straight 8 vibration

H

hivetool

Member
got my 51 special 3 speed purring but has a nasty vibration shakes steering n whole body 1200-2500rpm? have read about adding weights and drilling flywheel
but am reluctant to start that. dampner looks ok but cannot confirm. any ideas where to start to smooth it out ?
 
firstofeight

firstofeight

Active Member
hivetool said:
got my 51 special 3 speed purring but has a nasty vibration shakes steering n whole body 1200-2500rpm? have read about adding weights and drilling flywheel
but am reluctant to start that. dampner looks ok but cannot confirm. any ideas where to start to smooth it out ?
Click to expand...

Bet there is a cylinder or two missing at that speed.

Ben
 
S

suntreemcanic

Active Member
firsttofeight is right do the easiest checks first. Pull spark plug wires one at a time while engine is running. If there is no change then that cylinder is not firing.
 
H

hivetool

Member
definitly not a misfire. drove today and vibration occurs 30-35 mph in 3rd. not drivetrain. raise engine speed over 1200 rpm in neutral and you can feel it in whole car
 
H

hivetool

Member
car sat 20yrs before coming to me. not aware of any clutch work. clutch engages just as pedal gets all way up. am considering new clutch,
with clutch out, starting eng with weights in diff places on flywheel to find where its smoothest and drill/remove that amount of weight from opposite side of flywheel
been professional mech 40yrs. looking for possible straight 8 specific vibration solution
 
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S

suntreemcanic

Active Member
If you got the engine running it was probably running 20 years ago when parked. Remember that car would of been 50 years old then and there just was no interest in driving it. I just fought engine vibration and spent a lot of money and did not fix it. I had three new spark plugs that were randomly not firing and it made for vibration also. Consider everything external before you tear into it.
 
R

Rusty Rides

New Member
I think your on the right path. Your feeling first order engine harmonics. Have you started it with the belt off to eliminate the accessories? Look that flywheel/pressure plate over very well. Look for any weights that shouldn't be there. I don't think the crank pulleys have any weights on them. If you're up for the work, remove the belt, the trans, pressure plate and clutch disc. Fire it up and see if it still vibrates. If it does, you know it's internal. If it is, maybe it was rebuilt and had a couple pistons replaced with units of different weight. Be curious to see how this plays out.
 
Jenz38

Jenz38

Active Member
Firing order ok ?
Valve lash ok ?
Sparkplug wires are in good condition ?,
no short cut under itself ,while engine goes under load ?
Or the Plugs has a problem like,Suntreemcanic says, only under load .
You can see the timingmark somewhere on the flywheel on 1. Cylinder with an strobo Lamp ?...
If not,your Flywheel is in wrong position.

Good luck and keep us postin'😉
 
Bob

Bob

Team Member
The original spark plug wire cover is not a good idea, it sets the plug wires up for cross firing, take it off and spread the wires out. The cover is a real bad idea for people who upgrade to 12V ignition.

Do you have the plug wires tied together with zip ties or..., cut them and spread the wires apart?
 
H

hivetool

Member
vibration is there hot or cold, valves at .015 hot, comp. is 118-123 with one cyl at 105 after 4 pulses cold. has new plugs/wires/pertronics ign
timing set at yellow mark on flywheel, #1 4deg. BTDC. shakes with no load. under load, vib. is lessoned somewhat. I repeat, "not a misfire". a misfire wont shake the whole front end. has to be a balance issue?
 
Jenz38

Jenz38

Active Member
You have only a (somebody has selfmade) yellow mark on the flywheel ?...there is no visible iron ball that pressed in ?
 
H

hivetool

Member
on the 263 eng, there is a crosshatch area on flywheel that is yellow(now faded) that indicates 4degrees adv visible through timing window on block above starter. kinda hard to see but factory correct
 
J

jhodgson

Active Member
The clutch pressure plate was balanced as part of the crank, flywheel and pressure plate assembly. If at some time in the past somebody removed the pressure plate and failed to index it properly when putting it back on a vibration would be possible.
 
H

hivetool

Member
well, pulled the clutch cover down to take a close look. flywheel and pressure plate marked with "X" near bolt hole, also marked with black marker. 10 holes drilled in clutch and flywheel adjacent. turned crank 180 and found small weights welded on clutch. noticed ring gear looked "new", no wear.
my guess... someone did the clutch and got a vibration so took it all the way apart and had clutch and flywheel balanced off the crank when all the drilling, welding ,marking took place along with a new ring gear.
I added a couple washers to the welded side bolt to see if it got better or worse.....Better! still there but lesser and lower rpm. will drive it like that
thanks for all the replies
 
T

tom telesco

Member
You added washers & it appeared to be better so you are not thinking in a different direction for a vibration. I don't care if the mounts were solid welded to the frame. Adding washers made it better so I would concentrate on engine balance/mis-balance if it were me.

Tom T.
 
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