On a 383 engine build with the entire rotating assembly being balanced, should there be any vibration when the engine is reved up?

Pretty sure the machine shop did a terrible job with the balancing, as when the engine is reved up to around 3500rpm the entire car is vibrating. This does not seem normal and i don't remember the stock LS1 doing this. I know it isn't the transmission or torque converter as they are the same as before....

 

The balance shop, EVERY balance shop, will provide the "bob weight" sheet.

Provide this information, most here know the normal weights, as do I.

Upon inspection we will be able to give a more correct answer.

Your inspection reveals counter weight is too low.

There could be Flywheel/Pressure Plate problems.

Where these items "spun" ?

Lance

 

I'd try and find out what they came up with for a bob weight. My machine shop engraved it on the crank when they did my balance.

 

Here are the two sheets i got on the crank being balanced.

If you don't mind helping me read and understand them. I obviously understand the weights of the pistons and rods. What do you look for in the bob weights?

I never weight the pistons and rods myself as i was trusting them. it seems like the pistons and rods are almost too close to believe. I am running CP pistons for boost in 3.905" and eagle H beam rods and 4" crank.

any advice and help is appreciated.

 

The good news is you HAVE the Balance Sheet.

The art needed to create this is KNOWN, thus I would believe the shop did the correct work.

The front pulley could by "out", not installed correctly, broken ?

There is NO "key" in the pulley though you could check for "drilling" marks OR worst case have it "0" balanced.

My guess is that you WOULD NOT be able to "feel" the imbalance if the pulley was "out".

The "drill" marks seen in the FP, if any, are placed AFTER engine assemble, the GM OEM method.

Would you be able to rule out engine miss-fire ?

Lance

 

It is definitely not a miss fire. I am running all the same accessories and OEM balancer as the engine had before. The balancer is externally balanced so installing it in another position on the crank should not affect it. I think i have a truck balancer here i could try installing, but i don't think this is my issue. (be an easy test before pulling motor again)

The only other thing could be the transmission/converter. However it is the exact same transmission and torque convert as ran before and i had no issues or vibration, so pretty sure the converter is balanced (i have had converters not balanced cause vibration before).

Do the specs on the sheets and bob weight used look correct?

Reason I am suspecting the balancing of the crank, is because the shop that balanced the crank also was to line hone the mains (installed main studs) and install cam bearings. However when i got the engine back i could not install the cam because the bearings were so tight, and the crank was so tight i couldn't turn it over by hand. After measuring it was .0015" out of round from the arp studs. After taking it back to them twice and they didn't fix either i took the engine to another machine shop that properly line honed and clearanced the cam bearings. I'm kicking myself for not having the second machine verify the balancing of the crank.

 

Well that certainly does not sound promising. I think that it would have to be extremely out of balance to feel the kind of vibrations you are getting. I had a buddy throw together a 5.3 with forged rods/pistons on an LS1 crank with out having it balanced. Runs like a top.

 

Balancing is not rocket science, machine shops have been doing it for decades. Mistakes sometimes happen, but it looks like yours was done well. And, really, a proper balance vs. improper wouldn't be very noticeable at 3,500 rpm's

I'd be looking in other places. Make sure all cylinders are firing correctly - fuel and spark. Do all the spark plugs look good? Did all the electrical connectors get plugged in correctly?

 

Lets start with the cam, did you fit the cam sprocket using IT to try to "feel"
the cam turning torque ?

There are many engine assemblers that replace main bolts with studs.
The most common case is ONLY a "lite" hone is needed caused by the original GM block machine NOT the fastener replacement.

This will increase the housing bore size.

How did you measure the housing bore and what size did you measure ?

What was the main Torque Value, using the ARP 100.lbs WILL "strip" threads, I use 80-85 .lbs. (Aluminum Block only)

What is your block material iron/aluminum ?

YES, as stated, the Balance Sheet looks normal with a LOW bob-weight observed.

That in its self would be good news.

CP, Calvert/Pankl, PROVIDE the piston weight with the piston order.

Would you report that to be a match ?

Who installed the transmission ?

MY observation is that we have not identified a cause.

Lance

 

Before pulling the motor I would try to re-index the converter. Sometimes rotating it helps. Look at the converter to see if its weight has come off. Just a few things to check.

 

Maybe it could be a bad lifter or a dead cylinder causing the vibration? Not sure how to find or test for a bad lifter, but I was thinking I will do a compression test for all cylinders and a leak down test. then maybe swap coils or pull plug wires to see if this helps find a dead cylinder. (also might take temp of exhaust to make sure they are consistent) Although running it i really don't hear a misfire I would rather test now then pull engine for no reason.

Also to ensure the transmission/converter aren't the culprit I will unbolt the converter and move it back form the flex plate and start the engine again.

Some background on the car/engine. It is a 2002 camaro which had a stock LS1 and cam with turbo. I spun a bearing on it last year really bad (I think because the turbo boost was too high), so pulled the motor to rebuild. I installed a 4" eagle stroker crank, eagle rods, CP pistons. It has stock 241 heads that were reconditioned, new Morrel 3515 lifters, new push rods, and compression ratio set to 9.7:1. In installed new ARP main studs, ARP head studs, and all new bearings. I reused the same comp cam as before with same dual valve springs.

I verified all specs of the engine myself with bore gauges and micrometers. when the ARP main studs were installed it made the mains out of round by .001" and the cam was so tight with the new bearings I couldn't even install it. After taking it to the second machine shop the cam bearings had proper clearance and the mains were fixed and had the proper .0025" clearance. Also all rod bearings were correct as well. All torque settings were to what ARP recommended. All engine assembly and installation was performed by me as I am very particular and like to do it myself so I know it is done right, however I'm very busy and it has taken me about a year to get it installed and running.

 

Was it re tuned after the increase in displacement?

 

I changed the tune for the increase in displacement. It is running at a good a/f ratio with the same timing as before.

 

What RPM do you get the vibration?

 

Before you do anything check the crank end play, if its excessive lets say over .020 it will cause vibrations.

 

At an idle you can't tell if it is vibrating cause it has a bit of a rough idle from the cam. But as you rev it up it is very apparent by 2000rpm. By 3000 rpm it is so bad I don't want to rev it any higher from fear of engine damage.

 

Isn't the only way crank end play would be too large is if the main bearings were incorrect? Because when i assembled it I checked end play by shifting the crank back and forth and it was within spec. I will have to check my notes what exactly it was set to, but it wasn't anywhere near .020"

Or are you talking about the crank snouts run out?

 

OK, your latest statement reminds me of an out of balance engine.

MY FIRST test, a possible fix, would be to ADD weight to the Flywheel.
There are four placement areas, ones that are easy to add a counter weight.
I would create an "arc" of steel, 3" x 1" x .375", with a hole in the center.

Then bolt it to the flywheel at the converter stud locations, one test of four.

The next step would be to spin the engine looking for better/worse vibration.

Once the correct location is found, add/trim the weight.

I have done this with success.

This "test" would PROVE/ANSWER the balance question.

Lance