New stuff
 

New goody has arrived. :D

Daniel

Here's hoping it solves your issues. :thumbsup:

Still hunting...
 

I got the new trans installed the other weekend and went for a drive and...the vibrations are still there. :omg:

I guess we've eliminated one more possibility= the trans. So, it seems the issue is somewhere between the front of the engine and forward of the trans.

I've been reading various vibration threads and I'm wondering if the vibration is a result of a physical imbalance (i.e.- internal rotating assembly out of balance, flywheel counterweight incorrect) or an imbalance related to tuning (i.e.- misfire, incorrect timing, etc)?

Wouldn't a physical imbalance begin to vibrate at a certain RPM and continue to increase in severity through the RPM range?

In an effort to be concise, I'm going throw out some facts from what I know at this point:
-Vibration is not speed related.
-Vibration occurs around 1900-2100 RPM's, then goes away and returns around 4000 plus.
-Vibration decreases when I push the clutch in and engine speed begins to drop.
-Vibration seems load dependent.
-Vibration isn't noticeable/present when engine rev'd in neutral at a standstill.
-Engine seems to have normal water temp, oil PSI, power.
-Engine DOES have run-on/dieseling when I shut off the ignition. Usually around 3 seconds of continued rough idle before finally dying.

Regarding physical imbalance- I ordered a few different flywheel counterweights and was planning on trying to find a counterweight "sweet spot" via trial and error. Someone mentioned that the rotating assembly could have originally been balanced with the flexplate that came with the engine and now that I've installed a flywheel, it could be out of balance.

On a positive note, I did get around to making some valance opening inserts to match my grill...

great looking front end

What fuel/octane are you running?
Any other vitals for the motor (deck height, head gasket used, piston dome/dish volume)?

Seems you might have answered your own question. I also added to part of it about vibration getting worse.

Also since you've eliminated the drive line from the problem lets take a look at other rotating parts that I've seen cause vibration. The balancer, easy to check by setting cylinder 1 at TDC and seeing if the timing mark lines up with zero on the timing tab. Balancers have been known to slip and will cause the type of vibration you're having. Ironically your timing might be "correct" with the timing light, but if your balancer slipped its off in the engine causing your dieseling.

The accessory drive is another one. If you're using a cheap drive that things can flex around that can also cause a vibration. Free reving an engine doesn't always work, sometimes it needs a load on it like when driving. Misfires are the most common that need a load to show up. At this point I would get your timing corrected and go from there. If you have a GoPro you should mount it under the hood so you can watch the engine and see what its doing when the vibration happens.

Thanks slimjim.

ScotI- I'm running 93 octane. Unfortunately, I don't have all those specs. The engine compression is around 9.5-1 from what I understand.

CamaroAJ- Thanks for the input.

I replaced the original external balanced balancer with a brand new unit the end of last year. I verified TDC and the crank snout and key way looked fine before I installed the new balancer.

I am running a lower end front accessory kit, but I ran/revved the engine with the serpentine belt off and there was no change. BUT, I haven't driven the car/applied load while the belt was off. I might try to get my hands on a Go Pro and see what I see.

Daniel

Drop the original motor back in & see what happens.

The wrong combo on the 383 could be causing both the vibrations & run-on if things weren't done properly. Swapping a different power-plant definitely narrows the scope of things.

Update
 

ScotI- unfortunately, I don't have the original motor.

Well, I've tried a couple different flywheel weights recently with no luck. The original 156 gram counterweight seems to be the best and the other weights (heavier & lighter) caused the vibration to increase.

So, at this point, I'll just cruise around until winter. Doesn't look like I'll miss many/any autocrosses this summer with COVID hanging around. Then, I plan to pull the engine and have an internally balanced rotating assembly installed. As long as I keep the rpm's under 4000, the vibration is not that bad. I put about 40 miles on it yesterday cruising back roads.

I still have a few small details to finish (AC charge, alignment tweak, etc) but overall, the car is "complete."

I'll post a few gratuitous photos for grins.

Daniel

Couple more
 

Couple more photos

Beautiful build, clean and smooth, love the color. The fire extinguisher may be a little difficult to get to if you ever need it, lol. Good luck with that vibration

Nice clean car. Love the grille. Great job!

Nice to see a similar '68. I went through several rounds trying to figure out vibration, and for me it came down to driveline angles. Even with a Speedtech tunnel cover I can't get the T56 high enough to get rid of a minor vibration. Glad you'll be able to enjoy it this summer.

Very clean! Love the work you did on the car. Enjoy driving this summer.

It really sucks that such a beautifully finished car is giving you fits like this. Vibrations are so subjective, it would really help if you had a video of the vibration taking place, and from different angles (especially the underhood one). They can be great diagnosing tool.

My 383 always had a vibration I couldn't get rid off under a high load, low RPM situation, like 16-1800 RPM in 6th gear on the highway. Once I put the Holley Fuel injection on it, we figured out it was a miss (more like a shudder, not a hard miss) and we tuned about 90% of it out by fiddling with the timing and fuel in that area on the map.

There seems to be something about the stroker engines that enhance that type of harmonic and send it thru the whole car.

My builder putting my engine back together this time demanded that I bring him the pressure plate so he can balance the crank with the clutch assembly attached. He says if the clutch is out of balance you will definitely feel it. I'm interested to see how that turns out this go around as well.

Meanwhile, go enjoy your car... It's a beaut!!

[QUOTE=DWC;702651]I got the new trans installed the other weekend and went for a drive and...the vibrations are still there. :omg:

I guess we've eliminated one more possibility= the trans. So, it seems the issue is somewhere between the front of the engine and forward of the trans.

I've been reading various vibration threads and I'm wondering if the vibration is a result of a physical imbalance (i.e.- internal rotating assembly out of balance, flywheel counterweight incorrect) or an imbalance related to tuning (i.e.- misfire, incorrect timing, etc)?

Wouldn't a physical imbalance begin to vibrate at a certain RPM and continue to increase in severity through the RPM range?

In an effort to be concise, I'm going throw out some facts from what I know at this point:
-Vibration is not speed related.
-Vibration occurs around 1900-2100 RPM's, then goes away and returns around 4000 plus.
-Vibration decreases when I push the clutch in and engine speed begins to drop.
-Vibration seems load dependent.
-Vibration isn't noticeable/present when engine rev'd in neutral at a standstill.
-Engine seems to have normal water temp, oil PSI, power.
-Engine DOES have run-on/dieseling when I shut off the ignition. Usually around 3 seconds of continued rough idle before finally dying.

Regarding physical imbalance- I ordered a few different flywheel counterweights and was planning on trying to find a counterweight "sweet spot" via trial and error. Someone mentioned that the rotating assembly could have originally been balanced with the flexplate that came with the engine and now that I've installed a flywheel, it could be out of balance.



Just throwing out some suggestions so don't take this as offense to you. What type of stroker do you have? 2 pcs. rear main seal or 1 pce. seal, one is internal balance the other is external balance. Could you possibly have the the wrong type of harmonic balancer.
How about the frame mounts.
http://www.pozziracing.com/camaro_engine.htm
Could the flywheel or clutch assembly be out of balance?
Wrong throw-out bearing? There are a few different heights available.
Adjustment of the clutch pedal play & engagement?
Reciprocating assembly needs to be re-balanced, sorry its a possibly.
For the run on....try running a pvc system on the drivers side and a passenger side to air cleaner hose?
This one might be bull$#!t to do but how about running the distributor without the ignition box. I have a billet distributor on my SBC without a box and it runs great compared to the old points.
If its any consolation your car is looking too nice to be giving you trouble.

Thank everyone, I appreciate the compliments.

F'in mine-
No offense taken. I welcome any ideas to help troubleshoot.
I have a 2 pc rear main.
I installed a brand new externally balanced harmonic balancer the end of last year while troubleshooting. No change in vibration.
I verified the motor mounts are correct a few months ago.
The engine came with a flexplate and I installed a new flywheel. Both external balance. I think the flywheel/clutch could be the culprit.
The thow-out bearing came with the McCleod clutch and it's spec'd for my combo.
Clutch pedal/adjustment was verified when I installed the new trans.
Reciprocating assembly needs to be re-balanced- I think this is it. I think the original rotating assembly was balanced with the flexplate and the new flywheel/clutch is not quite balanced to match. I plan to pull the engine in the winter and have a shop install a new, internally balanced, rotating assembly.
Thanks for the run-on tips and the compliment!

Daniel

Any possibility that the vibration might be detonation?

Mike- I suppose it could be. Any tips on how I can rule that out? Here's a quick rundown on what I'm running.

93 octane gas
14.25 AFR at idle
15*/36* timing
180* thermostat (avg 190* driving)
13hg vacuum at 1500rpm
Aluminum radiator
New Holley 4779 carb (750 DP)
New MSD Street Fire ignition
New MSD billet distributor 85551
New MSD Blaster SS coil
New Taylor plug wires
New spark plugs
Aluminum heads- 64cc/210cc
TDC and firing order verified multiple times
Dynamic compression ratio is estimated to be about 9.5:1

Thanks,

Daniel

Daniel, you mentioned its a 2 pcs. rear main seal, if its a aftermarket crank then its probably internally balanced. It could have a 400 crank with spacer bearings for external balance.
Any chance you might know this or could ask from whoever you got the engine from about the internals. Do you have a pic of the crank flange?
As inexpensive 60 buck option to try an internal balancer?

Do you know the cam specs and what are the plugs like?

Simon- It had an external balancer and flexplate on it when I bought it. I was able to watch it run, on a stand, before I bought it. Only thing I changed from it running on the stand was an external balance flywheel. I've since installed a new external balancer during my troubleshooting as well.

This is the best picture I have of the crank flange. The crank flange is cast with a counterweight on it.

Here is my cam:
https://www.summitracing.com/parts/lun-60105

Here are the #3 and #4 cylinder plugs from last week. BUT, this was just after having the engine warm up at idle. I haven't done a proper shut down after WOT plug reading.

Daniel

Daniel, just throwing out all possibilities. If you're able to check with the guys you bought the engine from, try to see if you can find out the specific crank they used. I realize it had external components but just in case the wrong parts went on.
You purchased a new flywheel, is it the one with the weight pad that's bolted on? I realize this is a alot of bs but maybe take the weight off and see what happens.

The plugs look okay, the cam specs seem to be a bit high for the compression you're running. I'm wondering if that has an effect on the run cause Lunati says it requires a minimum of 10.5 compression.

Simon- I appreciate ANY ideas, really. At this point, I've resigned myself to pulling the engine this winter. So, I don't mind chasing any possibilities up until that point.

After I bought the engine, I removed the oil pan to verify it was a 383 stroker and see what the cylinders looked like, etc. I've attached the photos I took while the pan was off (sorry for the low quality). The number cast into the crank counterweight is hard to read. After a lot of research time online, I *believe* the crank is made by CAT (Cal Auto Transpeed). A lower quality, chinese import, that subsequently is out of business from what I can tell.

The guy I bought it from said PAR Racing in Spartanburg, SC assembled the engine for him. I'm waiting for a return phone call from them.

Yes, the flywheel I bought has removable weights. I've tried running without a weight and it was clearly not happy. I've also tried different amounts of weight trying to "sneak up" on the correct balance, but no luck.

As to the compression ratio, I used online calculators and the specs I was told to calculate the ratio. With that cam's overlap, the dynamic ratio estimate was about 9.5:1, with the static ratio about 10.5:1.

The calcs I used indicated 10.51:1 static/8.67:1 dynamic @ .020 deck height (or 10.89:1/8.98 w/a .005 deck) using typical generic 383 numbers & that Lunati cam. Seeing your cranking compression >200psi would suggest your in the ball park. I've been advised exceeding the 200# number on pump gas is pushing things & for worry free operation things needed to be optimized for every different combo.

Have you tried just backing off the timing to see what happens w/the 'run-on' scenario?

that plug does not look happy. have you verified which advance springs are installed? Are you using a non-digital timing light to time it?

ScotI- No, I haven’t had the timing lower than 36* total. I’ll decrease it 1 or 2 degrees and see what i get.

Mike- the 21* bushing is in it. I’m using a basic, non-digital, Craftsman timing light.

Daniel

I backed the timing down to 13*/34* and went for a short drive this weekend. The vibration did not change at all, still there.

Interestingly, the engine run-on still occurred as well. It *may* have been a bit less run-on then previously, but not a significant change.

Daniel

Try 32° total. This would be strictly for the run-on issue as I think there is something different causing your vibration.

If still experiencing run-on @ 32°, I would seek out some higher octane rated gas & utilize it to eliminate octane as a possible cause.

Daniel......which spark plug part number are u using?
Do you know if they are the right heat range?
Do you know how far they protrude into the combustion chamber?
Plugs are available in regular reach as well as long-reach.....maybe u have the long version. Look up plug manufacturer charts and cross-reference charts.
Call up the head manufacturer to get plug recommendation.
Try side-gapped plugs to minimize protrusion into chamber. Too much protrusion will create a hot spot because the ground electrode stays too hot and promotes "dieselling" which is also pinging. Auminum heads would draw enough heat from the plugs as not to be an issue if heat range is correct but not if protrusion is too much.
Colder heat range plugs are fatter in the center electrode thereby conducting heat back into coolant more quickly.

http://www.ngk-sparkplugs.jp/english...q13/index.html

As ScottI says, octane rating is critical. Octane booster is available as a concentrated additive. Try a half tank full.

13* static sounds way high to me. 10*_32* should take you out of the twilight zone......again ask the head manufacturer.

I'll reduce the timing to 32* and see what happens. Then try octane booster if needed.

The plugs are NGK BKR5E, per NGK's tech support that I spoke with.

I've also tried NGK BKR7E and Autolite 3922 plugs.

Not sure if I'll be able to wait until winter to pull the engine for a new rotating assembly...I'm getting antsy.

Daniel

Who's heads are on the engine?

Aluminum Chinese imports that have had some port work done. Pro Comp PC3003 (210cc, 64cc)

I had a long conversation with a machine shop (who is old friends with a buddy of mine and they have a great reputation) this afternoon about my engine and having them install an internal balanced rotating assembly. He thought it was interesting that the vibration is hardly noticeable when the engine is revved in neutral, at a standstill. He said anything is possible, but the out of balance engines he's dealt with in the past were noticeable both loaded and unloaded.

He suggested to revisit my driveshaft before pulling the engine. I've had the shaft balanced/checked twice by a reputable local shop and it's "within spec". But, he said has experienced "good" driveshafts on the bench, that present with strange harmonics/vibration on the car.

I'm going to see if I can borrow someone's (known good) Camaro driveshaft to try in my car.

Trying to exhaust all possibilities before pulling the engine...

Daniel

driveshaft does not relate to engine rpm as you have mentioned in the past when the vibration occurs. If it was the driveshaft then it would show up at the same mph every time.

I’ve been fighting this vibration so long, I think it is driving me crazy and my recollection is getting foggy. :confused18:

In my mind, I’ve been recalling that the vibration is much less noticeable at idle. So, I just went outside and warmed up the car and slowly raise the idle up to 2000 and there is definitely a noticeable vibration. Maybe not quite as much as when it’s under load, but it is definitely there.

I’ve been trying to take notes along the way as I’ve been troubleshooting, but this seems like a key piece of the puzzle that I’ve been recalling incorrectly. I’m just getting old I guess. :lostmarbles:

Mike- yes, you’re right, thanks for keeping me on track.

Daniel

I went back and scanned some of the posts. I don't see where you've confirmed 100% your timing.

Do this with a piston stop, or at a minimum, pull your balancer bolt and check the orientation of your keyway with your timing mark. I needed to confirm TDC on my car recently. Here's mine and it was correct:

https://i.hmjimg.com/images/2020/05/...E306E90351.jpg

https://i.hmjimg.com/images/2020/05/...E7722AD703.jpg

A couple of things to consider, if you hadn't yet, add weight to the crank pulley or dampner. Maybe a heavy putty, to look for change. I haven't see a pick of your front runner system, but if you can run it without a belt and try to eliminate accessories.
Best!

I've tried to locate CAT, the crankshaft manufacture that's in your engine and the only thing I could come up with is this company on Ebay. Looks like they work out of Corona, California selling a variety of internal engine parts. Maybe just a depot for distributing stuff from overseas?
https://www.ebay.com/usr/catracingproducts

If you scroll down a bit on the link they are following a company called Perfect Crank.

I know its a long shot but maybe send a message and see if either one of these companies can give any sort of info on your crankshaft. Worth a try?

Thanks for the responses.

I verified TDC with a piston stop a few months back (must have forgotten to mention that in my posts). I check/verified the crank keyway was good when I installed the new balancer over the winter.

I've also run it with the serpentine belt removed with no change in vibration.

I'm leaning towards just sucking it up and having another 383 built by a local shop. That way I'll have known engine specs/parts and local support if needed.

Live and learn...

Daniel

I'd tear into the motor. I bet that crank is jacked up somehow or the timing chain is a tooth off maybe?

I haven't gone all the way back, but have you done a compression test on all cylinders and then a running compression test?

Since you took the belt off that eliminates the of the engine, have you taken the trans and clutch off to see if its still there?