340 Vibrations!!

Hello everyone.... I hope someone can give me a few ideas in trying to fix the vibrations in my 340 before I loose my teeth driving to the next cruise night! I purchased a '72 340 for my 73 Roadrunner from a guy who said he rebuilt mopar engines for 30 years. The engine is freshly rebuilt with a forged crank. I installed the engine along with a new McLeud zero balance flywheel and new clutch. Problems started when I first started the engine, the lifters were LOUD and the engine vibrated big time! The guy who built the engine said this is normal! After about 100 miles, I couldn't take the lifter noise and upon further investigation, the rocker arms looked like they were incorrect (looks like big block rockers?). So i replaced the rocker arms from the 340 I removed from the car, lifter noise resolved and the engine seems a little smother, but I still have the vibrations that vary at different rpm's. So I removed the McLeud flywheel and replaced it with a stock neutral balance, still have vibrations. I removed the dampner and it did not look like the dampner on my 340? So I checked Galen's book and the number on my old 340 dampner is the correct one for a 340 forged crank engine, so i installed it and vibration still exists - but better. At least I can drive the car now and get the RPM's up to 4k without fear of destruction. Anyone have any ideas... Thanks!

30 years building mopar engines...wow, should run like a swiss watch. Miss match of parts I would say the engine should be tore down inspected and rebalanced? Check the trans pilot bushing in the crankshaft to trans input shaft ,engine and trans mounts. My brother had a 340 built years ago with a vibration that eventually broke a forged crank,#3 main cap bolt bottomed out when torqued allowing crank flex.

check your transmission tail mount.

Right now, before you do anything else, go out there and try to fill up your card on your digital camera with photos of parts that came off engine, and engine now. Also find a video cam and shoot a film of car running, as well as the sounds and vibrations, along with a narration. Get other people who know cars (esp Mopars) whom you trust and get their opinion, preferably on tape or written.

After this is done, go back to that shop and make your case. If he is unwilling to make it right, go to court and make your case. That is what a civil court is for, when all other efforts have led to no resolution.

I do hope this works out for you. You paid good Yankee currency for a job that evidently was not done right.

Using pistons that are not within factory weight tolerances can be a really easy way to screw up a build if you don't plan to balance the rotating assembly.

You can ask how the builder set up the bob weights or if it was even balanced.

markmine said:

Hello everyone.... I hope someone can give me a few ideas in trying to fix the vibrations in my 340 before I loose my teeth driving to the next cruise night! I purchased a '72 340 for my 73 Roadrunner from a guy who said he rebuilt mopar engines for 30 years. The engine is freshly rebuilt with a forged crank. I installed the engine along with a new McLeud zero balance flywheel and new clutch. Problems started when I first started the engine, the lifters were LOUD and the engine vibrated big time! The guy who built the engine said this is normal! After about 100 miles, I couldn't take the lifter noise and upon further investigation, the rocker arms looked like they were incorrect (looks like big block rockers?). So i replaced the rocker arms from the 340 I removed from the car, lifter noise resolved and the engine seems a little smother, but I still have the vibrations that vary at different rpm's. So I removed the McLeud flywheel and replaced it with a stock neutral balance, still have vibrations. I removed the dampner and it did not look like the dampner on my 340? So I checked Galen's book and the number on my old 340 dampner is the correct one for a 340 forged crank engine, so i installed it and vibration still exists - but better. At least I can drive the car now and get the RPM's up to 4k without fear of destruction. Anyone have any ideas... Thanks!

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Maybe this is normal with one of his rebuilds,the incorrect rockers would've been your first but not last clue. I'd yank the engine and pull it down,after what you've already described.
Personally speaking, i'd never have any confidence in the engine without knowing what else this guy deems normal.

Thanks for everyone's suggestions! When I installed the engine I used new motor mounts, new transmission mount and also installed new bell housing, clutch, TB and transmission. As fas as I'm concened, all bets are off with this engine. When I saw the rockers I couldn't believe my eyes..... who knows what is in this engine. I purchased the engine from a guy on Ebay (my first mistake!) I checked his feedback and talked with him several times before pulling the trigger and he sounded like he knew what he was doing... now $3,500 later I will be tearing into the engine - I just hope in can be fixed for a reasonable cost!

Check the casting number on the crank.Make sure it's not a cast crank!I worked on a friends 340 years ago that would shake the steering wheel when the rpm's were brought up.It was a '68 GTS 4-speed Dart with a '73 motor.The flywheel and balancer were neutral balance,the crank was a cast external balance piece.Had the flywheel drilled to mopar specs for a cast crank 340 and added the correct external balance damper.Problem solved,much smoother!This was a motor that had stock internals,yours may be the result of a bad or no balance job.
RT

Here's an update on my 340 engine vibration. Just to recap, i purchased the engine from a guy on ebay who claimed to be an experienced engine rebuilder. The engine vibrated since the first time I fired it up. Serious vibrations! I had many phone calls with the engine builder, but everything was suddenly put on hold. I had serious medical problems and the car has been in the garage until last June. Now that I'm better, it's time to get back to the roadrunner. But after close to 3 years, all hope was lost in trying to get money back from the engine builder. So time to move on.... I located a mopar mechanic who works on classic mopars. First he checked the flywheel and dampner balance, which was good. The engine is a 1972 340 with a steel crank. He removed the engine and tore it down and sent the rotating mass to the machine shop. The internals were out of balance over 300 grams - he said that was significant. The intake manifold was also cracked. Other than that, he said the engine looked really good, so it was reassembled with a new manifold and installed in my 73 roadrunner. Wow! What a difference! The engine runs great and smooth... I had a blast cruising the car for the remainder of the season. I also had him install 3.23 gears and now the car cruises great on the highway and still is fun off the line.

What a lesson learned, I will never again buy an engine off eBay! I understand that mistakes happen, but the engine was not balanced when it was originally assembled, a critical step skipped.

If you didn't leave him feedback yet, e mail him and tell him you want your money back or your giving him negative feedback.