Could backfiring cause this?
 

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What happened?

Long story short, engine was assembled, dyno'd, & tuned ran great. Installed in boat plug wires got crossed (don't ask) tried to start it was backfiring bad, got wires straightened out starts & runs but vibrates anything above idle. Checked timing, valves, carb, nothing wrong. pulled engine, pulled pan slight amount of I assumed assembly sludge, pulled #2 rod cap and #3 main to look & the pics are of what I found. Gen VI 502 .030 over aftermarket crank stock gm rods mild 515hp build. Approx 1 hour run time after dyno tuning.

A good backfire could cause a balancing issue.

randy,if you run your fingernail across the journal can you feel anything because from looking at the pick it looks ok.

Mike, I just pulled 1 of each but yes on the main & no on the rod journal. I can't remember what brand the crank is but the one that was replaced in this engine was a scat crank & it wiped the bearings with the static compression test that was done when it was originally built by Jasper Racing, that is why I had it gone through again so I wouldn't have these problems. The crank was replaced & short block built 5 yrs ago then stored until last yr then everything disassembled cleaned up & reassembled, dyno'd now this.

Can you see any ballancing weights on the crankshaft?? the viberation sounds like a ballancing issue..if they internally ballanced the engine then you will need a 396/427 harmonic ballancer and flywheel needs to ba machined off or 396/427 flywheel..

Probably not an issue since it dynoed fine.

When they run out of oil #3 main is the first to go. I don't know how hard you were running it for an hour...

If it ran smoothly on the dyno and now vibrates after installation, maybe it's a flywheel issue?

It sounds to me like fhe firing order might still be wrong, or you have a plug thats not firing, anything off idle would act like this, is this a C swap firing order cam, or standard, I know you said dont ask but !!!!!! I have to about the wires

I said don't ask because it's still a little tough to admit stupidity in a room full of gearheads. Lol. That being said the engine was delivered with plug wires installed as it just came off of the dyno, my buddy who I am putting the boat together for decided to paint the block. He pulled the wires, masked, & painted the block. After installation & hanging parts on it I made the mistake of looking at the intake & installing the wires accordingly thinking #1 was front starboard instead of port. I stand shamed but honest about it. Anyway after realizing MY mistake I reset the wires & the engine would start & run. I got the cam & valve train components from Bob at Marine Kinetics & the cam is nothing special as this is a mild build more for torque to move a heavy boat and called to ask if it was set up as a 4-7 swap, he said no. The flywheel is correct & pinned so it will only go on 1 way. Plugs were changed thinking it had fouled one. I think everything was done shy of having a witch doctor remove evil spirits. That is why it came out. It was not knocking & oil pressure was good so I was confident nothing broke but at this point I just wanted to be absolutely sure because I don't want to own every little thing down the line, I know too late. Any other info or pics I will do my best to provide. I NEED this to get done so I can get back to my Eliminator & Scarab projects!!!

Does it shake in gear, neutral, or both?

No shame here Randy, we all make mistakes but ur the bigger man to admit it, You must of been thinking of that 427 Cammer in your Ford Mustang when wiring LOL, Im still a bit puzzled, was anything added to the rotating assembly after it came off the dyno ?? how is there an hour of run time on it if its had a bad vibration.

I am or was a certified Ford tech, maybe that's it. Lol. The run time was just doing the checks normally associated with a new install. Making sure There Are No Leaks, Shifts OK and such. Most of this was at idle.

randy,normally the dyno shop uses there own flywheel for dyno pulls,id make sure you have the correct wheel for the application.

i must disagree,#1 is the farthest away from the oil pump but i have seen any and all go bad.

Haul that thing to KC we'll get her fixed up, :ernaehrung004:

Mike, the builder takes pics of his builds to verify what goes out the door & being that I have another 502 block to build I began to think the flywheels were switched when I was hanging parts on this one. He told me I have the correct one & that it is the one used during dyno testing. I was not wanting to but I think I am going to tear it down completely & start over for the 4th time. Between Jasper Racing & two local shops and a large sum of money between all 3 I have a large pile of crap I can't use so if I do it myself from scratch & check everything myself I can't do much worse. If you guys don't mind answering some stupid questions maybe I can get this done.

A vibration is different than a misfire.

Then again, I had a Ford Exploder have a harmonic damper come apart that I couldn't figure out the misfire. LOL. You would've thought it would have made noise (2 halves totally seperated) and felt like an out of balance vibration. Nope, still swear it felt like misfires. LOL. Dammit !

That's why they call them Exploders. LOL. I started my Ford career working on those piles, got into transmissions & the rest was history. The balancer is brand new but that might not matter as it was backfiring pretty hard. I'm beginning to wonder if it bent a rod.

Way back I used to get Mustang 5.0's every once in a while that had engine work done, including cam. They'd come in because running like ****. Supposedly back to the shop and/or buddy that put them together.

Quickest $100 one can ever make. Would put the wires to where they should have been. They didn't realize/read/whatever that the cams had firing order swaps.

Easy money. Big smiles on there faces. I didn't get any that had issues from running a long time with crossed wires.

And yes, they all got driven in. So ..... ????

Edit in: That is my experience only. I guess anything is possible.

i have never heard of backfiring causing balance problems but anything is possible i guess.

With humans, I have. LOL. In fact, has happened to me a few times. He, he.

I like that post above mine. :-D

This may be a silly thing to say, but was the flywheel and coupler bolted on good and square. No "crud" on the mating surfaces when they were bolted on and such. I could see that creating a "wobble" in the flywheel and make a vibration. Nick

No crud or anything between coupler & flywheel, I watched the coupler with engine running and no movement at all. That is the only piece added to the rotating assembly. I had to watch Street Outlaws to get my sitcom fix. Gonna take it apart & go from there. Stupid boats. Ugh

Really don't know if this may apply here, but this happened to me once. My wife had a 1993 Mustang. She came home one day after work and shut it off. The next day she goes out to leave for work and the car has a bad vibration. I've been around motors all my life and for the life of me could not figure it out, so I take it to a local shop. Being a stick shift they decide it has to be a clutch that went bad. I don't think so because it was fine when she parked it. How would a clutch go bad just sitting there for 12 hours? Anyway I say go ahead and pull the trans and check it out. Nothing. They check more and finally say bent rod. Again, I say how could that happen just sitting there? They want to put a new motor in it for $3500. I say drag it to my house. I get under it and start looking around again. I had already looked at the balancer and it looked just fine. But this time when I touched the outer ring it moved. The rubber had gone bad and the outer ring would just spin around. $80 for a new balancer and she was fine. Never even thought to check the timing because the motor fired right up and ran fine other then the vibration. If the shop or I checked the timing that would of shown the problem too. So, check the balancer to be sure it's good.

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Damn Randy you dont waist any time, any bent push rods ??

damn,looks like a bent rod

Just the way I was brought up.....

The only stupid question is the one not asked.

Where do you see a connecting rod in these two pics

My 1st thought was reversion on the one side the way the pistons are cleaned off. Oh and I cleaned out my inbox for PMs. I will look over the heads today.

3 and 5 should be at the same height,,looks to be different but then again,#1 may not be quit at top dead center.

any exhaust leaks on that side?that will help draw water back up.

Not that I am seeing, there was water spitting out between the riser and the riser extension that is a dry joint. I removed & pressure tested the manifold, extension, and riser as best that I could but found no leaks. I tore down the short block tonight but haven't looked it over yet. I will post some pics tomorrow.

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ATTACH=CONFIG]527078[/ATTACH]The crank & mains.

Weird discoloration on the journals, looks like the rods were hammering on it

I am questioning whether this crank is some brand of Chinese junk & if it would be worth it to try to polish it or make another door stop & find a chevy crank. Tried to remove the harmonic balancer & stripped the threads on a brand new puller. And yes I removed the center bolt first in case anyone was wondering. Lol

randy,what is the part # on the rod bearings,from the pic they look to be a p bearing and thats no good if you have a crank with a bigger radius on the journals,it restricts the flow of oil from exiting the bearing and boils the oil.