Thanks guys, I appreciate it.

Daniel

Need help- Engine imbalance??
 

Alright, I should be tearing up the streets at this point, but I haven't even made it out of the neighborhood.

My engine feels as though it is out of balance. I've tried a number of things to solve the issue, but I'm at a loss at this point. I'm all ears for suggestions, next steps, whatever. This post may be a bit long, but I want to include all the details in hopes someone can pick up on something I'm missing.

Here are the details-
383 stroker engine I purchased in person and we ran it on an engine stand to verify it ran good and all looked/sounded fine
Aluminum 64cc heads
Lunati hydraulic flat tappet cam- https://www.summitracing.com/parts/lun-60105
Hyper pistons
5.7" rods
Aluminum roller rockers
Edlebrock Performer 2701 intake manifold (new)
Windage tray
7 qt oil pan
Full length headers
Summit Racing external balanced harmonic balancer (called Summit to verify this)
Energy Suspension poly motor and trans mounts (new)
93 octane fuel

Other pertinent parts-
MSD Street Fire ignition box (new)
MSD Billet distributor (new)
NGK BKR7E spark plugs- gapped to .040 (new)
Taylor 8mm plug wires (new)
Holley 4779 double pumper 750cfm carb (new)
McLeod 75224 clutch (new)
PRW external balance, 168 tooth flywheel (new)
New pilot bushing, new throwout bearing, new clutch fork
Muncie M21 4 speed transmission

Above is the current engine setup. When I bought the engine, I removed and replaced the following parts:
Single plane intake
Holley 9381 830cfm carb
Valve covers
SFI external balance flexplate
Electric water pump

When I initially got the engine home, I removed the oil pan to check out the bottom end, etc. Everything looked good. I could still see hone marks on the cylinder walls, windage tray was secure, oil pump looked good, etc. I put a new Fel Pro gasket on and reinstalled the oil pan.

Engine has always had strong oil pressure- about 65psi. It ran rich with the 830cfm carb and was carbon fouling plugs extremely fast. It had big jets, and some other mods done to it, so I replaced it with the 750cfm. The engine starts fine and seems ok at idle. Once you rev over 1000 rpms, you can begin to feel the excessive vibration and it sounds almost like the timing is out of order. I don't hear any weird valvetrain or other engine noise and have no exhaust smoke. I checked the plug wire routing a billion times. I also have a Bluetooth bore camera that I've used to look in all the cylinders and all looks fine.

The static compression ratio is about 11.5:1, but with the ABDC of my cam and our altitude, it calculates to 9.5:1 dynamic compression ratio.

I never removed the Summit harmonic balancer that was on the engine when I bought it. I thought I may have oriented the flywheel incorrectly. But today, I looked up through the bottom opening of the bellhousing and where the crankshaft dowel hole is in relation to the weight I can see on the flywheel, it seems that the flywheel is correctly oriented. I went back and looked at a photo of the flexplate that was on the engine when I bought it and before I removed it and the counterweight on the flexplate looks to be in the same orientation that is now on my flywheel. I've called Summit to verify the harmonic balancer is for an externally balanced engine and I can see/feel the counterweight on the backside.

Any help is greatly appreciated, I'm beyond frustrated at this point.

Daniel

Did you have the new flywheel balanced matched to the old one? You can't just replaced an external balanced flywheel with another external balanced unit. They aren't necessarily counter weighted the same.

If you didn't do this, you need to take the old flywheel and clutch pressure plate along with the new flywheel and clutch pressure plate to a machine shop and tell them what you're trying to do. Don't ever assume a clutch pressure plate is zero balanced out of the box. Always include it when doing any balancing work.

Trey- Unfortunately, I did not do that because I was unaware it needed to be done. The engine had an SFI external balance flexplate on it when I bought it (he ran an auto trans). I called PRW, told them my setup, verified their flywheel would work with the McCleod clutch I was getting and ordered the flywheel. They did not mention any balancing was required.

Here is the flywheel I ordered.

https://www.jegs.com/i/PRW/228/1640081/10002/-1

Since the specs matched what I needed, I thought it was good to go out of the box. I sold the flexplate the engine came with. I guess I can try to get in touch with the buyer and see if I can get it back.

Thanks for the input,

Daniel

Are you convinced it is a balance issue and not a misfire? Maybe get it running where it is shaking at it's worse and put a infared heat gun on each header tube to verify they are all firing.

I have found that a long stroke SBC feels differently than just about any other engine, at times I've felt like mine was out of balance as well. I can tell you though now that I have EFI controlling both the timing and fuel delivery...it is buttery smooth everywhere and I didn't change any hard parts pertaining to balance.

Just a thought...

Lance- it's funny you mention that. When I was trying to tune the 830cfm carb and adjust timing, I used an infrared gun to check the header tubes. But, I did it quickly and didn't pay much attention because our attention was drawn to another issue that day.

I will check the tubes today now that the new carb is installed. Honestly, I was hoping it was a carb tune/timing issue that was causing the vibration, but the new carb didn't seem to have any effect on the vibration.

Thanks for the input,

Daniel

I the engine is truly out of balance this may sound low tech but if you don't want to re-balance the whole engine you could remove the trans and clutch. Then run the car with just the flywheel. this would take the clutch out of the equation. Then using the bolt holes for the clutch you can add weight to different areas to see if it helps you balance. If you find a combo that works you can take your flywheel and have weights added or removed.

I spoke with a PRW tech this morning and he had me verify my flywheel counterweight was bolted on in the correct position and had the correct part number stamping. Apparently, there are 2 positions. I verified my weight IS in the correct position and I have the correct part stamp. He advised me to remove the weight and verify it weighs 156.1 grams, which I'll do this evening. He says if it's a few grams or more off, it could cause vibration.

nicks67ca- Thanks for the tip. I really hope I don't have to pull the engine and tear it down.

Daniel

Interesting thing I discovered this evening. I brought home a cheap infrared temp gun from work to shoot the header tubes. Cylinders 1, 2, and 6 seem to heat up much quicker than the rest of the cylinders. Those cylinders are reaching 300* really quick, and the other cylinders are still in the mid 100's. I'm only letting it idle for less than a minute. I don't want to run it anymore than I have to until I figure out what's going on. I'm ASSuming if I were to let it get up to full temp, the cylinder temps would still be inconsistent.

Thoughts?

Daniel

1968 camero
 

Last time I saw that much heat difference
was when my dizzy was 180 out in my Pantera
I would double check. Yes it ran but not good

Bob