AGREE on questioning: did you have lower end balanced- if so, get VERY SPECIFIC of how it was done. What parts dropped off, etc
 
Rotating assembly is suspect, I have seen VERY bad balance issues with a stock assembly, add in a cast scat crank and the other items you mentioned the imbalance magnifies. I am in the process of balancing a build now and it is no wonder these break cranks and blocks. And imbalanced injectors will contribute to it.
 
Thanks everyone for the input, I'll film the flex plate with the engine cranking and see what that looks like. Surprised that a supposedly better crank would need to be re-balanced and matched. Kind of disappointing if that ends up being the issue. I've built a motor for my sandrail that would run 6+ all day in the sand for 5+years with no issues and lower assembly wasn't balanced, and it still ran strong when I sold it with little to no vibration.

I've re-build large 2 stoke outboards that will run 5-6K+ all day for several years and never had to balance an aftermarket crank, but this is the 1st diesel for me so it's a different animal for sure.. Either way it doesn't say much for Scat cranks if they have to be-re balanced.

The machine shop matched the pistons to the bore, they checked the block for straightness in the mains and that was it. I didn't think I'd have to get the main assembly balanced. I was thinking as its not a high rpm rotating assembly it wouldn't need it unfortunately.

It definitely seems to be related to the rotating assembly based on what I see and feel. I'm sure the stiffer motor mounts don't help it but the entire engine vibrates quite a bit, more than the old 6.5. When I purchased the Bosch injectors I paid extra to have the flow matched ones that were supposed to be closely matched. I ran them for a bit in the other engine before I pulled it to install this engine and the old engine was fine with them.

Hopefully its not the crank or this truck is finding a new home, too much time and money wasted on it. Its been nothing but a headache unfortunately.

I'll post video of the flex plate with starter cranking only to see if flex plate is out of round.

Thank you for the help
 
Scat is a china cast crank. This is a very heavy assembly, even tho it turns slow compared to other motors it is a un balanced motor. This is just the small end of the rods, lightest 328g heaviest 339g, that's 11g just on the small rod end.
 
Scott_2255 said:
Hello, I am experiencing some pretty intense vibrations on the 6.5. Between 1800 and 2100 it vibrates terribly, rattles the dash and the truck. Above 2100 and below 1800 it seems normal. I've had the truck several years and understand the 6.5 has vibrations but the old tired one seemed smooth compared to this. It vibrates when driving or in nutral or park. Here is the info on this thing...

Newly rebuilt engine, less than 40 miles on it due to faulty injection pump (Thanks SS Diesel for the faulty pump and not returning my warranty claim). The injection timing offset is currently -1.14, desired and actual are always matching and with advance timing off its around -3.05. Timing and offset confirmed and set with Tech II clone. I have tried turning off injectors one at a time and it doesn't change anything only rpm and rough sounding engine.

When I shut the engine off there are no clunks or anything, it sounds solid and tight.

List of parts on the engine besides, new pistons, bearings, rings, all internals
Refurbished Injection pump was repaired and tested by an authorized Stanadyne repair shop 2 weeks ago. Pump wasn't advancing (See other post on that)
New Bosch matched injectors
New Scat crank
New Fluid Damper
New Leroy Diesel accessory crank pulley
New timing chain
New Polyurethane motor mounts (Energy Suspension Black)
New water pump, new fan clutch
New heads
Vac pump removed.

I have tried running engine with the serpentine belt off to eliminate water pump, alternator, power steering and fan clutch issues. Its slightly smoother but issue is still there. If I can get the vibration issues resolved I might make an idler pulley to reduce belt vibrations. It's a gates belt and is the correct one for a 97 without vacuum pump, tension idler pulley is withing the marks for a belt that is good.

The only other thing I can't recall is if Scat Cranks come shipped with the locator pin in them and possibly I don't have the flex plate in the correct clocked position. Its been nearly a year since I started re-assembling it and l can't remember. I couldn't see the crank bolts very easily with flex plat installed but I'll look again tomorrow when its lighter and warmer.

I posted some videos of the torque converter unbolted from the flex plate and the belt vibrations on you tube. With the torque converter bolted up it was slightly smoother at idle. The flex plate does look like it has a slight wobble but not sure if that's it. The flex plate is mounted with the counterweight side of the flex plate towards the block and counter weight is installed.

Here's the links for the videos if that helps.

Thanks for the input and help.




Click to expand...
what about your crank shaft pully or the harmonic balancer? i see you replaced them in the list but it sure sounds like the noise they would make. take your belt off and run it see if the noise is still there ?
 
I've ran it with the belt off, no improvement. Hopefully its the flex wheel out of round. I'm going to get video of it this evening cranking over. Fingers crossed its that
 
Scott_2255 said:
Vid of Flex plate while cranking engine. It looks warped to me but I don't know what tolerance it can handle. At the present time with how it vibrates I'd say none :banghead:

Click to expand...
Why does it take so long to never light?

Based on the running video, I doubt the flex plate is the source of your vibrations problem. It’s something heavier than that in the rotating assembly. I would put a Fluidampner on there before doing any tear down.
 
I'm not an expert but I wouldn't run it anymore until you find the issue causing the wobble. That is wobbling like crazy and wouldn't make me feel good in any way. Hopefully it's as easy as replacing the flex plate. I hope it doesn't go deeper, as in what the plate is connected to (read crank)...
 
SnowDrift said:
I'm not an expert but I wouldn't run it anymore until you find the issue. Hopefully it's as easy as replacing the flex plate. I hope it doesn't go deeper, as in what the plate is connected to IE crank.
Click to expand...
Thank you, I hope it can be resolved with a new flex plate. If its a crank balance issue I am not sure I'm up for taking the engine out again.. Fingers crossed it can be resolved with a flex plate? It looks warped to me but not sure what is tolerable.
 
Big T said:
Why does it take so long to never light?

Based on the running video, I doubt the flex plate is the source of your vibrations problem. It’s something heavier than that in the rotating assembly. I would put a Fluidampner on there before doing any tear down.
Click to expand...
I intentionally disabled the fuel system to see any warping not seen when engine is running. It has a new fluidamper and solid pulley wheel that is new as well
 
Will L. said:
@Big T I told him unplug the fso to do this test.

That flex plate looks shot.

I have not yet seen a new scat that was bad. But being that bad- you need to set up a dial indicator to check that crankshaft face where flex plate mounts before installing the new one.
Click to expand...
Thanks, I think based on what I see a new plate will be replaced. I'll probably pull the plate, check the face of the crank for issues before ordering a new flex plate. Still puzzled as to if this would cause that much vibration. I guess it all adds up so any little thing could make it worse.
 
Yeah- the rods as Chris mentioned are amazingly horrible for this engine. The pistons are just as bad. Way more out of balance than any small block or big block gasser you will ever see. The fact that you put in the lighter scat crank will make the effect worse.

Do not skip measuring runout when the plate is off. This can be a crucial thing.
The other thing is measure fore and aft of the crankshaft itself with engine off.
I have seen many normal competent builders tank the center bearing (thrust).
 
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